Design and development of amperometric biosensor for the detection of lead and mercury ions in water matrix-a permeability approach

Intake of water contaminated with lead (Pb²⁺) and mercury (Hg²⁺) ions leads to various toxic effects and health issues. In this context, an amperometric urease inhibition-based biosensor was developed to detect Pb²⁺ and Hg²⁺ ions in water matrix. The modified Pt/CeO₂/urease electrode was fabricated by immobilizing CeO₂ nanoparticles and urease using a semi-permeable adsorption layer of nafion. With urea as a substrate, urease catalytic activity was examined through cyclic voltammetry. Further, maximum amperometric inhibitive response of the modified Pt/CeO₂/urease electrode was observed in the presence of Pb²⁺ and Hg²⁺ ions due to the urease inhibition at specific potentials of -0.03 and 0 V, respectively. The developed sensor exhibited a detection limit of 0.019 ± 0.001 μM with a sensitivity of 89.2 × 10^-3 μA μM^-1 for Pb²⁺ ions. A detection limit of 0.018 ± 0.003 with a sensitivity of 94.1 × 10^-3 μA μM^-1 was achieved in detecting Hg²⁺ ions. The developed biosensor showed a fast response time (<1 s) with a linear range of 0.5-2.2 and 0.02-0.8 μM for Pb²⁺ and Hg²⁺ ions, respectively. The modified electrode offered a good stability for 20 days with a good repeatability and reproducibility. The developed sensor was used to detect Pb²⁺ and Hg²⁺ ions contaminating Cauvery river water and the observed results were in good co-ordination with atomic absorption spectroscopic data.