Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 47

Therefore, Rank et al. (1995) constructed an automated ET for process moni-
toring.The equipment was installed inside a steel cabinet with cool,filtered air
to keep the temperature sufficiently constant. The enzyme column had to be
protected against microbial growth by adding sodium azide to the buffer solu-
tion.These facts show an obvious strong difference between biosensor employ-
ment in research laboratories and industrial plants.
TELISA systems for on-line-monitoring of proteins have not been applied so
far. Nevertheless, several TELISAs have been applied for off-line analysis of
cultivation samples.Birnbaum et al.(1986) used a competitive TELISA for human
proinsulin analysis produced from recombinant Escherichia coli .Lammers
(1996) describes a sandwich TELISA for monitoring monoclonal mouse anti-
bodies. Here, real samples of a hybridoma cell cultivation (Dr. Karl Thomae,
Germany) were analyzed and correlated well with conventional ELISA data. A
whole measuring cycle including incubation,detection and reequilibration needs
18 minutes.Due to the long cultivation time (two weeks and more) for mamm-
alian cells,it would be sufficient for on-line monitoring.But TELISAs have other
decisive disadvantages.Enzyme-labeled antibodies or antigens are expensive and
need a complicated monitoring performance.Thus,procedures working without
conjugates like fluorescence immunoanalysis might be more attractive.
In conclusion,ET employment is possible for on-line monitoring of industrial
fermentation processes under real conditions.Nevertheless,each process has its
own characteristics and needs a special monitoring concept. In special cases,
sensors other than the ET might be better for monitoring and control.
3.5
Environmental Analysis
Microorganisms are universal sensors for pollutant analysis. Toxins influence
the microorganisms'metabolism and are recognized via monitoring the state of
the cells. In comparison to specific biosensors, the unspecific response of the
microorganisms to different substances is a crucial advantage for toxicological
studies.Nevertheless,simple operation with immobilized microorganisms is of
tremendous importance for employing these kinds of toxiticy tests. Microbial
sensors might be attractive for domestic and industrial waste-water monitoring.
Sudden changes in metabolism bring about a fast response in temperature.
Thus, the ET has good prerequisites for use as a toxin guard system. Hundeck
(1991) investigated the response behavior of immobilized Saccharomyces cere-
visiae to different inhibitors (azide,Hg 2+ ,cyanide,arsenate,2,4-dinitrophenol).
Here,inhibitors were mixed with glucose,and after substrate injection,the com-
bined substrate-inhibitor-solution was used.Increasing inhibitor concentration
caused decreasing temperature signals.The inhibitors azide,cyanide and arse-
nate allowed multiple determinations to be made whereas Hg 2+ irreversibly
damage the cells. The substance 2,4-dinitrophenol (2,4-DNP) increases the
temperature signals by decoupling the respiration chain (i.e.oxidation ofNADH
and decoupling of ATP production).
Some different examples showing relevance to environmental monitoring are
listed in Table 6.In addition to microbial systems,immobilized enzymes that are