Immobilization of Urease on Porous Silicon for Chromium Detection in Drinking Water

Abstract

Enzymatic biosensors are becoming popular for the on-field analytic application in the research areas such as environmental and clinical monitoring, considering the significant impact of food and water quality of human life. Accurate and reliable analysis of a sample at an economical cost is the significant advantage of biosensors.In the present study, Porous silicon (PS) were utilized as a base material for immobilizing urease to detect chromium in drinking water was investigated.PS films were prepared by electrochemical etching method and urease immobilization were achieved by physical adsorption and covalent binding. Variation in the surface morphology confirmed the enzyme adsorption over the surface. Necessary modifications and activationof PS film surface for covalent binding method by organosilanes were confirmed by FTIR spectra study.Immobilization resulted in decline of enzyme activity (max) and substrate affinity (Km) while compared with free urease kinetics.Effects of Cr6+, Cr3+, Cu2+, Fe2+, Cd2+, Cd2+, and Ni2+ions on free and immobilized urease activity were studied for each metal ion individually over a concentration range of 0.0001 to 10 ppm. In order to comprehend the influence of other ions on Cr6+ detection, similar enzyme inhibition studies were performed in combination of Cr6+ with other heavy metals.Freeurease showed high sensitivity towards trace concentrations all of the tested metal ions except Cr6+. Combinations of metal ions with the Cr6+ showed a decrease in the degree of inhibition. Immobilized urease reported the decrease in the urease inhibition by tested metals ions in individual and in combinations with Cr6+. The observed variation in the activity of urease is due to the interaction of heavy metals with thiol groups of urease active site and mass transfer limitations offers by PS surface. The variation in the activity of urease by the presence of metals ions, especially Cr6+, can be related with the concentration of inhibitory metal ions present in the sample for the development of biosensors.