Needle enzyme electrodes for biological studies.

Needle enzyme electrodes have been produced for measurement of glucose and lactate. They comprise glutaraldehyde-crosslinked oxidases immobilised over less than 1.1 mm od needle-type sensors for H2O2. To obtain selectivity in blood, an underlying polyethersulphone membrane was used which excluded electrochemical interferents from the working (Pt) electrode. Linearity for the systems was extended to cover the clinical range by the use of outer low permeability polyurethane membranes. This type of external membrane also reduced the stirring dependence of electrodes. The glucose needle electrode was used in unstirred whole blood samples and gave an acceptable correlation with the routine spectrophotometric method (y = 0.954x + 0.202, r = 0.991, n = 48).