Glucose oxidase (GOx) modified poly-phenylenediamine (PPD) coated 250  m Pt-disk electrodes were prepared by electropolymerization in phenylenediamine solutions containing GOx. Both ortho and meta monomers were tested, and the ortho isomer was found to give better glucose responses. The response of Pt/o-PPD/GOx electrodes to glucose was well behaved with a rapid response time and displaying Michaelis-Menten kinetics. The behavior of these electrodes in vitro to ascorbic acid (a principal interferant in brain tissue) was complex in that the sensitivity was concentration dependent. At low ascorbate concentrations (<50 M), the sensitivity was similar to that of bare Pt (72 ± 13 nA/ mM, n = 10) whereas at higher levels it decreased sharply to 0.2 ± 0.1 nA/mM (n = 3) at 1 mmol/L ascorbate. At still higher concentrations (1 to 10 mmol/L), the sensitivity was concentration independent, 0.14 ± 0.02 nA/mM (n = 3). Calibrations for another potential interferant, uric acid, were linear in the range studied (0 to 100 M) with a slope of 0.41 ± 0.03 nA/mM (n = 3), indicating negligible interference by this substrate for concentrations present in brain extracellular fluid. Surprisingly, the permeability of both substrates was greater in PPD films containing no GOx. The results are discussed in terms of the suitability of these electrodes for monitoring brain glucose in vivo. |
