Biomedical Engineering Reference
In-Depth Information
The second approach [54] was based on the inhibition of acetylcholine
esterase. One unit of acetylcholine esterase was reversibly immobilized via lec-
tin binding to Con A-Sepharose and could be rinsed off with a pulse of 0.2 M gly-
cine-HCl, pH 2.2. Reversible immobilization of enzymes and whole cells in the
enzyme thermistor column, utilising specific lectin-glucoprotein interactions,
had been introduced earlier and was especially useful for inhibition studies,
where the enzyme had to be replaced very often. Enzyme activity was deter-
mined with 10 mM butyrylcholine as a substrate. A 5-10 min pulse of pesticide
solution was introduced into the flow buffer, followed by a second substrate
pulse. The decrease in activity was proportional to the amount of pesticide, with
a detection limit below 1 ppm.
In order to adapt the system to on-line monitoring, in wastewater control, for
example, the occurrence of pesticide in a flow buffer was investigated. It was
found possible to differentiate between reversible and irreversible inhibition
and to quantify a reversible inhibitor. Since it was possible with the calorimetric
method to use the natural substrate acetylcholine to assay cholinesterase,
instead of the commoly used thiocholines, this methodology might be useful in
medical research as well.
Whole cells were employed [55] as the monitoring element in which Pseudo-
monas capacia capable of metabolizing aromatic compounds were immobilized
in Ca +2 -alginate beads and their response to aromatic substances, e.g., salicylate,
was monitored with an enzyme thermistor.
3.4.4
Fluoride Sensing
More recently, it was demonstrated that the thermistor approach could be used
to monitor specific interactions of fluoride ions with silica-packed columns in
the flow injection mode. A thermometric method for detection of fluoride [56]
was developed that relies on the specific interaction of fluoride with hydroxy-
apatite. The detection principle is based on the measurement of the enthalpy
change upon adsorption of fluoride onto ceramic hydroxyapatite, by tempera-
ture monitoring with a thermistor-based flow injection calorimeter. The detec-
tion limit for fluoride was 0.1 ppm, which is in the same range as that of a com-
mercial ion-selective electrode. The method could be applied to fluoride in
aqueous solution as well as in cosmetic preparations. The system yielded highly
reproducible results over at least 6 months, without the need of replacing or
regenerating the ceramic hydroxyapatite column. The ease of operation of
thermal sensing and the ability to couple the system to flow injection analysis
provided a versatile, low-cost, and rapid detection method for fluoride.
3.4.5
Cellular Metabolism
The effects of ampicillin-induced spheroplast formation on the production of
molecular hydrogen by Escherichia coli carrying out fermentation in a lactose-
peptone broth with an osmolality of 342 mosmol/l was investigated previously
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