The Opsonized Electrode

Abstract

The superoxide anion is the one electron reduction product of molecular oxygen. For this reason it can be both produced from, and re-oxidised back to, dioxygen electrochemically in non-aqueous solvents. In aqueous solutions, however, electrochemical reduction of dioxygen always yields hydrogen peroxide. When superoxide is produced, in aqueous media, for example, enzymatically, then it disproportionates rather rapidly to dioxygen and hydrogen peroxide. Human neutrophils are well known to produce superoxide from dioxygen when stimulated (see, for example, Babior et al., 1973, Johnston et al., 1975, Green et al., 1979). The principle behind the work described in this chapter is that if neutrophils could be induced to produce their cytotoxic superoxide at, or close to, the surface of an electrode then it may be possible to re-oxidise electrochemically that superoxide back to dioxygen before disproportionation takes place. In this way an oxidation current response would detect the stimulation of the neutrophils. Such stimulation is always a result, however, of a membrane perturbation on the surface of the cell. The stimulus producing this can be soluble, as in the case of phorbol myristate acetate (De Chatelet, 1976) or, more commonly, it can be a surface coated with an immunoglobulin such as IgG. The latter generally takes the form of microscopic particles, for example, latex beads or invading bacteria, coated with IgG.