J. Svitel et al., COMPOSITE BIOSENSOR FOR SULFITE ASSAY - USE OF WATER-INSOLUBLE HEXACYANOFERRATE(III) SALTS AS ELECTRON-TRANSFER MEDIATORS, Electroanalysis, 10(9), 1998, pp. 591-596
Water-insoluble salts of hexacyanoferrate(III) and cationic surface ac
tive agents were synthetized and used as electron-mediators for sulfit
e oxidase. The biosensor was prepared from a composite consisting of m
odified graphite (50 % w/w) and n-eicosane (50 % w/w). Graphite was mo
dified with mediators or with both mediator and sulfite oxidase for su
rface- and bulk-modified electrode, respectively. The main advantage o
f biosensors with insoluble mediators is the possibility to operate at
a potential of 0 mV (vs. SCE), thus less interferences are expected,
in comparison to soluble hexacyanoferrate(III) where a potential of +3
00 mV must be used. The maximum sensitivity 7.8 x 10(-4) mu A/mu M was
obtained for bulk-modified biosensor, prepared from graphite modified
with 5 % w/w of hexadecyltrimethylammonium hexacyanoferrate(III) and
1.25 units/mg (of graphite) of sulfite oxidase. The sensitivity of the
biosensor decreased to 24% of the initial sensitivity after one month
storage in dry state at ambient temperature. The use of trehalose as
an enzyme stabilization agent has led to the improved stability: 40 %
of the initial stability was retained after one month.