A methylene blue-mediated enzyme electrode for the determination of trace mercury(II), mercury(I), methylmercury, and mercury-glutathione complex

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 ml(-1) Hg for HgCl2 and methylmercury, 0.2 ng ml(-1) Hg for Hg-2(NO3)(2) and 1.7 ng ml(-1) Hg for mercury-glutathione complex. Inactivation of the immobilized horseradish peroxidase was displayed in the AFM images of the enzyme membranes. (C) 2001 Published by Elsevier Science B.V.