Modifications to a carbon paste glucose-sensing enzyme electrode and a reduction in the electrochemical interference from L-ascorbate.

A glucose-sensing enzyme electrode was prepared by incorporating polyethylene glycol-modified glucose oxidase, horseradish peroxidase and 1,1'-dimethylferrocene into a carbon paste. The modification of glucose oxidase with polyethylene glycol was effective for increasing the enzyme activity in the carbon paste owing to the enhanced affinity of the polyethylene glycolmodified enzyme for the hydrophobic carbon paste matrix. In contrast, however, the enzyme activity of the polymer-modified peroxidase was lower than the unmodified peroxidase in the carbon paste matrix because of a severe loss of the enzyme activity during the modification with polyethylene glycol. Hence, the enzyme pair of polyethylene glycol-modified glucose oxidase and unmodified peroxidase was used for preparing the enzyme electrode. The reductive current response of the electrode to glucose was recorded at -0.2 V vs. Ag/AgCl. After the addition of glucose (100 microM), the current increased immediately and reached a plateau (delta = -0.12 microA) within 30 s. The current response was linear up to a glucose concentration of 500 microM and the detection limit was 20 microM (S/N = 5). Interference from ascorbate was very small: the current response to 1 mM glucose (-1.1 microA) was slightly reduced to -0.9 microA when 1 mM ascorbate was added to the glucose-containing solution. In biological and food samples, the concentration of ascorbate is generally quite low compared with the glucose concentration. The interference from ascorbate could actually be ignored for the purpose of determining glucose in soft drinks.