Regenerable ZnO/GaAs Bulk Acoustic Wave Biosensor for Detection of Escherichia coli in ``Complex'' Biological Medium

A regenerable bulk acoustic wave (BAW) biosensor is developed for the rapid, label-free and selective detection of Escherichia coli in liquid media. The geometry of the biosensor consists of a GaAs membrane coated with a thin film of piezoelectric ZnO on its top surface. A pair of electrodes deposited on the ZnO film allows the generation of BAWs by lateral field excitation. The back surface of the membrane is functionalized with alkanethiol self-assembled monolayers and antibodies against E. coli. The antibody immobilization was investigated as a function of the concentration of antibody suspensions, their pH and incubation time, designed to optimize the immunocapture of bacteria. The performance of the biosensor was evaluated by detection tests in different environments for bacterial suspensions ranging between 10(3) and 10(8) CFU/mL. A linear dependence between the frequency response and the logarithm of E. coli concentration was observed for suspensions ranging between 10(3) and 10(7) CFU/mL, with the limit of detection of the biosensor estimated at 10(3) CFU/mL. The 5-fold regeneration and excellent selectivity towards E. coli detected at 10(4) CFU/mL in a suspension tinted with Bacillus subtilis at 10(6) CFU/mL illustrate the biosensor potential for the attractive operation in complex biological media.