Description of Instrumentation and Procedures - Advances in Biochemical Engineering Biotechnology - page 14

for sealing the device. In order to determine two substrates simultaneously, the
enzyme regions E 1 and E 2 were charged with two different enzymes, which had
been covalently immobilized on NH S -activated ( N -hydroxy succinimide) agarose
beads (13

m in diameter, Pharmacia Biotech, Sweden). The E 0 region was
charged with similar beads without any enzymes, in order to damp the thermal
carryover downstream at region E 2 . In this scheme, T 1 /T 3 and T 0 /T 2 were
employed as the measurement- and the reference thermistor, respectively. The
agarose beads were held in place, using a filter made of a tiny piece of kleenex
tissue.A plexiglas cover, on which the inlet and outlet stainless-steel tubings and
electrical connectors were mounted, was used to seal the holder. This design was
rather bulky but was required in order to facilitate repeated access to the sensor
chip. A typical example of multisensing of penicllin, glucose and urea is shown
in Figure 6b.

m

2.4
Multisensing Devices

An important area in clinical diagnosis is the simultaneous determination of
multiple analytes. This approach could be extended to personal healthcare, bio-
process control, and sequential enzyme reactions. In particular, it is essential in
the realization of a personal healthcare system, as the information from multi-
ple metabolites improves the reliability of the clinical diagnosis. Immense
efforts have been made to develop biosensors for the determination of multiple
analytes. Many of these employ multi-channel or split-flow systems, combined
with electrochemical detection. A requisite of the multi-channel scheme lies in
avoiding interference from other reactions. Nevertheless, uniformity of the flow
rate in these multichannel systems (Fig. 7), especially in microchannels, is yet to
be improved. Earlier attempts made use of a single flow channel in multianalyte
determination. In applications involving electrochemical and optical detection,
the system must be suitably regulated, in order to minimize the interference that
can arise due to change in pH, ionic strength, electrocatalytic species, or chro-
mophores produced during the reaction. In addition, the specificity of the elec-
trode or the optical detector for the compound being measured is intrinsically
dependent on the applied potential or the wavelength. The number of analytes,
especially in whole blood, as well as the nature of the detection system, usually
govern the detection conditions. Apart from methods in biosensing, multiple
discrete samples [20] have also been measured by a centrifugal blood analyzer
method based on a rotating sampling distributor. However, the inherent com-
plexity of the latter technique prevents its routine application in delocalized cli-
nical diagnosis.
In the recent past, multianalyte determination has found increased applica-
tions, i.e. specific and multiple reactions favor a system that allows the specific
determination of each reaction, using the same principal measurement me-
thods, detectors and conditions. In keeping with this idea, a flow injection
thermometric method based on an enzyme reaction and an integrated sensor
device was proposed for the determination of multiple analytes. In principle the
technique relies on the specificity of enzyme catalysis and the universality of