Whole-cell MEMS biosensors for toxicity detection

At the heart of every biosensor is a biological entity, the purpose of which is to react with the target analyte(s) and generate a readily quantifiable signal. Traditional biosensors are based on the unique specificity of enzymes to their substrates, antibodies to antigens or that of nucleic acids to their complementary sequences. In recent years we have promoted the use of a different concept, that of whole cell biosensors. An intact live cell, containing a selected gene promoter fused to a reporter gene, serves both as the sensing and the reporting element; the specificity of the system is controlled by the choice of promoter. Using this approach we have constructed microbial sensing systems for the environmental detection of toxicants, genotoxicants, oxidants, and specific groups of halogenated organics, as well as cyanobacterial sensors of nutrients bioavailability. In order to turn these cells into a "real" biosensors, they need to be immobilized onto a solid platform and coupled into the signal transduction apparatus. Several directions that were pursued to achieve this aim will be mentioned including agar immobilization onto microtiter plates, alginate encapsulation at the tips of optic fibers, antibody-mediated adhesion to glass surfaces, embedding into sol-gel matrices and, most recently, integration into specialized biochip. The latter option will be described in detail.