3. Results and discussion
3.1. Optimisation of the micro-organism concentration in
the biocatalytic layer
The membranes with immobilised yeast were tested on a
0.5mM ethanol solution at 25 ◦C and pH 7. Response curves
were registered as the difference between steady-state signal
and base signal in oxygen-saturated buffer, as represented
in Fig. 1.
Low immobilised cell concentrations do not modify the
baseline of the biosensor in the presence of ethanol solution.
Increasing the cell concentration on the surface of the
membrane leads to a very low base signal for the microbial
biosensor. For a very high concentration of yeast cells, the
oxygen electrode could not detect dissolved oxygen around
the biocatalytic membrane. Membranes made by depositing
0.5 ml of a cell suspension with absorbance of 0.1 showed
the maximum variation of the potential. These membranes
were used for further experiments.