Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 62

the heat loss to the surroundings,to enhance the enzyme loading,and to physi-
cally protect the enzyme layer (Fig. 21). Nonspecific temperature changes are
obtained via a reference thermistor.Complicated thermostating procedures are
not necessary.Bio-thermochips with coimmobilized glucose oxidase and cata-
lase were placed in a polystyrene insulated box,and after 5 minutes of tempera-
ture equilibration, glucose solutions of 1 to 4 mmol/l were injected through a
sample inlet.
The most interesting point of the study is the possibility of not needing
thermo-stats due to direct contact between the enzyme and the thermistor bead.
However, the insulation box is still very large - 300 175 mm.Moreover,

direct enzyme immobilization on thermistors is very expensive because the
whole sensing part has to be exchanged after the utilization of the enzymes.

¥ 260 ¥

5.5
Compact Multichannel Enzyme Thermistors

Miniaturization of biosensors is of great importance in the field of clinical
analysis. However, in the case of bioprocess monitoring and control, small
set-ups are not necessary.What bioprocess engineers need are robust devices
within stable boxes, simple operating methods and data transfer protection.
Moreover,there must be the possibility of exchanging exhausted enzymes very
quickly.Within this scope,we continued the development on the whole success-
ful multi-channel ET. The system consists of a 19

-box for industrial applica-
tions containing a thermostated aluminium cylinder, an A/D-board for data
acquisition and a microcontroller for coordination of the electronic modules.
Thermistors resistances are measured via a multiplexer and constant current
supply.Thus,the drifting wheatstone bridges are not needed.The compact ET is
easily programmed via three buttons and a LED display. The digital data are
transferred via RS232 to a PC where complex analysis is performed.Due to digi-

≤

thermistor head

support for enzyme immobilization
(silicon tube)

lead wire

Fig.21. Sensing part of the bio-thermochip