Mathematical Modelling of a Non-enzymatic Amperometric Electrochemical Biosensor for Cholesterol

Thickness of the electro-polymerized layer grown on a substrate and used as the recognition element for the analyte is critical to measuring the response of a biosensor, with high sensitivity and accuracy. However, it is difficult to control the thickness during synthesis. A mathematical model is developed in this study that considers thickness of the electro-polymerized layer in simulating the electrochemical response of a non-enzymatic biosensor for cholesterol in blood. The model includes transient kinetics and one-dimensional diffusion of the analyte in the poly-methyl orange (PMO) recognition layer electrochemically grown on the electrode. The governing partial differential equations resulting from the species conservation balances in the PMO layer are numerically solved. Time and spatial concentration profiles of the analyte in the PMO layer are determined. Model predictions are calibrated with the experimental data for different PMO thicknesses. Interestingly, model predictions show a linear response over the calibrated concentration range of cholesterol for all PMO layer thicknesses. Based on the chronoamperometry measurements, the model predictions for the cholesterol concentrations measured in the laboratory samples were also found to be remarkably accurate. This is the first mathematical model developed to understand the transport and kinetics of an analyte in the electro-polymerized layer used as the recognition element of a non-enzymatic biosensor.