Inhibition of adsorbed alkaline phosphatase activity by an anti-enzyme antibody. An approach to carbon paste immunoelectrodes

The accumulation of alkaline phosphatase labeled immunoglobulin G (IgG-AP) on the surface of an electrochemically pretreated carbon paste electrode an d further enzyme inhibition with an anti-PLP antibody is presented in this work. The pretreatment is based on an anodization at a controlled potential of +1.5 V in 0.1 M NaOH solution. The obtained protein layer was detected by the electrodic oxidation of indigo, product of the 3-indoxyl phosphate h ydrolysis with AP. This molecule readily adsorbs on the electrode surface a nd displays a reversible electrodic process at -0.4 V (vs. Ag/AgCl) in 0.1 M Tris buffer pH 7.2. Thus, alternating current voltammetry was a very adeq uate electrochemical technique for its detection. Calibrations of the IgG-A P conjugate adsorbed are presented yielding a lower detection limit of 4 x 10(-13) M for the labeled IgG. Likewise, the determination of the anti-AP a ntibody was performed.,4 decrease of the electrode response was observed wh en it reacted with the enzyme label. Thus, a detection limit of 2 x 10(-10) M for this antibody was achieved.