A whole-cell biosensor has been designed to operate in the gas phase for determination of vapours of solvents. Methanol was chosen as an example of a volatile organic solvent to evaluate the algae sensor reponse. The use of whole cells as bioreceptors allows detection of those compounds in the gas phase without preliminary trapping of the analytes in a solution. In addition, near real-time monitoring is possible by the measurement ohf the algae photosynthetic activity with an oxygen electrode.