A biosensor using Chlorella microalgae immobilized on the membrane of an oxygen electrode has been designed to operate in the gas phase for determination of volatile organic compounds in the form of aerosols. Perchloroethylene (tetrachloroethylene) is used as an example to produce aerosols and vapours since it is toxic to the people working in dry-cleaning atmospheres and municipal treatment plants. A home-made controlled atmosphere chamber is constructed for perchloroethylene detection. Monitoring of perchloroethylene is achieved by the measurement of oxygen production during the algae photosynthetic process. The use of whole cells as bioreceptors allows the detection of a toxic aerosol in the gas phase without preliminary trapping of the analyte in solution.