Sensing Escherichia coli O157：H7 via frequency shift through a self-assembled monolayer based QCM immunosensor

By means of the specific immuno-recognition and ultra-sensitive mass detection, a quartz crystal microbalance （QCM） biosensor for Escherichia coli O157：H7 detection was developed in this work. As a suitable surfactant, 16-mercaptohexadecanoic acid （MHDA） was introduced onto the Au surface of QCM, and then self-assembled with N-hydroxysuccinimide （NHS） raster as a reactive intermediate to provide an active interface for the specific antibody immobilization. The binding of target bacteria with the immobilized antibodies decreased the sensor＇s resonant frequency, and the frequency shift was correlated to the bacterial concentration. The stepwise assembly of the immunosensor was characterized by means of the electrochemical techniques. Using the immersion-dry-immersion procedure, this QCM biosensor could detect 2.0×10^2 colony forming units （CFU）/ml E. coli O157：H7. In order to reduce the fabrication time, a polyelectrolyte layer-by-layer self-assembly （LBL-SA） method was adopted for fast construction. Finally, the reproducibility of this biosensor was discussed.