Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 49

Fig.8. Amplification system of lactate oxidase (LOD), lactate dehydrogenase (LDH) and
catalase (CAT)

range.Kirstein et al.(1989) describe an ET analyzing ATP with a detection limit
of 10 nmol/l.The enzymatic cycling system causes an amplifiction factor about
1700. Another amplification system uses a combination of lactate oxidase,
lactate dehydrogenase and catalase (LOD/LDH/CAT-system;Fig. 8).Due to evo-
lution of hydrogen peroxide from the cycling reaction, a coimmobilisation of
catalase effects an additional amplification.
The cycle represents an oxidation of NADH with oxygen accompanied by
a very high enthalpy ( H=-255 kJ/mol). The value agrees with the sum of

enthalpies taking part in the cycle (Scheller et al.1985).Mecklenburg et al.(1993)
used the LOD/LDH/CAT-system for an insulin-TELISA. Here,an amplification
factor of about 10 was observed.Nevertheless,the cycling system is expensive,
complicated and difficult to reproduce (Lammers,1996).Especially for TELISA
procedures,an optimized substrate for peroxidase labeled antibodies was devel-
oped. The substrate (2 mmol/l H 2 O 2 and 2 mmol/l aminoantipyrine) causes a
similar TELISA sensivity to that of the LOD/LDH/CAT cycle but is much easier
to use,cheaper and very reproducible (Lammers,1996).

D

4
New Fields for Enzyme Thermistors

4.1
Enantiomeric Analysis

In the pharmaceutical industry, the production of enantiomerically pure sub-
stances is oftremendous importance because the same compounds but ofoppo-
site chirality often have extremly different therapeutic effects.Thus,enantiome-
ric analysis is of special importance. Nowadays, enantioselective syntheses are
monitored via time-consuming, expensive and complicated procedures (e.g.,
chiral GC and HPLC).Biosensors might be an interesting alternative or a sup-
plement to existing techniques.Here,immobilized enzymes with different enan-