QCM immunosensor with nanoparticle amplification for detection of Escherichia coli O157:H7

A quartz crystal microbalance (QCM) immunosensor was developed and evaluated for detection of Escherichia coli O157:H7. The immunosensor was fabricated by self-assembling of protein A and affinity-purified anti-E. coli O157:H7 antibodies on the gold electrode of an AT-cut piezoelectric quartz crystal. To enhance the sensitivity of the QCM immunosensor, nanoparticle-antibody conjugates, which were prepared using streptavidin-conjugated nanoparticles (145 nm diameter) and biotinylated anti-E. coli antibodies, were used for signal amplification. After the binding of E. coli O157:H7 cells with the antibodies immobilized on the electrode, nanoparticle-antibody conjugates were introduced as mass amplifiers. Compared to the direct detection of E. coli O157:H7, the binding of the nanoparticle conjugates further resulted in a decrease in resonant frequency and an increase in resonant resistance, and the detection sensitivity was improved by five orders of magnitude by lowering the detection limit from 107 to 102 CFU/mL. The sensor specificity and nonspecific adsorption of nanoparticle-antibody conjugates were also investigated.