A methylene blue-mediated enzyme biosensor has been developed for the detection of inhibitors including mercury(II),
mercury(I), methylmercury, and mercury–glutathione complex. The inhibition to horseradish peroxidase was apparently reversible and noncompetitive in the presence of HgCl2 in less than 8 s and irreversibly inactivated when incubated with different concentrations of HgCl2 for 1–8 min. The binding site of horseradish peroxidase with HgCl2 probably was a cysteine residue SH.Mercury compounds can be assayed amperometrically with the detection limits 0.1 ng ml1 Hg for HgCl2 and methylmercury,0.2 ng ml1 Hg for Hg2(NO3)2 and 1.7 ng ml1 Hg for mercury–glutathione complex. Inactivation of the immobilizedhorseradish peroxidase was displayed in the AFM images of the enzyme membranes. © 2001 Published by Elsevier Science B.V.