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The detection of Cd (II) and Pb (II) ions have been done by modifying the glassy carbon electrode (GCE) with graphene oxide (GO) mixed ionic liquid (IL) (BMIM-PF₆) and nafion binder. The developed nanocomposite film combines the advantages of graphene and ionic liquid for enhanced detection. The estimated sensitivity for Cd (II) was 0.0711 µA/ppb and limit of detection found to be 0.33 ppb in the concentration range of 2.4–70 ppb. The effect of deposition potential (Dp), deposition time (Dt) and stirring speed(S) have been carried out for the response of Cd (II) current signal. The estimated sensitivity for Pb (II) was 0.0371 µA/ppb and limit of detection value of 0.42 ppb found in the linear calibration range of 5–15 ppb. Further the study of interaction effect of independent parameters (Dp, Dt, S) has also been studied by designing the experiment based on Box-Behnken design. The RSM modeling and optimization of process parameters for Cd (II) current response by IL/GO/GCE electrode was carried out with suitable empirical model. This developed sensor exhibited selective, good stability and reproducibility that could be explored for environmental, food and pharmaceutical analysis. Keywords: Electrochemical sensor, Graphene, Heavy metals, Voltammetry, RSM optimization

Fabrication of hydrogen peroxide (H2O2) biosensor for determination of Cr(VI) based on the inhibition of horseradish peroxidase (HRP) activity is reported herein. The sensor platform was developed by using electrochemically reduced graphene oxide (ERGO) film modified GCE electrode. The thionine layer is deposited over ERGO layer by two step electrodeposition process. Immobilization of HRP over the thionine modified ERGO electrode has been done by mixing with bovine serum albumin (BSA) and using glutaraldehyde as a crosslinker. The cathodic responses of the immobilized HRP for H2O2 detection is monitored using cyclic voltammetry and linear sweep voltammetry method. Cr(VI) as a trace metal ions inhibitor to the enzyme activity was proportional to concentration in the range of 0.039–0.78 µM with the sensitivity of 4.41% inhibition µM−1 and the limit of detection is 0.02 µM (S/N = 3). The inhibition mechanism determined from Dixon and Cornish-Bowden plots was found to be uncompetitive. Good stability and reproducibility of the developed sensor could provide an excellent sensing platform for the determination of peroxide and heavy metals in environmental analyses and clinical testing. Keywords: Electrodeposition, Electroreduced graphene oxide, Peroxide, Horseradish peroxidase, Chromium, Enzyme inhibition