Biosensors based on immobilization of biomolecules in sol-gel matrices - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 513

chemiluminescent signal generated upon reaction of hydrogen peroxide, and luminol
with the conjugate bound to RBP. Tsai and Doong [105] reported an array-based opti-
cal biosensor for the determination of urea, acetylcholine, and heavy metals. Urease
and acetyleholinesterase (AChE) were coentrapped with FITC-dextran in sol-gel and
fi xed on a sensing probe. The linear ranges of detection were 2.5 to 50

µ M for urea and

10 to 100 nM for Cd(II), Cu(II), and Hg(II).

16.3.1.5 Electrochemical biosensors
The most widely used enzymes in biosensor design are GOD and HRP due to their
well-known structure and mechanism of action. Metal alkoxides are more attractive
matrixes because they provide good conductivity and the possibility of manipulation
of polarity, rigidity, pore size, distribution, and electronic conductivity. Owing to the
advantages of metal alkoxides Glezer and Lev [106] prepared GOD-doped vanadium
pentoxide sol-gel fi lm-modifi ed platinum electrodes. Liu et al. [29] reported a glucose
biosensor based on immobilization of enzyme in alumina (aluminum iso-propoxide) sol-
gel fi lm on a platinized glassy carbon electrode. The low operating potential greatly
minimized the interference from coexisting electroactive species. Ju and coworkers
[35, 107] proposed a simple and mild vapor deposition method to prepare titania sol-
gel for immobilization of HRP, GOD, and other biomolecules, which retained their
catalytic activity and exhibited good analytical performance on electrode surface. The
titania sol-gel matrix had uniform porous structure and very low mass transport barrier
(Fig. 16.4).
As shown in Fig. 16.5a, no response of the enzyme electrode was observed in the
absence of catechol and H 2 O 2 . The electrode displayed a low background current.
When 1.0 mM catechol was added to PBS, the cyclic voltammogram showed a couple
of oxidation and reduction peaks for catechol (curve (ii) in Fig. 16.5a). Upon addition of

(a) (b)

FIGURE 16.4 Scanning electron micrographs of glassy carbon electrodes coated with (a) titania sol-gel
and (b) titania sol-gel doped with HRP (adapted from [35]).