Carbon-Based Nanomaterials for the Development of Sensitive Nanosensor Platforms

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Carbon-Based Nanomaterials for the Development of Sensitive Nanosensor Platforms MONIKA NEHRA • NEERAJ DILBAGHI • ASHRAF ALY HASSAN • SANDEEP KUMAR

INTRODUCTION Carbon is one of the most commonly found elements in nature and its understanding has reached new levels, from macroscopic to nanoscale, with continuous advancement in nanotechnology. The nanostructures of carbon in their different forms have been applied in diverse fields such as field emission displays, nanoelectronics, energy conversion and storage, biological and chemical sensors, and theranostics. In the 21st century, owing to their extraordinary properties in terms of structural perfection, carbon nanomaterials have in fact led general science to many advanced avenues. The structural properties of carbon materials have inspired the synthesis of novel nanomaterials with similar symmetries and structures, e.g., fullerenes, nanotubes, nanodots, and graphene. Carbon atoms have the ability to form robust mutual covalent bonds in different hybridization states such as sp, sp2, and sp3. Carbon atoms also interact with nonmetallic elements leading to the formation of a wide range of structures from small molecules to long chains. The major classification of carbon materials (such as carbon, diamond, and graphite) is based on the way of interconnection between carbon atoms, e.g., tetrahedral sp3 atom configuration in case of diamond and hexagonal sp2 carbon atom configuration in case of graphene monolayers. However, mixed states also exist and lay the basis for nanocrystalline diamond, diamond-like carbon, and

amorphous carbon. The carbon nanoallotropes belonging to same group or same arrangement of carbon atoms have common properties; however, there are significant differences because of their different sizes and shapes. A summary of carbon nanomaterials with different morphologies but unique chemical properties is shown in Fig. 1.1 (Yan et al., 2016). They can be classified according to their structural dimensionality as, e.g., (1) 0D nanostructures (fullerenes, carbon dots, nanodiamonds, etc.), (2) 1D nanostructures (carbon nanotubes [CNTs]/carbon nanofibers [CNFs], etc.), and (3) 2D nanostructures (graphene, graphene nanoribbons, etc.). Diamond, a metastable state of carbon, consists of a 3D cubic lattice with 3.57 Å lattice constant along a CeC bond length of 1.54 Å (Sque et al., 2006). In contrast, graphite possesses a 2D layered structure having a CeC bond length of 1.42 Å (Baughman et al., 1987). In graphene, the layers are single atom thick and interact through van der Waals forces having 3.35 Å interlayer spacing. Graphite corresponds to the most thermodynamically stable form of carbon at room temperature. Graphene is commonly referred as a 2D building block of sp2 hybridized carbonaceous nanomaterials; it can be rolled and/or distorted in order to form CNTs and fullerenes. The first successfully synthesized carbon nanomaterial was C60 (also known as buckminsterfullerene), through laser ablation of graphite

Advances in Nanosensors for Biological and Environmental Analysis. https://doi.org/10.1016/B978-0-12-817456-2.00001-2 Copyright © 2019 Elsevier Inc. All rights reserved.

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FIG. 1.1 Broad family of carbon nanomaterials. (Adapted from Yan, Q.L., Gozin, M., Zhao, F.Q.,

Cohen, A., Pang, S.P., 2016. Nanoscale 8, 4799e4851. Reprinted with permission from RSC.)

under helium flow (Kroto et al., 1985). However, some reports also exist on the development of even-numbered carbonaceous clusters before the development of C60, but these clusters were unsuitable for characterization because of their large size distributions (Rohlfing et al., 1984). Fullerenes are viewed as the 0D form of graphitic carbon and also referred as irregular sheets of graphene that are curled in the form of a sphere via pentagons incorporation in the structure. Furthermore, CNTs were isolated as an offshoot during the synthesis of fullerene. The elongation of fullerene in one dimension assumes the structure of CNTs with high aspect ratios (e.g., from 102 to 107). Different synthesis methods have been developed for the production of both single-walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs). These include arc discharge (Arora and Sharma, 2014), chemical vapor deposition (CVD) (Kumar et al., 2017a), and high-pressure carbon monoxide method (Liu et al., 2011a). The initial development of graphene was done by its growth on insulating substrates by Geim and coworkers (Novoselov et al., 2004). In the current perspective, graphene can be referred as the mother of all graphitic carbon. Graphene has further been investigated as monolayer to a fewlayered nanomaterial depending on the thickness requirement in a particular application (Liu et al., 2018). Carbon nanomaterials can possibly cover the characteristics of different substances on the earth,

such as hardest to softest materials, insulators to semiconductors and further to superconductors, and fully light-absorbing to completely transparent materials. The superiority of carbon nanomaterials is basically due to their hardness, radiation characteristics, optical properties, electric conductivity, chemical resistance, heat resistance, electric insulation, and surface/interface properties in comparison to many other materials.

CARBON-BASED NANOMATERIALS FOR NANOSENSOR DEVELOPMENT Nanosensors are becoming a crucial part of modern lifestyle, particularly in healthcare due to the demand of point-of-care devices, personalized medicine, and cheaper and reliable diagnostic tools. Carbon nanomaterials have motivated researchers to implement them as ideal transduction materials mainly because of their geometry, fast electron transfer kinetics, wide potential window, low residual current, fluorescent properties, and readily renewable surfaces (Jariwala et al., 2013). Voluminous research efforts have been dedicated to employ carbon nanomaterials in the development of highly sensitive and selective nanosensors.

Fabrication of Sensing Platforms The device architecture of electrochemical nanosensors can be broadly classified into two main categories: (1) the conventional three-electrode

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FIG. 1.2 (A and B) A schematic representation of functionalized carbon nanomaterialebased electrochemical biosensors. (Adapted from Yang, Y., Yang, X., Yang, Y., Yuan, Q., 2018a. Carbon 129, 380e395. Reprinted with permission from Elsevier.)

setup and (2) the chemiresistive/field-effect transistor (FET) setup. The three-electrode setup is commonly used for potentiometric, amperometric, and impedimetric nanosensors that comprise working, counter, and reference electrodes for detection of different analytes (Fig. 1.2) (Yang et al., 2018a). Carbon nanomaterials have been popularly used to modify the surface of glassy carbon electrode to develop them as a working electrode. As such, the electrochemical sensing techniques are particularly helpful in understanding the behavior of analytes and their associated electrochemical reaction mechanisms. The analyte species that can undergo redox transitions on glassy carbon electrodes can be detected via different categories of electrochemical techniques, e.g., amperometry and potentiometry. The transfer of ions takes place through a conductive electrolyte medium. Carbon nanomateriale based electrodes offer several benefits in terms of wide potential window, good electrocatalytic activities, and chemical inertness during redox reactions. In electrochemical biosensors, carbon nanomaterials also serve as a platform for biomolecule immobilization, thereby improving electrochemical transduction (Hu et al., 2016). Chemiresistive/FET sensors have attracted considerable attention because of their enormous benefits in terms of their fast response time, seamless integration with electronic manufacturing processes, potential for miniaturization, and

parallel sensing (Bandodkar et al., 2016; Barbaro et al., 2012). Carbon nanostructures, such as CNTs, have been reported as excellent electrode material for gas sensors in order to detect the gas molecules, with high sensitivity, low device cost, and fast response time even at room temperature (Dube et al., 2015). In a similar manner, the detection of gas molecules through graphene is based on the change in their electric conductivity as a result of the formation of surface adsorbates. These surface adsorbates can work as either donors or acceptors depending on their chemical nature, preferential adsorption sites, and the surrounding environment (Varghese et al., 2015). The different formats of FET sensors may be listed as ion-sensitive FET, unmodified complementary metal-oxide semiconductor, extendedgate FET, floating-gate FET, and dual-gate FET (Ramnani et al., 2016). Carbon nanomaterials have been found very useful to function as the functional channel in chemiresistor/FET nanosensor configuration; for example, both the tubular geometry of CNTs and the planar geometry of graphene ensure maximum exposure of surface atoms for the binding of target analyte molecules to the electrode material. The Debye length (lD) is a measure of field penetration into bulk materials and also causes significant modulation in the electronic properties of electrode materials upon exposure to the analytes. The lD is comparable to the dimensions of the carbon nanostructures,

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which ensures label-free sensing of analytes with relatively low limits of detection and high sensitivities. Carbon nanomaterials in an FET configuration can detect multiple analytes concurrently (Cullen et al., 1990). The fabrication of graphene-FET devices requires the bulk production of graphene films via different synthesis techniques such as the CVD method, which offers control over crystallinity, grain size, and number of layers over the desired substrate (Srivastava et al., 2010). CNTs can be synthesized as cylindrical tubes by rolling up single and/or multiple graphene sheets. The nature of CNTs, either metallic or semiconducting, depends on their chirality (armchair, zigzag, or chiral) and the diameter of the tubes (Dresselhaus et al., 2004). For instance, armchair SWCNTs are metallic in nature and, therefore, these cannot be used for fabrication of FET nanosensors.

Surface Functionalization of Nanocarbon Electrodes The surface chemistry of electrode materials has significant importance with respect to their interaction with analytes present in complex solutions/matrices. The surface functionalization of carbon nanomaterials has been reported through covalent/noncovalent interactions and/or decoration with some inorganic nanomaterials (Liu et al., 2015; Karimi et al., 2015; Balasubramanian and Burghard, 2005). Carbon nanomaterials with multiple functional groups at their surface/edges can satisfy the specific requirements of different kinds of sensors with specific intermolecular interactions. For instance, graphene plays a significant role in electrochemical sensing application because of its high carrier mobility, exceptional electrochemical properties (electron transfer rates), optical properties, and structural characteristics. Furthermore, its properties can be controlled/modulated through adoption of suitable preparation methods and or functionalization to generate specific target-sensing properties (Kybert et al., 2014). Likewise, the presence of functional groups such as carboxyl and amine makes CNTs compatible in their conjugation with biomolecules as well as other materials such as metallic nanoparticles (Kong et al., 2001;

Gao et al., 2012). For covalent functionalization, carboxylic (eCOOH) groups can be introduced on the edge planes and sidewalls of the carbon nanomaterials through oxidation. Some forms of carbon such as reduced graphene oxide have readily available eCOOH groups. As a matter of concern, the covalent functionalization can deteriorate the sp2 structure of the honeycomb lattice of carbon while also inducing some defects on their surface (such as disruption in p-electronic network), ultimately resulting in deflation of electronic properties of the materials. Noncovalent functionalization can be a solution to this limitation, which does not influence the intrinsic structure of carbon nanomaterials and also maintains their electronic and mechanical properties (Georgakilas et al., 2012). The functionalization of carbon nanomaterials helps in improving their dispersibility, biocompatibility, and sensing properties. In literature, carbon nanomaterials have been used in two major ways to modify the biosensing electrodes: (1) modification of the bulk material, for example, mixing the electrode material with carbon paste and (2) modification of the electrode surface, for example, preparation of films on premade electrode through CVD or any other method. The incorporation of carbon paste in electrode materials (e.g., other nanomaterials) enhances the overall electrocatalytic properties and supports improved signal transduction (Fig. 1.3) (Huang et al., 2006). Furthermore, the application of carbon paste in immobilizing the enzymes can offer protection of these protein molecules from the external environment, while also rendering better stability and durability in comparison to the system having enzyme immobilized over the bare electrode surface (Akyilmaz et al., 2017).

APPLICATIONS OF NANOCARBON ELECTRODES FOR SENSING OF DIFFERENT ANALYTES In the recent years, the nanosensor platforms have gained significant research interest for sensitive detection of a wide variety of analytes including both chemical (such as dopamine, ascorbic acid, uric acid, and norepinephrine) and biological

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FIG. 1.3 A schematic representation of the different strategies used to design functionalized carbon nanotube electrodes. SWCNTs, single-walled carbon nanotubes. (Adapted from Huang, X.J., Im, H.S., Yarimaga, O., Kim, J.H., Jang, D.Y., Lee, D.H., Kim, H.S., Choi, Y.K., 2006. Journal of Electroanalytical Chemistry 594, 27e34. Reprinted with permission from Elsevier.)

(such as airborne bacteria, folic and pantothenic acid, protein, and mycotoxins). The use of carbon nanomaterials as the functional electrode surface of nanosensor platform offers several advantages in terms of good electrocatalytic activity, enhanced interfacial adsorption properties, fast electron transfer kinetics, and high biocompatibility in comparison to traditional materials. There are different strategies for incorporation of these nanomaterials into electrochemical sensors, e.g., drop casting (Kaniyoor et al., 2009), direct growth on a substrate (Wang et al., 2009), polymer-based coatings (Barsan et al., 2015), use of binders such as Nafion or dihexadecyl hydrogen phosphate (Liao et al., 2015), and screen printing (Chen et al., 2016). In comparison to drop casting or dip coating, the direct growth of the carbon nanomaterials over electrode surface provides more homogeneous coating as well as supports the batch fabrication of nanosensors (Gooding, 2005). Furthermore, polymer-based coatings can aid in the physical and chemical properties of the carbon nanomaterials as well as their dispersion for deposition. Additional incorporation of metallic nanoparticles in polymer matrix is sometimes desired to maintain the requisite level of electrode conductivity (Chun et al., 2010).

Detection of Heavy Metal Ions The quantification/detection of heavy metal ions (including Hg2þ, Cd2þ, Cu2þ, Pb2þ, As3þ, etc.) is

a major concern among chemists, environmentalists, and biologists due to their toxic nature as well as prolonged persistence in the biosphere. The heavy metal ion contamination has mainly been caused by the fast industrial development and related activities such as electroplating, battery manufacturing, mining, and smelting. The metallurgical industries release various harmful toxins into our environment, which include nonbiodegradable chemicals and heavy metals. The existence of these contaminants, especially heavy metal ions in water bodies, has direct influence over the health of living systems (Bhanjana et al., 2015, 2017). The conventional methods for the analysis of heavy metal contamination are based on different techniques such as atomic absorption spectroscopy (AAS) (Luo et al., 2015), atomic emission spectroscopy (Zhang et al., 2014), inductively coupled plasma mass spectrometry (ICP-MS) (Li et al., 2015), and X-ray fluorescence spectrometry (Sitko et al., 2015). These techniques are very costly and not appropriate for on-site analysis. Moreover, these approaches can only quantify the total amount of heavy metals and it is not possible to analyze the bioavailable concentrations that are accessible to the living bodies. Electrochemical detection using nanosensors is among the simple, accurate, and sensitive methods for the detection of metal contamination in food and environment. The electrochemical sensing techniques offer several

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benefits in terms of low cost, portability, high sensitivity, short analytical time, and easy adaptability for in situ detections (Bhanjana et al., 2016). The working electrode of the threeelectrode electrochemical system can be modified with nanomaterials for improving the sensitivity of the nanosensors (Cheng et al., 2018). Such nanosensors are then operated by recording changes in their potential, current, electrochemical impedance, and electroluminescence upon the recognition of an analyte (Simpson et al., 2018). Among nanomaterials, carbon nanomaterials are most interesting materials as adsorbents/ preconcentrator agents or transducer materials used in the development of nanosensors. The carbon nanomaterials can respond to both organic and inorganic analytes. The functionalization of carbon nanomaterials with biological recognition elements (e.g., enzymes, antibodies, DNA, or microorganisms) enables highly specific and sensitive sensing of metal ions (Wanekaya et al., 2008). In particular, DNA-based nanosensors have gained much research interest in the recent years for the detection of heavy metal ions owing to their stability in biological pH environments (Primo et al., 2015). Wen et al. (2018) have reported the application of DNA-modified graphene oxide/Prussian blue nanoparticles for arsenite detection. The interaction of graphene oxide with 50 -thiolate-labeled (GT)21-ssDNA facilitated the generation of Prussian blue nanoparticles on gold electrode surface. The (GT)21-ssDNAecontaining arsenite recognition sequence offered excellent specificity for arsenite detection (detection limit down to 0.058 ppb) in real water samples. DNAzyme-functionalized carbon nanostructureebased biosensors have also been developed for some other metal ions including Pb2þ, Hg2þ, and Cu2þ (Zhou et al., 2016). The utility of carbon nanomaterials has also been demonstrated in the development of sensitive chemosensors. For example, Lu et al. (2018) proposed a novel 3D honeycomb structure of N-doped carbon nanosheet framework decorated with bismuth nanoparticles (Bi-NCNF) for selective and sensitive electrochemical sensing of

Pb2þ and Cd2þ (Fig. 1.4). The proposed system offered a detection limit of 0.04 and 0.02 mg L1 for Pb2þ and Cd2þ, respectively. In many reported cases, the performance of carbon nanomaterialebased nanosensors for detecting heavy metal ions has been successfully validated with standard techniques such as AAS and ICP-MS. A summary of the recently developed glassy carbonebased nanosensors (electrode surface modified with different carbon nanostructures) for heavy metal detection is provided in Table 1.1, which is intended to acquaint the readers about the main design and performance parameters of these related technologies. The coupling of nanosensitive platform with carbon nanomaterials has resulted in high sensitivity, fast response, multianalyte detection, and low detection limits. In spite of numerous benefits, there are a few challenges associated in this area: (1) accurate detection of metal ions in biological samples (involving blood, saliva, urine, etc.), (2) issue of false-positive signal interference and chemical fouling, (3) detection of heavy metal ions in their complex form, and (4) continuous monitoring of water resources for detection of metal ions (Gumpu et al., 2015). As per the commercialization perspective, the research efforts should be directed toward reusability, mass production, and system integration.

Detection of Food Additives and Pesticide Residues The innovation in food industry is increasing at an immense speed in terms of development and application of pesticides, food additives, and materials for food protection/processing/coating/ packaging. Pesticides are excessively used in agricultural activities to enhance the production yield by controlling pests, insects, weeds, etc. Food additives are introduced to deliver functional attributes in order to improve food life/safety. Undesirably high concentrations of food additives and accidental contamination of veterinary drug residues and pesticides in foodstuff and water resources have become issues of major health concern. The pesticide residues are very toxic substances and can lead to several health issues (such as cholinergic dysfunction) in both humans and

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FIG. 1.4 A schematic layout for fabrication of 3D N-doped carbon nanosheet framework decorated with bismuth nanoparticles (Bi-NCNF) followed by their application for electrochemical detection of Pb2þ and Cd2þ. EG, ethylene glycol; GCE, glassy carbon electrode; NPs, nanoparticles; PVP, polyvinylpyrrolidone. (Adapted from Lu, Z., Dai, W., Lin, X., Liu, B., Zhang, J., Ye, J., Ye, J., 2018. Electrochimica Acta 266, 94e102. Reprinted with permission from Elsevier.)

animals. The analysis of various types of contaminations (i.e., toxic food additives, veterinary drug residues, and pesticides) that can affect our food samples is usually carried out using methods such as high-performance liquid chromatography (HPLC) (Wahed et al., 2016), HPLC-mass spectrometry (Hoffmann et al., 2017), gas chromatography-mass spectrometry (JiménezSalcedo and Tena, 2017), and capillary electrophoresis (Omar et al., 2017). The development of nanosensors has been reported based on electrochemical biosensing of contaminants in foodstuff and water. The electrochemical biosensors offer fast operation and high selectivity, sensitivity, and reproducibility (Rotariu et al., 2016; Herzog et al., 2008). The incorporation of carbon nanostructures enhances the loading of bioreceptors on the electrode surface, apart from providing high stability. Carbon nanoparticles also serve as a

relay for transfer of electrons between biomolecules and the electrode. Elyasi et al. (2013) reported a Pt/CNT nanocompositeemodified ionic liquid carbon electrode for specific determination of Sudan I (a coloring agent) with an excellent limit of detection (0.003 mM). The immobilization of an enzyme (from Inga edulis) onto a carbon paste electrode containing MWCNTs and Nafion has been reported to provide a highly selective and sensitive detection of tert-butylhydroquinone (TBHQ, an antioxidant), with quantification and detection limits of 1.25 and 0.41 mg L1, respectively (de Oliveira et al., 2014). This sensing method can offer determination of TBHQ in commercial salad dressing samples with an acceptable level of accuracy (e.g., the relative error limiting to 5.4%). Likewise, a gold-modified carbon paste electrode has been demonstrated for electrochemical sensing of synthetic dyes (e.g., Sunset Yellow and tartrazine) in

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TABLE 1.1

List of Different Carbon Nanomaterials Used in Glassy Carbon ElectrodeeBased Nanosensors of Heavy Metal Ions.

Cadmium

Arsenic

Detection Mechanism

Details of the Electrode Interface Material/s

Limit of Detection 1

Sensitivity (9.7  2.5)  10 mA mg L1

References 3

Anodic stripping voltammetry

Cysteine functionalized SWCNTs

0.3 mg L

Differential pulse anodic stripping voltammetry

Reduced graphene oxide-chitosan/ ply-L-lysine nanocomposites

0.01 mg L1

d

Guo et al. (2016)

Square wave anodic stripping voltammetry

Phenylsulfonic groupegrafted MWCNTs with dye molecules

0.08 mM

d

Chen et al. (2018)

Square wave voltammetry

Calixarene-functionalized reduced graphene oxide

2  1011 M

d

Göde et al. (2017)

Cyclic voltammetry

Ruthenium(II)-textured graphene oxide nanocomposite

2.8 nM

3.43 mA mM1

Gumpu et al. (2017)

Differential pulse anodic stripping voltammetry

Gold-coated, boron-doped diamond thin film

0.005 mg L1

9.7  2.5 mA mg L1

Song and Swain (2007)

Anodic stripping voltammetry

Gold nanoparticleemodified carbon fiber ultramicroelectrodes

0.9 mg L1

0.0176 nA mg L1

Carrera et al. (2017)

Cyclic voltammetry

Clay-modified carbon paste

5e40 mg L1

d

Tiwari and Lee (2017)

Flow injection analysis

Gold nanoparticleedecorated carbon nanofiber-chitosane modified carbon

11.4 mg L1

218.1 nA mg L1

Nellaiappan et al. (2018)

Cyclic voltammetry

DNA-modified graphene oxide/ Prussian blue nanoparticles

0.058 mg L1

d

Wen et al. (2018)

Fluorescence spectrophotometry

Carbon quantum dots

0.086 mg L1

d

Pooja et al. (2017)

Square wave anodic stripping voltammetry

Amine-functionalized graphene oxideedecorated gold nanoparticles

0.162 mg L1

130.631 mA mg L1 cm2

Yang et al. (2017)

Cyclic voltammetry

Ruthenium(II)-textured graphene oxide nanocomposite

2.3 nM

2.11 mA mM1

Gumpu et al. (2017)

Gutierrez et al. (2017)

Advances in Nanosensors for Biological and Environmental Analysis

Metal Ion Detected

Mercury

Copper

Chromium

CNT/asymmetric N4 tetradentate Schiff base ligand N,N0 -bis(pyrrole-2-ylmethylene)-2aminobenzylamineecoated graphite

0.36 nM

d

Selvan and Narayanan (2018)

Cyclic voltammetry

Polypyrrole/carbon nanofiber nanocomposite

0.05 mg L1

d

Oularbi et al. (2017)

Cyclic voltammetry

Ruthenium(II)-textured graphene oxide nanocomposite

1.6 nM

d

Gumpu et al. (2017)

Square wave anodic stripping voltammetry

Nitrogen-doped and thiol groupe grafted MWCNTs

0.3 mg L1

d

Li et al. (2016)

Anodic stripping voltammetry

CNT/asymmetric N4 tetradentate Schiff base ligand N,N0 -bis(pyrrole-2ylmethylene)-2-aminobenzylaminee coated graphite

1.1 nM

d

Selvan and Narayanan (2018)

Square wave voltammetry

Carbon paste electrode impregnated with ion-imprinted polymer and MWCNTs

3.8 pM

20683 A L mol1

Alizadeh et al. (2017)

Square wave voltammetry

Calixarene functionalized reduced graphene oxide

2  1011 M

d

Göde et al. (2017)

Cyclic voltammetry

Ruthenium(II)-textured graphene oxide nanocomposite

1.41 nM

d

Gumpu et al. (2017)

Differential pulse anodic stripping voltammetry

Reduced graphene oxide-chitosan/ ply-L-lysine nanocomposites

0.02 mg L1

d

Guo et al. (2016)

Square wave anodic stripping voltammetry

Graphene quantum dots/gold nanoparticles

0.05 nM

3.69 mgA/nM

Ting et al. (2015)

Differential pulse anodic stripping voltammetry

Biochar-modified carbon paste

4.0  107 M

d

Oliveira et al. (2015)

Cyclic voltammetry

Manganese oxide nanoflakes/ MWCNTs/chitosan nanocomposites

0.3 mM

18.7 nA mM

Salimi et al. (2015)

Linear sweep voltammetry

Gold nanoparticleedecorated screen-printed carbon electrode

5.4 mg L1

1.1 nA mg L1

Tu et al. (2018)

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CNT, carbon nanotube; MWCNTs, multiwalled CNTs; SWCNTs, single-walled CNTs.

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development

Lead

Anodic stripping voltammetry

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commercially available soft drinks (Ghoreishi et al., 2012). The detection of pesticide residues (organophosphate, organochlorine, carbamates, pyrethrum, etc.) is generally carried out using gas or liquid chromatography. This technique is highly sensitive and selective, but requires expensive instrumentation and skilled personnel. Electrochemical biosensors are regarded as the potential choice for pesticide detection with desired selectivity, sensibility, and reproducibility. For example, a screen-printed electrode has been modified with carbon nanoparticles. After subsequent immobilization with butyrylcholinesterase, the electrode could detect the presence of paraoxon in spiked wastewater samples. This biosensor electrode was stable up to 78 days at room temperature under dry conditions. The inhibition of the enzyme activity was directly correlated with the concentration of paraoxon (up to 30 mg L1). Many other label-free nanosensor platforms have also been designed for the detection of pesticides. For instance, Li et al. (2018a) have reported the application of acetylcholinesterase (AChE)-immobilized fluorescence carbon dots for dual-mode (fluorometric as well as colorimetric) detection of organophosphate pesticides (Fig. 1.5). This sensor functioned on the principle of generation of fluorometric and colorimetric responses as a

result of the formation of a yellow reaction product (5-thio-2-nitrobenzoic acid [TNBA]) after the decomposition of 5,5-dithiobis(2-nitrobenzoic acid), which was triggered by the reaction of AChE with acetylthiocholine. TNBA functioned as a powerful absorber for quenching the fluorescence of carbon dots. Hence, this method could be used for the detection of pesticides, as the inhibition in enzyme activity of AChE led to the restoration of fluorescence signal alongside a reduction in the absorbance intensity. Research efforts have also been directed toward the development of nonenzymatic nanosensors for pesticides. Hsu et al. (2017) reported the peroxidase-like activity of Ag nanoparticlee decorated oxidized MWCNTs, which could be exploited in the fluorometric assay of dimethoate. This method offered good selectivity for sensing dimethoate in a linear range of 0.01e0.35 mg mL1 from lake water and fruit samples. Facure et al. (2017) reported a novel enzyme-free impedimetric electronic tongue (e-tongue) comprising graphene hybrid nanocomposites for sensing the trace levels of organophosphate pesticide mixture (i.e., malathion and cadusafos). This e-tongue system detected the presence of organophosphate at nanomolar concentrations (as low as 0.1 nM) in real samples. The use of reduced graphene oxide, containing

FIG. 1.5 Dual signalebased (fluorescence and colorimetry) detection of organophosphate pesticides using acetylcholinesterase (AChE)-immobilized fluorescence carbon dots (CDs). DTNB, 5,50 -dithiobis-(2-nitrobenzoic acid); OPs, organophosphates; TNBA, 5-thio-2-nitrobenzoic acid. (Adapted from Li, H., Yan, X., Lu, G., Su, X., 2018a. Sensors and Actuators B: Chemical 260, 563e570. Reprinted with permission from Elsevier.)

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development the residual oxygenecontaining functional groups, offered the realization of a sensing platform with high conductivity. The functional groups behaved as active sites for the sensing of pesticide residues and increased the sensitivity of the system. Table 1.2 lists some important carbon nanomaterialebased electrochemical nanosensors used for the detection of food additives and pesticide residues.

Detection of Bacterial Pathogens or Viruses Bacterial pathogens and viruses are potential threats to human health. Therefore the development of tools for simple and fast detection or diagnosis of bacterial pathogens is crucial to control their outbreak and to ensure appropriate therapeutic treatments. The existing methods of detection (including polymerase chain reaction and enzyme-linked immunosorbent assay) are sensitive enough and selective, but they involve complex steps of sample preparation and take long assay times (Berg et al., 2015; Nguyen et al., 2017). Several evidences have been projected in the literature about the potential usefulness of biosensors for the analysis of bacterial pathogens. Carbon nanomaterialemodified glassy carbon (Dekanski et al., 2001) and pyrolytic graphite electrode (Banks and Compton, 2005) have been usefully exploited in this context. In one of the important reports, Gheith et al. (2006) suggested that lateral currents in highly conductive SWCNT multilayers can cause the stimulation of neural cells. Therefore CNTs have a future in biomedical devices in which electrically responsive cells, such as the muscle cells, endocrine cells, can be examined at even single-cell level. CNTs can be used in systematic biosensors in order to monitor the immune response in case of immunodeficient patients (Fadel et al., 2008). These studies led to the development of cancer antibodyefunctionalized SWCNTs for the thermal ablation of tumor cells (Kostarelos et al., 2009). The selective nature of the treatment makes SWCNTs promising for biosensing applications as antibody-functionalized SWCNTs track only cancer cells upon irradiating them with infrared energy. The high sensitivity and selectivity

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of carbon-based electrochemical biosensors facilitate the sensing of the pathogens even in the complex sample matrices (Kumar et al., 2015; Mokhtarzadeh et al., 2017). Bhaisare et al. (2016) reported the fluorescent detection of pathogenic bacteria, i.e., Staphylococcus aureus and Escherichia coli (E. coli), in urine sample through their strong adhesion over amine-functionalized magnetic nanoparticles decorated with carbon dots. Carbon nanomaterials can also be functionalized to support the immobilization of various selective ligands, single-stranded DNA, and even other types of nanoparticles. For instance, CNTs immobilized with an antimicrobial peptide (clavanin A) have been reported to offer effective and sensitive detection of Klebsiella pneumoniae, Enterococcus faecalis, E. coli, and Bacillus subtilis in concentration of 102e106 colony-forming unit (CFU) mL1 (Fig. 1.6) (Andrade et al., 2015). The antibody-conjugated SWCNTs have also been proposed for highly specific and sensitive electrochemical immunosensing of S. aureus with a low detection limit of 13 CFU mL1 (Bhardwaj et al., 2017). The biosensors were able to quantify S. aureus in spiked milk samples even in the presence of other bacteria, e.g., E. coli B, Staphylococcus epidermidis, and B. subtilis. The recognition and quantification of cyanobacterial bloom are of great importance, as it may cause many structural and functional disturbances to the liver because of the inhibition of protein phosphatase (type 1 and 2A) (Zamyadi et al., 2016). Besides complex and expensive chromatography and protein phosphatase inhibition assays (Catanante et al., 2015), the electrochemical immunosensors have emerged as viable options due to their high sensitivity, simplicity, low cost, and easy miniaturization (Zhang et al., 2010b). Carbon nanomaterials have also been integrated in FET designebased electrochemical immunosensors for real-time identification of pathogens (Yamada et al., 2016). Thiha et al. (2018) developed a lab-on-chip device for labelfree chemiresistive biosensing of Salmonella typhimurium using carbon nanowires functionalized with aptamers. The device offered highly sensitive and specific detection of Salmonella, with a

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TABLE 1.2

List of Different Carbon NanomaterialeModified Glassy Carbon ElectrodeeBased Voltammetric Nanosensors of Food Additives and Pesticides. Food Samples Analyzed

Target Analytes

Linear Detection Range

Limit of Detection

References

(A) NANOSENSORS FOR FOOD ADDITIVES Pt/CNT nanocomposites with 1-methyl-3-butylimidazolium bromide as binder

Chilli sauce, chilli powder, tomato sauce, strawberry sauce

Sudan I

0.008e600 mM

0.003 mM

Elyasi et al. (2013)

Nanocomposite comprising hydrophobic ionic liquid ([P6,6,6,14][NTf2]), MWCNTs, and cationic gemini surfactants

Chilli powder, ketchup sample

Sudan I

0.05e2 mM

0.03 mM

Mo et al. (2010)

MWCNTs-ionic liquids gel

Soft drink samples

Sudan Sudan Sudan Sudan

0.005e15 ppm 0.005e20 ppm 0.05e20 ppm 0.10e25 ppm

0.001 ppm 0.001 ppm 0.005 ppm 0.025 ppm

Chailapakul et al. (2008)

Immobilized peroxidase enzymes (Inga edulis Mart.) in carbon paste containing MWCNTs and mineral oil, and Nafion

Commercial salad dressing samples

tertButylhydroquinone

1.65e9.82 mg L1

0.41 mg L1

de Oliveira et al. (2014)

Gold nanoparticleemodified carbon paste

Commercially available soft drinks

Sunset Yellow Tartazine

1.0  107 to 2.0  106 M 5.0  108 to 1.6  106 M

3.0  108 M 2.0  109 M

Ghoreishi et al. (2012)

MWCNTs

Commercially available soft drinks

Ponceau 4R Allura Red

25 mg L1 to 1.5 mg L1 50 mg L1 to 0.6 mg L1

15 mg L1 25 mg L1

Zhang et al. (2010a)

Boron-doped diamond

Commercial food products

Butylated hydroxyanisole and butylated hydroxytoluene

0.60e10 mM for both

0.14 and 0.25 mM

Medeiros et al. (2010)

I II III IV

Advances in Nanosensors for Biological and Environmental Analysis

Details of Modification of Electrode by Carbon Nanomaterials

(B) NANOSENSORS FOR PESTICIDES Wastewater samples

Atrazine

1.0  1012 M to 1.0  1010 M

1.5  1013 M

Yola and Atar (2017)

MWCNT-functionalized polyamide 6/poly(allylamine hydrochloride)

Standard solution

Dopamine

1e70 mM

0.15 mM

Mercante et al. (2015)

Butyrylcholinesteraseimmobilized carbon black nanoparticles

Wastewater samples

Paraoxon

Up to 30 mg L1

5 mg L1

Arduini et al. (2015)

AChE-immobilized reduced graphene oxide-Au nanoparticles-b-cyclodextrin and Prussian blue-chitosan nanocomposite

Standard solution

Malathion Carbaryl

7.98 to 2.0  103 pg mL1 4.3 to 1.0  103 pg mL1

4.14 pg mL1 1.15 pg mL1

Zhao et al. (2015)

AChE controlled fluorescence carbon dots

Standard solution

Paraoxon

0e0.5 mg mL1

0.4 ng mL1

Li et al. (2018a)

Ag nanoparticleemodified oxidized MWCNTs

Lake water and fruit samples

Dimethoate

0.01e0.35 mg mL1

0.003 mg mL1

Hsu et al. (2017)

Screen-printed carbon electrode modified with graphene oxide and Au nanoparticles

Real cucumber and rice samples

Carbofuran

1e250 mM

0.22 mM

Jirasirichote et al. (2017)

Praseodymium molybdatee decorated reduced graphene oxide

Water and vegetable/ fruit samples

Methyl parathion

0.002e1.55 mM and 1.55e114 mM

1.8 nM

Karthik et al. (2018)

AChE, acetylcholinesterase; CNT, carbon nanotube; MWCNTs, multiwalled CNTs.

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development

Molecular imprinting polymer and platinum nanoparticles/ carbon nitrite nanotubee based nanocomposite

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Advances in Nanosensors for Biological and Environmental Analysis

FIG. 1.6 Schematic fabrication of a carbon nanotube (CNT)-based biosensor for the detection of pathogenic bacteria: (1) formation of a cysteine self-assembled monolayer over bare gold surface, (2) activation of electrode surface for coupling of CNTs, (3) binding of antimicrobial peptide clavanin A (ClavA) on CNT surface, and (4) interaction of electrode surface with analyte bacteria. (Adapted from Andrade, C.A., Nascimento, J.M., Oliveira, I.S., de Oliveira, C.V., de Melo, C.P., Franco, O.L., Oliveira, M.D., 2015. Colloids and Surface B: Biointerfaces 135, 833-839. Reprinted with permission from Elsevier.)

FIG. 1.7 Fabrication of a microfluidic chip, with the application of graphene oxide (GO) nanosheetewrapped multiwalled carbon nanotubes (MWCNTs). This chip was used for the detection of Salmonella typhimurium bacterial cells. EDC-NHS, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxysuccinimide; StAb, Salmonella typhimurium antibody. (Adapted from Singh, C., Ali, M.A., Reddy, V., Singh, D., Kim, C.G., Sumana, G., Malhotra, B.D., 2018. Sensors and Actuators B: Chemical. 255, 2495e2503. Reprinted with permission from Elsevier.)

detection limit of 10 CFU mL1 with reduced sample volume requirement (5 mL). Singh et al. (2018) reported a novel microfluidic chip developed on a graphene oxide wrapped carboxyl MWCNT platform for the detection of S. typhimurium, with a detection limit of 0.376 CFU mL1 (Fig. 1.7). This biosensor offered negligible interference even in the copresence of E. coli O157: H7. Such microfluidic chipebased biosensing platforms offer important feature in terms of sample volume miniaturization, reduced processing

time, and reduced use of expensive chemicals. These microfluidic immunosensors can also be applied for the detection or quantification of other pathogens by immobilizing the electrode surface with suitable bioreceptors. Future research efforts are needed to further elaborate intricate sensor designs and fabrication processes of carbon nanomaterialebased FET devices and related biosensors. Table 1.3 lists some important examples of carbon nanomaterialebased biosensors for pathogens or viruses.

TABLE 1.3

List of Different Carbon NanomaterialeBased Bionanosensors for Detection of Bacterial Pathogens or Viruses. Details of Modification of Electrode by Carbon Nanomaterials

Bacterial Pathogens or Viruses

Type of Biosensor Signal

Bioreceptor Used

Linear Range

Limit of Detection

References

Vibrio parahaemolyticus and Salmonella typhimurium

Fluorescence

DNA sequence

50e106 CFU mL1

25 CFU mL1 and 35 CFU mL1

Duan et al. (2015)

SWCNTs

Staphylococcus aureus

Electrochemical

Antibody

d

13 CFU mL1

Bhardwaj et al. (2017)

Gold tungsten wires coated with PEI and SWCNTs

S. aureus and Escherichia coli K-12

Electrochemical immunesensors in FET design

Streptavidin and bio-tinylated antibodies

102e105 CFU mL1

102 CFU mL1

Yamada et al. (2016)

Amine-functionalized magnetic iron oxide nanoparticles decorated with carbon dots

S. aureus and E. coli

Fluorescence

d

d

3  102 and 3.5  102 CFU mL1

Bhaisare et al. (2016)

Polypyrrole/Au nanoparticles/ MWCNTs/chitosan nanocomposite

E. coli O157:H7

Electrochemical

Antibody

3  101 to 3  107 CFU mL1

30 CFU mL1

Güner et al. (2017)

CNTs

Klebsiella pneumoniae, Enterococcus faecalis, E. coli, and Bacillus subtilis

Electrochemical

Antimicrobial peptide clavanin A (ClavA)

102e106 CFU mL1

102 CFU mL1

Andrade et al. (2015)

Carbon nanowires

S. typhimurium

Chemiresistive

Salmonella-specific aptamer probes

10 CFU mL1

d

Thiha et al. (2018)

Graphene-wrapped copper(II)-assisted cysteine hierarchical structure

E. coli O157:H7

Electrochemical

Monoclonal antibodies

10e108 CFU mL1

3.8 CFU mL1

Pandey et al. (2017)

Continued

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Quantum dots (greenand red-emitting)amorphous carbon nanoparticles

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development

(A) BACTERIAL PATHOGENS

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TABLE 1.3

List of Different Carbon NanomaterialeBased Bionanosensors for Detection of Bacterial Pathogens or Viruses.dcont'd Bacterial Pathogens or Viruses

Type of Biosensor Signal

Bioreceptor Used

Linear Range

S. aureus

Fluorescence

S. aureus antibody

1  102 to 1  104 CFU mL1

30 CFU mL1

Yang et al. (2018b)

Graphene oxide

HIV

Electrochemical

38-Base synthetic sequence (ssDNA)

1.0  1012 to 1.0  106 M

1.1  1013 M

Hu et al. (2012)

Graphene quantum dots

HBV

Electrochemical

Probe DNA

10 e500 nM

1 nM

Xiang et al. (2018)

MWCNTs/polypyrrole nanowires/gold nanoparticles

AIV

Electrochemical

DNA aptamer

5.0  1012 M to 1.0  109 M

4.3  1013 M

Liu et al. (2011b)

Graphene oxide

DNA (H1V1) and protein (thrombin)

Fluorescence

ss DNA

0.1 pM to 10 nM

0.1 pM

Bi et al. (2012)

MWCNTs

Influenza virus (type A)

Electrochemical

DNA sequence

d

0.5 nM

Tam et al. (2009)

Fullerenefunctionalized polyaniline-doped tufted CNTs

MTB

Electrochemical

DNA sequence

1015 M to 109 M

3.3  1016 M

Chen et al. (2018)

Porous reduced graphene oxide/ molybdenum disulfide

HPV

Electrochemical

RNA (Sc5-c3) Aptamers

0.2e2 ng mL1

0.1 ng mL1

Chekin et al. (2018)

Carbon dote encapsulated organosilica nanocapsules

Limit of Detection

References

(B) VIRUSES

AIV, avian influenza virus, CNTs, carbon nanotubes; FET, field-effect transistor; HBV, hepatitis B virus; HIV, human immunodeficiency virus; HPV, human papilloma virus; MTB, Mycobacterium tuberculosis; MWCNTs, multiwalled CNTs; PEI, polyethylenimine; ssDNA, single-stranded DNA; SWCNTs, singe-walled CNTs.

Advances in Nanosensors for Biological and Environmental Analysis

Details of Modification of Electrode by Carbon Nanomaterials

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development

17

TABLE 1.4

Carbon NanomaterialeBased Important Gas Sensors. Electrode Material

Gas Molecules Detected

Detection Limit/ Sensitivity

CNT-TFR

NO2

125 ppt

Kumar et al. (2017b)

CNT-mR

NO2

165 ppt

Kumar et al. (2017b)

Wood-based activated carbon

NH3

100e500 ppm

Travlou et al. (2015)

3D wool-ball-like ZnO/ MWCNTs

SO2

70 ppm

Septiani et al. (2018)

Platinum-decorated MWCNTs

C7H8

1 ppm

Kwon et al. (2016)

Polyaniline-functionalized MWCNTs

NH3

2e10 ppm

Abdulla et al. (2015)

Metal oxideedecorated graphene

Formaldehyde and NH3

5 ppm

Zhang et al. (2017)

Reduced graphene oxidee decorated yarn

NO2

0.25 ppm

Yun et al. (2015)

Carbon adhesive tape

NO2 and N2

w5 ppm

Lee et al. (2018)

References

CNT-mR, SWCNT aligned network; CNT-TFR, SWCNT random network; MWCNTs, multiwalled carbon nanotubes; SWCNT, single-walled carbon nanotube.

Detection of Gas Molecules The presence of hazardous gases in our surroundings can have serious or deadly effects on human health and vegetation. Various types of toxic gases in varying amounts/concentrations are generated from natural or artificial activities such as burning of fossil fuels, automobile exhausts, cleaning agents (Wang et al., 2018; Mirzaei et al., 2016). In comparison to traditional analytical methods of gas sensing (such as gas chromatography), the electric and electrochemical transduction offer several benefits in terms of minimal power consumption, high sensitivity, and possibility of miniaturization. The electrochemical gas sensors offer high sensitivity, especially in highly humid environments. Over the past decade, several nanomaterials have been reported in electrochemical gas sensors to detect gas molecules, e.g., carbon nanomaterials, polymers, and metallic nanoparticles (Goldoni et al., 2018). Among these materials, carbon nanomaterials have a huge potential due to their superior electric properties

(Table 1.4). The mechanism of gas detection is controlled by change in electric conductivity of the electrode surface through charge transfer during gas interaction. Kumar et al. (2017b) reported the fabrication of SWCNT-based gas sensors by either SWCNT random network (CNT-TFR) or SWCNT aligned network (CNT-mR). The NO2 sensing response of CNT-mR was higher than that of CNT-TFR due to the nature of the surface network, mainly contributing in adsorption capacity of the sensor. Beyond outdoor gas pollution, the indoor air pollutants (e.g., formaldehyde and ammonia) are also very serious pollutants that are released from decorative and building materials. Zhang et al. (2017) fabricated a metal oxideedecorated graphene oxide sensor array, provided with back propagation neural network, for sensing indoor air pollutants. The use of graphene can overcome the limitation of existing electrochemical sensors that usually operate at high temperature. The novel physical and mechanical properties and

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Advances in Nanosensors for Biological and Environmental Analysis

unprecedented structure of graphene make it a very promising electrode material for potential applications in gas sensing. Furthermore, neural networks can be integrated with graphene sensors in order to enable the detection of a target gas from a mixture of several gases. A sensor proposed by Zhang et al. (2017) offered detection of toxic gaseous mixture in a concentration range of 5e500 ppm within a small period of 200 s. This type of sensor is quite useful for real-time monitoring of hazardous gases. FET-based gas sensors using CNTs have been reported due to their excellent sensitivity in comparison to other existing devices. For instance, Nguyet et al. (2017) designed an n-p-n heterojunction of CNTs and SnO2 nanowires for the detection of NO2 gas. The sensor was able to detect the concentration of NO2 gas down to 20 ppb. Nonetheless, proper understanding of the sensing mechanism of FET devices still demands further investigation (Dube et al., 2015). New trends in gas sensors are beginning to emerge through the development of CNT sensor arrays. Lee et al. (2018) have fabricated a carbon adhesive tape (CAT) to detect NO2 gas molecules (Fig. 1.8). The CAT offered a disposable, rapid (detection time of <3 min), and robust NO2 gasesensing

platform with a high sensitivity of w5 ppm. Many examples have been cited in the literature wherein carbon-based nanocomposites have been documented to allow the development of highly sensitive gas sensors for H2, NO2, CO, etc. A summary of carbon nanomaterialebased different gas sensors is provided in Table 1.4.

Detection of Organic Molecules The sensing of toxic organic molecules (such as pharmaceutical and biological compounds, explosives, toxins or antibiotics, and personal care products) has significant importance from the point of view of environmental monitoring. The detection of biological agents has become a critical part of modern life. The unique properties of carbon nanomaterials have been exploited for developing nanosensors for specific and sensitive quantitative analysis of organic molecules. Endocrine-disrupting chemicals are the organic molecules that mimic the natural hormones of the endocrine system and can adversely affect human health, such as skin sensitization, obesity, reproductive failure, diabetes, immune system failure. These chemicals can lead to the disruption of cell function even at low doses (in nanomolar

FIG. 1.8 (A) Schematic layout for the fabrication of a bare carbon adhesive tape (CAT) chip and analysis of its electric conductivity through a current analyzer. (B) Application of CAT chips for the detection of NO2 and N2 through their controlled exposure. (Adapted from Lee, S.W., Lee, W., Lee, D., Choi, Y., Kim, W., Park, J., Lee, J.H., Lee, G., Yoon, D.S., 2018. Sensors and Actuators B: Chemical 266, 485e492. Reprinted with permission from Elsevier.)

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development level) (Annamalai and Namasivayam, 2015; Braun et al., 2014). Therefore biosensors should be efficient enough to accurately determine even trace levels of these chemicals/toxins. Yan et al. (2018) reported a self-powered sensor for specific detection of bisphenol A (BPA) using molecular imprinted polymer-modified graphitic carbon nitride photoanode. This photofuel cell configuration offered electrocatalytic sensing of BPA, with accessible range from 5 to 200 mM and with a detection limit of 1.3 mM. Jiang et al. (2013) reported a DNA-functionalized SWCNT/Nafion composite for the detection of BPA, with a detection limit of 5 nM. The sensor offered high selectivity without any fouling and/or activity loss in the presence of other interferences such as acetate, chlorides, metal ions, phosphate, and phenolic compounds. Nitroaromatic and nitramine-type compounds are released into the environment mainly from dye manufacturing, pesticides, plasticizers, and military activities. These hazardous chemicals contaminate soil and water with longer persistence. A novel biosensor based on reduced graphene oxide/CNT nanocomposite has been reported for rapid and highly sensitive sensing of 2,4,6-trinitrotoluene (TNT) (Castro et al., 2018). Briefly, boron-doped diamond electrode

19

was modified with a mixture of MWCNT/reduced graphene oxide. The synergistic effect between MWCNTs and reduced graphene oxide offered detection of TNT concentrations within 0.5e1100 mM with a detection limit of 0.019 mM. Pan et al. (2016) explored the active sites of carbon nanomaterials for highly selective and/or anti-interference detection of nitroaromatic compounds, such as nitrobenzene, dinitrobenzene, and trinitrobenzene, with a low detection limit of 0.88e1.8 mg L1. Likewise, carbon nanodots have been proposed for the detection of different nitroaromatic compounds as illustrated in Fig. 1.9 (Ren et al., 2018). Beyond industrial pollutants, water contamination due to antibiotics (tetracycline, nitrofurans, etc.) is one of the major concerns. This type of water pollution is caused by household wastewater and commercial livestock farming. In particular, nitrofuran drugs are commonly used in the treatment of urinary tract diseases of humans and animals. However, several reports are available on mutagenic, toxic, and carcinogenic effects of these drugs and their metabolites. Based on useful properties of CNTs in terms of good chemical stability, high surface area, and electric conductivity, Chiu et al. (2018) developed a screen-printed carbon electrode sensor after modifying it with a

FIG. 1.9 Selectivity of carbon nanodots in sensing 2,4,6-trinitrophenol (TNP); nitrobenzene (NB);

2,4,6-trinitrotoluene (TNT); 3-nitrophenol (3-NP); toluene; 3-nitrotoluene (3-NT); 2,4-dinitrotoluene (DNT); 2-nitrophenol (2-NP); and 4-nitrophenol (4-NP). (A) Ultravioletevisible absorption spectra of carbon nanodots dispersed in analytes containing ethanol-water solution, (B) relative fluorescence emission intensity of carbon nanodots when tested for different nitroaromatics, and (C) fluorescence spectra of the probe during the selective analysis of TNP. (Adapted from Ren, G., Yu, L., Zhu, B., Tang, M., Chai, F., Wang, C., Su, Z., 2018. RSC Advances. 8, 16095e16102. Reprinted with permission from RSC.)

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nanocomposite of MWCNTs with conducting poly(melamine). The sensing electrode offered excellent electrochemical detection of nitrofurans in lake water and milk samples. Zhou et al. (2012) reported an aptamer-MWCNT-modified glassy carbon paste electrode for detecting tetracycline. The carboxyl groupemodified MWCNTs were incubated with amine-modified antitetracycline aptamer (76-base sequence). The sensor showed good sensitivity and selectivity for tetracycline, with a detection limit of 5 nM upon testing spiked milk samples. An electrochemical aptasensor

based on the nanocomposite of mesoporous carbon-gold nanoparticles and CNFs offered an ultrasensitive detection of kanamycin and streptomycin, with detection limits of 87.3 and 45.0 pM, respectively (Li et al., 2018b). Besides the good conductivity of CNFs, the mesoporous carbongold nanoparticles helped in improving the efficiency of electron transfer because of their mesoporous structure as well as excellent electron transfer kinetics. Some literature on the sensing of toxic organic molecules using carbonaceous nanomaterials is summarized in Table 1.5.

TABLE 1.5

Summary of Some Recent Carbon NanomaterialeBased Electrochemical Nanosensors for Small Organic Molecules. Details of Electrode Fabrication

Analyte

Linear Range

Limit of Detection

References

(A) ENDOCRINE-DISRUPTING CHEMICALS Molecular imprinted polymer-modified graphitic carbon nitride

Bisphenol A

5e200 mM

1.3 mM

Yan et al. (2018)

Magnetic molecularly imprinted polymermodified Au nanoparticles/carbon black nanoparticles

Bisphenol A

0.07e10 mM

8.8 nM

Messaoud et al. (2018)

Fe3O4/MWCNT composite

Parabens (butyl, ethyl, isopropyl, isobutyl, methyl, pentyl, phenyl, propyl, and benzylparaben)

0.5e150 ng mL1

Between 0.03 and 2.0 ng mL1

Pastor-Belda et al. (2018)

Silver nanoparticles/ MWCNTs

Hydroquinone Catechol Bisphenol A Phenol

2.5e260 mM 20e260 mM 5.0e152 mM 2.4e152 mM

0.16 mM 0.2 mM 2.4 mM 3.0 mM

Goulart et al. (2018)

(B) NITROAROMATIC COMPOUNDS MWCNT/reduced graphene oxide

2,4,6Trinitrotoluene

0.5e1100 mM

0.019 mM

Castro et al. (2018)

Hydroxyl-rich carbon submicrospheres

Nitrobenzene Dinitrobenzene Trinitrobenzene

0.2e12.3 mg L1 0.01e16.8 mg L1 0.2e1.0 mg L1

1.3 mg L1 0.88 mg L1 1.8 mg L1

Pan et al. (2016) (continued)

CHAPTER 1 Carbon-Based Nanomaterials for Nanosensor Development

21

TABLE 1.5

Summary of Some Recent Carbon NanomaterialeBased Electrochemical Nanosensors for Small Organic Molecules.dcont'd Details of Electrode Fabrication

Analyte

Linear Range

Limit of Detection

References

Nitrogen- and sulfurco-doped graphene nanoribbons

2,4,6Trinitrotoluene

0.0008e5.1 ppm

0.1 ppb

Zhang et al. (2018)

Carbon nanodots

2,4,6-Trinitrophenol

d

0.127 mM

Ren et al. (2018)

CNFs/mesoporous carbon-gold nanoparticles

Kanamycin and streptomycin

0.1e1000 nM

87.3 and 45.0 pM

Li et al. (2018b)

MWCNTs and conducting poly(melamine) nanocomposite

Nitrofurantoin Nitrofurazone Furaltadone Furazolidone

0.05e2.0 mM 0.05e5.0 mM 0.05e2.0 mM 0.05e2.0 mM

0.012 mM 0.014 mM 0.007 mM 0.006 mM

Chiu et al. (2018)

Aptamer-MWCNTs

Tetracycline

10 nM to 100 mM

5 nM

Zhou et al. (2012)

Fluorescent carbon dots

Oxytetracycline

d

0.06 mM

Qiao et al. (2018)

(C) ANTIBIOTICS

CNFs, carbon nanofibers; MWCNTs, multiwalled carbon nanotubes.

CONCLUSIONS AND FUTURE PERSPECTIVES This chapter has discussed the role of diverse nanosensitive platforms based on carbon nanomaterials for environmental analyses and food safety applications. Carbon nanomaterials offer several interesting properties important for sensing different pollutants such as heavy metal ions, food additives, pesticides, biological pathogens and viruses, toxic gaseous molecules, and small organic molecules. Graphene and CNTs offer highly selective and sensitive detection of numerous environmental analytes without any strict requirement of labeling or amplification steps. Beyond excellent electric properties of carbon nanomaterials, there are several other parameters that make them ideally suitable for rapid, multianalyte, and field-deployable environmental monitoring, e.g., low cost manufacturing, less power consumption, compact size, and robustness. The miniaturization of sensing platforms can offer

several benefits in terms of reduction of sample volume and bioreceptor as well as highthroughput analysis with enhanced sensitivity. In this context, latest research trends can be observed in the development of lab-on-a-chip technology that offers accurate and compact sensing in point-of-care assessment. However, there are several factors that can limit the performance of carbon nanomaterials for analyte detection, such as (1) selecting CNTs of the right nature (either metallic or semiconducting), diameter, and length; (2) optimizing graphene-based sensors, as the sensitivity of graphene depends on the number of layers, edge structure, impurities, etc.; and (3) controlling the level of agglomeration during device development. With the ever-happening advancement in materials technology, it has now become possible to fabricate biosensors that can offer consistent as well as reproducible sensing performances.

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ACKNOWLEDGMENTS Monika Nehra thanks the University Grant Commission, India for providing financial assistance in the form of JRF (award No. 3608 dated February 29, 2016). Sandeep Kumar thanks the Department of Science and Technology (Government of India), University of Nebraska (Lincoln), Daugherty Water for Food Institute (DWFI), and Indo-US Science and Technology Forum (IUSSTF) for financial support through Water Advanced Research and Innovation (WARI) research grant vide letter No. IUSSTF/WARI/2018/F-029-2018 dated January 03, 2018, along with DST-PURSE sanctioned to Guru Jambheshwar University of Science and Technology (GJUS&T), Hisar under PURSE program No. SR/PURSE Phase 2/40(G).

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