Development of a biosensor for E. coli based on a flexural plate wave (FPW) transducer

To fulfill the need for rapid, cost-effective and sensitive methods for the detection of bacteria in medical diagnostics, food technology, biotechnology and environmental monitoring, a development of a bacterial sensor was initiated. Our approach of a biosensor for E. coli is based on an acousto-gravimetric flexural plate wave (FPW) transducer (gravimetric detection limit of less than 6 ng in a 32 μm thick sensitive layer in aqueous media), and an immunoaffinity layer on the transducer membrane for the molecular recognition of the target bacteria. An intermediate layer of covalently coupled poly(acrylic acid) yielded a major reduction of the non- specific binding to the metal surface. Such a biosensor, using antibodies against E. coli K12 and E. coli J5 outer surface antigens, yielded a detection range of 3.0 x 10⁵ to 6.2 x 10⁷ cells/ml for samples with the corresponding bacteria. To increase the sensitivity further, an amplification method using microspheres coupled with antibodies against E. coli was tested as a sandwich assay, and up to now a five-fold amplification of the signal has been achieved.