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In this study, electrochemical sensors were developed for the determination of pesticides andrnpharmaceutical drugs based on poly(4-amino-3-hydroxynaphthalene sulfonic acid)rn(poly(AHNSA)), multi-walled carbon nanotubes (MWCNTs), mercury film (MF) andrncomposites of cobalt nanoparticles-polypyrrole (CoNPs/PPy), graphene oxide-polypyrrolern(GO/PPy) and multi-walled carbon nanotubes-poly(4-amino-3-hydroxynaphthalene sulfonicrnacid) (MWCNTs/poly(AHNSA)) modified glassy carbon electrode (GCE).rnCoNPs/PPy/GCE composite electrode was fabricated by electropolymerization of pyrrole inrnLiClO4 solution onto the GCE using cyclic voltammetry followed by drop coating CoNPs on thernsurface of PPy/GCE. The morphological structure and surface analysis of the electrodes wererncharacterized using scanning electron microscopy, transmission electron microscopy, energyrndispersive spectroscopy (EDS), Ultra violet-Visible spectroscopy (UV–Vis), Fourier TransformrnInfrared Spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS) and cyclicrnvoltammetry (CV). The characterization results demonstrated that PPy chains interacted withrnCoNPs in the composite through donor-acceptor bonds. The sensor exhibited a high electroactivernsurface area and a low electron transfer resistance towards phoxim. Under the optimalrnconditions, the sensor showed linear relationship between the peak current and the concentrationrnof phoxim in the range of 0.025 uM12 uM with the detection limit of 0.0045 uM. Besides, thernsensor exhibited excellent reproducibility, good stability and selectivity towards possiblerninterfering substances. The sensor was also successfully applied for the determination of phoximrnin water samples.rnGraphene oxide-polypyrrole modified glassy carbon electrode (GO/PPy/GCE) composite wasrnprepared by electrochemical polymerization of a mixture containing 30 uL of GO suspensionrnand 10 uL of 0.25 M pyrrole in 0.1 M LiClO4 using cyclic voltammetry. SEM, FT-IR, UV-Visrnand Raman spectroscopy were used to study the morphology and composition of GO/PPy/GCE.rnThe results showed that GO layers have been successfully incorporated into the PPy film. Thernelectrochemical behavior of the sensor was also characterized using EIS and CV. Thernvoltammetric response showed a higher current response and a lower reduction potential atrnrnGO/PPy/GCE for phenothrin reduction. The potential shift and current enhancement at thernsurface of GO/PPy/GCE demonstrated that the sensor exhibited favorable electron transferrnkinetics and electrocatalytic activity towards the reduction of phenothrin. The sensor showed arnlinear response for phenothrin between 0.025 μM to 20 μM and a detection limit of 0.0138 μM.rnThe applicability of the proposed method was carried for the determination of phenothrin in fruitrnjuice samples.rnFenitrothion was determined electrochemically on the surface of multiwall carbon nanotubesrnmodified glassy carbon electrode (MWCNTs/GCE). The modified electrode showed three timesrnhigher surface active area as compared with glassy carbon electrode. The experimentalrnparameters (amount of MWCNTs, pH of the fenitrothion solution and adsorption parameters)rnwere optimized. The reduction current showed a linear relationship with the concentration ofrnfenitrothion in a range of 0.01 uM to 5.0 uM, with a detection limit of 0.0064 uM. The practicalrnapplicability of method was demonstrated in the assessment of fenitrothion in soil and teffrnsamples and good recoveries varied from 86.7% to 93.3% were obtained.rnThe electrochemical behavior of endosulfan was investigated at the surface of glassy carbonrnelectrode modified with mercury film (MF/GCE). The electrode showed a linear response tornendosulfan in the concentration range of 0.01-5.0 uM, with a detection limit of 0.0059 uM. Thernmodified electrode also exhibited good stability and reproducibility. The sensor was successfullyrnapplied for the determination of endosulfan in onion and tomato samples.rnA poly(4-amino-3-hydroxynaphthalene sulfonic acid) modified glassy carbon electrode wasrnemployed for the simultaneous determination of caffeine and paracetamol using square-wavernvoltammetry. Poly(AHNSA)/GCE were electrochemically deposited on a glassy carbonrnelectrode by scanning the potential in the potential range of -0.8 V to 2.0 V at a scan rate of 0.1rnV s-1 for fifteen cycles in 0.1 M HNO3 solution. The performance of the sensor was investigatedrnusing CV and SWV and it showed a linear response for both caffeine and paracetamol in thernconcentrations range of 10–125 uM. The detection limits were 0.79 uM and 0.45 uM forrncaffeine and paracetamol, respectively. The effects of some interfering substances in therndetermination of caffeine and paracetamol were also studied and their interferences were foundrniiirnto be negligible which proved the selectivity of the modified electrode. The method wasrnsuccessfully applied for the quantitative determination of caffeine and paracetamol in Coca-Cola,rnPepsi-Cola and tea samples.rnFinally, a sensitive voltammetric method was developed based on glassy carbon electrodernmodified with a combination functionalized MWCNTs and poly(AHNSA) for the determinationrnof uric acid (UA). The sensor was prepared by drop coating MWCNTs solution on the surface ofrnpoly(AHNSA)/GCE. A significant enhancement in the oxidation peak current of UA wasrnobserved at MWCNTs/poly(AHNSA)/GCE compared with bare GCE, poly(AHNSA)/GCE andrnMWCNTs/GCE. The electrode demonstrated a wide linear response in the range from 1.0–100rnuM, with a low detection limit of 0.046 uM and was successfully employed for quantification ofrnUA in urine samples

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