Biosensors based on immobilization of biomolecules in sol-gel matrices - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 522

16.4 WHOLE-CELL ENCAPSULATION IN SOL-GELS AND
THEIR APPLICATIONS

16.4.1 Microbial cells
The sol-gel-entrapped microbial cells have shown excellent tolerance to different
alcohols [99]. The immobilized E. coli cells followed the Michaelis-Menten equation
when quantifi ed with the

-
D-galactopyranosdie [142]. The sol-gel matrices doped with gelatin prevented the cell
lysis, which usually occurs during the initial gelation process [143]. Microorganisms
are now widely used in the biosorption of different pollutants and toxicants. Bacillus
sphaericus JG-A12 isolated from uranium mining water has been entrapped in aque-
ous silica nanosol for the accumulation of copper and uranium [144]. Premkumar
et al. [145] immobilized recombinant luminous bacteria into TEOS sol-gel to study
the effect of sol-gel conditions on the cell response (luminescence). The entrapped
and free cells showed almost the same intensity of luminescence (little lower), but the
entrapped cells were more stable than the free cells (4 weeks at 4ºC). This kind of sta-
ble cell could be employed in biosensors in the near future.

β -glucosidase activity via the hydrolysis of 4-nitrophenyl- β

16.4.2 Plant and animal cells
The cell-based biosensors are highly useful for the functional characterization and
detection of various compounds such as drugs and toxins, and in drug testing. The sol-
gel immobilized whole cells can also be employed in biotechnological processes for
the production of various primary and secondary metabolites. However, the entrap-
ment of plant and animal whole cell in sol-gel matrices is still at an early stage. A
new sol-gel method for biosil immobilization has been introduced, in which sol-gel
siliceous layers were deposited through airfl ow on to the cell surface. This method is
employed for entrapment of plant and animal cells [19]. Pressi et al. [37] immobilized
Ajuga reptans AYN-IRB1 plant cells by the biosil method for invertase production.
Carturan et al. [146] immobilized Catharanthus roseus plant cells though the biosil
method for production of the alkaloids vincristin and vinblastin. The immobilized cells
were stable up to 100 days. Human hepatoblastoma (HepG2) and human T leukaemia
Jurkat cells have been encapsulated in alginate silica microspores for the production of
albumin (HSA) and human interleukin 2 (IL2), respectively [23]. The main limitation
in the development of sol-gel-entrapped whole cell-based biosensors is signal transfer.
The process of the signal to the transducer surface has to cross two main barriers, cell
walls and sol-gel layer, leading to signal decay or sometimes signal hindrance.

16.5 CONCLUSIONS

The functionality of immobilized biomolecules is mainly governed by their nature,
preparation method as well as the nature and structure of the immobilization matrix.