Thermal Biosensors in Biotechnology - Advances in Biochemical Engineering Biotechnology - page 52

bilized glutaminase (50 units) and glutamate decarboxylase (100 units). Glut-
aminase deaminates L -glutamine with release of L -glutamate.The latter inhibits
the deaminating enzyme and reduces its maximum production.Thus,glutamate
decarboxylase is coimmobilized in order to remove the inhibitor.The biosensor
response substantially depends on the buffer's pH (Fig. 11).Even at 100 mmol/l
L -glutamine,no signal is observed with a buffer of pH 7.0.On the other hand,
acid buffer (pH 4.9) cause very good signals.Thus,cultivation samples have to
be imperatively acidified before analysis. This is automatically mastered in a
computer controlled FIA system (Lammers,1996).
4.3
Medical Monitoring
Due to requirements for individual medical treatment,on-line medical or bed-
side monitoring is one of the most promising tasks for biosensors.Especially,in
hemodialysis treatment.Here,patient's blood is purified by removing enriched
urea using a dialysis cell. The procedure requires about four to seven hours.
A shorter hemodialysis time might be harmful whereas a long purification
restricts the patient's quality of life.Thus,an individual monitoring of the purifi-
cation progress is very desirable.
In hemodialysis devices,urea analysis makes it possible to monitor the effect
of the medical treatment continuously. For this purpose, the ET feasibility in
urea monitoring was investigated. In comparison to other transducers, the ET
glutaminase/
glutamate decarboxylase
pH 4,9
glutaminase
pH 4,9
glutaminase
pH 7,0
L-glutamine [mmol/l]
Fig.11. Analysis of L -glutamine at pH 7.0 and pH 4.9