Development of polyindole/tungsten carbide nanocomposite-modified electrodes for electrochemical quantification of chlorpyrifos
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The present investigation deals with the development of a novel polymer nanocomposite (PNCs) electrodes for simple, selective and sensitive detection of chlorpyrifos (CHL). PNCs were developed using surfactant facilitated polymerization of indole using different concentrations (wt%) of WC ranging 5–30. Formation of PNCs was ascertained through diversified analytical methods. Electrodes were derived from PNCs over stainless steel substrate for electrochemical quantification of CHL. With concentration of WC, the DC conductivity (10−2 × S/cm) of electrodes was increased ranging 3.54–0.75 at 313 K. Electrochemical impedance spectroscopy reveals well stability of electrodes in phosphate buffer (PBS, 0.1 M) at pH 7.4. The performance of electrodes towards detection and quantification of CHL was investigated through square wave voltammetry. Study reveals that detection and quantification of CHL were dependent on concentration of WC in nanocomposites. Square wave voltammetry reveals that the electrode derived from PNCs with 5 wt% of WC has rendered highest limits of detection and quantification of CHL (10−8 mol/L) up to 5.94 and 18. This work describes a viable method of preparation of synergistic blend of WC in PIN matrix having high electrical conductivity, rapid electron shift, huge surface area and enhanced stability for fast and précised electrochemical detection of CHL.
KeywordsNanocomposite Chlorpyrifos Electrochemical sensing Cyclic voltammetry Square wave voltammetry Quantification
Organophosphates (OPs) are the esters, amide and thiol derivatives of phosphorous-based acid [1, 2, 3]. Low water solubility and high absorption coefficient impart long residual effect of OPs in soil. This allows the entry of OPs into food chain causing neurotoxicity to animals due to irreversible inhibition of acetyl cholinesterase (AChE) [4, 5, 6]. For such reasons, development of novel methods of detection of OPs has been the subject of investigation over decades. In this context, various chromatographic, mass spectrometric, electrophoretic, [7, 8, 9, 10] and electrochemical [11, 12, 13, 14] methods were developed for detection of OPs.
Chlorpyrifos (CHL, o,o-diethyl-o-(3,5,6-trichloro-2-pyridinyl)phosphorothioate) belongs to the family of OPs, used for crop protection as insecticide and nematicide. Realizing health hazards imposed over ecosystem, there has been growing concern on advancement of selective, precise, rapid and reliable approach for CHL detection. In this context, the quantification of CHL through chromatographic [15, 16] and electrochemical [17, 18] methods has been well established. Among such methods, based on chromatography involves expensive instrumentation, multiple steps of preparation, immobilization and regeneration of samples, large consumption of chemicals, time along with low sensitivity of detection [19, 20]. However, electrochemical methods, specially based on square wave voltammetry (SWV), have received immense acceptance because of reasonable simplicity, high sensitivity and potential towards selective quantification of detection of CHL down to ng level [21, 22, 23]. SWV has also been used for detection of a wide range of OPs over nanocomposite-modified GCE. Nanocomposites employed for electrochemical detection of OPs were parathion [24, 25, 26, 27, 28], malathion [29, 30] and paraoxon [31, 32]. The nanocomposites employed for modification of GCE for OPs detection were zeolite , ZrO2 , Au/Graphene [26, 27], ZrO2 , SWNT/GO , MWCNT , Au/Pt  and ZrO2/MWCNT . The nanomaterials used for detection of CHL were graphene , MWCNT [33, 34, 35], with nano-TiO2 , carbon nitride , ferrocene , CuO . Conducting polymers have been used as such or in the form of their nanocomposites for detection of CHL through SWV [24, 30]. Literature revealed that a wide range of nano-composites has been employed for the detection of various OPs [24, 25, 26, 27, 28, 29, 30, 31, 32], including CHL [33, 34, 35, 36, 37, 38, 39]. To the best of our knowledge, no records are available on electrochemical detection of CHL over PNCs derived through immobilization of WC into PIN matrix.
Recently, conducting polymer-based nanostructures containing carbonaceous and inorganic nanomaterials have been used in electrochemical studies for various applications [40, 41, 42, 43, 44]. Amongst the family of conducting polymers, polyindole (PIN) has an edge over other, due to its sustained polymerization, high electrical conductivity, low manufacturing cost and less toxicity [45, 46, 47, 48, 49]. Sensing behavior of PIN is modified through doping transition metal-based dopants that chanalize the electron transfer mechanism through polaron formation . In this context, common dopants employed for PIN are gold , oxides of zinc and nickel , tin , iron , vanadium  and copper . Nanocomposite of titanium carbide and poly(3,4-ethylenedioxythiophene) were prepared as an alternative electrocatalyst for dye-sensitized solar cell applications [57, 58, 59, 60]. The present work proposed a novel and economical sensor for the trace level electrochemical detection of CHL, by utilizing WC-doped PIN nanocomposite.
Materials and methods
CHL with purity (≥ 99.9%), chlorosulfonic acid (> 99%), indole (> 99%) and cetyltrimethylammonium bromide (CTAB) (> 99%) were purchased from Sigma-Aldrich. Rest of the chemicals and solvents (purity > 98%) were indigenously procured and used without further purification. Phosphate buffer (pH 7.4, 0.1 M) and stock solution of CHL (1.0 × 10−4 M) were prepared through traditional methods. In the present results, bare electrode, 5 wt% and 30 wt% PNCs-coated electrode are represented by [I], [II] and [III], respectively.
Preparation of nanocomposites
PIN along with various wt% fractions of WC ranging 5–30 [I–III] was synthesized by cationic surfactant method placed in two-necked glass reaction vessel implemented with mechanical stirrer and dropping funnel. To this, CTAB (2.7 × 10−3 mol) was added and the content was stirred @500 rpm over 6 h. To initiate the polymerization process, a solution of freshly prepared FeCl3 (3.5 M) was added to content @1 mL/min keeping stirring to be continued over 24 h. A dark brown precipitate was produced, that was subsequently filtered and successively washed with deionized water till the filtrate became free from chloride ions. Isolated PNCs was left for 6 h at room temperature and then dried at 40 °C at 400 mmHg for additional 8 h. PIN was also prepared under similar reaction conditions in the absence of WC [61, 62].
Preparation of electrodes
SEM images were recorded on JEOL, JSM 6610 LV at 0.2 KX (7 µm) and 15 kV. For this purpose, the electrodes were prepared via mentioned procedure. The SEM images were scanned under identical conditions for comparable results. The conductivity data were recorded over Keithley four-point probe conductivity nanovoltmeter with current (6221 A) and voltage source (2182 V) in the range of 313–373 K.
FT-IR spectra were recorded on Thermo Nicolet ranging 4000–500 cm−1 in KBr. XRD spectra were recorded over Rigaku-Geigerflex, X-Ray diffractometer using Cu-Kα radiation (λ = 0.154 nm) with 2θ ranging 10°–90° at 30 kV and 15 mA. Simultaneous TG–DTA–DTG was conducted over EXSTAR TG/DTA 6300 at sample weight (mg) ranging 10.50–10.55 at 10 °C/min in air.
The electrochemical studies of prepared electrodes were performed in PBS (0.1 M) over IVIUM Potentiostat–Galvanostat using a triple-electrode cell assembly. WE were fabricated through depositing PNCs over SS plates. Pt foil (1 cm2) and Ag/AgCl were used as auxiliary and reference electrodes. All peak currents (µA) and peak potentials (V) were expressed in due units. Calibration curves were obtained from SWV by plotting maximum peak current and respective increasing concentration of CHL.
Limit of detection (LOD) and limit of quantification (LOQ) were calculated from calibration curve using formula: LOQ = 10 s/m and LOD = 3.3 s/m, where s is intercept and m is slope of the calibration curve. Stability of electrodes was investigated through electrochemical impedance spectra (EIS) and circuit simulation was conducted using Randles diagrams.
Results and discussion
PIN shows characteristic wave numbers (cm−1) corresponding to vN–H (3138.00), vC–H (2925.39), ν δO–H (1617.78) vC–C (1454.64) and δAr–H (745.48). The wave numbers at 2925.39 and 2852.80 attribute to interaction of CTAB with PIN. The wave number at 1110.96, 1334.07 and 1568.39 cm−1 correspond to vC–N, vC=N and δ N–H deformation .
WC has shown by the low-frequency fingerprint region at 665.82 cm−1 .
Surface morphology of electrodes
Morphology of fabricated electrodes along with quantitative elemental composition was analyzed through SEM–EDX study. To compare the morphology, all electrodes were imaged under identical conditions at 1 KX, 10 μM and camera width of 10 ± 1 nm. EDX spectrum shows the presence of W and high C content in the EM as well as quantity of other elements. EDX represents qualitative detection of elements present in EM. To simulate the emission of X-rays, high-energy beam of charged particles was focused on to the EM. The difference between energies of higher and lower energy shell is released in the form of X-rays which is measured by spectrometer.
PIN was decomposed with TG onset at 337 °C leaving 79.4% Wr. Decomposition of PIN was progressed at the rate of 197.6 × 10−3 mg/°C at 559 °C with DTA signal (0.65 mV) at 543 °C. Decomposition of PIN was concluded at 573 °C leaving char residue of 1.90 wt%. DTA reveals fusion of PIN with ∆Hf of − 10.6 × 103 mJ/mg (Fig. 4b). [III] shows single-step decomposition with TG onset at 328 °C leaving 85% Wr. The collective weight loss of 15.0% wt indicates that due to filling of WC, the thermal stability of PIN was compromised. Decomposition of [III] was progressed at the rate of 0.858 mg/°C at 519 °C with DTA signal (0.61 mV) at 520 °C. TG endset of [III] was appeared at 538 °C leaving 36.2% char residue. DTA reveals fusion of [III] with ∆Hf of − 7.44 × 103 mJ/mg (Fig. 4c). Thermal data reveal that due to addition of WC, the thermal stability of [III] was compromised.
EC behavior of modified electrode
CV is the most popular continuous wave technique employed to investigate the redox behavior and electron transfer kinetics of molecules over electrochemically active surface. CV presents the set of anodic (Epa) and cathodic peak (Epc) potentials along with respective anodic (ipa) and cathodic (ipc) peak currents. Potential applied across WE moves back and forth past the formal potential. This leads to current flow across the electrode that renders the redox behavior of analyte [72, 73].
Effect of scan rate on CV
Square wave voltammetry
The proposed sensor demonstrates acceptable quantification of CHL with significantly low LOD values. The calibration plots for quantification of CHL at [I], [II] and [III] was obtained by studying the effect of increase in CHL concentration on peak current. The LOD obtained for [I], [II] and [III] are 4.8 × 10−8 mol L−1, 5.94 × 10−8 mol L−1 and 4.49 × 10−8 mol L−1. LOQ for [I], [II] and [III] are 14.5 × 10−8 mol L−1, 18 × 10−8 mol L−1 and 13.6 × 10−8 mol L−1 , respectively. The correlations between the concentration and peak current were in linear relation with correlation coefficient (r) for [I], [II] and [III] was 0.979, 0.982, 0.971, respectively, indicating good correlation.
Electrochemical impedance spectroscopy
A series of electrochemical polymer nanocomposite (PNC)-based electrode was developed by an easy and effective chemical oxidative polymerization method using various concentrations of WC ranging 0–30 wt%. Electrodes from PNCs were developed over SS plates and used for electrochemical quantification of chlorpyrifos (CHL) in phosphate buffer (PBS, 0.1 M) at 7.4. Electroanalytical methods based on square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) reveal immense feasibility of electrodes towards quantification of CHL with stability in PBS. The electrical and electrochemical behavior of electrodes was found synergistic with concentration of WC in PIN. DC conductivity of electrodes was found in increasing order with concentration of WC. Electrodes with 5 wt% of WC have shown enhanced redox behavior of CHL with limits of detection and quantification (10−8 mol L−1) up to 5.94 and 18. Study reveals that incorporation of WC in PIN provides a novel nanohybrid electrode coating material for efficient detection of CHL.
Financial support by the Ministry of Defence No. ERIP/ER/0703649/M/01 is hereby acknowledged.
Compliance with ethical standards
Conflict of interest
No potential conflict of interest was reported by the author.
- 6.Berijani, S., Assadi, Y., Anbia, M., Hosseini, M. R. M., Aghaee, E.: Dispersive liquid–liquid microextraction combined with gas chromatography-flame photometric detection: very simple, rapid and sensitive method for the determination of organophosphorus pesticides in water. J. Chrom. A. 1123(1), 1–9 (2006)PubMedCrossRefGoogle Scholar
- 7.Saunders, M., Magnanti, B.L., Carreira, S.C., Yang, A., Alamo-Hernández, U., Riojas-Rodriguez, H., Bartonova, A.: Chlorpyrifos and neurodevelopmental effects: a literature review and expert elicitation on research and policy. Environ. Health. 11(1), S5 (2012)PubMedPubMedCentralCrossRefGoogle Scholar
- 8.Guardino, X., Obiols, J., Rosell, M.G., Farran, A., Serra, C.: Determination of chlorpyrifos in air, leaves and soil from a greenhouse by gas-chromatography with nitrogen–phosphorus detection, high-performance liquid chromatography and capillary electrophoresis. J. Chrom. A 823(1–2), 91–96 (1998)CrossRefGoogle Scholar
- 15.Ramasubramanian, T., Paramasivam, M.: Development and validation of a multiresidue method for the simultaneous determination of organophosphorus insecticides and their toxic metabolites in sugarcane juice and refined sugar by gas chromatography with flame photometric detection. J. Sep. Sci. 39(11), 2164–2171 (2016)PubMedCrossRefGoogle Scholar
- 16.Shamili, A., Dadfarnia, S., Shabani, A.M.H., Saeidi, M., Moghadam, M.R.: High performance liquid chromatographic determination of diazinon after its magnetic dispersive solid-phase microextraction using magnetic molecularly imprinted polymer. Food Anal. Method. 9, 2621–2630 (2016)CrossRefGoogle Scholar
- 20.Bebeselea, A., Manea, F., Burtica, G., Nagy, L., Nagy, G.: Electrochemical degradation and determination of 4-nitrophenol using multiple pulsed amperometry at graphite based electrodes. Chem. Bull. Politech. Univ. Timisoara. 53(67), 1–2 (2008)Google Scholar
- 30.Upadhyay, S., Rao, G.R., Sharma, M.K., Bhattacharya, B.K., Rao, V.K., Vijayaraghavan, R.: Immobilization of acetylcholineesterase–choline oxidase on a gold–platinum bimetallic nanoparticles modified glassy carbon electrode for the sensitive detection of organophosphate pesticides, carbamates and nerve agents. Biosens. Bioelectron. 25(4), 832–838 (2009)PubMedCrossRefGoogle Scholar
- 32.Xia, N., Gao, Y.: Carbon nanostructures for development of acetylcholinesterase electrochemical biosensors for determination of pesticides. Int. J. Electrochem. Sci. 10, 713–724 (2015)Google Scholar
- 33.Chen, D., Liu, Z., Fu, J., Guo, Y., Sun, X., Yang, Q., Wang, X.: Electrochemical acetylcholinesterase biosensor based on multi-walled carbon nanotubes/dicyclohexyl phthalate modified screen-printed electrode for detection of chlorpyrifos. J. Electroanal. Chem. 801, 185–191 (2017)CrossRefGoogle Scholar
- 35.Chen, D., Jiao, Y., Jia, H., Guo, Y., Sun, X., Wang, X., Xu, J.: Acetylcholinesterase biosensor for chlorpyrifos detection based on multi-walled carbon nanotubes–SnO2–chitosan nanocomposite modified screen-printed electrode. Int. J. Electrochem. Sci. 10, 10491–10501 (2015)Google Scholar
- 41.Elkodous, M.A., El-Sayyad, G.S., Mohamed, A.E., Pal, K., Asthana, N., de Souza Junior, F.G., El-Batal, A.I: Layer-by-layer preparation and characterization of recyclable nanocomposite (CoxNi1–xFe2O4, X = 0.9/SiO2/TiO2). J. Mater. Sci-Mater El. 30(9), 8312–8328 (2019)Google Scholar
- 44.Pal, K.: Hybrid Nanocomposites: Fundamentals, Synthesis, and Applications”, CRC Press, 2019Google Scholar
- 47.Tebyetekerwa, M., Yang, S., Peng, S., Xu, Z., Shao, W., Pan, D., Zhu, M.: Unveiling polyindole: freestanding As-electrospun polyindole nanofibers and polyindole/carbon nanotubes composites as enhanced electrodes for flexible all-solid-state supercapacitors. Electrochim. Acta 247, 400–409 (2017)CrossRefGoogle Scholar
- 59.El-Nasser, S.A., Kim, S., Yoon, H., Toth, R., Pal, K., Bechelany, M.: Sodium-assisted TiO2 nanotube arrays of novel electrodes for photochemical sensing platform. Org. Electron. 76, 105443–105450 (2020)Google Scholar
- 60.Govindasamy, G., Pal, K., Elkodous, M. A., El-Sayyad, G.S., Gautam, K., Murugasan, P.: Growth dynamics of CBD-assisted CuS nanostructured thin-film: optical, dielectric and novel switchable device applications. J. Mater. Sci-Mater. El. 30(17), 16463–16477 (2019)Google Scholar
- 61.Nihmath, A.M., Ramesan, T.: Effect of hydroxylapatite nanoparticles on structural and electrical properties of ethylene propylene diene monomer rubber. J. Chem. Pharm. Sci. 38–44 (2016)Google Scholar
- 74.Cannon, R.D.: Electron transfer reactions. Butterworth-Heinemann ISBN 0-408-10646-8 (2016)Google Scholar
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