DETERMINATION OF SELECTED HEAVY METALS USING AMPEROMETRIC HORSERADISH PEROXIDASE (HRP) INHIBITION BIOSENSOR

Fabrication of an amperometric biosensor for determination of heavy metals in tap water based on the inhibition of horseradish peroxidase activity is reported. The inhibition of the biosensor's response to 0.95mM H2O2 at -200mV (vs. Ag/AgCl) followed the order, Cd2+ < Cu2+ < Pb2+. The detection limits were 0.09 ppb, 0.03 ppb, and 0.10 ppb for Cd2+, Pb2+, and Cu2+, respectively. Kinetic parameters K-M(app) (apparent Michaelis-Menten constant) and I-max (maximum current) obtained in the absence (K-M(app =) 1.16mM, I-max = 0.51 mu A) and the presence (K-M(app) = 1.13mM, I-max = 0.36) of 3.13 ppm Cd2+ showed that the enzyme inhibition process was reversible and non-competitive, and the corresponding KI (inhibition constant) value was 0.026mM. After two weeks, the biosensor retained > 95% of its initial response and gave a reproducibility of 3.8% and precision of 2.1%.