Colorimetric determination of Cu2+ ions in water and milk by apo-tyrosinase disc

A novel and simple, colorimetric bio sensing system for specific determination of Cu2+ ions in water and milk using apo tyrosinase has been constructed. Tyrosinase extracted from Agaricus bisporus was entrapped in polyacrylamide gel, to fabricate the optic sensing disc for the detection of copper ions. The apo form of tyrosinase has been generated by treating it with 0.01 M EDTA, followed by activation in to holo form, and copper ions acts as a co factor for the conversion of L-DOPA in to dopachrome. The presence of copper ions modified the disc colour from colourless to orange. Under standard conditions, the biosensor has shown good linearity from 0.1 to 25 μg/l, with a lowest detection limit of 0.01 μg/l for Cu2+ ions with an optimized response time of 15 min. The sensing disc is stable for more than 50 days at 4 °C and it is found to be highly specific for copper ions, exhibited zero interference by other heavy metal ions like Pb2+, Cd2+, Zn2+, Ni2+ and Co2+. The present study has confirmed that the developed biosensor is consistent, stable, miniaturized, repeatable, reproducible, highly specific, selective, sensitive, suitable and applicable in real water and milk samples for analysis of Cu2+ ions with a sample volume of 10 μl.