K. Miyata et al., MICRO ENZYME-SENSOR WITH AN OSMIUM COMPLEX AND POROUS CARBON FOR MEASURING GALACTOSE, Bulletin of the Chemical Society of Japan, 68(7), 1995, pp. 1921-1927
A micro enzyme-sensor, based on galactose oxidase (EC 1.2.3.9) and a t
ris(2,2'-bipyridine) complex of osmium(II/III) as a redox mediator ([O
s(bpy)(3)](2+)/(3+)), fabricated on a carbon electrode (25 mu m diamet
er), was developed for measuring galactose. To obtain the carbon elect
rode, a platinum-disk electrode (25 mu m diameter) was etched in hot a
qua regia to create a cavity (depth of ca. 3-5 mu m) at its tip. A por
ous carbon material was prepared from 90% acetylene black and 10% Tefl
on emulsion as a binder, and then packed into the cavity of the platin
um-disk electrode's tip. The carbon electrode was immersed in the osmi
um complex with 0.1 mol dm-3 LiClO4 in order to adsorb it in the carbo
n pores, which was monitored based on an increase in the anodic peak c
urrent and the cathodic peak current based on the osmium complex redox
potential by the cyclic voltammogram. The tip of the carbon electrode
was dipped overnight in a buffer solution of pH 7.00 containing galac
tose oxidase so as to immobilize it on this surface by adsorption. The
characteristics of the porous-carbon material surface by X-ray diffra
ction (XRD) and scanning electron microscopy (SEM), the calibration cu
rve for measuring of galactose, and the effects of the pH, temperature
and concomitant compounds were investigated. By the XRD measurement,
the porous carbon after treating a Zonyl FSN fluoro-carbon surfactant
solution, a 5% NafionR solution with methanol, and an osmium complex w
ith 0.1 mol dm-3 LiClO4 showed good crystallinity compared with carbon
powder. The structure of the carbon-electrode surface was visually co
nfirmed using SEM photographs. The carbon surface had many pores, and
galactose oxidase existed on it after adsorption. Under the optimum co
nditions the amperometric response of this sensor was linear over conc
entration ranges of 0.01-5.00 mmol dm(-3) galactose; the correlation c
oefficient was 0.999.