IMMUNOSENSING WITH AMPEROMETRIC DETECTION, USING GALACTOSIDASE AS LABEL AND P-AMINOPHENYL-BETA-D-GALACTOPYRANOSIDE AS SUBSTRATE

p-Aminophenyl-beta-D-galactopyranoside (PAPG) was shown to be a suitab le substrate for the amperometric detection of galactosidase activity at neutral pH. The application of this amplification system for immuno assay was demonstrated. The product of the enzyme reaction, p-aminophe nol (PAP), was detected at 200 mV, vs. Ag/AgCl, by now-injection analy sis (FIA), with a 50 nM detection limit. PAPG was hydrolyzed more than 2.5 times faster than p-nitrophenyl-beta-D-galactopyranoside, by the enzyme, Both PAP and PAPG were stable at pH 7. The galactosidase conce ntration could be measured down to a concentration of 100 fM, and mous e IgG could be assayed by sandwich immunoassay down to 700 fM. PAPG wa s found to be a promising reagent for heterogeneous systems, like the one described, and for homogenous assays of biological fluids.