Amperometric determination of cadmium, lead, and mercury metal ions using a novel polymer immobilised horseradish peroxidase biosensor system

Abstract

This work was undertaken to develop a novel Pt/PANI-co-PDTDA/HRP biosensor system for environmental applications to investigate the inhibition studies by specific heavy metals, to provide data suitable for kinetic studies and further application of the biosensor to environmental samples. The newly constructed biosensor was compared to the data of the well-researched Pt/PANI/HRP biosensor. Optimised experimental conditions, such as the working pH for the biosensor was evaluated. The functionality of the amperometric enzyme sensor system was demonstrated by measuring the oxidation current of hydrogen peroxide followed by the development of an assay for determination of metal concentration in the presence of selected metal ions of Cd²⁺, Pb²⁺ and Hg²⁺. The detection limits were found to be 8 × 10⁻⁴ μg L⁻¹ for cadmium, 9.38 × 10⁻⁴ μg L⁻¹ for lead and 7.89 × 10⁻⁴ μg L⁻¹ for mercury. The World Health Organisation recommended that the maximum safety level of these metals should not exceed 0.005 mg L⁻¹ of Cd²⁺, 0.01 mg L⁻¹ of Pb²⁺ and 0.001 mg L⁻¹ of Hg^2+., respectively. The analytical and detection data for the metals investigated were observed to be lower than concentrations recommended by several bodies including World Health Organisation and Environmental Protection Agencies. Therefore the biosensors developed in this study can be used to screen the presence of these metals in water samples because of its low detection limit. The modes of inhibition of horseradish peroxidase by Pb²⁺, Cd²⁺ and Hg²⁺ as analysed using the double reciprocal plots of the Michaelis–Menten equation was found to be reversible and uncompetitive inhibition. Based on the K_m^app and I_max values for both biosensors the results have shown smaller values. These results also proved that the enzyme modified electrode is valuable and can be deployed for the determination or screening of heavy metals.

Keywords:

• Amperometric biosensor
• PANI-co-PDTDA conducting polymer
• HRP
• portable potentiostat
• lead
• cadmium
• mercury

Additional information

Funding

This study was financially supported by the Water Research Commission (WRC), Council for Scientific and Industrial Research (CSIR) and the National Research Foundation (NRF) of South Africa. The authors also acknowledge the support from the Sensor Lab, Chemistry Department, University of the Western Cape, Bellville.