Comparison of Cobalt Hexacyanoferrate and Poly(Neutral Red) Modified Carbon Film Electrodes for the Amperometric Detection of Heavy Metals Based on Glucose Oxidase Enzyme Inhibition

Abstract

Electrochemical biosensors have been developed for the determination of cadmium, cobalt, and copper cations through their inhibitory effect on glucose oxidase activity, using cobalt hexacyanoferrate or poly(neutral red) as redox mediators. Cobalt hexacyanoferrate and poly(neutral red) were used to modify carbon film electrodes by electrodeposition and glucose oxidase was then immobilized on the electrode by crosslinking with glutaraldehyde. A comparison between the two redox mediated biosensors for the determination of the metal ions was performed under the same experimental conditions. In fixed-potential amperometry at −0.35 V vs. the saturated calomel electrode, the detection limits for the metal cations studied were in the low micromolar range, lower at glucose oxidase/cobalt hexacyanoferrate/carbon film electrode, and the lowest achieved with glucose oxidase inhibition measurements. The linear dynamic ranges were wider at the glucose oxidase/poly(neutral red)/carbon film electrode for all three metal ions. The 10% and 50% inhibition values (I₁₀ and I₅₀) for the metal cations were calculated and the degree of inhibition at the biosensors was compared. Copper ions inhibited glucose oxidase to the highest degree for both biosensors. The application for the analysis of tap water was demonstrated.

Keywords:

• Carbon film electrodes
• Electrochemical biosensor
• Enzyme inhibition
• Heavy metal cations
• Redox mediators