Detoxification and Sensing of Organophosphate-Based Pesticides and Preservatives in Beverages

DETOXIFICATION AND SENSING OF ORGANOPHOSPHATE-BASED PESTICIDES AND PRESERVATIVES IN BEVERAGES

14

Amanpreet Singh⁎,1, Pushap Raj⁎,1, Navneet Kaur†, Narinder Singh⁎ *

Department of Chemistry, Indian Institute Technology Ropar, Rupnagar, India, Department of Chemistry, Panjab University, Chandigarh, India

†

14.1 Introduction The role of pesticides in the green revolution cannot be emasculated; it protects the crop from the damage caused by pests and weeds and enhances the cultivation of crops (Fig. 14.1). Particularly in the high humidity environment, no another alternate of pesticides is available. In such a kind of environment, the growth of pests is very fast and the damage caused by them is unaffordable. Along with huge benefits of these, adverse effects on human health are a major threat. Excess of pesticides cannot be degraded even at higher pH and hazard conditions. Therefore, reliable methods for monitoring the exact concentration of pesticide in beverages are needed. Along with their detection, complete removal or detoxification is necessary to provide the best quality of beverages to the consumer.

14.1.1  Pesticides Used in Agriculture Sector Most of the beverages are made up from milk, fruits, and coffee or tea. Among these, coffee and tea belong to alkaloids, the class of natural products. For the cultivation of both of these, less amount of pesticides is needed. However, for good cultivation of fruits and vegetables, pesticides are used on a large scale. The commonly used pesticides are either organophosphates or carbamates (Liu et al., 2012; Qian and Lin, 2015; Sharma et  al., 2016b). The organophosphate-based commercial pesticides are parathion, paraoxon, azamethiphos, methyl 1

Equal contribution.

Preservatives for the Beverage Industry. https://doi.org/10.1016/B978-0-12-816685-7.00014-8 © 2019 Elsevier Inc. All rights reserved.

467

468  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Fig. 14.1  Cartoon diagram showing the need for a catalyst for detoxification of pesticides.

parathion, ­diazinon, chlorpyrifos, dichlorvos, and ethion. Whereas carbamate-based pesticides are featured the carbamate ester functional group. The commercially available carbamate pesticides are aldicarb, carbofuran, carbaryl, ethienocarb, fenobucarb, and methomyl. Generally, all of these are stable at a wide range of pH for long times. The carbamate-based pesticides are less toxic to humans as compared to organophosphates because they bind with acetylcholine esterase enzyme reversibly, whereas organophosphates bind with Acetylcholine esterase in an irreversible manner. Once it binds to the enzyme, it will completely inhibit the activity of an enzyme which may cause death in a few hours. Therefore it can contaminate the fruits also; to avoid any harmful effect caused by such pesticide, its detection is important.

14.1.2  Mechanism of Action of Organophosphates in Humans Due to their inhibitory activity toward acetylcholine esterase enzyme, Organophosphates are widely used as pesticides. Acetylcholine esterase catalyzes the conversion of acetylcholine into choline (Gillon et al., 2011; Hörnberg et al., 2007; Kovarik et al., 2003; Liu and Lin, 2006).

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   469

X EtO OH Serine residue

Active site of acetyl cholinesterase Free

Y

X

EtO P

P

O

OEt

X = O, S Y = Leaving group

OEt

Serine

Active site of acetyl cholinesterase blocked

In this catalytic process, serine amino acid residue of enzyme play a significant role, the hydroxyl group attack at carbonyl center of acetylcholine to catalyze the hydrolysis process. However, on reaction with organophosphate, this amino acid residue covalently binds with organophosphate by substitution reaction and inhibits the activity of this enzyme (Fig. 14.2). Choline is an important neurotransmitter; its deficiency may cause death within a few minutes; that is why nowadays some countries start their use for destruction purpose as chemical warfare agents. Therefore, a catalyst for their destruction and sensing is needed (Singh et al., 2015a, 2016).

14.1.3  Analytical Techniques for Detection of Pesticides Various analytical techniques are available to monitor the concentration of contaminants. Mostly in the industry, chromatographic techniques such as high-performance liquid chromatography, gas chromatography, or a ion channel spectrophotometer are used for the analysis of contaminants. In case of beverages, thousands of other natural products are present in the solution that will interfere with the quantitative analysis of pesticides using chromatography-based techniques. Therefore, fluorescence detection of contaminants is an encouraging approach to rule out this deficiency. To achieve this highly selective and sensitive fluorescence, probes are required to be developed. In the last decades, a lot of work was published for detection of pesticides.

14.1.4  Detoxification of Organophosphates Detoxification of organophosphates is important to improve the food quality. To achieve this, various catalysts are developed that can detoxify these compounds by hydrolysis process. Among these, metal nanoparticles, metal organic frameworks, and the ionic liquid-based catalyst are promising candidates. All of these catalysts have their own advantages and disadvantages. The nanoparticle-based catalyst suffers from

Fig. 14.2  Inhibition of acetylcholine esterase enzyme through serine residue.

470  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

l­ imitations of nonstability for a long time, whereas metal complexes lose the activity due to hydration of the metal center in an aqueous medium. To eliminate such kinds of limitations, a metal-organic framework has been developed which is stable at different pH and temperature conditions for a long time and used for detection and detoxification of pesticides. Along with these, Organocatalysis is another promising approach to construct antidotes for pesticides. In this context, some organic compounds were explored as catalysts for detoxification of organophosphates which involve oxime-based organic molecules and ionic liquids. It is worth mentioning here that only those catalysts are important which can work at physiological conditions and take lesser time to detoxify the pesticides. Another major challenge is the applicability of these catalysts to large-scale detoxification of organophosphates.

14.2  Sensor and Catalysts for Detoxification of Organophosphates Using Organic Receptors The organophosphates are generally reacted with strong nucleophilic species such as pyridine and phenoxide ion. Thereby, we can construct a fluorescence sensor and chemodosimeter chemosensor by conjugating a fluorescence unit with such kinds of nucleophilic species (Zhang et al., 2014). Another approach is a urea and thiourea-based sensor that gives response by abstraction of a proton from NH hydrogen by phosphate species; along with photophysical properties, the NMR signal also shifted during this anion-induced transformation. Besides the organic probe, metal complexes are also used for detection of pesticides as well as its detoxifications. Recently, Hupps and coworker synthesized various zirconium and zinc-based metal-organic frameworks for detoxification of pesticides as well as their detection. We will discuss all of these approaches below.

14.2.1  Urea/Thiourea-Based Receptor for Encapsulation of Organophosphate Through Hydrogen Bonding Urea and thiourea-based receptors are well known for their affinity to interact with anionic species or electron rich neutral molecules through hydrogen bonding provided by NH protons (Jia et  al., 2016; Singh et al., 2014; Zhang et al., 2013, 2015). Their binding tendency can be modulated by changing the subgroups. The partial abstraction of NH proton for such kinds of receptors will lead to change in electronics of the probe, resulting in a change in absorption and emission properties.

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Philip A. Gale and coworkers have synthesized (Sambrook et al., 2012) various derivatives of urea-based receptors (UR1–UR4) to encapsulate organophosphates (Fig. 14.3). The receptor was designed in such a way that it can bind with organophosphates through various hydrogen bonding interactions. The binding studies were performed using NMR spectroscopy, as on interaction with organophosphates the NH proton was shifted downfield. The chemical shift in proton signals was used to analyze the binding constant and stoichiometry of complex formation which was found to be 1:1 (host:organophosphate). To further validate the binding, DFT calculations were performed that revealed formation of host-guest complex through four hydrogen bonds (three NH protons from urea and one from indole). Among all the prepared receptors, the compound UR1 was found to be most compatible for the chemical warfare agents soman (GD). O

N H

NH

NH

N H

N H

N H

O HN

O HN

NH UR2

UR1

O NH

O N H

N H

HN O

O NH

HN

NH

N H

HN

O

O HN

NH

UR4

UR3

F

O

H

N H

HN

NH

N

HN

O

B

N H O

N H P

H

N

F

O

CF3

F N

N

S

H

H O P

O O

UR1 + organophosphate

UR6

Fig. 14.3  Chemdraw structures of various ureabased receptors. Optimized structure of receptor UR1 showing interaction of organophosphates through hydrogen bonding.

472  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

In another work, they have synthesized neutral ditopic and negatively charged monotopic host molecules UR5 and explored their binding studies with organophosphates (Hiscock et  al., 2016). Urea and thiourea moiety were introduced to achieve organophosphate binding through hydrogen bonding, whereas insertion of negatively changed anion (BF3−) provides selectivity to the prepared probe over another competing anionic species. The coulombic repulsion caused by negatively changed boron to the another anionic species, inhibit the anion binding. The prepared probes are showing a chemical shift in the NH proton on binding with organophosphate species. The stoichiometry of binding on receptor with organophosphate was found to be 1:1, with a binding constant of Kassoc = 1500 ± 250 M−1.

14.2.2  Detection of Organophosphate-Based Nerve Agents by Intramolecular Cyclization Approach It was well known that the hydroxyl group reacts with organophosphate to eliminate the leaving group which results in the formation of a new PO bond. In this process, the bond of that oxygen with carbon becomes weak; thereby, it is easily eliminated though attack of nucleophilic species within the molecules. A few examples are reported in which intramolecular cyclization takes place on reaction with ­organophosphate-based nerve agents (Fig. 14.4). Julius Rebek and coworkers are working in this direction to develop a sensor for nerve agents (Dale and Rebek, 2006). The have synthesized pyrene-based compound IC2 containing the shortest spacer between the pyrene fluorophore and tertiary amine. The lone pair of the amine group quenches the fluorescence intensity of the probe through the photoinduced electron transfer (PET) mechanism. However, conversion of the amine to ammonium salt, either by protonation or by cyclization process, will lead to enhancement in emission profile due to cancellation of PET mechanism. It was interesting that the fluorophore is not restricted to pyrene, as it is not involved in the phosphorylating process; it just gave response on the formation of ammonium salt. Therefore, they have designed another probe IC1 which has fluorophore moiety dimethoxycoumarin, whereas other subunits are the same as the probe IC1. It also shows significant enhancement in the emission profile; however, the detection limit with various fluorophores may be different. Similarly, they have used perylene- and coronene-based polyaromatic fluorophores to attain better quantum yields. For the development of a sensor for organophosphates, David G. Churchill has done tremendous work. His research group has developed a lot of fluorescence sensors for various organophosphate-based pesticides with high sensitivity. They have prepared fluorescence

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   473

Fig. 14.4  Fluorescence probe for detection of organophosphate-based nerve agents by intramolecular cyclization approach.

probe IC4 containing a coumarin-4-dimethyaminoaryl entity and explored it for detection of diethyl chlorophosphate (DCP). The probe was showing a large enhancement in fluorescence intensity on interaction with DCP, whereas little change in the emission profile was observed with another organophosphate. As shown in Fig. 14.4, benzyl alcohol entity of probe react with DCP, result into the substitution of chloride ion and form a new OP bond which will favor the intramolecular cyclization that leads to the formation of the ammonium salt. The cyclization reactions greatly influence the emission properties of the probe due to inhibition of the PET process. The fluorescence intensity of the probe enhanced around 10-fold on binding with DCP. Youjun Yang and Z. Lei have adopted a unique approach for colorimetric detection of organophosphate-based nerve agents (Lei and Yang, 2014). They have synthesized a probe IC3 that gave response toward Op-based pesticides the intramolecular rearrangement called the Vilsmeier-Haack reaction. The electron deficient center of organophosphates will activate the probe containing 4-diethylaminobenzaldehyde by interacting through the aldehyde group. The elimination of the phosphate entity results in the formation of the highly conjugated xanthene dye. The electron donating subgroup (diethyl aniline) attached

474  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

with the probe will catalyze the formation of xanthene dye by removal of the phosphate unit. The xanthene dye has a dramatically different absorbance and emission profile. Thereby, the prepared probe has potential practical applications with advantages such as a compact probe structure, easy synthesis, and turn-on signal. Diethyl chlorophosphate is a nerve agent; besides pesticide, it is also used as chemical warfare agents. Here, Hong Zheng and coworkers have developed a near-infrared probe using heptamethine chromophore which was explored for sensitive detection of DCP using fluorescence and absorption spectroscopy (Hu et al., 2015). As shown in the mechanism, the probe containing a free carboxyl group reacts with DCP and forms a covalent bond between oxygen and phosphorus (Fig.  14.5). Further, a lone pair of nitrogens attacked at the carboxylic center, which resulted in the elimination of diethyl hydrogen phosphate. On formation of cyclic amide, absorption properties of the probe greatly influenced due change in the electron donating ability of the amine group in the bridgehead site of heptamethine cyanine. The absorbance maxima of the probe shifted toward the red wavelength on interaction with DCP; also, the fluorescence intensity of the probe enhanced significantly. The prepared probe can detect nerve agents with a detection limit of 0.12 nM using photoluminescence. Another advantage of the prepared probe includes fast response, high productivity, and frequent color change.

14.2.3  Oxime-Based Sensors and Scavengers for Organophosphates Initially, the oxime group has been utilized to develop fluorescence probes by Rebek and Anslyn; further, they developed similar molecules for detoxification of organophosphates. Thereafter, many probes were developed for sensing of pesticides in aqueous medium or vapor phase. The oxime entity reacts very fact with organophosphate compounds, thereby giving a spontaneous response. The colorimetric probe can be constructed by attachment of the oxime moiety with the conjugated system because in such a case the charge transfer between the conjugated ring and oxime moiety is affected significantly, which results in a change in photophysical properties (Fig. 14.6). Similarly, Karl J. Wallace et  al. have developed an N,N‑carbonylbridgeddipyrrinone oxime (OX1)-based probe for detection of ­organophosphate-based pesticides (Walton et  al., 2012). On reacting with dimethoate, a new adduct was formed which has a dramatically different colorimetric response, whereas minimal enhancement in fluorescence intensity was observed. The interesting thing in this probe is that on deprotonation in the basic medium, it shows a crimson red color which disappears completely on the addition of ­organophosphate

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   475

O EtO

O

OEt P

HO

O O

DCP

HN N

N

HN N

N

IC5

O

Fluorescence turn-ON N

Fig. 14.5  Mechanism of detection of diethyl hydrogen phosphate using probe IC5.

or pesticides. The absorbance intensity at 561 nm decreased, whereas at 410 nm it increased significantly, resulting in ratiometric determination of pesticides. Thereby, the prepared probe can be used for naked-eye detection of pesticide. Jiangong Cheng et  al. have developed a tripodal receptor (OX2) having an oxime end group as the electron withdrawing group and a phenol moiety as the electron donating group (Xu et  al., 2016). The presence of the electron withdrawing and electron donating group in a single molecule will lead to intramolecular charge transfer (ICT). This phenomenon will contribute to interesting photophysical properties which can be altered by a small change in the structure of the compound. Moreover, stronger π-π stacking along with strong hydrogen bonding between the hydroxyl group of phenol and oxime will lead to enhancing the reactivity of the probe in the aggregation state. In aggregation state, pours film structure formed that made the probe more compatible for vapor-phase detection. On interaction with the probe, the oxime group attack on phosphorus center and catalyze the hydrolysis process. Now, a new conjugate bond will be formed between phosphorus and oxygen of oxime that will alter the ICT as well as the aggregation behavior of the probe. On absorption of DCP vapors, fluorescence intensity decreased significantly and the probe was efficient to detect DCP at a concentration of 1.2 ppb, which is much lower from a toxic level of nerve agents.

N N

476  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

S

Color—Purple

N O

(A)

P

S

N

H

O

N O

O N

H

P

OMe OMe

OX1

HO

O-

N

N

HO

OH DCP

N

N

OX2

R N

OH N

OH

H HO

N OH OX3

N

N B F

O N

O

HO

P O O

N

N OH

Nonfluorescence

O

OH

O

N OH

NH OH

(B)

S N

O

OH

O

Color—Yellow

OMe OMe

O

N O

H N

O

OH N OH

Highly fluorescence

MeO N

MeO

Ph

O n = 1, 2

O

n

N

OH NOH

F OX4

OX5

OX6

Fig. 14.6  Oxime-based probe for the detection of organophosphate compounds. (A) The mechanism involved in detection of organophosphates using oxime-based probes. (B) Structures of oxime-based fluorescent probes.

Similarly, Hae Jo Kim et al. have conjugated the rhodamine fluorophore (OX5) with the oxime moiety to construct a probe for nerve agents. The prepared probe undergoes two-step reactions with the nerve agent (DCP). The first step involves the activation of oxime by organophosphate, which is a fast step. The second step implicates the cyclization by removal of the less toxic adduct of organophosphate ­(diethyl hydrogen phosphate) and the final formation of the highly fluorescent adduct having a nitrile unit. This conversion of carbonyl to the nitrile moiety leads to large enhancement in the emission spectra. Thereby, the prepared probe was efficient to detect nerve agents with a low detection limit of 10 nM in the HEPES buffer. In this field, David G. Churchill et  al. have also developed an ­oxime-based probe for detection of organophosphate (Online et  al., 2014). They have constructed a Boron-dipyrromethene (BODIPY)— salicylaldehyde oxime (OX4) which has high affinity to interact with

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   477

organophosphates. The imine group in the BODIPY—salicylaldehyde oxime causes quenching in emission intensity due to the PET mechanism. On activation of organophosphate (diethyl cyanophosphate) with oxime, a new covalent bond between phosphorus and oxygen was formed, which results in the release of a nontoxic phosphate adduct. During this process, the oxime bond converts into cyanide and thereby the PET mechanism is canceled, which results in enhancement in the emission profile. The prepared probe was efficient to detect diethylcyanophosphate with a detection limit of 997 nm. In another work, they have constructed a 1,8-naphthalimide-based fluorescent probe (OX3) for the detection of nerve agents (Kim et  al., 2017a). The probe was showing around 50-fold enhancement in fluorescence on reaction with diethyl cyanophosphate. The most interesting thing in this probe was that it can work in an aqueous medium in a wide range of pH. As shown in Fig. 14.6, the probe has two reactive groups (hydroxyl and oxime), thereby giving dual emission with different kinetic reaction. Cashman and coworkers have synthesized a series of amidine-­ oxime reactivators of organophosphate; in  vitro and in  vivo studies were carried out to determine the reactivation behavior of probes (Ralph et al., 2011). The strongly basic amidine group mimics the quaternary center of pyridinium oxime that enhances the binding affinity of the probe with the cholinesterase enzyme. On the other hand, the oxime group acts as a powerful nucleophile that hydrolyzes the phosphylated enzyme and reactivates its activity. Pierre-Yves Renard et al. have developed some receptors that can reactivate the activity of the acetylcholine esterase enzyme (Gillon et al., 2011). They have attached an oxime moiety with a pyridine derivative; as we have described earlier, both the pyridine moiety and oximehave a high affinity for organophosphates. As shown in Fig.  14.6, they have joined oxime OX6 with a ligand which selectively binds to the peripheral site of the enzyme. The oxime and ligand were attached through the alkyl chain; the number of carbons in this chain was varied to modulate the activity of the compound. They have performed molecular docking analysis to choose the perfect candidate for this job, which revealed that nonquaternary pyridine aldoximes were a perfect candidate for reactivation of AChE. In another work, they have synthesized aβ-cyclodextrin-oxime conjugates and explored them as an antidote for the pesticides (Le Provost et al., 2011). Here the cavity formed by β-cyclodextrin was occupied by the lipophilic part of organophosphate; also, the hydroxyl group of the cyclic oligosaccharide was able to interact with lipophilic compounds. They have synthesized a variety of oligosaccharides and compared their ability to detoxify the pesticides. All the synthesized compounds were able to hydrolyze the organophosphates; however, the rate of detoxification was highly dependent on the position of the linker between β-CD and the reactive moiety.

478  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

14.2.4  Pyridine and Amine-Based Probes for Detection of Pesticides It is well documented in the literature that strong nucleophilic species are capable to bind with organophosphates species. Among these, pyridine and amine-based receptors are well explored for sensing of pesticides due to their high affinity toward organophosphates. In the free state, generally the amine group causes fluorescence quenching, whereas on interacting with the organophosphates species, fluorescence intensity enhanced due to the cancellation of the PET mechanism. Similarly, a lone pair of pyridines influenced the photophysical properties of the probe if it extends the conjugation. On reaction with organophosphates, the nitrogen of pyridine gets protonated, which results in a change in the photophysical properties and determination of organophosphates. Par Wasterby et  al. have developed an array of the fluorogenic probe AM1 to discriminate the variety of organophosphates (Borja et al., 2014). As shown in Fig. 14.7, they have conjugated the donor-­ acceptor group, which leads to an ICT in the system. The lone pair of nitrogens was causing PET and quenches the emission intensity of the probe. However, on interaction of organophosphate, the PET mechanism canceled out, which resulted in an enhancement in fluorescence and detection of nerve agents. As they have synthesized a series of molecules having different subgroups, it was interesting that these molecules gave different responses for different organophosphate derivatives. The responses given by a variety of molecules are charted as a fingerprint of the fluorescence response of different nerve agents. Therefore, using all of these probes, differentiation of different organophosphates can be achieved easily. In addition, the probe has another advantage, such as an easy synthesis method and lower detection limit; thereby, it can be suitable for practical applications in the field.

PET cancel

Nerve agent

Less fluorescent

Fig. 14.7  Mechanism of detection of nerve agents using probe AM1.

Fluorescence ON

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   479

Fig. 14.8  Chemdraw structures of pyridine and benzimidazolebased probes for detection of nerve agents.

Similarly, A.M. Costero and coworkers have developed a simple probe AM2 having a pyridine ring (electron acceptor) and N-methyl aniline (electron donor) connected through an azo group (Royo et al., 2011). These conjugated dyes have two nucleophilic centers that can attack the electron deficient phosphorus center of organophosphate (Fig. 14.8). The two reaction centers (pyridine and N-methyl aniline) have different tendencies to interact with different phosphate species and thereby gave different photophysical responses. Initially, the probe was showing absorbance maxima at 475 nm, which on reaction with the pyridine entity shifted to 575 nm, whereas reaction through the N-methyl aniline moiety gave absorbance maxima at 452 nm. On addition of DCP to the solution of probe AM2, the color of the solution changes from pale orange to magenta. Therefore, the prepared probe was efficient to detect organophosphate through the naked eye with high sensitivity. The benzimidazole entity is also a good nucleophile for the highly electron deficient phosphate center. Therefore, Mondal and coworkers have synthesized a probe AM3 having a benzimidazole ring as the electron acceptor and triphenyl amine as the electron donor group (Aich et  al., 2017). This donor-acceptor conjugate results in an ICT which can be modulated as electronic properties of the probe will change. The mechanism of sensing of organophosphate using probe AM3 involved the nucleophilic attack from the N-atom of benzimidazole to the electron deficient phosphonyl group of organophosphate, followed by hydrolysis and protonation of benzimidazole. The protonated benzimidazole has different electronic properties than the pure receptor that influences the ICT, resulting in a red shift in absorbance and enhancement in emission intensity at 573 nm. This probe has advantages over the existing probe such as ratiometric sensing with a large stoke shift, detection limit in the range of 10 nM, and vapor phase detection. Singh et  al. have developed a rhodamine-based probe for determination of organophosphate-based nerve agents in the vapor state (Singh et  al., 2015b). They have constructed a micromotor-based fluorescent “ON-OFF” probe AM4 for real-time monitoring of nerve

480  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

agents. The prepared probe was designed in such a way that the amine group on rhodamine extended the conjugation result into a strong emission intensity at 510 nm. The receptor AM4 is showing a strong affinity toward DCP over another derivatives of organophosphates. Jiangong Cheng et al. have synthesized a fluorescent probe AM5 for vapor phase detection of DCP (Fig.  14.9) (Yao et  al., 2016). Here they have conjugated tri-phenyl amine (TPA) with pyridyl (Py) unit in such a way that the charge can transfer from TPA to pyridyl unit that was highly selective for a specific analyte. The tetra butyl unit plays an important role in enhancing the quantum yield and affinity of the compound for vapor absorption. By absorbing vapors of DCP, the reaction between the fluorescent probe and DCP takes place, which results in the elimination of the chloride ion from DCP. The protonation of the pyridyl unit resulted in strong spectral changes that were used for detection of DCP vapors. The prepared probe was efficient to detect DCP at the detection limit of 2.6 ppb, which is better than other methods and can be used for real-time, on-site monitoring of DCP. Wei Wang et al. have designed a fluorescent probe AM6 for determination of DCP using the FRET (Chen et al., 2013; Ghenuche et al., 2015; Gravier et  al., 2014; Kim et  al., 2015) mechanism (Fig.  14.10) (Xuan et al., 2013). Two different fluorophores have been conjugated through amide linkage which showed emission at 460 and 536 nm, respectively, for coumarin and rhodamine fluorophore. On excitation at 410 nm,

Fig. 14.9  Mechanism of detection of DCP using a tri-phenyl amine-based fluorescent probe.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   481

NEt2

NEt2

ex.

ex.

em.

FRET ON

FRET ON

DCP

COO- K+

O

N

O N Probe AM6

O

O EtO

O

O

O O

O

O

O

P

N

O N

Cl

OEt

Fig. 14.10  Mechanism of sensing of DCP using a rhodamine-based fluorescent probe.

strong emission at 536 nm appeared. However, on reacting with DCP, the free carboxylate group of the probe converted into the closed spironolactone ring which breaks out the conjugation. Due to this fluorescence, intensity at 536 nm decreased significantly, which was used for ratiometric detection of DCP. The advantages of the prepared probe include fast and high sensitive response to the OP nerve agent mimic DCP to lower the detection limit of 0.17 ppm. Also, the probe was efficiently detecting nerve agents in the liquid as well as gas phase. The change in the absorbance and emission profile on the addition of DCP made the utility of the probe simple for naked eye detection.

14.2.5  Supramolecular Architecture for Encapsulation of Organophosphate To develop the antidotes (CLX1-2) for organophosphates, Kubik et  al. have developed a variety of sulfonatocalix[4]arenes having appended a hydroxamic acid moiety (Schneider et  al., 2016). The hydroxamic acid undergoes phosphorylation on reaction with a variety of organophosphates, followed by the removal of a nontoxic derivative of organophosphate by loosening the rearrangement reaction, whereas the calix moiety acts as a binding unit for cationic pesticides (organophosphates) which arrange the nucleophilic group that mediates the selective cleavage of the PS bond of nerve agents (Fig. 14.11). These calix-based receptors are stoichiometric scavengers; therefore, they cannot be compared with bio scavengers which act catalytically. The scavengers to be used for practical applications should have a half-life in a few seconds. Although the half-life of prepared receptors is not in this range, it can be used for skin treatment damage by pesticides or chemical warfare agents. Thus, calixarene-based receptors should be a lead for the development of highly active scavengers for pesticides.

O

O EtO

P

OEt

482  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

O HO

HO

H N

O

N H N

NaO3S

NaO3S

OH

SO3Na HN

O

NaO3S

HO

OH OH

NaO3S

OH

CLX1

OH O

X O OH HO

O

N

HO

N

N

N OH

HO

HN

OH

O

N

N

N

O

O

O OH O OH

HO OH O OH O

HO

O O

O OH

OH OH

O

CLX2

X =

HO

SO3Na HN

N

N

N

HO

O

N

O

O

OH OH OH O

OH OOH

HN

N

N

N

OH

O

O OH CLX3

N

N

N

OH

N O

Fig. 14.11  Chemical structure of calix-based receptors for detoxification of pesticides.

In another work, they have constructed a variety of cyclodextrin rings (CLX3) attached with hydroxamic acid and used them for detoxification of organophosphate-based nerve agents (Brandhuber et  al., 2013). The cyclodextrin-based probe efficiently detoxifies the organophosphate (cyclosarin) at pH 7.40 and 37°C, having a half-life of 3 min.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   483

On reaction with Tabun (ethyl dimethylphosphoramidocyanidate, GA), the hydroxamic acids modified irreversibly; thereby, the catalysis involved in this process is stoichiometric, not catalytic. For quantitative determination of the compounds formed on degradation of organophosphates, GS-MS, NMR, and mass spectrometry analysis were carried out. From NMR studies, it was revealed that after 30 min of reaction, the NMR signal corresponding to Tabun completely disappeared. Jovica D. Badjic and coworkers have developed a variety of Amino Acid Functionalized Baskets to encapsulate the pesticides (Ruan et al., 2014). The molecular Baskets CV1 were prepared by the condensation of tris(anhydride) and hydrophobic amino acids having alkyl chain functional groups and purified using column chromatography. After that, its carboxylate salt was formed by deprotonation using tetra methyl ammonium hydroxide. It will be beneficial to solubilize the probe in aqueous medium, so that it can be used for real applications. Also, carboxylate ion forms a hydrophilic belt in between two hydrophobic cavities. The interaction studies of baskets with dimethyl methylphosphonate (DMMP) were carried out using NMR spectroscopy, which revealed the formation of a 1:1 complex between host and guest, with a binding constant of Ka = 465 ± 10 M−1. On increasing the concentration of DMMP in the solution of receptor, a significant shift in proton signals was observed due to the change in magnetic environment of proton nuclei in both host and guest. In particular, a greater shift in the proton signal of PCH3 indicates the insertion of the PCH3 group inside the cup-shaped scaffold of the receptor. To find the exact binding mode of the receptor with DMMP, theoretical calculations were carried out. The alkyl chain attached with amino acid also affects the binding affinity of various receptors due to the steric effect. In another work, they have synthesized three cuplike cavitands CV2 for encapsulation of pesticides (Ruan et al., 2013). The lower part of cavitands is composed of hydrophobic aromatic rings, whereas the upper part is made up of hydrophilic functional groups such as COOH, OH, and histidine (Fig. 14.12). From the theoretical calculations, it was revealed that the receptor can encapsulate only that organophosphate species which has a size comparative to the chemical warfare agent (DCP). As the size of the organophosphate increases, the binding constant between the receptor and guest molecule decreases. To find out the binding mode of the receptor, NMR spectra were recorded in the presence of organophosphate species. The maximum shift was observed in the 1H NMR signal of PCH3; thereby, all binding studies were carried out by monitoring the shift in this signal. A slight shift in signals of dihedral protons on interaction with organophosphates revealed the change in conformation of cavitands. To find out conformation of cavitands in free and binding states, theoretical calculations were carried out. The molecular docking simulation studies revealed

484  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Fig. 14.12  Amino-acid functionalized baskets for encapsulation of organophosphates.

that the organophosphate with larger alkyl groups preferred to point toward the hydrophobic base of cavitands. Thereby, on increase in the size of the alkyl group, the preference of the guest molecule in this orientation also increases.

14.2.6  Boron-Dipyrromethene-Based Chromogenic and Fluorogenic Sensor for Organophosphates Due to the fascinating photophysical properties of BODIPY, it is widely used in the field of sensing and bio-imaging applications (Fig.  14.13). Youngmi Kim et  al. have synthesized the BODIPY derivative B2 having a phenol group that has high affinity to bind with organophosphate species (Kim et al., 2016). The probe undergoes internal rotation around the sigma bond between BODIPY and phenol which influences its emission properties. It was interesting that on

Fig. 14.13  Borondipyrromethene (BODIPY)based probes for organophosphate-based nerve agent.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   485

phosphorylation of the OH group restrict the rotation which result into ­enhancement of fluorescence intensity at 527 nm. The reaction between the probe and organophosphate was fast and the sensor gave response within 60 s. To confirm the mechanism of sensing, a control experiment was carried out. Another probe was synthesized having the hydroxyl group at para position and it performed its binding test with organophosphate-based analytes. Interestingly, it did not show a significant change in emission profile on interaction with nerve agents. It revealed the role of the ortho-hydroxyl group in detection of DCP. Further, to validate the mechanism, theoretical calculations were carried out, which also revealed that the restriction of sigma bond rotation leads to a change in the electronics of the probe, result in inhibition of the PET mechanism and enhancement in emission intensity. The probe has advantages, that is, easy synthetic method, low response time, and high selectivity. Also it did not show any interference caused by acid or phosgene. A similar kind of probe B3 was developed by Zhengliang Lu and coworkers using the BODIPY moiety (Lu et al., 2018). They have attached a cyanobenzene ring to the phenol entity of the probe. The PET mechanism was involved in donor to acceptor molecule probes which quench the fluorescence intensity. The charge transfer in the probe can be modulated by substitution in the hydroxyl group. Just like probe (B2), the hydroxyl group of probe c also has affinity to react with organophosphate species through nucleophilic substitution reaction, result in the formation of a new PO bond. It will resist the intramolecular rotation in the probe and resist the PET phenomenon; consequently, a large enhancement in fluorescence intensity was observed. Further, the mechanism of sensing was validated using theoretical calculations. The presence of the electron withdrawing group (CN) in the probe quenched the fluorescence intensity more efficiently and thereby decreased the background fluorescence. The probe exhibited high emission enhancement, low detection limit, and fast response time. Using the BODIPY entity, David G. Churchill et al. have also synthesized a probe B1 having a pyridine ring (Kim et al., 2017b). Pyridine is well known for its reaction with organophosphates; it acts as a strong ­nucleophile which attack on phosphorous center and form new NP bond by eliminating the suitable leaving group. During this process, the fluorescence intensity of the probe gets quenched and the absorbance maxima is shifted to a high wavelength. Therefore, the prepared probe was efficient to detect organophosphates with a detection limit of 3.36 μM.

14.2.7  Colorimetric Hydrogel Polymers for Organophosphate-Based Pesticides As nerve agents are easily absorbed through skin, therefore, to protect humans from their harmful effects, scientists are now trying to

486  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

construct polymer-based antidotes for pesticides that can be coated on fabric to construct protecting jackets. Other advantages of polymeric sensors include high sensitivity and low detection limit (Seyedin et al., 2015; Wei et al., 2014; Yao et al., 2013). Timothy M. Swager et al. have developed two sensitive probes for detection of nerve agents and incorporated them into copolymers (Belger et al., 2015). They have chosen ROMPolymers for construction of polymeric probe P1 due to its easy tunability. A highly arylated tertiary alcohol unit was chosen as a reactive site for phosphorylation. On reaction with phosphate species, a new bond will form between oxygen and phosphorus which results in weakening the CO bond. Thereby, on breakage of the CO bond, sp3 carbon will change into sp2 and conjugation will extend (Fig. 14.14). The dimethyl aniline unit will donate its lone pair of electrons in the ring, thereby playing a significant role in the sensing mechanism. The conjugated system has completely different photophysical properties; therefore, it can be used for detection of organophosphate species. The major advantage of this hydrogel-based probe is its reversibility; the probe can be reactivated by the addition of tetrabutylammonium hydroxide. Hyung-il Lee et  al. have developed a polymer named poly-(glycidyl methacrylate-co-dimethylacrylamide) from copolymerization of Glycidyl methacrylate (GMA) and dimethylacrylamide (DMA) (Gupta and Lee, 2017). To this polymeric architecture, pyrene fluorophore was attached. However, the prepared polymer did not show strong fluorescence due to the PET mechanism caused by the amine group. Also, there is a free alcoholic group for the phosphorylation of organophosphate. As shown in the mechanism, on phosphorylation of CO, the bond becomes weak and is therefore easily eliminated to give a cyclic ammonium ion. During this process, a lone pair of amines will consume which result into cancellation of PET mechanism and enhancement in fluorescence intensity. The detection of the limit of probe P2 was found to be 0.1 mM, which was close to the toxicity level of nerve agents. It was interesting that the sensing behavior of the probe can be tunable by altering the pH of the solution or by the addition of carbon dioxide gas.

Fig. 14.14  Detection of diethyl chlorophosphate polymeric probe.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   487

Fig. 14.15  Schematic representation of mechanism of detection of diethylcyanophosphate using probe P2 and P3.

In another work, Hyung-il Lee et al. used a similar polymer as P2 to construct another probe P3 (Balamurugan and Lee, 2016), except that the pyrene fluorophore was replaced with a pyrimidine-based photosensitive group (Fig. 14.15). In the presence of light, the probe undergoes a ring closing reaction which yields a colorless product; however, in the absence of light, the closed ring will reopen to give a highly conjugated probe. It was interesting that due to the ring closing in visible light, the probe was inactive in visible light. Similar to Probe P2, it also contains a free hydroxyl group which acts as a nucleophile and attack at electron deficient phosphorus center. As shown in the mechanism, during this process the phosphate group will be eliminated, result in the formation of six-membered rings of morpholino cations. The new product formed by the reaction of nerve agents has entirely different photophysical properties, leading to selective colorimetric detection of organophosphate in solution and in the vapor phase.

488  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

14.3  Luminescent Metal Complexes for Sensing and Degradation of Organophosphates Luminescent metal complexes have been gaining significant attention over the last few years owing to their photophysical properties (Kitchen et al., 2012; Ma et al., 2012). After the pioneering work in the ligand field theory, and deep understanding of electronic transition state and spectroscopic analysis of transition metal complexes, these luminescent complexes found widespread application in Organic optoelectronics, photochemistry, and luminescent sensors (Demas et al., 2001; Wong and Yam, 2007; Yamaguchi et al., 2007; You and Park, 2009; Zhou et  al., 2011). In sensing, the transition metal complexes have distinctive properties, such as high luminescence quantum yield, long excited state lifetime, large Stokes shift, easy for preparation, and tunable photophysical properties (Bai et al., 2013; Li et al., 2010; Lopez et al., 2012; Wang et al., 2013). These properties of metal complexes make them suitable candidates for chemosensor application. The most widely metal centers used for sensor application are included: Copper, Zinc, Nickel, Europium, Gadolinium, Platinum, Ruthenium, Iridium, Osmium, and Gold (Happ et al., 2012; Yam et al., 2011; Yamaguchi et  al., 2007). The excited state properties of these complexes comprise ligand to metal charge transfer, Metal to ligand charge transfer, intra-ligand charge transfer, and metal to metal charge transfer (Lamansky et al., 2001; You and Park, 2005; Zhao et al., 2010). These transitions are highly sensitive to the local environment and their photophysical properties can be easily tuned in sensor application (Polson et al., 2005). In this part of the review, we will discuss the detection of organophosphate by the use of metal complexes. The metal complex-based organophosphate is divided into two parts. The first part included the use of metal complex for the organophosphate sensor and the second part included the use of metal organic framework for organophosphate recognition.

14.3.1  Metal Complex-Based Organophosphate Sensor The most successful approach of metal complexes for organophosphate detection was cation displacement assay (Dennison et al., 2014; He et al., 2008; Hiscock et al., 2014). In the cation displacement ­approach, the target analyte has more affinity to the metal center as compared to its ligand and it can extract metal ion from its coordination sphere (Lou et  al., 2012; Saluja et  al., 2012; Sharma et  al., 2016a). The coordinated and uncoordinated metal complexes have

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   489

­ ifferent photophysical properties, which is the basis of analyte detecd tion (Chopra et al., 2014; Hamilton et al., 2015). C. Weder et al. have synthesized La3+, Eu3+, and Zn2+ complexes of the 2,6-bis(1′-methylbenzimidazolyl)pyridine ligand and used for fluorogenic detection of triethylphosphate and tri-o-tolylphosphate and the sensing mechanism is based on the cation displacement approach (Knapton et al., 2006). The 25 μM solution of complex 1 in the CHCl3-CH3CN (9:1 v/v) solvent system exhibited emission at 493 nm. On addition of triethylphosphate, an immediate blue shift (493–420 nm) and enhancement was observed in the fluorescence spectrum, demonstrating the release of free ligand (λem at 420 nm) from the complex and simultaneous formation of the La3+ phosphate complex. Furthermore, the addition of tri-o-tolylphosphate to the metal complex solution shows a very small change in the emission spectrum, even at higher concentration of aromatic phosphate. These observations indicate that the metal complex shows excellent selectivity for detection of triethylphosphate over the aromatic phosphate (Fig.  14.16). The sensory responses of the other metal complexes of Eu3+ and Zn2+ were also observed. The Eu3+ complex exhibited similar response toward aliphatic phosphate as shown in the Ln3+ complex. However, the Zn2+ complex did not exhibit any remarkable change in the emission spectrum on reaction of triethylphosphate. These observations indicate that Zn2+ binds more strongly with ligand as compared to Ln3+ and Eu3+ and hinders the cation displacement approach (Burnworth et al., 2007). In order to facilitate the practical utility of these complexes, the Eu3+ complex was adsorbed on the hydrophobic silica surface, resulting in solid power, which changed its fluorescence color from pink to blue on exposure of triethylphosphate.

Sensor "ON"

Sensor "OFF"

N N N

N

Mn3+

O OEt P EtO OEt

N N N

N N

1

Mn3+

N

O P OEt EtO OEt

Mn3+ = La3+ and Eu3+

Fig. 14.16  Detection of nerve agent through the cation displacement assay approach by using complex 1.

490  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Fig. 14.17  Detection of azamethiphos through the cation displacement assay approach by using complex 2.

Recently, Singh et  al. have explored the naphthalimide-based copper complex (Fig.  14.17) for selective sensing of azamethiphos (Raj et  al., 2017). The copper complex 2 had shown a low emission band at 430 nm. On treatment of the complex with the library of organophosphate/biophosphate, a remarkable change in emission intensity was observed in the case of azamethiphos. The emission spectrum of complex 2 exhibits fourfold enhancements on addition of azamethiphos. The emission enhancement was due to the removal of copper from the coordination sphere of the complex into free ligand and formation of the copper: azamethiphos complex. The binding mechanism was based on the cation displacement assay; the bound and unbound copper complex has different photophysical properties which can be used for detection of azamethiphos in nanomolar range. The zinc complex of fluorescein hydroxyl benzothiazole (FHC) conjugates (Fig.  14.18) has been reported for sensing of DCP and DCNP via a PET-decoupled ESIPT process (Ii et  al., 2017). With the addition of DCP to the FHC-Zn2+ complex, a fluorescence change from cyan to orange was observed in the emission region. The change caused a ratiometric pattern (quenching at λem = 484 and enhancement at λem = 536 nm) in the fluorescence spectrum. However, in case of DCNP, the FHC-Zn2+ complex did not show a similar emission pattern as observed in case of DCP. The emission peak at 484 nm is slightly increased on addition of DCNP and no peak is observed at 536 nm.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   491

T SIP

F"

"OF

E

F"

"OF

" FF "O T PE

14.3.2  Luminescent Metal Organic Framework for Detection of Organophosphate The metal organic framework has gained tremendous attention since the last two decades, due to their application in gas storage, separation, catalysis, and chemical sensing (Bobbitt et  al., 2017; Liu et al., 2017). These materials are a good choice for these applications as metal organic framework (MOFs) are crystalline and have a large surface area, high porosity, and tunability in the structure (Figs. 14.19 and 14.20) (Rudd et al., 2016). MOFs contain organic linkers and inorganic metal oxide in their structural framework as shown in Fig. 14.19, and therefore it is easy to tune the intrinsic properties of MOF by modifying the organic linker for the desired application (Furukawa et al., 2013; Lustig et al., 2017). A luminescent metal organic framework used for the chemosensor purpose contains the following ingredients in their structure framework: aromatic ligands, d10-transition metals, some F-block metal ions, and specific guest molecules fit into the pores (Cui et al., 2016; Zhao et al., 2016). The π conjugated organic linkers emitting fluorescence are assembled in rigid MOFs which are composed of metal ions. The organic linkers are closely positioned in the MOF and give out emission which is different from the pure organic ligand. Moreover, the guest molecules fit into the cavity of the MOF and interact with the active center of framework, as well as modulate the emission intensity with respect to free guest or pure host materials (Su et al., 2017; Yan, 2017). Host-guest interaction can be modulating the emission

" FF "O

The interference studies were carried out with other type of pesticides but no interference was observed, and this shows the selective sensing of DCP/DCNP through the FHC-Zn2+complex.

T

Fig. 14.18  Systematic representation of probable binding modes of DCP and DCNP toward the FHC-Zn2+ complex.

PE

ON"

" PET

PE T"

ON

"

T ESIP

492  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

+ Metal ions or clusters

= Organic linkers or struts

Metal-organic framework (MOF)

Fig. 14.19  Systematic representation of metal-organic framework (MOF) showing metal ion and organic linkers. Image taken from Liu, Y., Howarth, A.J., Vermeulen, N.A., Moon, S.-Y., Hupp, J.T., Farha, O.K., 2017. Catalytic degradation of chemical warfare agents and their simulants by metal-organic frameworks. Coord. Chem. Rev. 346, 101–111.

Fig. 14.20  The metal organic frameworks showing tunability in emission and color in presence of different analyte. Image taken from Cui, Y., Zhang, J., Chen, B., Qian, G., 2016. Lanthanide metal-organic frameworks for luminescent applications. In: Bünzli, J.-C.G., Pecharsky, V.K.B.T.-H. (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Including Actinides. Elsevier (Chapter 290), pp. 243–268.

intensity which depends on the electronic properties of the materials. There are two mechanisms operating in MOFs for the sensing of analytes that is, Fluorescence “ON” and Fluorescence “OFF.” In the fluorescence “ON” case, the fluorescence enhancement occurs due to the transfer of excited state electrons from the guest molecules to the conduction band of host material and in the fluorescence “OFF”

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   493

case, it takes place when excited state electrons aree promoted from the MOF center to the electron deficient analyte, such as in the case of nitro aromatic compound (Lim et al., 2017). B.Z. Tang et  al. have synthesized the luminescent metal-organic framework [Zn2(bpdc)2(BPyTPE)] (1) (BPyTPE = (E)-1,2-diphenyl1,2-bis(4-(pyridin-4-yl)phenyl)ethene) for the detection of pesticides 2,6-dichloro-4-nitroaniline in trace amount (Tao et al., 2017). The emission intensity of solvent free MOF (1) shows quenching in the presence of 2,6-dichloro-4-nitroaniline due to the excited electron transfer from donor (LMOF) to acceptor (nitroaniline) molecules. Furthermore, the titration experiment confirmed the quenching in emission intensity with increase in the concentration of 4-nitroaniline. The quenching efficiency was estimated with formula (I0 − I)/I0, where I0 and I are the emission intensities of solvent-free 1 before and after adding the analyte. The emission starts to decrease from 58 ppm of nitroaniline to 98% on addition of 1800 ppm of analyte. The MOF showing the lowest detection limit is 4.7 × 10−2 ppm, which was less than the China National Food Safety Standard-Maximum Residue Limits for Pesticides in Food. T. Hupp et al. have synthesized numerous zirconium-based metal organic frameworks for the catalytic degradation of chemical warfare and organophosphate compounds (Liu et al., 2015). The catalytic activity of organophosphate is enhanced due to the strong Lewis acid character of zirconium which increases the electrophilicity of the PO bond and 78% of hydrolysis occurs within 60 min (Mondloch et al., 2015). P. Cheng et al. have synthesized the lanthanide-based luminescent metal organic framework of (Ln-MOF), {[Eu2(L)3(DMF)2]·DMF·MeOH}n (Ln-MOF 1, H2L = 5-(4H-1,2,4-triazol-4-yl)benzene-1,3-dicarboxylic acid) for the detection of the polychlorinated organic pollutant (Wang et al., 2017). The synthesized MOF exhibited red emission in their fluorescence spectra owing to the antenna effect of the ligand. However, on addition of polychlorobenzene, significant quenching in the emission spectrum was noted. The quenching in the emission profile of MOF was due to the excited p state energy transfer from the ligand to LUMO of the analyte.

14.4  Nanoparticle for Pesticide Detection Semiconductor nanoparticles offer good optical and electronic properties for chemosensing/biosensing and cell imaging (Li et  al., 2015; Marchese Robinson et al., 2016). They hold diverse advantages over organic receptors, such as high quantum yield, tunable color, broad absorption and emission band, and good photostability (Jans and Huo, 2012). The nanoparticle-based chemosensor has become one of the fastest growing fields as nanoparticle-based products hold a wide range of materials that can be used to enhance the selectivity, sensitivity, and stability of sensor systems (Zeng et al., 2014).

494  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

14.4.1  Gold Nanoparticle for Organophosphate Sensor Gold nanoparticle-based colorimetric assays have been become one of the most important techniques for detection of analytes with routine experiment, because the specific binding events undergo color changes (Dykman and Khlebtsov, 2012). The color changes of gold nanoparticles are highly sensitive to shape, size, capping agents, medium refractive index, and aggregation state. The modulation in the aggregate state of gold nanoparticles has been widely used for colorimetric assay of various analytes (Van Rie and Thielemans, 2017). Generally, the gold nanoparticles in solution state are red in color; however, in aggregate state, the color changes from purple to blue. The change in color can also be confirmed from the shift in absorption band of the UV-Visible spectrum. M.R.H. Nezhad et al. have developed a colorimetric array consisting of citrate capped gold nanoparticles for detection and discrimination of several organophosphates (Fahimi-Kashani and Hormozi-Nezhad, 2016). The detection mechanism of organophosphates based on the aggregation of citrate capped gold nanoparticles under different pH/ionic strength leads to different color change. Furthermore, the absorption spectra have been utilized to identify the Organophosphates through multivariate analysis methods, such as hierarchical cluster analysis (HCA) and linear discriminate analysis (LDA). The prepared sensor array was successfully used for real sample analysis of Organophosphates in rice and paddy water. In recent years, the Chemiluminescent assays for detection of analyte gain remarkable interest due to their high sensitivity and simplicity in operation. X. Jiang et  al. have designed a rhodamine 6B–functionalized gold nanoparticle assay for highly selective and sensitive detection of AChE in the cerebrospinal fluid of transgenic mice suffering from Alzheimer's disease (Liu et  al., 2012). The assay exhibits both colorimetric and fluorimetric monitoring of AChE. The ligand rhodamine 6B was chosen for functionalization of gold nanoparticles because it has excellent photostability, water solubility, and strong fluorescence and readily adsorbs on the surface of nanoparticles through electrostatic interaction, which causes fluorescence quenching (Fig. 14.21). On addition of Acetylthiocholine (ATC) and AChE to RB-AuNP, the solution exhibits color change from red to purple, simultaneously involving the enhancement in the fluorescence intensity. The binding mechanism is based on the fact that the AChE hydrolyzes ATC to thiocholine, which has a stronger tendency to bind with the Au nanoparticle surface than RB and thus replaces the RB with thiocholine on the surface of AuNPs and restores the original fluorescence intensity of RB. The thiocholine and residual RB were linked to the surface of AuNPs through electrostatic interaction, which is confirmed

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   495

Fig. 14.21  Dual-readout (colorimetric and fluorometric) assay for analysis of organophosphates.

through the change in color from red to purple as shown in Fig. 14.21. Further, the AChE pretreated with organophosphate and carbamates inhibits the activity of AChE and stops hydrolysis of ATC to thiocholine; as a result, the color of RB-AuNPs remains red and fluorescence remains quenched. By use of this method, the different pesticides such as carbaryl, diazinon, malathion, and phorate were measured in the lowest detection limit as 0.1, 0.1, 0.3, and 1 μg/L, respectively which is much lower than the maximum residue limits (MRL) as reported in the European Union pesticides database as well as those from the US Department of Agriculture (USDA). This assay was further utilized for real sample analysis of some food and agriculture products and the results agree with those detected with High performance liquid chromatography. T.J. Park et  al. have developed AuNPs and utilized them for the detection of organophosphates in agricultural samples (Baek et  al., 2017). The imidazole, along with organophosphate, was added to AuNPs solution and the color of the solution changed from red to purple, which caused the absorbance shift from 520 to 660 nm (Fig. 14.22). This was due to the aggregation of AuNPs; in the presence of imidazole, small aggregates were formed; whereas, large aggregates were formed in presence of both imidazole and OPs. Furthermore, the aggregation-based AuNPs were utilized for the fabrication of small

496  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Fig. 14.22  Optical detection of contaminations through the aggregation effect of AuNPs.

portable devices for the detection of organophosphate, as shown in Fig. 14.22. The device senses the different agricultural complexes in very selective and sensitive ways. The reliability of the device was investigated by comparing the detection results with the HPLC results.

14.4.2  Silver Nanoparticle for Organophosphate Sensor Y. He et al. have developed a simple, facile, and highly sensitive ­silver nanoparticle-based chemiluminescent sensor for detection of organophosphate and carbamate pesticides (He et  al., 2015). The ­luminol functionalized silver nanoparticles react with H2O2 and p ­ roduce a CL emission. The Lum-AgNP-H2O2 CL system is slower process then LumAgNP and therefore, show dynamic tunability on varying the reaction conditions. The Lum-AgNP-H2O2 CL system show CL intensity, the time for CL emission, and time to reach the CL peak value (triple channel properties), all of these parameters can be measured be in a single experiment. The triple channel properties of Lum-AgNP-H2O2 CL were varied with the interaction of pesticides and showed different CL response spectra, which is used as a fingerprint to determine and distinguish the specific pesticides. The synthesized sensor system detected the five different organophosphates and carbamate pesticides with the lowest detection limit as shown in Fig. 14.23.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   497

H2O2

CL intensity

Ag

Pesticides

CL response

Ta

Tp

Luminol

Fig. 14.23  The representation of the principle of the chemiluminescent array based on the triple-channel properties of the Lum-AgNP-H2O2 CL system.

14.4.3  Aptamer-Based Organophosphate Sensor The nonstereotypical synthetic nucleic acid has become one of the outstanding molecular recognition elements, as they have secondary and tertiary structures to bind with the specific target (Fig. 14.24). These synthetic nucleic acids have several advantages over the antibodies, such as easy to functionalize, low synthetic cost, and high stability, which makes them outstanding recognition element. The single stranded DNA and RNA molecules that are synthesized in vitro through selection process called aptamers. The most significant aspect of an aptamer is that it can be generated in the presence of a large number of biomolecules such as antibodies, antibiotics, amino acid, biomolecules, carbohydrate and prokaryotic, and eukaryotic cell. V. Bansal et al. have synthesized S-18 aptamer-based gold nanoparticles for pesticide sensing (Weerathunge et al., 2014). It is reported that gold nanoparticles exhibit peroxidases-like activity, and these activities can be inhibited by its surface charged with S-18 aptamer, which has a specific binding site for acetamiprid. On binding with acetamiprid, the aptamer leaves the gold nanoparticle surface and reactivates the GNP Nano enzyme activity. The reversibility of GNP activity can be quantify through the color change or change in emission spectrum. This assay detects the acetamiprid in 0.1 ppm within 10 min of time. The approach was further used for the sensing of environmental sample.

Fig. 14.24  Acetamipridspecific S-18 ssDNA aptamer as reversible inhibitor of the nanozyme activity of GNPs.

498  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

14.4.4  Semiconductor Quantum Dot for Organophosphate Detection Quantum dots are very minute semiconductor particles having excellent brightness, size tunability, fluorescence, and resistance to photo bleaching. Due to their excellent optoelectronic properties, these nanomaterials have found good use in the sensor field. Silicon quantum dots (SiQDs) have more unique optical and electronic properties than other QDs, especially in biocompatibility, and therefore play an important role in various applications. S. Yao et al. have developed silicon-based quantum dots for a highly selective and sensitive sensor for organophosphate (Yi et al., 2013). The sensing strategy was based on the hydrolysis of acetylcholine by the acetylesterase enzyme to yield choline, which oxidizes by choline oxidase (CHOx) to form betaine and H2O2, and this can quench the fluorescent intensity of SiQDs (Fig. 14.25). On addition of pesticides, the activity of acetylcholine is inhibited and this caused the decrease in concentration of generated H2O2 and increase in the fluorescence intensity of SiQDs. This fluorescence “ON” method was used for the detection of five organophosphates carbaryl, parathion, diazion, and phorate in the lowest detection limit of 7.25 × 10−9, 3.25 × 10−8, 6.76 × 10−8, 1.9 × 10−7 g/L, respectively, which is showing good agreement with the result interpreted from the HPLC method.

Fig. 14.25  Systematic representation of SiQDs as pesticide biosensor.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   499

H N

O

S

= DDTC

S

O

O

O

O

O

PET "ON" OC2H5 C2H5O P OC2H5 O S S P OC2H5 ZnS:Mn O S NC O HN S S P OC2H5 OC2H5

NH ZnS:Mn NC

S

DDTC

S HN

Dual emission at 435 and 600 nm

S S ZnS:Mn NC

NH S S

DEP

S S HN O O

O O

O O

Quenchining at 600nm

Fluorescence turn "ON" at600nm

Fig. 14.26  Systematic representation for synthesis of the dual-emitting probe and the mechanism for ratiometric detection of DEP.

S. Wang et  al. have synthesized a hybrid nanoparticle consisting of a manganese-doped ZnS nanocrystal showing ratiometric emission for detection of the hydrolysis product of diethylphosphothioate (Zhang et al., 2014). The sensing strategy for DEP determination of the designing nanocrystal was based on the photo induced electron transfer mechanism. The manganese-doped ZnS nanocrystal was synthesized through the chemical precipitation method and functionalized with dopamine through covalent bonding (Fig.  14.26). The ZnS:Mn nanocrystal exhibited two emission bands at 435 nm of blue emission and 600 nm of red emission under a single wavelength excitation. The functionalized nanocrystals show the selective quenching of fluorescence intensity of red emission due to the PET mechanism from the excited nanoparticle to oxidized dopamine-quinone of DDTC. On addition of DEP, the enhancement in red emission was occurring and the blue shift remains unchanged due to stable internal reference. The enhancement in fluorescence at 600 nm was due to the replacement of DDTC to DEP as DEP is strongly coordinated to the nanoparticle; as a result, the PET pathway created by DDTC is switched off. Moreover, with the increase in addition amount of DEP, the duel intensity ratio of nanocrystal increase which result into change in color from dark blue to pink, which can be clearly visible to naked eyes. The grapheme oxide (GQDs) quantum dots fabricated on ­paper-based device were reported for detection of two phenolic compounds in food and environmental samples (Fig.  14.27). The paper

500  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

on

on

ati

ati

it xc V-e

cit -ex UV

U

FRET quenchning

FRET quenchning

Fig. 14.27  Fluorescence quenching of quantum dots in the presence of an analyte by the FRET phenomenon.

was coated with fluorescence GQDs and introduced into a homemade dark chamber irradiated with UV light with an LED. The fluorescence intensity of GQDs was dramatically quenched on interaction with the analyte. This is due to the excited state energy of GQDs which was transfer to acceptor of analyte through FRET mechanism. The loss in fluorescence intensity was monitored by mobile phone camera and fluorescent count were extracted. Further, the paper-based device was used for the selective detection of 4-nitroaromatic and paraoxon from the environment pollutant. The inner filter effect (IFE) involves the absorption of excitation or emission intensity of fluorophore in the sensor system, which, as a result, caused several errors in the sensor system. However, the IFE can be overcome and utilized for a better detection system by converting the absorption signal to emission signal. The change in the absorbance of the absorber can transfer the exponential change in the fluorescence of fluorophore and enhance the better selectivity and sensitivity of the sensor system. Moreover, the sensor system does not require the covalent bonding between the absorber and emitter; they can be used as such. The limited choice of absorber and emitter limited the use of IFE for sensor development, It is worth to be mention here that the IFE system work effectively when absorbance band of absorber overlap with emission band of the fluorophore. The gold nanoparticle has a larger extinc-

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   501

tion coefficient which makes it a better absorber than other convention chromophores in the IRF-based assay. C. Sun et al. have detected methamidophos pesticides via IFE of the Au nanoparticle on the fluorescence of CdTe (Guo et al., 2014). The proposed IRF assay contains AuNPs as an absorber and CdTe as a fluorophore unit (Fig. 14.28). The citrate capped gold nanoparticles are well stabilized, red in color, and exhibit absorbance band at 522 nm. The fluorescence intensity of thioglycolic acid capped CdTe showed quenching in the presence of citrate capped gold nanoparticles due to the IRF effect. The positively charged ATC provides a substrate for AChE and adsorbs on the surface of negatively charged gold nanoparticles through electrostatic interaction. AChE convert acetylthiocholine into thiocholine which is positive charged molecule, have thiol group. High affinity of thiocholine to strongly binding with gold nanoparticle and simultaneously removal of citrate ion cause aggregation of AuNPs. The aggregation occurs by electrostatic interaction and covalent interaction of thiol with the gold nanoparticle surface; as a result, the decrease in absorbance occurs (due to decrease in the IRF) and the fluorescence intensity of CdTe increases. On addition of organophosphate, the activity of acetylcholinesterase (AChE) is restricted and again the quenching in the emission of fluorescence occurs due to the IFE of gold nanoparticles. Thus, the modulation of fluorescence intensity of CdTe quantum dots through gold nanoparticles in the presence of organophosphate is the basis of pesticide detection. Furthermore, the prepared method was successfully utilized for organophosphate detection in the vegetable sample.

Fig. 14.28  Detection of organophosphates based on enzyme inhibition using inner filter effect of AuNPs on the fluorescence of CdTe QDs.

502  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

14.5  Enzyme-Based Biosensor for Pesticides To date, the number of biosensors has been established for organophosphates based on the AChE or butyryl cholinesterase (BChE) inhibition through different organophosphates (Sassolas et  al., 2012). The enzyme-based sensor for organophosphate can be classified into two categories based on their working mechanism (1) AChE; (2) organophosphorus hydrolyses (OPH). The natural enzymes AChE and BChE preferably hydrolyze acetyl ester and butyrylcholine and produce acid formation as shown in the equation given below: AChE

Acetylcholine + H2 O → Choline + Acetic acid BChE

Butyrylcholine + H2 O → Choline + Butyric acid The acid formations can be detected by the number of analytical methods, such as electrochemical, potentiometric, or pH sensitive spectrophotometric indicator or fluorometric indicator methods (Obare et al., 2010). Roger et al. have used AChE connected fluorescein isocyanate (FITC) dye for organophosphate detection (Rogers et al., 1991). The enzyme-dye complex was immobilized on the surface of the quartz fiber, which is attached to the fluorescence spectrophotometer, and emission intensity was measured. In the absence of organophosphate, the enzyme hydrolyzes the acetylcholine into choline and acetic acid. The evolution of acid from enzymatic reaction causes the reduction in emission intensity of FITC, which is due to protonation in the conjugation of fluorescein dye as shown in Fig. 14.29. However, in the presence of organophosphate, the activity of acetylcholinesterase is inhibited and did not produce any acid; as a result, the fluorescence intensity did not suffer from any quenching in emission. This method has one serious drawback as the acetylcholine enzyme activity was inhibited in the presence of heavy metal ions, fluorides, nerve gas, and nicotinic acid. Therefore, this method exhibits the selectivity and specificity problem in the presence of these interfering ions. The second method of enzymatic-based biosensors involves the use of OPH as detection of organophosphates. The mechanism of action of OPH is somewhat different from that of acetylcholinesterase; it can hydrolyze the organophosphate molecules into its component instead of covalently binding it. Thus, it can directly measure the organophosphate instead of observing the enzyme inhibition assay. The OPH assay is broadly used as biosensors owing to its ability to hydrolyze a large number of compounds holding PO, PF, PCN, and PS bonds (Cao et al., 2007).

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   503

Fig. 14.29  Variation in the structure of fluorescein isothiocyanate (FITC) at different pH. O R1

P X

O R2 + R2O

OPH

R1

P

R2 + HX

OH

X. Cao et  al. have developed the Langmuir monolayer of OPH linked with FITC dye and explored it as bioassay for paraoxon detection (Cao et al., 2004). The results of the Langmuir–Blodgett OPH ­bioassay are highly reproducible and display quick response time and a broad range of linear responses of the analyte. Furthermore, the paraoxon detection through the OPH-FITC bioassay was also confirmed through fluorescence methods which show a decline in the emission intensity of fluorescein.

14.6  Conclusion and Future Prospects Fluorescence detection and detoxification of pesticides are emerging areas of agriculture and environmental science. In this report, we have discussed various organic and inorganic-based probes for detection of organophosphates. In addition, oxime-based organocatalyst and transition metal-based frameworks were also discussed for detoxification of organophosphates. In recent years, organic farming is promoted by government and social societies in the world. Organic products are available in the market at a slightly higher cost than products produced by using pesticides and commercial fertilizers. Due to the lack of simple tools for detection of pesticides, consumers cannot distinguish between organic and contaminated foods. If these probes can be commercialized through industry, it will not only boost organic

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farming but also promote health care. Therefore, the future strategy should be the development of low cost devices that can be used in the field for detection of organophosphates. Although some organic and inorganic catalysts are developed for detoxification of pesticides, it is still doubtful whether these are safe for humans if added to beverages. In vivo and in vitro biocompatibility should be tested; before commercialization, it should go through various clinical trials. In the near future, we are expecting that some of these probes will be commercialized and give a boost to the beverages industry. In addition, these probes can be further used for construction of protective cloths and electronic noses.

Acknowledgment This work was supported with a research grant from DST New Delhi, project number (Project No. EMR/2014/000613). A. S. and P. R. are thankful to CSIR-New Delhi (9/1005(0010)/2014-EMR-1), India and UGC (New Delhi), respectively, for fellowship.

References Aich, K., Das, S., Gharami, S., Patra, L., Mondal, T.K., 2017. Triphenylamine–­ benzimidazole based switch offers reliable detection of organophosphorus nerve agent (DCP) both in solution and gaseous. New J. Chem. 41, 12562–12568. Baek, S.H., Lee, S.W., Kim, E.J., Shin, D., Lee, S., Park, T.J., 2017. Portable agrichemical detection system for enhancing the safety of agricultural products using aggregation of gold nanoparticles. ACS Omega 2, 988–993. Bai, R., Gao, W., Bai, S., Yang, F., Chen, H., 2013. A novel fluorescent Fe3+ sensor based on a europium complex. Opt. Mater. 35, 833–836. Balamurugan, A., Lee, H., 2016. A visible light responsive on–off polymeric photoswitch for the colorimetric detection of nerve agent mimics in solution and in the vapor phase. Macromolecules 49, 2568–2574. Belger, C., Weis, J.G., Egap, E., Swager, T.M., 2015. Colorimetric stimuli-responsive hydrogel polymers for the detection of nerve agent surrogates. Macromolecules 48, 7990–7994. Bobbitt, N.S., Mendonca, M.L., Howarth, A.J., Hupp, J.T., Farha, K., Snurr, R.Q., Bobbitt, N.S., 2017. Metal-organic frameworks for the removal of toxic industrial chemicals and chemical warfare agents. Chem. Soc. Rev. 46, 3357–3385. Borja, D., Gren, D., Moreno, D., Berg, A., Gunnars, J., Nilsson, T., Nyman, R., Persson, M., Pettersson, J., Eklind, I., 2014. Fluorescent discrimination between traces of chemical warfare agents and their mimics. J. Am. Chem. Soc. 136, 4125–4128. Brandhuber, F., Zengerle, M., Porwol, L., Bierwisch, A., Koller, M., Reiter, G., Woreka, F., Kubik, S., 2013. Tabun scavengers based on hydroxamic acid containing cyclodextrins. Chem. Commun. 49, 3425–3427. Burnworth, M., Rowan, S.J., Weder, C., 2007. Fluorescent sensors for the detection of chemical warfare agents. Chem. Eur. J. 13, 7828–7836. Cao, H., Nam, J., Harmon, H.J., Branson, D.H., 2007. Spectrophotometric detection of organophosphate diazinon by porphyrin solution and porphyrin-dyed cotton fabric. Dyes Pigments 74, 176–180. Cao, X., Mello, S.V., Leblanc, R.M., Rastogi, V.K., Cheng, T., Defrank, J.J., 2004. Detection of paraoxon by immobilized organophosphorus hydrolase in a Langmuir–Blodgett film. Colloids Surf. A Physicochem. Eng. Asp. 250, 349–356.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   505

Chen, W., Gong, W., Ye, Z., Lin, Y., Ning, G., 2013. FRET-based ratiometric fluorescent probes for selective Fe3+ sensing and their applications in mitochondria. Dalton Trans. 1, 10093–10096. Chopra, S., Singh, J., Singh, N., Kaur, N., 2014. Fluorescent organic nanoparticles of tripodal receptor as sensors for HSO4- in aqueous medium: application to real sample analysis. Anal. Methods 6, 9030–9036. Cui, Y., Zhang, J., Chen, B., Qian, G., 2016. Lanthanide metal-organic frameworks for luminescent applications. In: Bünzli, J.-C.G., Pecharsky, V.K.B.T.-H. (Eds.), Handbook on the Physics and Chemistry of Rare Earths. Including ActinidesElsevier, pp. 243– 268. (Chapter 290). Dale, T.J., Rebek, J., 2006. Fluorescent sensors for organophosphorus nerve agent mimics. J. Am. Chem. Soc. 128, 4500–4501. Demas, J.N., Degraff, B.A., Madison, J., 2001. Applications of luminescent transition platinum group metal complexes to sensor technology and molecular probes. Coord. Chem. Rev. 211, 317–351. Dennison, G.H., Sambrook, R., Johnston, M.R., 2014. Interactions of the G-series organophosphorus chemical warfare agent sarin and various simulants with luminescent lanthanide complexes. RSC Adv. 4, 55524–55528. Dykman, L., Khlebtsov, N., 2012. Gold nanoparticles in biomedical applications: recent advances and perspectives. Chem. Soc. Rev. 41, 2256–2282. Fahimi-Kashani, N., Hormozi-Nezhad, M.R., 2016. Gold-nanoparticle-based colorimetric sensor array for discrimination of organophosphate pesticides. Anal. Chem. 88, 8099–8106. Furukawa, H., Cordova, K.E., O’Keeffe, M., Yaghi, O.M., 2013. The chemistry and applications of metal-organic frameworks. Science 341 (6149). Ghenuche, P., Mivelle, M., de Torres, J., Moparthi, S.B., Rigneault, H., Van Hulst, N.F., García-Parajó, M.F., Wenger, J., 2015. Matching nanoantenna field confinement to fret distances enhances förster energy transfer rates. Nano Lett. 15, 6193–6201. Gillon, E., Mercey, G., Verdelet, T., Wagner, A., Baati, R., Jean, L., Nachon, F., Renard, P., 2011. First efficient uncharged reactivators for the dephosphylation of poisoned human acetylcholinesterase. Chem. Commun. 47, 5295–5297. Gravier, J., Sancey, L., Hirsjärvi, S., Rustique, E., Passirani, C., Benoît, J.-P., Coll, J.-L., Texier, I., 2014. FRET imaging approaches for in vitro and in vivo characterization of synthetic lipid nanoparticles. Mol. Pharm. 11, 3133–3144. Guo, J., Li, H., Xue, M., Zhang, M., 2014. Highly sensitive detection of organophosphorus pesticides represented by methamidophos via inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots. Food Anal. Methods 7, 1247–1255. Gupta, M., Lee, H., 2017. A pyrene derived CO2 responsive polymeric probe for the turn-on fluorescent detection of nerve agent mimics with tunable sensitivity. Macromolecules 50, 6888–6895. Hamilton, G.R.C., Sahoo, S.K., Kamila, S., Singh, N., Kaur, N., Hyland, B.W., Callan, J.F., 2015. Optical probes for the detection of protons, and alkali and alkaline earth metal cations. Chem. Soc. Rev. 44, 4415–4432. Happ, B., Winter, A., Hager, D., Schubert, U.S., Winter, A., 2012. Photogenerated avenues in macromolecules containing Re(I), Ru(II), Os(II), and Ir(III) metal complexes of pyridine-based ligands. Chem. Soc. Rev. 41, 2222–2255. He, G., Zhao, Y., He, C., Liu, Y., Duan, C., 2008. “Turn-on” fluorescent sensor for Hg2+ via displacement approach. Inorg. Chem. 47, 5169–5176. He, Y., Xu, B., Li, W., Yu, H., 2015. Silver nanoparticle-based chemiluminescent sensor array for pesticide discrimination. J. Agric. Food Chem. 63, 2930–2934. Hiscock, J.R., Sambrook, M.R., Ede, J.A., Wells, J., Gale, P.A., 2014. Disruption of a binary organogel by the chemical warfare agent soman (GD) and common organophosphorus simulants. J. Mater. Chem. A 3, 1230–1234.

506  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Hiscock, J.R., Wells, N.J., Ede, J.A., Gale, A., Sambrook, M.R., 2016. Biomolecular chemistry towards chemical warfare agent recognition. Org. Biomol. Chem. 14, 9560–9567. Hörnberg, A., Tunemalm, A.K., Ekström, F., 2007. Crystal structures of acetylcholinesterase in complex with organophosphorus compounds suggest that the acyl pocket modulates the aging reaction by precluding the formation of the trigonal bipyramidal transition state. Biochemistry 46, 4815–4825. Hu, X., Su, Y., Ma, Y., Zhan, X., Zheng, H., Jiang, Y., 2015. A near infrared colorimetric and fluorometric probe for organophosphorus nerve agent mimics by intramolecular amidation. Chem. Commun. 51, 15118–15121. Ii, Z., Manna, A., Jana, K., 2017. Discrimination of tabun mimic diethyl cyanophosphonate from sarin mimic diethyl. New J. Chem. 41, 6661–6666. Jans, H., Huo, Q., 2012. Gold nanoparticle-enabled biological and chemical detection and analysis. Chem. Soc. Rev. 41, 2849–2866. Jia, C., Zuo, W., Zhang, D., Yang, X., Wu, B., 2016. Anion recognition by oligo-(thio)ureabased receptors. Chem. Commun. 52, 9614–9627. Kim, T., Maity, S.B., Bouffar, J., Kim, Y., 2016. Molecular rotors for the detection of chemical warfare agent simulants. Anal. Chem. 88, 9259–9263. Kim, Y., Jang, G., Lee, T.S., 2015. New fluorescent metal-ion detection using a p ­ aper-based sensor strip containing tethered rhodamine carbon nanodots. ACS Appl. Mater. Interfaces 7, 15649–15657. Kim, Y., Jang, J., Mulay, S.V., Nguyen, T.T., 2017a. Fluorescent sensing of a nerve agent simulant with dual emission over wide pH range in aqueous solution. Chem. Eur. J. 23, 7785–7790. Kim, Y., Jeong, Y., Lee, D., Kim, B., Churchill, D.G., 2017b. Real nerve agent study assessing pyridyl reactivity: selective fluorogenic and colorimetric detection of soman and simulant. Sensors Actuators B Chem. 238, 145–149. Kitchen, J.A., Boyle, E.M., Gunnlaugsson, T., 2012. Synthesis, structural characterisation and luminescent anion sensing studies of a Ru (II) polypyridyl complex featuring an aryl urea derivatised 2,2′-bpy auxiliary ligand. Inorg. Chim. Acta 381, 236–242. Knapton, D., Burnworth, M., Rowan, S.J., Weder, C., 2006. Fluorescent organometallic sensors for the detection of chemical-warfare-agent mimics. Angew. Chem. 118, 5957–5961. Kovarik, Z., Radić, Z., Berman, H., Simeon-Rudolf, V., Reiner, E., Taylor, P., 2003. Acetylcholinesterase active centre and gorge conformations analysed by combinatorial mutations and enantiomeric phosphonates. Biochem. J. 373, 33–40. Lamansky, S., Djurovich, P., Murphy, D., Abdel-Razzaq, F., Lee, H.-E., Adachi, C., Burrows, P.E., Forrest, S.R., Thompson, M.E., 2001. Highly phosphorescent bis-­ cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes. J. Am. Chem. Soc. 123, 4304–4312. Le Provost, R., Wille, T., Louise, L., Masurier, N., Müller, S., Reiter, G., Renard, P.-Y., Lafont, O., Worek, F., Estour, F., 2011. Optimized strategies to synthesize β-­cyclodextrin-oxime conjugates as a new generation of organophosphate scavengers. Org. Biomol. Chem. 9, 3026. Lei, Z., Yang, Y., 2014. A concise colorimetric and fluorimetric probe for sarin related threats designed via the “covalent-assembly” approach. J. Am. Chem. Soc. 136, 6594–6597. Li, B., Chen, Q.-Y., Wang, Y.-C., Huang, J., Li, Y., 2010. Synthesis, characterization and fluorescence studies of a novel europium complex based sensor. J. Lumin. 130, 2413–2417. Li, N., Su, X., Lu, Y., 2015. Nanomaterial-based biosensors using dual transducing elements for solution phase detection. Analyst 140, 2916–2943. Lim, K.S., Jeong, Y., Kang, W., Song, H., Jo, H., 2017. Luminescent metal-organic framework sensor: exceptional Cd2+ turn-on detection and first in situ visualization of Cd2+ ion diffusion into a crystal. Chem. Eur. J. 4803–4809.

Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES   507

Liu, D., Chen, W., Wei, J., Li, X., Wang, Z., Jiang, X., 2012. A highly sensitive, dual-­readout assay based on gold nanoparticles for organophosphorus and carbamate pesticides. Anal. Chem. 84, 4185–4191. Liu, G., Lin, Y., 2006. Biosensor based on self-assembling acetylcholinesterase on carbon nanotubes for flow injection/amperometric detection of organophosphate pesticides and nerve agents. Anal. Chem. 78, 835–843. Liu, Y., Howarth, A.J., Vermeulen, N.A., Moon, S.-Y., Hupp, J.T., Farha, O.K., 2017. Catalytic degradation of chemical warfare agents and their simulants by metal-­ organic frameworks. Coord. Chem. Rev. 346, 101–111. Liu, Y., Moon, S.Y., Hupp, J.T., Farha, O.K., 2015. Dual-function metal-organic framework as a versatile catalyst for detoxifying chemical warfare agent simulants. ACS Nano 9, 12358–12364. Lopez, I.S., Luisa Mendonça, A., Fernandes, M., Bermudez, V.d.Z., Morgado, J., Del Pozo, G., Romero, B., Cabanillas-Gonzalez, J., 2012. Europium complex-based thermochromic sensor for integration in plastic optical fibres. Opt. Mater. 34, 1447–1450. Lou, X., Ou, D., Li, Q., Li, Z., 2012. An indirect approach for anion detection: the displacement strategy and its application. Chem. Commun. 48, 8462–8477. Lu, Z., Fan, W., Shi, X., Black, C.A., Fan, C., Wang, F., 2018. A highly specific BODIPYbased fluorescent probe for the detection of nerve-agent simulants. Sensors Actuators B Chem. 255, 176–181. Lustig, W.P., Mukherjee, S., Rudd, N.D., Desai, A.V., Li, J., Ghosh, S.K., 2017. Metalorganic frameworks: functional luminescent and photonic materials for sensing applications. Chem. Soc. Rev. 46, 3242–3285. Ma, D.-L., Ma, V.P.-Y., Chan, D.S.-H., Leung, K.-H., He, H.-Z., Leung, C.-H., 2012. Recent advances in luminescent heavy metal complexes for sensing. Coord. Chem. Rev. 256, 3087–3113. Marchese Robinson, R.L., Lynch, I., Peijnenburg, W., Rumble, J., Klaessig, F., Marquardt, C., Rauscher, H., Puzyn, T., Purian, R., Aberg, C., Karcher, S., Vriens, H., Hoet, P., Hoover, M.D., Hendren, C.O., Harper, S.L., 2016. How should the completeness and quality of curated nanomaterial data be evaluated? Nanoscale 8, 9919–9943. Mondloch, J.E., Katz, M.J., Isley III, W.C., Ghosh, P., Liao, P., Bury, W., Wagner, G.W., Hall, M.G., Decoste, J.B., Peterson, G.W., Snurr, R.Q., Cramer, C.J., Hupp, J.T., Farha, O.K., 2015. Destruction of chemical warfare agents using metal–organic frameworks. Nat. Mater. 14, 512–516. Obare, S.O., De, C., Guo, W., Haywood, T.L., Samuels, T.a., Adams, C.P., Masika, N.O., Murray, D.H., Anderson, G.a., Campbell, K., Fletcher, K., 2010. Fluorescent chemosensors for toxic organophosphorus pesticides: a review. Sensors 10, 7018–7043. Online, V.A., Jang, Y.J., Tsay, O.G., Murale, D.P., Jeong, J.A., Segev, A., Churchill, D.G., 2014. Novel and selective detection of tabun mimics. Chem. Commun. 50, 7531–7534. Polson, M., Ravaglia, M., Fracasso, S., Garavelli, M., Scandola, F., 2005. Iridium cyclometalated complexes with axial symmetry: time-dependent density functional theory investigation of trans-bis-cyclometalated complexes containing the tridentate ligand 2,6-diphenylpyridine. Inorg. Chem. 44, 1282–1289. Qian, S., Lin, H., 2015. Colorimetric sensor array for detection and identification of organophosphorus and carbamate pesticides. Anal. Chem. 87, 5395–5400. Raj, P., Singh, A., Singh, A., Singh, N., 2017. Syntheses, crystal structures and photophysical properties of Cu(ii) complexes: fine tuning of a coordination sphere for selective binding of azamethiphos. Dalton Trans. 46, 985–994. Ralph, E.C., Zhang, J., Cashman, J.R., 2011. Amidine–oximes: reactivators for organophosphate exposure. J. Med. Chem. 54, 3319–3330. Rogers, K.J.M.R., Cao, C.J., Valdes, J.J., Eldefrawi, A.T., Eldefrawi, M.E., 1991. Acetylcholinesterase fiber-optic biosensor for detection of anticholinesterases. Fundam. Appl. Toxicol. 820, 810–820.

508  Chapter 14  DETOXIFICATION AND SENSING OF PESTICIDES

Royo, S., Costero, A.M., Parra, M., Gil, S., 2011. Chromogenic, specific detection of the nerve-agent mimic DCNP (a tabun mimic). Chem. Eur. J. 17, 6931–6934. Ruan, Y., Dalkiliç, E., Peterson, P.W., Pandit, A., Dastan, A., Brown, J.D., Polen, S.M., Hadad, C.M., Badjić, J.D., 2014. Trapping of organophosphorus chemical nerve agents in water with amino acid functionalized baskets. Chem. Eur. J. 20, 4251–4256. Ruan, Y., Taha, H.A., Yoder, R.J., Maslak, V., Hadad, C.M., Badjic, J.D., 2013. The prospect of selective recognition of nerve agents with modular basket-like hosts. A structure– activity study of the entrapment of a series of organophosphonates in aqueous media. J. Phys. Chem. B 117, 3240–3249. Rudd, N.D., Wang, H., Fuentes-Fernandez, E.M.A., Teat, S.J., Chen, F., Hall, G., Chabal, Y.J., Li, J., 2016. Highly efficient luminescent metal–organic framework for the simultaneous detection and removal of heavy metals from water. ACS Appl. Mater. Interfaces 8, 30294–30303. Saluja, P., Kaur, N., Singh, N., Jang, D.O., 2012. A benzimidazole-based fluorescent sensor for Cu2+ and its complex with a phosphate anion formed through a Cu2+ displacement approach. Tetrahedron Lett. 53, 3292–3295. Sambrook, M.R., Hiscock, J.R., Cook, A., Green, A.C., Holden, I., Vincent, J.C., Gale, P.A., 2012. Hydrogen bond-mediated recognition of the chemical warfare agent soman (GD). Chem. Commun. 48, 5605–5607. Sassolas, A., Prieto-simón, B., Marty, J., 2012. Biosensors for pesticide detection: new trends. Am. J. Anal. Chem. 3, 210–232. Schneider, C., Bierwisch, A., Koller, M., Worek, F., Kubik, S., 2016. Antidote development hot paper detoxification of VX and other V-type nerve agents in water at 37°C and pH 7.4 by substituted sulfonatocalix[4] arenes. Angew. Chem. Int. Ed. 55, 12668–12672. Seyedin, S., Razal, J.M., Innis, P.C., Jeiranikhameneh, A., Beirne, S., Wallace, G.G., 2015. Knitted strain sensor textiles of highly conductive all-polymeric fibers. ACS Appl. Mater. Interfaces 7, 21150–21158. Sharma, H., Kaur, N., Singh, A., Kuwar, A., Singh, N., 2016a. Optical chemosensors for water sample analysis. J. Mater. Chem. C 4, 5154–5194. Sharma, R., Gupta, B., Yadav, T., Sinha, S., Sahu, A.K., Karpichev, Y., Gathergood, N., Marek, J., Kuca, K., Ghosh, K.K., 2016b. Degradation of organophosphate pesticides using pyridinium based functional surfactants. ACS Sustain. Chem. Eng. 4, 6962–6973. Singh, A., Raj, P., Singh, N., 2016. Benzimidazolium-based self-assembled fluorescent aggregates for sensing and catalytic degradation of diethylchlorophosphate. ACS Appl. Mater. Interfaces 8, 28641–28651. Singh, A., Singh, J., Singh, N., Jang, D.O., 2015a. A benzimidazolium-based mixed ­organic–inorganic polymer of Cu(II) ions for highly selective sensing of phosphates in water: applications for detection of harmful organophosphates. Tetrahedron 71, 6143–6147. https://doi.org/10.1016/j.tet.2015.06.096. Singh, J., Singh, A., Singh, N., 2014. Urea based organic nanoparticles for selective determination of NADH. RSC Adv. 4, 61841–61846. Singh, V.V., Kaufmann, K., Orozco, J., Li, J., Galarnyk, M., Arya, G., Wang, J., 2015b. Micromotor-based on–off fluorescence detection of sarin and soman simulants. Chem. Commun. 51, 11190–11193. Su, Q., Feng, W., Yang, D., Li, F., 2017. Resonance energy transfer in upconversion nanoplatforms for selective biodetection. Acc. Chem. Res. 50, 32–40. Tao, C.-L., Chen, B., Liu, X.-G., Zhou, L.-J., Zhu, X.-L., Cao, J., Gu, Z.-G., Zhao, Z., Shen, L., Tang, B.Z., 2017. A highly luminescent entangled metal-organic framework based on pyridine-substituted tetraphenylethene for efficient pesticide detection. Chem. Commun. 53, 9975–9978. Van Rie, J., Thielemans, W., 2017. Cellulose-gold nanoparticle hybrid materials. Nanoscale 9, 8525–8554.

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Walton, I., Davis, M., Munro, L., Catalano, V.J., Cragg, P.J., Huggins, M.T., Wallace, K.J., 2012. A fluorescent dipyrrinone oxime for the detection of pesticides and other organophosphates. Org. Lett. 14, 6931–6934. Wang, L., Fan, G., Xu, X., Chen, D., Wang, L., Shi, W., Cheng, P., 2017. Organic pollutants by a luminescent sensor based on a lanthanide metal –organic framework. J. Mater. Chem. A 5, 5541–5549. Wang, L., Li, B., Zhang, L., Li, P., Jiang, H., 2013. An optical anion chemosensor based on a europium complex and its molecular logic behavior. Dyes Pigments 97, 26–31. Weerathunge, P., Ramanathan, R., Shukla, R., Sharma, T.K., Bansal, V., 2014. Aptamercontrolled reversible inhibition of gold nanozyme activity for pesticide sensing. Anal. Chem. 86, 11937–11941. Wei, G., Jiang, Y., Li, F., Quan, Y., Cheng, Y., Zhu, C., 2014. “Click”-BINOL based chiral ionic polymers for highly enantioselective recognition of tryptophan anions. Polym. Chem. 5, 5218. Wong, K.M., Yam, V.W., 2007. Luminescence platinum (II) terpyridyl complexes—from fundamental studies to sensory functions. Coord. Chem. Rev. 251, 2477–2488. Xu, W., Fu, Y., Yao, J., Fan, T., Gao, Y., He, Q., Zhu, D., Cao, H., Cheng, J., 2016. Aggregation state reactivity activation of intramolecular charge transfer type fluorescent probe and application in trace vapor detection of sarin mimics. ACS Sens. 1, 1054–1059. Xuan, W., Cao, Y., Zhou, J., Wang, W., 2013. A FRET-based ratiometric fluorescent and colorimetric probe for the facile detection of organophosphonate nerve agent mimic DCP. Chem. Commun. 49, 10474–10476. Yam, V.W., Wong, K.M., Wong, K.M., Wong, K.M., 2011. Luminescent metal complexes of d6, d8 and d10 transition metal centres. Chem. Commun. (42)11579–11592. Yamaguchi, Y., Ding, W., Sanderson, C.T., Borden, M.L., Morgan, M.J., Kutal, C., 2007. Electronic structure, spectroscopy, and photochemistry of group 8 metallocenes. Coord. Chem. Rev. 251, 515–524. Yan, B., 2017. Lanthanide-functionalized metal–organic framework hybrid systems to create multiple luminescent centers for chemical sensing. Acc. Chem. Res. 50, 2789–2798. Yao, G., Liang, R., Huang, C., Wang, Y., Qiu, J., 2013. Surface plasmon resonance sensor based on magnetic molecularly imprinted polymers amplification for pesticide recognition. Anal. Chem. 85, 11944–11951. Yao, J., Fu, Y., Xu, W., Fan, T., Gao, Y., He, Q., Zhu, D., Cao, H., Cheng, J., 2016. Concise and efficient fluorescent probe via an intromolecular charge transfer for the chemical warfare agent mimic diethylchlorophosphate vapor detection. Anal. Chem. 88, 2497–2501. Yi, Y., Zhu, G., Liu, C., Huang, Y., Zhang, Y., Li, H., Zhao, J., Yao, S., 2013. A label-free silicon quantum dots-based photoluminescence sensor for ultrasensitive detection of pesticides. Anal. Chem. 85, 11464–11470. You, Y., Park, S.Y., 2009. Phosphorescent iridium(III) complexes: toward high phosphorescence quantum efficiency through ligand control. Dalton Trans. 1267–1282. You, Y., Park, S.Y., 2005. Inter-ligand energy transfer and related emission change in the cyclometalated heteroleptic iridium complex: facile and efficient color tuning over the whole visible range by the ancillary ligand structure. J. Am. Chem. Soc. 127, 12438–12439. Zeng, S., Baillargeat, D., Ho, H.-P., Yong, K.-T., 2014. Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications. Chem. Soc. Rev. 43, 3426–3452. Zhang, D., Jiang, X., Yang, H., Su, Z., Gao, E., Martinez, A., Gao, G., 2013. Novel ­benzimidazolium–urea-based macrocyclic fluorescent sensors: synthesis, ratiometric sensing of H2PO4− and improvement of the anion binding performance via a synergistic binding strategy. Chem. Commun. 49, 6149–6151.

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Zhang, K., Yu, T., Liu, F., Sun, M., Yu, H., Liu, B., Zhang, Z., Jiang, H., Wang, S., 2014. Selective fluorescence turn-on and ratiometric detection of organophosphate using dual-emitting Mn-doped ZnS nanocrystal probe. Anal. Chem. 86, 11727–11733. Zhang, Z.-H., Liu, J., Wan, L.-Q., Jiang, F.-R., Lam, C.-K., Ye, B.-H., Qiao, Z., Chao, H.Y., 2015. Synthesis, characterization, photophysics, and anion binding properties of platinum(II) acetylide complexes with urea group. Dalton Trans. 44, 7785–7796. Zhao, D., Cui, Y., Yang, Y., Qian, G., 2016. Sensing-functional luminescent metal-organic frameworks. CrystEngComm 18, 3746–3759. Zhao, Q., Li, F., Huang, C., 2010. Phosphorescent chemosensors based on heavy-metal complexes. Chem. Soc. Rev. 39, 3007–3030. Zhou, G., Wong, W.-Y., Yang, X., 2011. New design tactics in OLEDs using functionalized 2-phenylpyridine-type cyclometalates of iridium(III) and platinum(II). Chem. Asian J. 6, 1706–1727.