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Highly sensitive plasmonic metal nanoparticle-based sensors for the detection of organophosphorus pesticides
Author’s Accepted Manuscript Highly Sensitive Plasmonic Metal NanoparticleBased Sensors for the Detection of Organophosphorus Pesticides Niluka M. Dissanayake, Jaliya S. Arachchilage, Tova A. Samuels, Sherine O. Obare www.elsevier.com/locate/talanta
PII: DOI: Reference:
S0039-9140(19)30294-2 https://doi.org/10.1016/j.talanta.2019.03.042 TAL19720
To appear in: Talanta Received date: 3 December 2018 Revised date: 6 March 2019 Accepted date: 8 March 2019 Cite this article as: Niluka M. Dissanayake, Jaliya S. Arachchilage, Tova A. Samuels and Sherine O. Obare, Highly Sensitive Plasmonic Metal NanoparticleBased Sensors for the Detection of Organophosphorus Pesticides, Talanta, https://doi.org/10.1016/j.talanta.2019.03.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highly Sensitive Plasmonic Metal Nanoparticle-Based Sensors for the Detection of Organophosphorus Pesticides Niluka M. Dissanayake1, Jaliya S. Arachchilage1, Tova A. Samuels1, Sherine O. Obare1,2,3* 1
2
Department of Chemistry, Western Michigan University, Kalamazoo, MI 49008
Department of Nanoscience, Joint School of Nanoscience and Nanoengineering, University of North Carolina at Greensboro and 3North Carolina A&T State University, Greensboro, NC 27401, USA *
To whom correspondence should be addressed: [email protected]
Abstract Plasmonic nanoparticles offer attractive benefits for the detection of environmental contaminants due to their high extinction coefficients and unique optical properties. Excess use of OP pesticides has been found to have adverse effects on human health and the environment. Here, we demonstrate the use of plasmonic silver (Ag), gold (Au) and bimetallic silver-gold (AgAu) nanoparticles (NPs) to detect and distinguish between organophosphorus (OP) pesticides. The NPs were found to detect the thion pesticides: ethion, parathion, malathion, and fenthion) in real time. In each case, the interaction of the pesticides with the plasmonic NPs were found to result in wavelength shifts of the localized surface plasmon resonance (LSPR) accompanied by color changes. The wavelength shifts were characteristic of the pesticide structure and concentration. The interaction between the sensors and the pesticide was a result of the soft metal surface binding to the soft sulfur atom of the pesticide. Similarly, oxon pesticides showed no effect on the LSPR of the NPs. The three plasmonic NPs showed limits of detections (LOD) in ppm range for all pesticides under real-time analysis. The LOD of Ag NPs with ethion, fenthion,
malathion, and parathion were 9 ppm, 11 ppm, 18 ppm, and 44 ppm, respectively. The LOD of Au NPs with ethion, fenthion, malathion, parathion were 58 ppm, 53 ppm, 139 ppm, and 3,203 ppm, respectively. Ag-Au NPs with ethion, fenthion, malathion, and parathion showed LOD values of 228 ppm, 231 ppm, 1,189 ppm, and 1,835 ppm, respectively. The ability of the plasmonic NPs to detect the selected pesticides in natural environments was tested under simulated natural conditions in the presence of dissolved organic matter (DOM). Steep gradients in the sedimentation plots revealed that the time dependent interaction of each OP pesticide with the NP surface was accompanied by a considerable change in the LSPR indicative of colloidal destabilization over time. All pesticides showed nearly the same trend in their sedimantation with the plasmonic NPs. The stability of the nanoparticles in the colloidal medium was described by classical DLVO theory, which showed that the net interaction was attractive. Graphical Abstract:
Keywords: organophosphorus
pesticides,
localized
surface
nanoparticles, plasmonic nanoparticles, sensors
plasmon
resonance,
bimetallic
1. Introduction Organophosphorus pesticides are a large group of chemicals used to protect crops, and livestock. Depending on their structure, OP pesticides can be divided into thirteen groups [1]. Among those, paraoxon-ethyl belongs to the “phosphates”, group, while fenthion and parathion belong to the “phosphothionates” and ethion and malathion belong to the “phosphodithionates” [2]. These compounds can be inhaled, ingested, or absorbed by the skin. Exposure to such compounds has detrimental health effects due to their impact on the neurologic system. One of the major concerns of OP pesticides arises from their basic mechanism of action, i.e. inhibition of acetylcholinesterase (AChE), thus impacting the nervous system. Inhibition of AChE results in accumulation of acetylcholinesterase (Ach), which results in cholinergic toxicity [3,4]. There is an urgent need to develop colorimetric methods that allow real-time detection of OP pesticides. There have been a variety of other approaches for sensing pesticides including immunoassays [5] and enzyme-based biosensors that function by inhibiting cholinesterase activity [6,7]. Furthermore, luminescence methods using lanthanides, [8,9] surface acoustic waves, [10,11] fluorescent organic molecules, [12,13] and interferometry have also been reported for OP pesticide detection. Conventional methods, including gas chromatography (GC) and high-performance liquid chromatography (HPLC) have been coupled with mass spectrometric methods (MS), for the detection and quantification of pesticides due to their low detection limits [14,15]. While these methods are highly effective, they are often costly and require sophisticated instrumentation. Methods that allow detection of OP pesticides in real-time using colorimetric methods that are also visible by the naked-eye, are highly needed for environmental applications.
Significant advances have been made recently using nanoparticles as sensors. Plasmonic nanoparticles are highly attractive for environmental sensing applications due to their high extinction coefficients and ability to tune their properties by controlling their size, shape, composition and surface [16–18]. Notable strategies using NPs as sensors have been as result of their size, large surface to volume ratio, their physicochemical properties, composition, shape, and target binding characteristics [19]. Recent reports in the literature have shown that a variety of NPs including gold [20–22], silver [23,24], iron oxide [25–27], zirconia [28], titanium dioxide [29], silica [30], carbon nanotubes [31–34], graphene nanosheets [31,35,36] and quantum dots (QDs) [37–39] have been used for pesticide detection. Furthermore, a recent report demonstrated a Rayleigh scattering method for the determination of ethion using Ag NPs [40]. This method is effective in that it provides detection limits as low as 3.7 ppb and does not require sample pretreatment. For effective detection of OP pesticides, sensors that function in the ppm-ppb range are effective. However, one there is a need for sensors that are able to easily distinguish between pesticides with no required chemical identification is needed. The work herein shows three types of NPs that can differentiate between OP pesticides. An advantage of the described NPs is that they allow real-time detection with the naked eye, without sample pre-treatment. In contrast to the other recent reports on pesticide sensors, this work demonstrates the ability of the materials to detect and differentiate between five different pesticides. Here, we demonstrate the use of Ag NPs, Au NPs, and Ag-Au NPs as three independent sensors for the detection of five OP pesticides (ethion, fenthion, malathion, parathion and paraoxon-ethyl) (Fig. 1). The thion pesticides show a significant difference in their wavelength shift compared to the oxon pesticides. The pesticides can be differentiated from each
using wavelength shifts of the LSPR. The effectiveness of the plasmonic NPs as highly sensitive and selective sensors for the detection of OP pesticides are investigated.
2. EXPERIMENTAL SECTION 2.1 Materials All chemicals used were of analytical grade. Sodium borohydride (purity 99%), sodium citrate tribasic (purity 99%), sodium chloride, potassium chloride (purity 99%), calcium chloride, gold (III) chloride hydrate (purity 99.99%), ethion, fenthion, parathion, malathion and paraoxon-ethyl were all purchased from the Sigma Aldrich Company and were of analytical grade. Silver nitrate (purity 99.8%) was purchased from J.T. Baker. Ethanol (200 proof) and milliQ water were used in the synthesis process and solution preparation. 2.2 Methods Synthesis of Ag NPs: Colloidal silver nanoparticles were prepared following a procedure previously reported [41]. Briefly, 18.5 mL of milliQ water were placed in an Erlenmeyer flask. To the flask, 0.50 mL of 1.0× 10-2 M silver nitrate, 0.50 mL of 1.0× 10-2 M of sodium citrate tribasic were added and stirred. To this solution, 0.50 mL of 1.0× 10-2 M sodium borohydride was added and gently stirred. The solution was then placed in a refrigerator at 4 °C. The final concentration of Ag NPs by Ag atoms is 2.5× 10-4 M Synthesis of Au NPs: Colloidal gold nanoparticles were prepared following the above procedure. Briefly, 18.5 mL of milliQ water were placed in an Erlenmeyer flask. To the flask, 0.50 mL of 1.0× 10-2 M tetrachloroauric (III) acid (HAuCl4), 0.50 mL of 1.0× 10-2 M of sodium citrate tribasic (0.05 mL) were added and stirred. To this solution, 0.50 mL of 1.0× 10-2 M sodium
borohydride was added and gently stirred. The solution was then placed in a refrigerator at 4 °C. The final concentration of Au NPs by Au atoms is 2.5× 10-4 M. Synthesis of Ag-Au bimetallic NPs: Colloidal Ag-Au bimetallic NPs were synthesized by combining, aqueous stock solutions of, 0.50 mL of 2.0× 10-2 M sodium citrate (Na3C6H5O7), 0.50 mL of 8.0× 10-3 M silver nitrate and 0.50 mL of 2.0× 10-3 M tetrachloroauric(III) acid (HAuCl4) (in a Ag: Au ratio of 4:1) in a flask containing 18.0 mL of milliQ water. Once thoroughly mixed, 0.50 mL of freshly prepared 1.0× 10-2 M NaBH4 was slowly added to the reaction solution and very gently swirled. After remaining sealed and undisturbed in the dark overnight, the Ag/Au NP colloids were then centrifuged at 14,000 rpm for 10 minutes. The supernatant was extracted, characterized, stored in the dark. The colloidal solutions of (Ag NPs, Au NPs. Ag-Au NPs) were covered with aluminum foil and kept under 4 ◦C for 2 hours before use.
2.3 Instrumentation. Synthesized nanoparticles of Ag, Au, Ag-Au were characterized using UV-visible absorbance spectroscopy, transmission electron microscopy (TEM), and . UV-visible absorbance spectra were collected using a Cary 50 Bio Spectrophotometer. A JEOL JEM 1230 TEM was used to observe the morphology of NPs and to measure the NP size. Samples were prepared for TEM by drying a drop of NP solution on a carbon-coated copper grid at room temperature.
3. RESULTS AND DISCUSSION 3.1 Effect of OP pesticides on LSPR changes of plasmonic nanoparticles. Five different types of OP pesticides were used in this study (ethion, malathion, fenthion, parathion and paraoxon-ethyl).
Colloidal NPs of Ag, Au, and Ag-Au in the presence of
phosphate buffered saline (PBS) solutions at pH 7 were titrated with five different OP pesticides. For each titration, 3 mL aliquots of nanoparticle solutions were titrated with continuous addition of 5 μL amounts of 1.0×10-2 M OP pesticides. UV-visible spectroscopy was used to characterize the changes in the LSPR band with the addition of each type of pesticides. Noble metal NPs that are exposed to light induces collective oscillation of electron around the particle surface. This causes a charge separation with respect to the ionic lattice forming a dipole oscillation along the direction of the electric field of the light. The amplitude of the oscillation reaches a maximum at a certain frequency and known as LSPR [42–44]. The SPR induces a strong absorption of light and can be measured using UV-Vis absorption spectrophotometer. This LSPR intensity and wavelength depends on factors such as metal type, particle size, shape, structure, composition and the dielectric constant of the surrounding medium. As mentioned above, all plasmonic NPs are having unique (LSPR) bands depending on their size and dispersity. The characteristic LSPR band for Ag NPs arises at 390 nm, for Au NPs at 520 nm and for Ag-Au NPs at 444 nm, which are shown in UV-visible absorbance spectra (Fig. 2). Ag nanoparticles are yellow in color, Au nanoparticles are wine red in color, and Ag-Au nanoparticles are pale yellow in color. The TEM images show the spherical geometry of all Ag,
Au and Ag-Au bimetallic nanoparticles. Furthermore, the size distribution histograms show the diameter distribution of Ag NPs, Au NPs and Ag-Au NPs (Fig. 3). In order to detect the colorimetric sensing capability of plasmonic NPs, the five different OP pesticides were added separately in to 3 mL of the plasmonic NP solutions at pH 7. Changes in the LSPR and distinct color changes were observed unique to each particle type as described below. Ag NPs show its chracteristic optical absorbance peak at 390 nm. A considerable decrease in this characteristic peak at 390 nm and a peak broadening was observed upon addition of ethion, fenthion, malathion, and parathion pesticides. Formation of a new low intensity peak was observed around 600 nm (Fig. 4 (A) ) for Ag NPs with all the four thion pesticides. Ag NPs exposed to a ethion concentration of 1.48 × 10-4 M, resulted in the formation of a new peak at 605 nm. Ag NPs with the same concentration of fenthion resulted the new peak formation at 600 nm, malathion at 555 nm, and parathion at 590 nm. For each pesticide, wavelength shift was calculated between the characteristic LSPR peak of the plasmonic NPs and the newly arised peak at the right side of the each spectrum of that perticular plasmonic NP. Furthermore, peak broadening was observed for all pesticides except paraxon ethyl. Depending on the type of pesticide, the Ag NPs has shown a characteristic wavelength shift accompanied by the color changes are shown in Fig. 4 (B). Upon addition of paraoxon-ethyl, a considerable change in the LSPR was not observed compared to that with other OP pesticides. The only change it showed was a slight decrease in peak intensity for the characteristic peak at 390 nm. The decrease in intensity and the broadening of the characteristic peak at 520 nm for Au NPs was prominent upon addition of OP pesticides to the colloidal Au NPs. The red shift of the 520
nm LSPR peak was observed for all OP pesticides. Addition of ethion at a concentration of 1.80 × 10-4 M shifted the Au NP LSPR from 520 nm to 630 nm. The same concentration of fenthion resulted in the shift to 620 nm, malathion to 590 nm, and parathion to 565 nm (Fig. 5 (A). The addition of paraoxon-ethyl did not result in a considerable change in the Au NP LSPR relative to other OP pesticides. The corresponding wavelength shifts with the pesticides accompanied by the color changes are shown in Fig. 5 (B). Similar changes in LSPR were also observed for the Ag-Au NPs when exposed to each OP pesticide. The characteristic 444 nm peak was red shifted to 495 nm in the presence of ethion at a concentration of 1.64 × 10-4 M. The same concentration of fenthion resulted in the shit to 490 nm, malathion to 470 nm, and parathion to 465 nm. Finally, no considerable change in the LSPR was observed upon addition of paraoxon-ethyl (Fig. 6 (A)). The corresponding wavelength shift values with each of the OP pesticides was accompanied by the color changes shown in (Fig. 6 (B)).
3.3 Limits of Detection (LOD) for the sensing of OP pesticides by each type of NPs. The limit of detection (LOD) for Ag, Au and Ag-Au NPs with each pesticide was calculated using
the
following
equation:
where, K is a numerical factor chosen according to the level of confidence (K=3) following a procedure reported by Patel et al. [45]. S0 is the standard deviation of the blank and is constant for the blank solution used for the nanoparticle preparation and absorbance measurement. S is
the slope of the calibration curve with different types of the pesticides and various concentrations. Callibration plots were constructed using pesticide concentration and the absorbance ratio of the characteristic LSPR peak of each sensor, that gives a linear relationship. Each pesticide with each of the NP sensor gave a calibration plot which counts to 15 calibration plots all together. Depending on the calibration plots, 15 different S values were calculated. (Supplementary information S1 (a),(b),(c))The limit of detection (LOD) values were calculated using the Eq. 1 calibration plots and are displayed as follow (Table 1). The selectivity of the NP sensors toward each pesticide is evaluated using the unique wavelength shifts in each type of NP upon addition of different OP pesticides. The structural diversity of OP pesticides shows a difference in their sensitivity by each type of plasmonic NP sensor. The three types of NPs used: Ag NPs, Au NPs, and Ag-Au NPs were found to be selective to each of the five pesticides. The detection limit for each sensor with each pesticide were found to be in the ppm range.
3.4 Time dependant stability of synthesized plasmonic nanoparticles. Nanoparticle stability in the presence of OP pesticides was measured by monitoring changes in LSPR using UV-visible spectroscopy. The unique optical property of plasmonic NPs arises from the collective oscillation of the electrons on their surface known as LSPR [46]. Due to the high surface area to volume ratio in plasmonic NPs, the LSPR frequency is sensitive to the refractive index of the surrounding medium. Any change in the environment including surface adsorption and desorption of chemical agents, aggregation, the medium refractive index will shift the LSPR frequency and result in a colorimetric change that can be utilized as optical signals for detection[47]
The morphology of the nanoparticles can be easily observed with the help of TEM. Since this gives information about the changes in NPs before and after exposure with the OP pesticides, Ag NPs, Au NPs and Ag-Au NPs were imaged before and after addition of the OP pesticides with each. The stability of the NPs in the presence of the OP pesticides was investigated by measuring the change in absorbance with respect to time, as shown in Fig. 7. If the NPs are stable in the colloidal medium, we would expect the ratio of A/A0 to be constant throughout the timeframe (where, A = absorbance at time t and A0 = absorbance at time 0). For example, the sedimentation plots for the plasmonic NPs alone (i.e. with no addition of pesticides) as shown in Fig. 7. (A) (i), (B) (i) and (C) (i), shows a straight line. However, if the particles undergo changes due to the presence of pesticides their instability should be reflected by changes in the A/A0 ratio. Instability of the particles could lead to particle aggregation, precipitation, or dissolution depending on the [47]. Ethion was found to cause the highest instability as shown in Fig. 7. (A) (ii), (B) (ii) and (C) (ii). Paraoxon-ethyl did not result in considerable change in plasmonic NPs LSPR absorbance ratio changes over the time. All five pesticides showed nearly the same trend in their colloidal instability with the three types of the plasmonic NPs. The order of highest instability to the lowest instability observed for the nanoparticle colloids are in the presence of ethion > fenthion > malathion > parathion > paraoxon-ethyl. The consequences of particle instability were clearly observed under the TEM after addition of pesticides to the NPs. The TEM image showed the nanoparticles aggregated in the presence of pesticides (Fig. 8). The lowest extent of an aggregation was observed in the presence of the oxon pesticide (paraoxon-ethyl) relative to the thion pesticides (ethion, fenthion, malathion, parathion).
The observed variation in the sensitivity of OP pesticides toward the NPs was found to rely on the diversity of the OP pesticide structure and can be explained based on several theories. OP pesticides are esters of phosphoric acids and their derivatives. The general structure of an OP pesticide comprises the central phosphorus (P) atom and the characteristic thiophosphoryl (P=S) or phosphoryl (P=O) group [48]. The general trend in the sensitivity of the sensors toward the pesticides is: ethion>fenthion>malathion>parathion>paraoxon-ethyl. The higher affinity observed in (P=S) group containing OP pesticides with the NPs than that of the (P=O) group containing pesticides, can be explained in terms of hard-soft acid-base (HSAB) theory. Soft acids interact more strongly with soft bases while hard acids interact more strongly with hard bases [49,50]. The surface atoms on the Ag and Au nanoparticle surfaces are acting as soft acids, while the sulfur (S) atom in the thion pesticides (P=S) are acting as soft bases. Once pesticides are added to the NP colloidal medium, they act as ligands that bind via S atoms or O atoms with the NP surface. These pestcides have a tendency to displace existing citrate groups surrounding the NP surface [51]. The differnce in the sensitivity between thion peasticides can be explained using chelate effect. According to the chelate effect, complexes containing chelate rings are usually more stable than similar complexes without rings[52]. Ethion has four S atoms, which can act as chelating agents for the pesticide coordination with Au and Ag, so we expect a stronger affinity. In the case of fenthion and malathion, each having two S atoms on their structures, will have a strong affinity but, will be less than that of ethion due to less tendency of making a chelate ring. Parathion having a single S atom would have the least affinity relative to the other three pesticides discussed. Paraoxon-ethyl has no S atoms in its structure but, O atoms shows no affinity with the Ag or Au NP sensors. Studies have shown higher affinity of Ag for the coordination with S and N containing ligands on their surface. Depending on the capability of
chelation due to the presence of S or N in ligands, contribute for higher values in formation constants for the ligand coordination with the metal. These formation constants are high in several orders compared to that of O containing ligands without N and S [53,54]. Higher formation constants lead to stable metal ligand complexes hence higher sensitivity for the detection of pesticides in this case. The bond between S atoms in the molecules and noble metals has been investigated by others [55-57]. Sulfur atoms in organosulfur compounds have been shown to have a high affinity for noble metal surfaces, and through the formation of the dative bond, are able to displace adsorbed organic materials from the surface. In most cases the bond is formed spontaneously. [55-57]. All the experiments reported in this article were carried out under laboratory conditions. However, the interferences that may result from natural environments have been taken into consideration by simulating a system, in which humic acid (HA) has been introduced to the medium to serve as a representation of DOM, a key component of any natural environment [58]. The presence of HAs interferes with the interactions between NPs and pesticides, minimizing the pesticides’ ability to interact with the NP surface [59]. It is expected that the HAs can adsorb on to the NP surface via several mechanisms depending on the type of the metal core and the surface coating. This makes a protective mechanism on the surface preventing the interactions of pesticides with NP surface and reduce the sensitivity of the sensor.
Stability of particles in the colloidal medium is described by classical DLVO theory of aggregation. This theory describes two types of forces among the particles. Those are Van der Waals attraction (vdW) and electric double layer repulsion (Velec).The sum of the forces determines the net interaction is repulsive or attractive [60,61]. According to the theory Van der
Waals attraction energy between particles and charge on particles plays a key role in their colloidal stability. Some studies have shown that particle size, shape, chemical composition, coating, and crystal structure influence the surface charge on the NPs [62]. The studies have found that the surface charge of the citrate stabalized plasmonic NPs are negative, and thus keep particles well dispersed in the colloidal medium via electric double layer repulsion (Velec). The electrostatic stabilization of the NPs in the colloidal medium is measured via zeta potential. The zeta potential values for the Ag NPs are recorded from -26.8 to -53.1 mV [63–65]. Zeta potential value range for Au NPs is recorded from -35.9 to -42.9 mV [66] and for Ag NPs-Au NPs core shell from 21.9 to 24.0 mV range [67] in the literature. Solutions having zeta potential values above 20 mV and below -20 mV are considered stable [68]. However, the ligand displacement reaction of OP pesticides with citrate can results in changes in the charge on the particle surface and diminish the Velec forces between particles [69]. Depending on these changes, the NPs tend to aggregate making changes in the LSPR of plasmonic NPs as clearly observed by a color change to the naked eye. As a result, the particles have a greater tendency for aggregation, which is concluded by the TEM images of the plasmonic NPs exposed to pesticides (Fig. 8). Recent research work shows the application of extended DLVO theory (xDLVO) is more accurate over the classical DLVO theory. Since van der Waals and electrostatic interactions alone are insufficient to describe the nanoparticle stability and fate in the colloidal systems, xDLVO theory is widely used which includes the contribution from interparticle separation distances and various medium conditions[70]. Within the xDLVO framework, functionalized nanoparticles interact via van der Waals, electrostatic, and steric (osmotic and elastic) contributions to the potential energy [62,71,72].
Ag NPs showed the highest molar absorptivity and Ag-Au NPs showed the lowest molar absorptivity. Bimetallic Ag-Au NPs were synthesized by a wet chemistry method where, gold ions and silver ions were added simultaneously in the presence of reducing agents [43,73]. This method allows the formation of alloy Ag-Au NPs and is confirmed by the presence of a single plasmonic band in the optical absorbance spectrum as shown in Fig. 2 Ag-Au NPs. Changes in molar absorptivity result due to variation in the molar fraction of Au in the Ag-Au bimetallic NPs [74]. The variation in molar absorptivity in the three plasmonic NPs to their respective sensitivity in pesticide detection, so that the Ag-Au alloy NPs displayed longer stability but had the least sensitivity.
4. Conclusion The resulting work shows the affinity of OP pesticides toward plasmonic NPs. The binding of the OP pesticide to the surface depends on the chemical structure as well as the nature of the NP surface. The extent of the change in LSPR was used to differentiate between the five types of pesticides. It was found that of the three types of NPs, Ag NP, Au NP and Ag-Au NP sensors, Ag NPs showed the highest sensitivity and Ag-Au NPs shows the lowest sensitivity, while Au NPs showed medium sensitivity. The results indicate that the bimetallic systems are less sensitive relative to their monometallic counterparts. The work shows that the plasmonic nanoparticles can be used for different concentration ranges of OP pesticides. The three sensors based on Ag, Au, and Ag-Au NPs easily allowed detection of OP pesticides at ppm levels. This range of pesticide detection is important if these materials are to be further developed into practical units within devices.
Acknowledgements The authors would like to thank the National Science Foundation for financial support under award DMR 0963678. References [1] R.C. Gupta, Toxicology of organophosphate and carbamate compounds, Academic Press, 2011. [2] B.E. Mileson, J.E. Chambers, W.L. Chen, W. Dettbarn, M. Ehrich, A.T. Eldefrawi, D.W. Gaylor, K. Hamernik, E. Hodgson, A.G. Karczmar, Common mechanism of toxicity: a case study of organophosphorus pesticides, Toxicol. Sci. 41 (1998) 8–20. [3] X. Hua, J. Yang, L. Wang, Q. Fang, G. Zhang, F. Liu, Development of an enzyme linked immunosorbent assay and an immunochromatographic assay for detection of organophosphorus pesticides in different agricultural products, PLoS One. 7 (2012) e53099. [4] E.W. Roex, R. Keijzers, C.A. Van Gestel, Acetylcholinesterase inhibition and increased food consumption rate in the zebrafish, Danio rerio, after chronic exposure to parathion, Aquat. Toxicol. 64 (2003) 451–460. [5] L. Wang, D. Du, D. Lu, C.-T. Lin, J.N. Smith, C. Timchalk, F. Liu, J. Wang, Y. Lin, Enzyme-linked immunosorbent assay for detection of organophosphorylated butyrylcholinesterase: A biomarker of exposure to organophosphate agents, Anal. Chim. Acta. 693 (2011) 1–6. [6] D.N. Kumar, A. Rajeshwari, S.A. Alex, M. Sahu, A.M. Raichur, N. Chandrasekaran, A. Mukherjee, Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides, RSC Adv. 5 (2015) 61998–62006. [7] J. Li, Q. Ba, J. Yin, S. Wu, F. Zhuan, S. Xu, J. Li, J.K. Salazar, W. Zhang, H. Wang, Surface display of recombinant Drosophila melanogaster acetylcholinesterase for detection of organic phosphorus and carbamate pesticides, PloS One. 8 (2013) e72986. [8] S. Wang, X. Wang, X. Chen, X. Cao, J. Cao, X. Xiong, W. Zeng, A novel upconversion luminescence turn-on nanosensor for ratiometric detection of organophosphorus pesticides, RSC Adv. 6 (2016) 46317–46324. [9] H.A. Azab, A. Duerkop, Z.M. Anwar, B.H. Hussein, M.A. Rizk, T. Amin, Luminescence recognition of different organophosphorus pesticides by the luminescent Eu (III)–pyridine-2, 6-dicarboxylic acid probe, Anal. Chim. Acta. 759 (2013) 81–91. [10] M. Zourob, K.G. Ong, K. Zeng, F. Mouffouk, C.A. Grimes, A wireless magnetoelastic biosensor for the direct detection of organophosphorus pesticides, Analyst. 132 (2007) 338– 343. [11] D. Chen, J. Wang, Y. Xu, D. Li, L. Zhang, Z. Li, Highly sensitive detection of organophosphorus pesticides by acetylcholinesterase-coated thin film bulk acoustic resonator mass-loading sensor, Biosens. Bioelectron. 41 (2013) 163–167.
[12] S.O. Obare, C. De, W. Guo, T.L. Haywood, T.A. Samuels, C.P. Adams, N.O. Masika, D.H. Murray, G.A. Anderson, K. Campbell, Fluorescent chemosensors for toxic organophosphorus pesticides: a review, Sensors. 10 (2010) 7018–7043. [13] I. Walton, M. Davis, L. Munro, V.J. Catalano, P.J. Cragg, M.T. Huggins, K.J. Wallace, A fluorescent dipyrrinone oxime for the detection of pesticides and other organophosphates, Org. Lett. 14 (2012) 2686–2689. [14] V. Tripathy, A. Saha, D.J. Patel, B.B. Basak, P.G. Shah, J. Kumar, Validation of a QuEChERS-based gas chromatographic method for analysis of pesticide residues in Cassia angustifolia (senna), J. Environ. Sci. Health Part B. 51 (2016) 508–518. [15] G. Du, Y. Xiao, H.-R. Yang, L. Wang, Y. Song, Y.-T. Wang, Rapid determination of pesticide residues in herbs using selective pressurized liquid extraction and fast gas chromatography coupled with mass spectrometry, J. Sep. Sci. 35 (2012) 1922–1932. [16] A. Philippe, G.E. Schaumann, Interactions of dissolved organic matter with natural and engineered inorganic colloids: a review, Environ. Sci. Technol. 48 (2014) 8946–8962. [17] T.-J. Lin, K.-T. Huang, C.-Y. Liu, Determination of organophosphorous pesticides by a novel biosensor based on localized surface plasmon resonance, Biosens. Bioelectron. 22 (2006) 513–518. [18] H. Li, F. Li, C. Han, Z. Cui, G. Xie, A. Zhang, Highly sensitive and selective tryptophan colorimetric sensor based on 4, 4-bipyridine-functionalized silver nanoparticles, Sens. Actuators B Chem. 145 (2010) 194–199. [19] G. Aragay, F. Pino, A. Merkoci, Nanomaterials for sensing and destroying pesticides, Chem. Rev. 112 (2012) 5317–5338. [20] Q. Xu, X. Guo, L. Xu, Y. Ying, Y. Wu, Y. Wen, H. Yang, Template-free synthesis of SERS-active gold nanopopcorn for rapid detection of chlorpyrifos residues, Sens. Actuators B Chem. 241 (2017) 1008–1013. [21] N. Shams, H.N. Lim, R. Hajian, N.A. Yusof, J. Abdullah, Y. Sulaiman, I. Ibrahim, N.M. Huang, Electrochemical sensor based on gold nanoparticles/ethylenediamine-reduced graphene oxide for trace determination of fenitrothion in water, RSC Adv. 6 (2016) 89430– 89439. [22] R. Karami, A. Mohsenifar, S.M. Mesbah Namini, N. Kamelipour, T. Rahmani-Cherati, T. Roodbar Shojaei, M. Tabatabaei, A novel nanobiosensor for the detection of paraoxon using chitosan-embedded organophosphorus hydrolase immobilized on Au nanoparticles, Prep. Biochem. Biotechnol. 46 (2016) 559–566. [23] Y. Bian, C. Li, H. Li, para-Sulfonatocalix [6] arene-modified silver nanoparticles electrodeposited on glassy carbon electrode: preparation and electrochemical sensing of methyl parathion, Talanta. 81 (2010) 1028–1033. [24] D. Xiong, H. Li, Colorimetric detection of pesticides based on calixarene modified silver nanoparticles in water, Nanotechnology. 19 (2008) 465502. [25] N.-N. Li, T.-F. Kang, J.-J. Zhang, L.-P. Lu, S.-Y. Cheng, Fe3O4@ZrO2 magnetic nanoparticles as a new electrode material for sensitive determination of organophosphorus agents, Anal. Methods. 7 (2015) 5053–5059. [26] G.-H. Yao, R.-P. Liang, C.-F. Huang, Y. Wang, J.-D. Qiu, Surface plasmon resonance sensor based on magnetic molecularly imprinted polymers amplification for pesticide recognition, Anal. Chem. 85 (2013) 11944–11951. [27] N. Chauhan, C.S. Pundir, An amperometric biosensor based on acetylcholinesterase immobilized onto iron oxide nanoparticles/multi-walled carbon nanotubes modified gold
electrode for measurement of organophosphorus insecticides, Anal. Chim. Acta. 701 (2011) 66–74. [28] H. Wang, Y. Su, H. Kim, D. Yong, L. Wang, X. Han, A Highly Efficient ZrO2 Nanoparticle Based Electrochemical Sensor for the Detection of Organophosphorus Pesticides, Chin. J. Chem. 33 (2015) 1135–1139. [29] B. Song, W. Cao, Y. Wang, A methyl parathion electrochemical sensor based on NanoTiO2, graphene composite film modified electrode, Fuller. Nanotub. Carbon Nanostructures. 24 (2016) 435–440. [30] X. Xia, P. Xu, H. Yu, X. Li, Resonant micro-cantilever chemical sensor with one-step synthesis of-COOH functionalized mesoporous-silica nanoparticles for detection of tracelevel organophosphorus pesticide, in: Sens. 2012 IEEE, IEEE, 2012: pp. 1–4. [31] X.-C. Fu, J. Zhang, Y.-Y. Tao, J. Wu, C.-G. Xie, L.-T. Kong, Three-dimensional mono6-thio-β-cyclodextrin covalently functionalized gold nanoparticle/single-wall carbon nanotube hybrids for highly sensitive and selective electrochemical determination of methyl parathion, Electrochimica Acta. 153 (2015) 12–18. [32] Q. Tang, X. Shi, X. Hou, J. Zhou, Z. Xu, Development of molecularly imprinted electrochemical sensors based on Fe3O4@ MWNT-COOH/CS nanocomposite layers for detecting traces of acephate and trichlorfon, Analyst. 139 (2014) 6406–6413. [33] D. Huo, Q. Li, Y. Zhang, C. Hou, Y. Lei, A highly efficient organophosphorus pesticides sensor based on CuO nanowires–SWCNTs hybrid nanocomposite, Sens. Actuators B Chem. 199 (2014) 410–417. [34] B. Wu, L. Hou, M. Du, T. Zhang, Z. Wang, Z. Xue, X. Lu, A molecularly imprinted electrochemical enzymeless sensor based on functionalized gold nanoparticle decorated carbon nanotubes for methyl-parathion detection, RSC Adv. 4 (2014) 53701–53710. [35] Y. Mao, H. Fa, Y. Cheng, Y. Du, W. Yin, C. Hou, D. Huo, D. Zhang, An electrode modified with AuNPs/Graphene nanocomposites film for the determination of methyl parathion residues, Nano. 9 (2014) 1450096. [36] R. Xue, T.-F. Kang, L.-P. Lu, S.-Y. Cheng, Electrochemical sensor based on the graphene-nafion matrix for sensitive determination of organophosphorus pesticides, Anal. Lett. 46 (2013) 131–141. [37] N. Fahimi-Kashani, A. Rashti, M.R. Hormozi-Nezhad, V. Mahdavi, MoS2 quantum-dots as a label-free fluorescent nanoprobe for the highly selective detection of methyl parathion pesticide, Anal. Methods. 9 (2017) 716–723. [38] X. Li, Z. Zheng, X. Liu, S. Zhao, S. Liu, Nanostructured photoelectrochemical biosensor for highly sensitive detection of organophosphorous pesticides, Biosens. Bioelectron. 64 (2015) 1–5. [39] X. Yan, H. Li, X. Han, X. Su, A ratiometric fluorescent quantum dots based biosensor for organophosphorus pesticides detection by inner-filter effect, Biosens. Bioelectron. 74 (2015) 277–283. [40] H. Parham, S. Saeed, Resonance Rayleigh scattering method for determination of ethion using silver nanoparticles as probe, Talanta. 131 (2015) 570–576. [41] A.N. Brown, K. Smith, T.A. Samuels, J. Lu, S.O. Obare, M.E. Scott, Nanoparticles functionalized with ampicillin destroy multiple-antibiotic-resistant isolates of Pseudomonas aeruginosa and Enterobacter aerogenes and methicillin-resistant Staphylococcus aureus, Appl. Environ. Microbiol. 78 (2012) 2768–2774.
[42] G. Mie, Articles on the optical characteristics of turbid tubes, especially colloidal metal solutions, Ann Phys. 25 (1908) 377–445. [43] G.C. Papavassiliou, Surface plasmons in small Au-Ag alloy particles, J. Phys. F Met. Phys. 6 (1976) L103. [44] M. Kerker, The Scattering of Light and Other Electromagnetic Radiation (New York: Academic) Ch 6, (1969). [45] G.M. Patel, J.V. Rohit, R.K. Singhal, S.K. Kailasa, Recognition of carbendazim fungicide in environmental samples by using 4-aminobenzenethiol functionalized silver nanoparticles as a colorimetric sensor, Sens. Actuators B Chem. 206 (2015) 684–691. [46] L. Wang, W. Ma, L. Xu, W. Chen, Y. Zhu, C. Xu, N.A. Kotov, Nanoparticle-based environmental sensors, Mater. Sci. Eng. R Rep. 70 (2010) 265–274. [47] S.-W. Bian, I.A. Mudunkotuwa, T. Rupasinghe, V.H. Grassian, Aggregation and dissolution of 4 nm ZnO nanoparticles in aqueous environments: influence of pH, ionic strength, size, and adsorption of humic acid, Langmuir. 27 (2011) 6059–6068. [48] T. Elersek, M. Filipic, Organophosphorous pesticides-mechanisms of their toxicity, in: Pestic.- Impacts Pestic. Expo., InTech, 2011. [49] R.G. Pearson, Acids and bases, Science. 151 (1966) 172–177. [50] R.G. Pearson, Hard and soft acids and bases, J. Am. Chem. Soc. 85 (1963) 3533–3539. [51] Y.-C. Yeh, B. Creran, V.M. Rotello, Gold nanoparticles: preparation, properties, and applications in bionanotechnology, Nanoscale. 4 (2012) 1871–1880. [52] S.F.A. Kettle, Physical Inorganic Chemistry: A Coordination Chemistry Approach, Springer, 2013. [53] C. Levard, E.M. Hotze, G.V. Lowry, G.E. Brown Jr, Environmental transformations of silver nanoparticles: impact on stability and toxicity, Environ. Sci. Technol. 46 (2012) 6900– 6914. [54] R.A. Bell, J.R. Kramer, Structural chemistry and geochemistry of silver-sulfur compounds: Critical review, Environ. Toxicol. Chem. 18 (1999) 9–22. [55] J.C. Love, L.A. Estroff, J.K. Kriebel, R.G. Nuzzo, G.M. Whitesides, Self-assembled monolayers of thiolates on metals as a form of nanotechnology, Chem. Rev. 105 (2005) 1103–1170. [56] M.-A. Neouze, U. Schubert, Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands, Monatshefte Für Chem. - Chem. Mon. 139 (2008) 183–195. [57] The gold–sulfur interface at the nanoscale | Nature Chemistry, (n.d.). https://www.nature.com/articles/nchem.1352 (accessed January 21, 2019). [58] G. Aiken, Humic Substances In Soil, Sediment, And Water : Geochemistry, Isolation, And Characterization, CU Authors Book Gallery. (1985). [59] D. Vaughan, D.G. Lumsdon, D.J. Linehan, Influence of dissolved organic matter on the bio-availability and toxicity of metals in soils and aquatic systems, Chem. Ecol. 8 (1993) 185–201. [60] B.V. DERJAGUIN, Theory of the stability of strongly charged lyophobic sols and the adhesion of strongly charged particles in solutions of electrolytes, Acta Physicochim USSR. 14 (1941) 633–662. [61] E.J.W. Verwey, Theory of the stability of lyophobic colloids: the interaction of sol particles having an electric double layer, 1962.
[62] E.M. Hotze, T. Phenrat, G.V. Lowry, Nanoparticle Aggregation: Challenges to Understanding Transport and Reactivity in the Environment All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher., J. Environ. Qual. 39 (2010) 1909– 1924. [63] J.S. Kim, E. Kuk, K.N. Yu, J.-H. Kim, S.J. Park, H.J. Lee, S.H. Kim, Y.K. Park, Y.H. Park, C.-Y. Hwang, Antimicrobial effects of silver nanoparticles, Nanomedicine Nanotechnol. Biol. Med. 3 (2007) 95–101. [64] Z. Sadowski, I.H. Maliszewska, B. Grochowalska, I. Polowczyk, T. Kozlecki, Synthesis of silver nanoparticles using microorganisms, Mater. Sci.-Pol. 26 (2008) 419–424. [65] S. Agnihotri, S. Mukherji, S. Mukherji, Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy, Rsc Adv. 4 (2014) 3974–3983. [66] G. Sonavane, K. Tomoda, K. Makino, Biodistribution of colloidal gold nanoparticles after intravenous administration: effect of particle size, Colloids Surf. B Biointerfaces. 66 (2008) 274–280. [67] M.E. El-Naggar, T.I. Shaheen, M.M. Fouda, A.A. Hebeish, Eco-friendly microwaveassisted green and rapid synthesis of well-stabilized gold and core–shell silver–gold nanoparticles, Carbohydr. Polym. 136 (2016) 1128–1136. [68] J. Eastman, Colloid stability, Colloid Sci. Princ. Methods Appl. (2005) 36–49. [69] J.L. Ferry, P. Craig, C. Hexel, P. Sisco, R. Frey, P.L. Pennington, M.H. Fulton, I.G. Scott, A.W. Decho, S. Kashiwada, Transfer of gold nanoparticles from the water column to the estuarine food web, Nat. Nanotechnol. 4 (2009) 441. [70] L.A. Wijenayaka, M.R. Ivanov, C.M. Cheatum, A.J. Haes, Improved Parametrization for Extended Derjaguin, Landau, Verwey, and Overbeek Predictions of Functionalized Gold Nanosphere Stability, J. Phys. Chem. C. 119 (2015) 10064–10075. [71] S.R. Saunders, M.R. Eden, C.B. Roberts, Modeling the precipitation of polydisperse nanoparticles using a total interaction energy model, J. Phys. Chem. C. 115 (2011) 4603– 4610. [72] S. Skoglund, T.A. Lowe, J. Hedberg, E. Blomberg, I.O. Wallinder, S. Wold, M. Lundin, Effect of laundry surfactants on surface charge and colloidal stability of silver nanoparticles, Langmuir. 29 (2013) 8882–8891. [73] K. Torigoe, Y. Nakajima, K. Esumi, Preparation and characterization of colloidal silverplatinum alloys, J. Phys. Chem. 97 (1993) 8304–8309. [74] S. Link, Z.L. Wang, M.A. El-Sayed, Alloy formation of gold- silver nanoparticles and the dependence of the plasmon absorption on their composition, J. Phys. Chem. B. 103 (1999) 3529–3533.
Ethion
Malathion
Fenthion
Parathion
Paraxon-ethyl
Fig.1. Chemical structures of selected organophosphorus pesticides studied
Fig. 2. UV-visible spectra of the plasmonic nanoparticles (a) ( nm), (b) (
)Au NPs (SPR peak at 520 nm), (c) (
)Ag NPs (SPR peak at 390
)Ag-Au NPs (SPR peak at 444 nm).
Fig. 3. TEM mages of (a) Ag NPs, (b) Au NPs, (c) Ag-Au NPs with particle size distribution histograms. The scale bar represents 50 nm.
Fig. 4. (A) Ag NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon-ethy (B) Plots of
shifts in wavelength with increased pesticide concentration, accompanied by color changes
Fig. 5. (A) Au NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M, 1.64× 10-4 M, 1.8× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon ethy B) Plots of shifts in wavelength with increased pesticide concentration,
accompanied by color changes
Fig. 6. (A) Ag-Au NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M, 1.64× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon ethyl B)
Plots of shifts in wavelength with increased pesticide concentration, accompanied by color changes
Fig. 7. Sedimentation plots of (A) (i) Ag nanoparticles (B) (i) Au nanoparticles (C) (i) Ag-Au nanoparticles alone. Plasmonic nanoparticles in each case in the presence of (ii) ethion, (iii) fenthion, (iv) malathion (v) parathion, and (vi) paraoxon-ethyl.
Fig. 8. TEM images for Ag NPs, Au NPs, Ag-Au NPs after exposure to OP pesticides. The scale bar represents 100 nm.
Table 1 Limit of detections for OP pesticides detection by plasmonic NPs.
Pesticide Ethion Fenthion
Ag NPs LOD LOD (M) (ppm) -5 9 2.4×10 11 4.1×10-5
Malathion 5.4×10-5 Parathion 1.5×10-4 Paraoxonethyl 0
Limit of Detection (LOD) Au NPs Ag-Au NPs LOD LOD LOD (M) (ppm) LOD (M) (ppm) -4 -4 58 228 1.5×10 7.5×10 -4 53 231 1.9×10 8.3×10-4
18 44
4.2×10-4 1.1×10-2
0
0
139 3203
3.6×10-3 6.3×10-3
1189 1835
0
0
Highlights:
The three types sensors can detect five diverse types of OP pesticides (ethion, fenthion, malathion, parathion, and paraoxon-ethyl).
Each of the plasmonic nanoparticle sensor can differentiate between the five types of the pesticides depending on the maximum shift of the characteristic localized surface plasmon resonance (LSPR) band.
The time dependent sedimentation of the plasmonic NPs in the presence of OP pesticides support the sensitivity order of each sensor toward five different OP pesticides.
PII: DOI: Reference:
S0039-9140(19)30294-2 https://doi.org/10.1016/j.talanta.2019.03.042 TAL19720
To appear in: Talanta Received date: 3 December 2018 Revised date: 6 March 2019 Accepted date: 8 March 2019 Cite this article as: Niluka M. Dissanayake, Jaliya S. Arachchilage, Tova A. Samuels and Sherine O. Obare, Highly Sensitive Plasmonic Metal NanoparticleBased Sensors for the Detection of Organophosphorus Pesticides, Talanta, https://doi.org/10.1016/j.talanta.2019.03.042 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highly Sensitive Plasmonic Metal Nanoparticle-Based Sensors for the Detection of Organophosphorus Pesticides Niluka M. Dissanayake1, Jaliya S. Arachchilage1, Tova A. Samuels1, Sherine O. Obare1,2,3* 1
2
Department of Chemistry, Western Michigan University, Kalamazoo, MI 49008
Department of Nanoscience, Joint School of Nanoscience and Nanoengineering, University of North Carolina at Greensboro and 3North Carolina A&T State University, Greensboro, NC 27401, USA *
To whom correspondence should be addressed: [email protected]
Abstract Plasmonic nanoparticles offer attractive benefits for the detection of environmental contaminants due to their high extinction coefficients and unique optical properties. Excess use of OP pesticides has been found to have adverse effects on human health and the environment. Here, we demonstrate the use of plasmonic silver (Ag), gold (Au) and bimetallic silver-gold (AgAu) nanoparticles (NPs) to detect and distinguish between organophosphorus (OP) pesticides. The NPs were found to detect the thion pesticides: ethion, parathion, malathion, and fenthion) in real time. In each case, the interaction of the pesticides with the plasmonic NPs were found to result in wavelength shifts of the localized surface plasmon resonance (LSPR) accompanied by color changes. The wavelength shifts were characteristic of the pesticide structure and concentration. The interaction between the sensors and the pesticide was a result of the soft metal surface binding to the soft sulfur atom of the pesticide. Similarly, oxon pesticides showed no effect on the LSPR of the NPs. The three plasmonic NPs showed limits of detections (LOD) in ppm range for all pesticides under real-time analysis. The LOD of Ag NPs with ethion, fenthion,
malathion, and parathion were 9 ppm, 11 ppm, 18 ppm, and 44 ppm, respectively. The LOD of Au NPs with ethion, fenthion, malathion, parathion were 58 ppm, 53 ppm, 139 ppm, and 3,203 ppm, respectively. Ag-Au NPs with ethion, fenthion, malathion, and parathion showed LOD values of 228 ppm, 231 ppm, 1,189 ppm, and 1,835 ppm, respectively. The ability of the plasmonic NPs to detect the selected pesticides in natural environments was tested under simulated natural conditions in the presence of dissolved organic matter (DOM). Steep gradients in the sedimentation plots revealed that the time dependent interaction of each OP pesticide with the NP surface was accompanied by a considerable change in the LSPR indicative of colloidal destabilization over time. All pesticides showed nearly the same trend in their sedimantation with the plasmonic NPs. The stability of the nanoparticles in the colloidal medium was described by classical DLVO theory, which showed that the net interaction was attractive. Graphical Abstract:
Keywords: organophosphorus
pesticides,
localized
surface
nanoparticles, plasmonic nanoparticles, sensors
plasmon
resonance,
bimetallic
1. Introduction Organophosphorus pesticides are a large group of chemicals used to protect crops, and livestock. Depending on their structure, OP pesticides can be divided into thirteen groups [1]. Among those, paraoxon-ethyl belongs to the “phosphates”, group, while fenthion and parathion belong to the “phosphothionates” and ethion and malathion belong to the “phosphodithionates” [2]. These compounds can be inhaled, ingested, or absorbed by the skin. Exposure to such compounds has detrimental health effects due to their impact on the neurologic system. One of the major concerns of OP pesticides arises from their basic mechanism of action, i.e. inhibition of acetylcholinesterase (AChE), thus impacting the nervous system. Inhibition of AChE results in accumulation of acetylcholinesterase (Ach), which results in cholinergic toxicity [3,4]. There is an urgent need to develop colorimetric methods that allow real-time detection of OP pesticides. There have been a variety of other approaches for sensing pesticides including immunoassays [5] and enzyme-based biosensors that function by inhibiting cholinesterase activity [6,7]. Furthermore, luminescence methods using lanthanides, [8,9] surface acoustic waves, [10,11] fluorescent organic molecules, [12,13] and interferometry have also been reported for OP pesticide detection. Conventional methods, including gas chromatography (GC) and high-performance liquid chromatography (HPLC) have been coupled with mass spectrometric methods (MS), for the detection and quantification of pesticides due to their low detection limits [14,15]. While these methods are highly effective, they are often costly and require sophisticated instrumentation. Methods that allow detection of OP pesticides in real-time using colorimetric methods that are also visible by the naked-eye, are highly needed for environmental applications.
Significant advances have been made recently using nanoparticles as sensors. Plasmonic nanoparticles are highly attractive for environmental sensing applications due to their high extinction coefficients and ability to tune their properties by controlling their size, shape, composition and surface [16–18]. Notable strategies using NPs as sensors have been as result of their size, large surface to volume ratio, their physicochemical properties, composition, shape, and target binding characteristics [19]. Recent reports in the literature have shown that a variety of NPs including gold [20–22], silver [23,24], iron oxide [25–27], zirconia [28], titanium dioxide [29], silica [30], carbon nanotubes [31–34], graphene nanosheets [31,35,36] and quantum dots (QDs) [37–39] have been used for pesticide detection. Furthermore, a recent report demonstrated a Rayleigh scattering method for the determination of ethion using Ag NPs [40]. This method is effective in that it provides detection limits as low as 3.7 ppb and does not require sample pretreatment. For effective detection of OP pesticides, sensors that function in the ppm-ppb range are effective. However, one there is a need for sensors that are able to easily distinguish between pesticides with no required chemical identification is needed. The work herein shows three types of NPs that can differentiate between OP pesticides. An advantage of the described NPs is that they allow real-time detection with the naked eye, without sample pre-treatment. In contrast to the other recent reports on pesticide sensors, this work demonstrates the ability of the materials to detect and differentiate between five different pesticides. Here, we demonstrate the use of Ag NPs, Au NPs, and Ag-Au NPs as three independent sensors for the detection of five OP pesticides (ethion, fenthion, malathion, parathion and paraoxon-ethyl) (Fig. 1). The thion pesticides show a significant difference in their wavelength shift compared to the oxon pesticides. The pesticides can be differentiated from each
using wavelength shifts of the LSPR. The effectiveness of the plasmonic NPs as highly sensitive and selective sensors for the detection of OP pesticides are investigated.
2. EXPERIMENTAL SECTION 2.1 Materials All chemicals used were of analytical grade. Sodium borohydride (purity 99%), sodium citrate tribasic (purity 99%), sodium chloride, potassium chloride (purity 99%), calcium chloride, gold (III) chloride hydrate (purity 99.99%), ethion, fenthion, parathion, malathion and paraoxon-ethyl were all purchased from the Sigma Aldrich Company and were of analytical grade. Silver nitrate (purity 99.8%) was purchased from J.T. Baker. Ethanol (200 proof) and milliQ water were used in the synthesis process and solution preparation. 2.2 Methods Synthesis of Ag NPs: Colloidal silver nanoparticles were prepared following a procedure previously reported [41]. Briefly, 18.5 mL of milliQ water were placed in an Erlenmeyer flask. To the flask, 0.50 mL of 1.0× 10-2 M silver nitrate, 0.50 mL of 1.0× 10-2 M of sodium citrate tribasic were added and stirred. To this solution, 0.50 mL of 1.0× 10-2 M sodium borohydride was added and gently stirred. The solution was then placed in a refrigerator at 4 °C. The final concentration of Ag NPs by Ag atoms is 2.5× 10-4 M Synthesis of Au NPs: Colloidal gold nanoparticles were prepared following the above procedure. Briefly, 18.5 mL of milliQ water were placed in an Erlenmeyer flask. To the flask, 0.50 mL of 1.0× 10-2 M tetrachloroauric (III) acid (HAuCl4), 0.50 mL of 1.0× 10-2 M of sodium citrate tribasic (0.05 mL) were added and stirred. To this solution, 0.50 mL of 1.0× 10-2 M sodium
borohydride was added and gently stirred. The solution was then placed in a refrigerator at 4 °C. The final concentration of Au NPs by Au atoms is 2.5× 10-4 M. Synthesis of Ag-Au bimetallic NPs: Colloidal Ag-Au bimetallic NPs were synthesized by combining, aqueous stock solutions of, 0.50 mL of 2.0× 10-2 M sodium citrate (Na3C6H5O7), 0.50 mL of 8.0× 10-3 M silver nitrate and 0.50 mL of 2.0× 10-3 M tetrachloroauric(III) acid (HAuCl4) (in a Ag: Au ratio of 4:1) in a flask containing 18.0 mL of milliQ water. Once thoroughly mixed, 0.50 mL of freshly prepared 1.0× 10-2 M NaBH4 was slowly added to the reaction solution and very gently swirled. After remaining sealed and undisturbed in the dark overnight, the Ag/Au NP colloids were then centrifuged at 14,000 rpm for 10 minutes. The supernatant was extracted, characterized, stored in the dark. The colloidal solutions of (Ag NPs, Au NPs. Ag-Au NPs) were covered with aluminum foil and kept under 4 ◦C for 2 hours before use.
2.3 Instrumentation. Synthesized nanoparticles of Ag, Au, Ag-Au were characterized using UV-visible absorbance spectroscopy, transmission electron microscopy (TEM), and . UV-visible absorbance spectra were collected using a Cary 50 Bio Spectrophotometer. A JEOL JEM 1230 TEM was used to observe the morphology of NPs and to measure the NP size. Samples were prepared for TEM by drying a drop of NP solution on a carbon-coated copper grid at room temperature.
3. RESULTS AND DISCUSSION 3.1 Effect of OP pesticides on LSPR changes of plasmonic nanoparticles. Five different types of OP pesticides were used in this study (ethion, malathion, fenthion, parathion and paraoxon-ethyl).
Colloidal NPs of Ag, Au, and Ag-Au in the presence of
phosphate buffered saline (PBS) solutions at pH 7 were titrated with five different OP pesticides. For each titration, 3 mL aliquots of nanoparticle solutions were titrated with continuous addition of 5 μL amounts of 1.0×10-2 M OP pesticides. UV-visible spectroscopy was used to characterize the changes in the LSPR band with the addition of each type of pesticides. Noble metal NPs that are exposed to light induces collective oscillation of electron around the particle surface. This causes a charge separation with respect to the ionic lattice forming a dipole oscillation along the direction of the electric field of the light. The amplitude of the oscillation reaches a maximum at a certain frequency and known as LSPR [42–44]. The SPR induces a strong absorption of light and can be measured using UV-Vis absorption spectrophotometer. This LSPR intensity and wavelength depends on factors such as metal type, particle size, shape, structure, composition and the dielectric constant of the surrounding medium. As mentioned above, all plasmonic NPs are having unique (LSPR) bands depending on their size and dispersity. The characteristic LSPR band for Ag NPs arises at 390 nm, for Au NPs at 520 nm and for Ag-Au NPs at 444 nm, which are shown in UV-visible absorbance spectra (Fig. 2). Ag nanoparticles are yellow in color, Au nanoparticles are wine red in color, and Ag-Au nanoparticles are pale yellow in color. The TEM images show the spherical geometry of all Ag,
Au and Ag-Au bimetallic nanoparticles. Furthermore, the size distribution histograms show the diameter distribution of Ag NPs, Au NPs and Ag-Au NPs (Fig. 3). In order to detect the colorimetric sensing capability of plasmonic NPs, the five different OP pesticides were added separately in to 3 mL of the plasmonic NP solutions at pH 7. Changes in the LSPR and distinct color changes were observed unique to each particle type as described below. Ag NPs show its chracteristic optical absorbance peak at 390 nm. A considerable decrease in this characteristic peak at 390 nm and a peak broadening was observed upon addition of ethion, fenthion, malathion, and parathion pesticides. Formation of a new low intensity peak was observed around 600 nm (Fig. 4 (A) ) for Ag NPs with all the four thion pesticides. Ag NPs exposed to a ethion concentration of 1.48 × 10-4 M, resulted in the formation of a new peak at 605 nm. Ag NPs with the same concentration of fenthion resulted the new peak formation at 600 nm, malathion at 555 nm, and parathion at 590 nm. For each pesticide, wavelength shift was calculated between the characteristic LSPR peak of the plasmonic NPs and the newly arised peak at the right side of the each spectrum of that perticular plasmonic NP. Furthermore, peak broadening was observed for all pesticides except paraxon ethyl. Depending on the type of pesticide, the Ag NPs has shown a characteristic wavelength shift accompanied by the color changes are shown in Fig. 4 (B). Upon addition of paraoxon-ethyl, a considerable change in the LSPR was not observed compared to that with other OP pesticides. The only change it showed was a slight decrease in peak intensity for the characteristic peak at 390 nm. The decrease in intensity and the broadening of the characteristic peak at 520 nm for Au NPs was prominent upon addition of OP pesticides to the colloidal Au NPs. The red shift of the 520
nm LSPR peak was observed for all OP pesticides. Addition of ethion at a concentration of 1.80 × 10-4 M shifted the Au NP LSPR from 520 nm to 630 nm. The same concentration of fenthion resulted in the shift to 620 nm, malathion to 590 nm, and parathion to 565 nm (Fig. 5 (A). The addition of paraoxon-ethyl did not result in a considerable change in the Au NP LSPR relative to other OP pesticides. The corresponding wavelength shifts with the pesticides accompanied by the color changes are shown in Fig. 5 (B). Similar changes in LSPR were also observed for the Ag-Au NPs when exposed to each OP pesticide. The characteristic 444 nm peak was red shifted to 495 nm in the presence of ethion at a concentration of 1.64 × 10-4 M. The same concentration of fenthion resulted in the shit to 490 nm, malathion to 470 nm, and parathion to 465 nm. Finally, no considerable change in the LSPR was observed upon addition of paraoxon-ethyl (Fig. 6 (A)). The corresponding wavelength shift values with each of the OP pesticides was accompanied by the color changes shown in (Fig. 6 (B)).
3.3 Limits of Detection (LOD) for the sensing of OP pesticides by each type of NPs. The limit of detection (LOD) for Ag, Au and Ag-Au NPs with each pesticide was calculated using
the
following
equation:
where, K is a numerical factor chosen according to the level of confidence (K=3) following a procedure reported by Patel et al. [45]. S0 is the standard deviation of the blank and is constant for the blank solution used for the nanoparticle preparation and absorbance measurement. S is
the slope of the calibration curve with different types of the pesticides and various concentrations. Callibration plots were constructed using pesticide concentration and the absorbance ratio of the characteristic LSPR peak of each sensor, that gives a linear relationship. Each pesticide with each of the NP sensor gave a calibration plot which counts to 15 calibration plots all together. Depending on the calibration plots, 15 different S values were calculated. (Supplementary information S1 (a),(b),(c))The limit of detection (LOD) values were calculated using the Eq. 1 calibration plots and are displayed as follow (Table 1). The selectivity of the NP sensors toward each pesticide is evaluated using the unique wavelength shifts in each type of NP upon addition of different OP pesticides. The structural diversity of OP pesticides shows a difference in their sensitivity by each type of plasmonic NP sensor. The three types of NPs used: Ag NPs, Au NPs, and Ag-Au NPs were found to be selective to each of the five pesticides. The detection limit for each sensor with each pesticide were found to be in the ppm range.
3.4 Time dependant stability of synthesized plasmonic nanoparticles. Nanoparticle stability in the presence of OP pesticides was measured by monitoring changes in LSPR using UV-visible spectroscopy. The unique optical property of plasmonic NPs arises from the collective oscillation of the electrons on their surface known as LSPR [46]. Due to the high surface area to volume ratio in plasmonic NPs, the LSPR frequency is sensitive to the refractive index of the surrounding medium. Any change in the environment including surface adsorption and desorption of chemical agents, aggregation, the medium refractive index will shift the LSPR frequency and result in a colorimetric change that can be utilized as optical signals for detection[47]
The morphology of the nanoparticles can be easily observed with the help of TEM. Since this gives information about the changes in NPs before and after exposure with the OP pesticides, Ag NPs, Au NPs and Ag-Au NPs were imaged before and after addition of the OP pesticides with each. The stability of the NPs in the presence of the OP pesticides was investigated by measuring the change in absorbance with respect to time, as shown in Fig. 7. If the NPs are stable in the colloidal medium, we would expect the ratio of A/A0 to be constant throughout the timeframe (where, A = absorbance at time t and A0 = absorbance at time 0). For example, the sedimentation plots for the plasmonic NPs alone (i.e. with no addition of pesticides) as shown in Fig. 7. (A) (i), (B) (i) and (C) (i), shows a straight line. However, if the particles undergo changes due to the presence of pesticides their instability should be reflected by changes in the A/A0 ratio. Instability of the particles could lead to particle aggregation, precipitation, or dissolution depending on the [47]. Ethion was found to cause the highest instability as shown in Fig. 7. (A) (ii), (B) (ii) and (C) (ii). Paraoxon-ethyl did not result in considerable change in plasmonic NPs LSPR absorbance ratio changes over the time. All five pesticides showed nearly the same trend in their colloidal instability with the three types of the plasmonic NPs. The order of highest instability to the lowest instability observed for the nanoparticle colloids are in the presence of ethion > fenthion > malathion > parathion > paraoxon-ethyl. The consequences of particle instability were clearly observed under the TEM after addition of pesticides to the NPs. The TEM image showed the nanoparticles aggregated in the presence of pesticides (Fig. 8). The lowest extent of an aggregation was observed in the presence of the oxon pesticide (paraoxon-ethyl) relative to the thion pesticides (ethion, fenthion, malathion, parathion).
The observed variation in the sensitivity of OP pesticides toward the NPs was found to rely on the diversity of the OP pesticide structure and can be explained based on several theories. OP pesticides are esters of phosphoric acids and their derivatives. The general structure of an OP pesticide comprises the central phosphorus (P) atom and the characteristic thiophosphoryl (P=S) or phosphoryl (P=O) group [48]. The general trend in the sensitivity of the sensors toward the pesticides is: ethion>fenthion>malathion>parathion>paraoxon-ethyl. The higher affinity observed in (P=S) group containing OP pesticides with the NPs than that of the (P=O) group containing pesticides, can be explained in terms of hard-soft acid-base (HSAB) theory. Soft acids interact more strongly with soft bases while hard acids interact more strongly with hard bases [49,50]. The surface atoms on the Ag and Au nanoparticle surfaces are acting as soft acids, while the sulfur (S) atom in the thion pesticides (P=S) are acting as soft bases. Once pesticides are added to the NP colloidal medium, they act as ligands that bind via S atoms or O atoms with the NP surface. These pestcides have a tendency to displace existing citrate groups surrounding the NP surface [51]. The differnce in the sensitivity between thion peasticides can be explained using chelate effect. According to the chelate effect, complexes containing chelate rings are usually more stable than similar complexes without rings[52]. Ethion has four S atoms, which can act as chelating agents for the pesticide coordination with Au and Ag, so we expect a stronger affinity. In the case of fenthion and malathion, each having two S atoms on their structures, will have a strong affinity but, will be less than that of ethion due to less tendency of making a chelate ring. Parathion having a single S atom would have the least affinity relative to the other three pesticides discussed. Paraoxon-ethyl has no S atoms in its structure but, O atoms shows no affinity with the Ag or Au NP sensors. Studies have shown higher affinity of Ag for the coordination with S and N containing ligands on their surface. Depending on the capability of
chelation due to the presence of S or N in ligands, contribute for higher values in formation constants for the ligand coordination with the metal. These formation constants are high in several orders compared to that of O containing ligands without N and S [53,54]. Higher formation constants lead to stable metal ligand complexes hence higher sensitivity for the detection of pesticides in this case. The bond between S atoms in the molecules and noble metals has been investigated by others [55-57]. Sulfur atoms in organosulfur compounds have been shown to have a high affinity for noble metal surfaces, and through the formation of the dative bond, are able to displace adsorbed organic materials from the surface. In most cases the bond is formed spontaneously. [55-57]. All the experiments reported in this article were carried out under laboratory conditions. However, the interferences that may result from natural environments have been taken into consideration by simulating a system, in which humic acid (HA) has been introduced to the medium to serve as a representation of DOM, a key component of any natural environment [58]. The presence of HAs interferes with the interactions between NPs and pesticides, minimizing the pesticides’ ability to interact with the NP surface [59]. It is expected that the HAs can adsorb on to the NP surface via several mechanisms depending on the type of the metal core and the surface coating. This makes a protective mechanism on the surface preventing the interactions of pesticides with NP surface and reduce the sensitivity of the sensor.
Stability of particles in the colloidal medium is described by classical DLVO theory of aggregation. This theory describes two types of forces among the particles. Those are Van der Waals attraction (vdW) and electric double layer repulsion (Velec).The sum of the forces determines the net interaction is repulsive or attractive [60,61]. According to the theory Van der
Waals attraction energy between particles and charge on particles plays a key role in their colloidal stability. Some studies have shown that particle size, shape, chemical composition, coating, and crystal structure influence the surface charge on the NPs [62]. The studies have found that the surface charge of the citrate stabalized plasmonic NPs are negative, and thus keep particles well dispersed in the colloidal medium via electric double layer repulsion (Velec). The electrostatic stabilization of the NPs in the colloidal medium is measured via zeta potential. The zeta potential values for the Ag NPs are recorded from -26.8 to -53.1 mV [63–65]. Zeta potential value range for Au NPs is recorded from -35.9 to -42.9 mV [66] and for Ag NPs-Au NPs core shell from 21.9 to 24.0 mV range [67] in the literature. Solutions having zeta potential values above 20 mV and below -20 mV are considered stable [68]. However, the ligand displacement reaction of OP pesticides with citrate can results in changes in the charge on the particle surface and diminish the Velec forces between particles [69]. Depending on these changes, the NPs tend to aggregate making changes in the LSPR of plasmonic NPs as clearly observed by a color change to the naked eye. As a result, the particles have a greater tendency for aggregation, which is concluded by the TEM images of the plasmonic NPs exposed to pesticides (Fig. 8). Recent research work shows the application of extended DLVO theory (xDLVO) is more accurate over the classical DLVO theory. Since van der Waals and electrostatic interactions alone are insufficient to describe the nanoparticle stability and fate in the colloidal systems, xDLVO theory is widely used which includes the contribution from interparticle separation distances and various medium conditions[70]. Within the xDLVO framework, functionalized nanoparticles interact via van der Waals, electrostatic, and steric (osmotic and elastic) contributions to the potential energy [62,71,72].
Ag NPs showed the highest molar absorptivity and Ag-Au NPs showed the lowest molar absorptivity. Bimetallic Ag-Au NPs were synthesized by a wet chemistry method where, gold ions and silver ions were added simultaneously in the presence of reducing agents [43,73]. This method allows the formation of alloy Ag-Au NPs and is confirmed by the presence of a single plasmonic band in the optical absorbance spectrum as shown in Fig. 2 Ag-Au NPs. Changes in molar absorptivity result due to variation in the molar fraction of Au in the Ag-Au bimetallic NPs [74]. The variation in molar absorptivity in the three plasmonic NPs to their respective sensitivity in pesticide detection, so that the Ag-Au alloy NPs displayed longer stability but had the least sensitivity.
4. Conclusion The resulting work shows the affinity of OP pesticides toward plasmonic NPs. The binding of the OP pesticide to the surface depends on the chemical structure as well as the nature of the NP surface. The extent of the change in LSPR was used to differentiate between the five types of pesticides. It was found that of the three types of NPs, Ag NP, Au NP and Ag-Au NP sensors, Ag NPs showed the highest sensitivity and Ag-Au NPs shows the lowest sensitivity, while Au NPs showed medium sensitivity. The results indicate that the bimetallic systems are less sensitive relative to their monometallic counterparts. The work shows that the plasmonic nanoparticles can be used for different concentration ranges of OP pesticides. The three sensors based on Ag, Au, and Ag-Au NPs easily allowed detection of OP pesticides at ppm levels. This range of pesticide detection is important if these materials are to be further developed into practical units within devices.
Acknowledgements The authors would like to thank the National Science Foundation for financial support under award DMR 0963678. References [1] R.C. Gupta, Toxicology of organophosphate and carbamate compounds, Academic Press, 2011. [2] B.E. Mileson, J.E. Chambers, W.L. Chen, W. Dettbarn, M. Ehrich, A.T. Eldefrawi, D.W. Gaylor, K. Hamernik, E. Hodgson, A.G. Karczmar, Common mechanism of toxicity: a case study of organophosphorus pesticides, Toxicol. Sci. 41 (1998) 8–20. [3] X. Hua, J. Yang, L. Wang, Q. Fang, G. Zhang, F. Liu, Development of an enzyme linked immunosorbent assay and an immunochromatographic assay for detection of organophosphorus pesticides in different agricultural products, PLoS One. 7 (2012) e53099. [4] E.W. Roex, R. Keijzers, C.A. Van Gestel, Acetylcholinesterase inhibition and increased food consumption rate in the zebrafish, Danio rerio, after chronic exposure to parathion, Aquat. Toxicol. 64 (2003) 451–460. [5] L. Wang, D. Du, D. Lu, C.-T. Lin, J.N. Smith, C. Timchalk, F. Liu, J. Wang, Y. Lin, Enzyme-linked immunosorbent assay for detection of organophosphorylated butyrylcholinesterase: A biomarker of exposure to organophosphate agents, Anal. Chim. Acta. 693 (2011) 1–6. [6] D.N. Kumar, A. Rajeshwari, S.A. Alex, M. Sahu, A.M. Raichur, N. Chandrasekaran, A. Mukherjee, Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides, RSC Adv. 5 (2015) 61998–62006. [7] J. Li, Q. Ba, J. Yin, S. Wu, F. Zhuan, S. Xu, J. Li, J.K. Salazar, W. Zhang, H. Wang, Surface display of recombinant Drosophila melanogaster acetylcholinesterase for detection of organic phosphorus and carbamate pesticides, PloS One. 8 (2013) e72986. [8] S. Wang, X. Wang, X. Chen, X. Cao, J. Cao, X. Xiong, W. Zeng, A novel upconversion luminescence turn-on nanosensor for ratiometric detection of organophosphorus pesticides, RSC Adv. 6 (2016) 46317–46324. [9] H.A. Azab, A. Duerkop, Z.M. Anwar, B.H. Hussein, M.A. Rizk, T. Amin, Luminescence recognition of different organophosphorus pesticides by the luminescent Eu (III)–pyridine-2, 6-dicarboxylic acid probe, Anal. Chim. Acta. 759 (2013) 81–91. [10] M. Zourob, K.G. Ong, K. Zeng, F. Mouffouk, C.A. Grimes, A wireless magnetoelastic biosensor for the direct detection of organophosphorus pesticides, Analyst. 132 (2007) 338– 343. [11] D. Chen, J. Wang, Y. Xu, D. Li, L. Zhang, Z. Li, Highly sensitive detection of organophosphorus pesticides by acetylcholinesterase-coated thin film bulk acoustic resonator mass-loading sensor, Biosens. Bioelectron. 41 (2013) 163–167.
[12] S.O. Obare, C. De, W. Guo, T.L. Haywood, T.A. Samuels, C.P. Adams, N.O. Masika, D.H. Murray, G.A. Anderson, K. Campbell, Fluorescent chemosensors for toxic organophosphorus pesticides: a review, Sensors. 10 (2010) 7018–7043. [13] I. Walton, M. Davis, L. Munro, V.J. Catalano, P.J. Cragg, M.T. Huggins, K.J. Wallace, A fluorescent dipyrrinone oxime for the detection of pesticides and other organophosphates, Org. Lett. 14 (2012) 2686–2689. [14] V. Tripathy, A. Saha, D.J. Patel, B.B. Basak, P.G. Shah, J. Kumar, Validation of a QuEChERS-based gas chromatographic method for analysis of pesticide residues in Cassia angustifolia (senna), J. Environ. Sci. Health Part B. 51 (2016) 508–518. [15] G. Du, Y. Xiao, H.-R. Yang, L. Wang, Y. Song, Y.-T. Wang, Rapid determination of pesticide residues in herbs using selective pressurized liquid extraction and fast gas chromatography coupled with mass spectrometry, J. Sep. Sci. 35 (2012) 1922–1932. [16] A. Philippe, G.E. Schaumann, Interactions of dissolved organic matter with natural and engineered inorganic colloids: a review, Environ. Sci. Technol. 48 (2014) 8946–8962. [17] T.-J. Lin, K.-T. Huang, C.-Y. Liu, Determination of organophosphorous pesticides by a novel biosensor based on localized surface plasmon resonance, Biosens. Bioelectron. 22 (2006) 513–518. [18] H. Li, F. Li, C. Han, Z. Cui, G. Xie, A. Zhang, Highly sensitive and selective tryptophan colorimetric sensor based on 4, 4-bipyridine-functionalized silver nanoparticles, Sens. Actuators B Chem. 145 (2010) 194–199. [19] G. Aragay, F. Pino, A. Merkoci, Nanomaterials for sensing and destroying pesticides, Chem. Rev. 112 (2012) 5317–5338. [20] Q. Xu, X. Guo, L. Xu, Y. Ying, Y. Wu, Y. Wen, H. Yang, Template-free synthesis of SERS-active gold nanopopcorn for rapid detection of chlorpyrifos residues, Sens. Actuators B Chem. 241 (2017) 1008–1013. [21] N. Shams, H.N. Lim, R. Hajian, N.A. Yusof, J. Abdullah, Y. Sulaiman, I. Ibrahim, N.M. Huang, Electrochemical sensor based on gold nanoparticles/ethylenediamine-reduced graphene oxide for trace determination of fenitrothion in water, RSC Adv. 6 (2016) 89430– 89439. [22] R. Karami, A. Mohsenifar, S.M. Mesbah Namini, N. Kamelipour, T. Rahmani-Cherati, T. Roodbar Shojaei, M. Tabatabaei, A novel nanobiosensor for the detection of paraoxon using chitosan-embedded organophosphorus hydrolase immobilized on Au nanoparticles, Prep. Biochem. Biotechnol. 46 (2016) 559–566. [23] Y. Bian, C. Li, H. Li, para-Sulfonatocalix [6] arene-modified silver nanoparticles electrodeposited on glassy carbon electrode: preparation and electrochemical sensing of methyl parathion, Talanta. 81 (2010) 1028–1033. [24] D. Xiong, H. Li, Colorimetric detection of pesticides based on calixarene modified silver nanoparticles in water, Nanotechnology. 19 (2008) 465502. [25] N.-N. Li, T.-F. Kang, J.-J. Zhang, L.-P. Lu, S.-Y. Cheng, Fe3O4@ZrO2 magnetic nanoparticles as a new electrode material for sensitive determination of organophosphorus agents, Anal. Methods. 7 (2015) 5053–5059. [26] G.-H. Yao, R.-P. Liang, C.-F. Huang, Y. Wang, J.-D. Qiu, Surface plasmon resonance sensor based on magnetic molecularly imprinted polymers amplification for pesticide recognition, Anal. Chem. 85 (2013) 11944–11951. [27] N. Chauhan, C.S. Pundir, An amperometric biosensor based on acetylcholinesterase immobilized onto iron oxide nanoparticles/multi-walled carbon nanotubes modified gold
electrode for measurement of organophosphorus insecticides, Anal. Chim. Acta. 701 (2011) 66–74. [28] H. Wang, Y. Su, H. Kim, D. Yong, L. Wang, X. Han, A Highly Efficient ZrO2 Nanoparticle Based Electrochemical Sensor for the Detection of Organophosphorus Pesticides, Chin. J. Chem. 33 (2015) 1135–1139. [29] B. Song, W. Cao, Y. Wang, A methyl parathion electrochemical sensor based on NanoTiO2, graphene composite film modified electrode, Fuller. Nanotub. Carbon Nanostructures. 24 (2016) 435–440. [30] X. Xia, P. Xu, H. Yu, X. Li, Resonant micro-cantilever chemical sensor with one-step synthesis of-COOH functionalized mesoporous-silica nanoparticles for detection of tracelevel organophosphorus pesticide, in: Sens. 2012 IEEE, IEEE, 2012: pp. 1–4. [31] X.-C. Fu, J. Zhang, Y.-Y. Tao, J. Wu, C.-G. Xie, L.-T. Kong, Three-dimensional mono6-thio-β-cyclodextrin covalently functionalized gold nanoparticle/single-wall carbon nanotube hybrids for highly sensitive and selective electrochemical determination of methyl parathion, Electrochimica Acta. 153 (2015) 12–18. [32] Q. Tang, X. Shi, X. Hou, J. Zhou, Z. Xu, Development of molecularly imprinted electrochemical sensors based on Fe3O4@ MWNT-COOH/CS nanocomposite layers for detecting traces of acephate and trichlorfon, Analyst. 139 (2014) 6406–6413. [33] D. Huo, Q. Li, Y. Zhang, C. Hou, Y. Lei, A highly efficient organophosphorus pesticides sensor based on CuO nanowires–SWCNTs hybrid nanocomposite, Sens. Actuators B Chem. 199 (2014) 410–417. [34] B. Wu, L. Hou, M. Du, T. Zhang, Z. Wang, Z. Xue, X. Lu, A molecularly imprinted electrochemical enzymeless sensor based on functionalized gold nanoparticle decorated carbon nanotubes for methyl-parathion detection, RSC Adv. 4 (2014) 53701–53710. [35] Y. Mao, H. Fa, Y. Cheng, Y. Du, W. Yin, C. Hou, D. Huo, D. Zhang, An electrode modified with AuNPs/Graphene nanocomposites film for the determination of methyl parathion residues, Nano. 9 (2014) 1450096. [36] R. Xue, T.-F. Kang, L.-P. Lu, S.-Y. Cheng, Electrochemical sensor based on the graphene-nafion matrix for sensitive determination of organophosphorus pesticides, Anal. Lett. 46 (2013) 131–141. [37] N. Fahimi-Kashani, A. Rashti, M.R. Hormozi-Nezhad, V. Mahdavi, MoS2 quantum-dots as a label-free fluorescent nanoprobe for the highly selective detection of methyl parathion pesticide, Anal. Methods. 9 (2017) 716–723. [38] X. Li, Z. Zheng, X. Liu, S. Zhao, S. Liu, Nanostructured photoelectrochemical biosensor for highly sensitive detection of organophosphorous pesticides, Biosens. Bioelectron. 64 (2015) 1–5. [39] X. Yan, H. Li, X. Han, X. Su, A ratiometric fluorescent quantum dots based biosensor for organophosphorus pesticides detection by inner-filter effect, Biosens. Bioelectron. 74 (2015) 277–283. [40] H. Parham, S. Saeed, Resonance Rayleigh scattering method for determination of ethion using silver nanoparticles as probe, Talanta. 131 (2015) 570–576. [41] A.N. Brown, K. Smith, T.A. Samuels, J. Lu, S.O. Obare, M.E. Scott, Nanoparticles functionalized with ampicillin destroy multiple-antibiotic-resistant isolates of Pseudomonas aeruginosa and Enterobacter aerogenes and methicillin-resistant Staphylococcus aureus, Appl. Environ. Microbiol. 78 (2012) 2768–2774.
[42] G. Mie, Articles on the optical characteristics of turbid tubes, especially colloidal metal solutions, Ann Phys. 25 (1908) 377–445. [43] G.C. Papavassiliou, Surface plasmons in small Au-Ag alloy particles, J. Phys. F Met. Phys. 6 (1976) L103. [44] M. Kerker, The Scattering of Light and Other Electromagnetic Radiation (New York: Academic) Ch 6, (1969). [45] G.M. Patel, J.V. Rohit, R.K. Singhal, S.K. Kailasa, Recognition of carbendazim fungicide in environmental samples by using 4-aminobenzenethiol functionalized silver nanoparticles as a colorimetric sensor, Sens. Actuators B Chem. 206 (2015) 684–691. [46] L. Wang, W. Ma, L. Xu, W. Chen, Y. Zhu, C. Xu, N.A. Kotov, Nanoparticle-based environmental sensors, Mater. Sci. Eng. R Rep. 70 (2010) 265–274. [47] S.-W. Bian, I.A. Mudunkotuwa, T. Rupasinghe, V.H. Grassian, Aggregation and dissolution of 4 nm ZnO nanoparticles in aqueous environments: influence of pH, ionic strength, size, and adsorption of humic acid, Langmuir. 27 (2011) 6059–6068. [48] T. Elersek, M. Filipic, Organophosphorous pesticides-mechanisms of their toxicity, in: Pestic.- Impacts Pestic. Expo., InTech, 2011. [49] R.G. Pearson, Acids and bases, Science. 151 (1966) 172–177. [50] R.G. Pearson, Hard and soft acids and bases, J. Am. Chem. Soc. 85 (1963) 3533–3539. [51] Y.-C. Yeh, B. Creran, V.M. Rotello, Gold nanoparticles: preparation, properties, and applications in bionanotechnology, Nanoscale. 4 (2012) 1871–1880. [52] S.F.A. Kettle, Physical Inorganic Chemistry: A Coordination Chemistry Approach, Springer, 2013. [53] C. Levard, E.M. Hotze, G.V. Lowry, G.E. Brown Jr, Environmental transformations of silver nanoparticles: impact on stability and toxicity, Environ. Sci. Technol. 46 (2012) 6900– 6914. [54] R.A. Bell, J.R. Kramer, Structural chemistry and geochemistry of silver-sulfur compounds: Critical review, Environ. Toxicol. Chem. 18 (1999) 9–22. [55] J.C. Love, L.A. Estroff, J.K. Kriebel, R.G. Nuzzo, G.M. Whitesides, Self-assembled monolayers of thiolates on metals as a form of nanotechnology, Chem. Rev. 105 (2005) 1103–1170. [56] M.-A. Neouze, U. Schubert, Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands, Monatshefte Für Chem. - Chem. Mon. 139 (2008) 183–195. [57] The gold–sulfur interface at the nanoscale | Nature Chemistry, (n.d.). https://www.nature.com/articles/nchem.1352 (accessed January 21, 2019). [58] G. Aiken, Humic Substances In Soil, Sediment, And Water : Geochemistry, Isolation, And Characterization, CU Authors Book Gallery. (1985). [59] D. Vaughan, D.G. Lumsdon, D.J. Linehan, Influence of dissolved organic matter on the bio-availability and toxicity of metals in soils and aquatic systems, Chem. Ecol. 8 (1993) 185–201. [60] B.V. DERJAGUIN, Theory of the stability of strongly charged lyophobic sols and the adhesion of strongly charged particles in solutions of electrolytes, Acta Physicochim USSR. 14 (1941) 633–662. [61] E.J.W. Verwey, Theory of the stability of lyophobic colloids: the interaction of sol particles having an electric double layer, 1962.
[62] E.M. Hotze, T. Phenrat, G.V. Lowry, Nanoparticle Aggregation: Challenges to Understanding Transport and Reactivity in the Environment All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher., J. Environ. Qual. 39 (2010) 1909– 1924. [63] J.S. Kim, E. Kuk, K.N. Yu, J.-H. Kim, S.J. Park, H.J. Lee, S.H. Kim, Y.K. Park, Y.H. Park, C.-Y. Hwang, Antimicrobial effects of silver nanoparticles, Nanomedicine Nanotechnol. Biol. Med. 3 (2007) 95–101. [64] Z. Sadowski, I.H. Maliszewska, B. Grochowalska, I. Polowczyk, T. Kozlecki, Synthesis of silver nanoparticles using microorganisms, Mater. Sci.-Pol. 26 (2008) 419–424. [65] S. Agnihotri, S. Mukherji, S. Mukherji, Size-controlled silver nanoparticles synthesized over the range 5–100 nm using the same protocol and their antibacterial efficacy, Rsc Adv. 4 (2014) 3974–3983. [66] G. Sonavane, K. Tomoda, K. Makino, Biodistribution of colloidal gold nanoparticles after intravenous administration: effect of particle size, Colloids Surf. B Biointerfaces. 66 (2008) 274–280. [67] M.E. El-Naggar, T.I. Shaheen, M.M. Fouda, A.A. Hebeish, Eco-friendly microwaveassisted green and rapid synthesis of well-stabilized gold and core–shell silver–gold nanoparticles, Carbohydr. Polym. 136 (2016) 1128–1136. [68] J. Eastman, Colloid stability, Colloid Sci. Princ. Methods Appl. (2005) 36–49. [69] J.L. Ferry, P. Craig, C. Hexel, P. Sisco, R. Frey, P.L. Pennington, M.H. Fulton, I.G. Scott, A.W. Decho, S. Kashiwada, Transfer of gold nanoparticles from the water column to the estuarine food web, Nat. Nanotechnol. 4 (2009) 441. [70] L.A. Wijenayaka, M.R. Ivanov, C.M. Cheatum, A.J. Haes, Improved Parametrization for Extended Derjaguin, Landau, Verwey, and Overbeek Predictions of Functionalized Gold Nanosphere Stability, J. Phys. Chem. C. 119 (2015) 10064–10075. [71] S.R. Saunders, M.R. Eden, C.B. Roberts, Modeling the precipitation of polydisperse nanoparticles using a total interaction energy model, J. Phys. Chem. C. 115 (2011) 4603– 4610. [72] S. Skoglund, T.A. Lowe, J. Hedberg, E. Blomberg, I.O. Wallinder, S. Wold, M. Lundin, Effect of laundry surfactants on surface charge and colloidal stability of silver nanoparticles, Langmuir. 29 (2013) 8882–8891. [73] K. Torigoe, Y. Nakajima, K. Esumi, Preparation and characterization of colloidal silverplatinum alloys, J. Phys. Chem. 97 (1993) 8304–8309. [74] S. Link, Z.L. Wang, M.A. El-Sayed, Alloy formation of gold- silver nanoparticles and the dependence of the plasmon absorption on their composition, J. Phys. Chem. B. 103 (1999) 3529–3533.
Ethion
Malathion
Fenthion
Parathion
Paraxon-ethyl
Fig.1. Chemical structures of selected organophosphorus pesticides studied
Fig. 2. UV-visible spectra of the plasmonic nanoparticles (a) ( nm), (b) (
)Au NPs (SPR peak at 520 nm), (c) (
)Ag NPs (SPR peak at 390
)Ag-Au NPs (SPR peak at 444 nm).
Fig. 3. TEM mages of (a) Ag NPs, (b) Au NPs, (c) Ag-Au NPs with particle size distribution histograms. The scale bar represents 50 nm.
Fig. 4. (A) Ag NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon-ethy (B) Plots of
shifts in wavelength with increased pesticide concentration, accompanied by color changes
Fig. 5. (A) Au NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M, 1.64× 10-4 M, 1.8× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon ethy B) Plots of shifts in wavelength with increased pesticide concentration,
accompanied by color changes
Fig. 6. (A) Ag-Au NPs (0.25 mM) titrated with pesticides in concentrations equal to (from top to bottom) [1.66× 10-5 M, 3.32× 10-5 M, 4.98× 10-5 M, 6.62× 10-5 M, 9.90× 10-5 M, 1.15× 10-4 M, 1.32× 10-4 M, 1.48× 10-4 M, 1.64× 10-4 M], (i) ethion (ii) fenthion iii) malathion iv) parathion and (v) paraoxon ethyl B)
Plots of shifts in wavelength with increased pesticide concentration, accompanied by color changes
Fig. 7. Sedimentation plots of (A) (i) Ag nanoparticles (B) (i) Au nanoparticles (C) (i) Ag-Au nanoparticles alone. Plasmonic nanoparticles in each case in the presence of (ii) ethion, (iii) fenthion, (iv) malathion (v) parathion, and (vi) paraoxon-ethyl.
Fig. 8. TEM images for Ag NPs, Au NPs, Ag-Au NPs after exposure to OP pesticides. The scale bar represents 100 nm.
Table 1 Limit of detections for OP pesticides detection by plasmonic NPs.
Pesticide Ethion Fenthion
Ag NPs LOD LOD (M) (ppm) -5 9 2.4×10 11 4.1×10-5
Malathion 5.4×10-5 Parathion 1.5×10-4 Paraoxonethyl 0
Limit of Detection (LOD) Au NPs Ag-Au NPs LOD LOD LOD (M) (ppm) LOD (M) (ppm) -4 -4 58 228 1.5×10 7.5×10 -4 53 231 1.9×10 8.3×10-4
18 44
4.2×10-4 1.1×10-2
0
0
139 3203
3.6×10-3 6.3×10-3
1189 1835
0
0
Highlights:
The three types sensors can detect five diverse types of OP pesticides (ethion, fenthion, malathion, parathion, and paraoxon-ethyl).
Each of the plasmonic nanoparticle sensor can differentiate between the five types of the pesticides depending on the maximum shift of the characteristic localized surface plasmon resonance (LSPR) band.
The time dependent sedimentation of the plasmonic NPs in the presence of OP pesticides support the sensitivity order of each sensor toward five different OP pesticides.