Description of Instrumentation and Procedures - Advances in Biochemical Engineering Biotechnology - page 12

Fig. 5. Schematic diagram of the thermal microbiosensor based on an integrated thermopile
fabricated on a quartz chip. Glucose oxidase immobilized on CPG beads was charged into the
channel

ion implantation and then annealed in nitrogen at 950 °C for 30 min. Next, the
layer was patterned by wet chemical etching, using negative photoresist as an
etch mask. Metalization was accomplished through aluminum vapour deposi-
tion and an additional photolithographic patterning procedure. As a final step,
the chip was annealed at 200 °C for 30 min. The surface of the chip was covered
by a 30

m thick layer of polyimide membrane to insulate the transducer
electrically from flow liquid. The voltage output per degree of the integrated
thermopile was about 2 mV/K at 22 °C.
On the chip,a silicone rubber membrane (0.32 mm thick was used to form the
microchannel (17.5

m

0.32 mm) and to serve as a seal between the chip and
the plexiglass cover. The inlet and outlet stainless steel tubing, as well as the elec-
trical connectors, were mounted on the cover. The entire unit was held together
with a screw-mounted delrin holder. This rather bulky construction was re-
quired in order to facilitate repeated access to the sensor chip. The CPG beads
were charged into the microchannel by sucking them in from the outlet end. The
beads were stopped at the hot junction using a filter made from a tiny piece of
kleenex tissue. Two thirds of the channel from the hot junction were filled with
the enzyme-containing beads. The remaining third was filled with similar beads
without any enzyme, in order to reduce carryover of heat to the cold junction.

¥ 3.6 ¥

2.3.2
Thermistor-Based Microbiosensor

The thermistor-based device (Fig. 6), is composed of a transducer chip
(21 0.57 mm), a spacer, and electrical and liquid flow connections. Five

thermistors (T 0 -T 4 ) with a temperature coefficient of 1.7% per degree (25 °C)

¥ 9 ¥