Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 39

3.1
Clinical Analysis

Worldwide, about 12 to 15 billion US$ per annum are spent for analytical
purposes.Nearly 50 million US$ of this sum is devoted to enzymes.In clinical
chemistry, several metabolites and their concentrations give important in-
formation about patients'health (see Table 1).
Due to the development of new immobilization techniques,the routine use of
enzymes in clinical analysis was given a tremendous fresh impetus.Immobilized
enzymes enable multiple applications,simple operation and an essential simpli-
fication of analyzers.Thus,biosensors including the ET were predicted to hold a
predominant position in clinical chemistry.
Most clinical analysis deals with blood or urine metabolites in the micro- and
millimolar range. Table 2 shows a collection of low molecular weight analytes
that were successfully determined with the ET.So far,its use is limited to a few
research laboratories. On account of the high expenditure and relatively low
measuring frequency (about 12 analyses per hour),a wider acceptance has been
difficult (Scheller and Schubert,1989).Moreover,economical aspects have to be
taken into account. Especially in medical analysis, biosensors have to compete
with the well-established test strips. Companies like Boehringer Mannheim
(Mannheim, Germany), Bayer Diagnostics (Munich, Germany) or Merck
(Darmstadt,Germany) supply disposable tests with a complete enzyme chem-
istry including simple-to-operate pocket devices.Although these tests have only
moderate precision,they fulfil a good marketing strategy due to high unit costs.
Thus,disposable tests are of interest for patients to be able test themselves and
for small clinical laboratories.Due to these aspects,biosensors for clinical ana-
lysis - including the ET - will probably only be applied where high sampling
frequencies or on-line-analysis are of interest (e.g.,bed-side monitoring).

3.2
Immunoanalysis

In biochemistry, non-enzymatic proteins are analyzed by immunochemical
methods.Especially the popular enzyme-linked immunosorbent assay (ELISA)

Table 1. Important clinical analytes and normal ranges in blood (Pschyrembel,1993)

Analyte Diagnostical use Range [mmol/l]

cholesterol arteriosclerosis 2.62-7.62

creatinine kidney diseases 0.05-0.11

glucose diabetes mellitus 3.60-5.60

uric acid arthritis urica (gout) 0.12-0.40

urea kidney diseases 3.60-5.40

lactate liver diseases 1.00-1.78

triglycerides arteriosclerosis 0.45-1.70