Bismuth-nanocomposites modified Screen Printed Carbon Electrodes for Non-Enzymatic Electrochemical Sensors

Main aim is to develop new non-enzymatic electrochemical sensors and study their performance in terms of kinetic rate constant, sensitivity and limit of detection. New sensors were developed by exploiting the functionalization of bismuth-composites on the surface of commercially available Screen Printed Carbon Electrodes. 12 different Bismuth composites based on HO-BiONO3, with organic surfactants such as polyethylene glycol (PEG) and polyvinyl butyral (PVB) coatings to HO-BiONO3, Bi5O7NO3, and also Bismuth (Bi3+) coated Biochar (pyrolysis at 10000C) based materials were synthesized in carbon group at Politecnico Di Torino. Scanning electron microscopic experiments showed that different materials have different sizes and shapes. HO-BiONO3 particles have been distributed with rod shaped structure and Bi5O7NO3 showed a sphere like structure by forming aggregates. Commercially available Screen Printed Carbon Electrodes with working carbon electrode (area 0.12 cm2) and silver reference electrode were brought from DropSens. Homogeneous suspensions of all Bismuth-composites were prepared by using different solvents depending on their solubility. 5uL drops of each suspension were dispensed on the surface of different working electrodes and left them for drying (Drop casting technique). Modified electrodes were used for electrochemical measurements of 1mM Paracetamol in 0.1M PBS pH 7 by performing Cyclic Voltammetry with the help of AutoLab in potentiostatic mode with the potential ranging from -0.4 V to 0.8 V vs Ag/AgCl at a scan rate of 100 mV/s. Observed that there is a significant improvement in oxidation peak currents compared to the bare or unmodified electrodes. Cyclic Voltammograms with scan rates ranging from 50 mV/s to 300 mV/s in steps of 50 mV/s were also measured to demonstrate that electrochemical system is a freely diffusing quasi-reversible system. Oxidation peak currents are linearly varying with square root of scan rate and also oxidation and reduction peak positions varying linearly with natural logarithm of scan rate. Slopes of these plots were used to find the electron transfer coefficient (alpha) and rate constant (k) with the help of Laviron model. Diffusion coefficient (D) of paracetamol was also calculated at 100 mV/s using Randles-Sevcik equation. Also a cleaning procedure was followed by dipping modified SPCEs in 0.2M H2SO4 and performing a step of cyclic voltammetry in the potential range of -1.2V to 1.5V at 100 mV/s. Calibration curves were obtained by taking the oxidation peak currents with respect to the concentration (0.5mM to 3mM) and found the sensitivity of modified electrodes by taking the slope of the calibration curves. Higher sensitivity was observed for all modified electrodes compared to unmodified electrode. Quantitatively, unmodified electrode has a sensitivity of 20.02+??0.23 uA/mM with a limit of detection of 2.32+??0.03 mM (n=3) and a relative standard deviation of 1.15%. Obtained maximum sensitivity for PEG coated BiONO3 modified electrode was registered as more than double compared to unmodified electrode at the value of 43.50+??0.54 uA/mM and limit of detection of 2.24+??0.03 mM (n=3) with relative standard deviation of 1.24%. Very low limit of detection was observed for PEG and PVB coated BiONO3 modified electrode at the value of 1.50+??0.01 mM. In order to understand the behaviour of these electrodes, further study on surface chemistry of working electrodes has been planned for the future.