Description of Instrumentation and Procedures - Advances in Biochemical Engineering Biotechnology - page 23

3.3.3
Bedside Monitoring
A prototype for a bedside monitoring system was developed for semi-con-
tinuous monitoring of blood-glucose concentration, requiring only one calibra-
tion point [35]. This was made possible by using the special advantage of the
thermometric sensing technique in combination with the adjustment of flow.
The glucose concentration was determined from the difference between the
sensor response and an estimated background signal. Using standard addition
technique, calibration factors for background and sensitivity were set and
remained unchanged during the monitoring. Recovery in whole blood was
90-98% with an injection interval of 3 min and the precision of the sensor was
< 3% over more than 100 blood samples. Response time was about 60 s. The cal-
culated glucose values correlated well with a YSI glucose analyser over a range of
2-20 mmol/l.
3.3.4
Multianalyte Determination
Multiple analytes were determined simultaneously by a flow injection thermal
micro-biosensor. The biosensor consisted of five or more thin film thermistors
located along a single microchannel. The device was fabricated on a quartz chip
by micromachining. The feasibility of employing this system for the detection of
two independent enzyme reactions was demonstrated using two different pairs
of enzymes, urease/penicillinase and urease/glucose oxidase [37]. The enzymes
were immobilized on agarose beads which were then sequentially packed into
distinct regions of the microchannel. Using this method, samples containing
urea mixed with penicillin-V or with glucose were determined simultaneously.
The sensor was capable of analysing 25 samples/hour. This study was followed
by three and four analyte measurements [19].
3.3.5
Hybrid Sensors;Enzyme Substrate Recycling
A combination of calorimetric and electrochemical detection principles led to
the creation of a novel biosensor [38] that retained the principal advantages of
both techniques. In order to demonstrate the feasibility of such an approach, a
ferrocene-mediated thermal flow-injection glucose sensor was fabricated and
tested (see Scheme 2). The electrochemical reaction was accomplished by ap-
plying a voltage between a platinum column (working electrode), in contact with
a crushed reticulated vitreous carbon RVC matrix onto which glucose oxidase
was immobilized; and platinum wires (counter electrode) were located at the
inlet and outlet of the column. For detection, the thermal signal generated by the
glucose oxidation reaction was measured in conjunction with the electrochemi-
cal signal. By using this method, a linear range of glucose concentration upto
20 mmol/l was achieved, independent of the oxygen concentration in the buffer.
In a similar approach catechol was measured using tyrosinase [30]. The
enzyme column was constructed of a platinum foil in electrical contact with a