Rapid assessment of Escherichia coli by growth rate on piezoelectric-excited millimeter-sized cantilever (PEMC) sensors

A piezoelectric-excited millimeter sized glass cantilever with a 1 mm2 sensing surface was fabricated for the purpose of detecting the growth of Escherichia coli (E. coli) JM101 in real-time. The resonance characteristic of the fundamental mode in air was 31.08 ± 0.01 kHz. Upon the addition of the agar film to the cantilever sensing surface the fundamental resonance frequency decreased by 2 ± 0.01 kHz. Upon subsequent inoculation of E. coli JM101, the fundamental frequency decreases an additional 0.1 ± 0.01 kHz. The E. coli was grown at 29 °C in a temperature-controlled chamber. The E. coli went through a lag phase of 1 h followed by a continuous decrease in resonant frequency due to growth of the bacteria. The total change in resonant frequency during the growth phase was 5.08 ± 0.01 kHz. After 6 h, the resonant frequency reached a constant value as growth ended. A model was developed to relate resonant frequency to specific growth rate (μ). The E. coli exhibited exponential growth rate of 1.31 ± 0.05 h−1 and a late exponential growth rate of 0.55 ± 0.05 h−1 which compared favorably with growth rate obtained in submerged culture of 1.28 ± 0.02 h−1 at 29 °C. The significance of the results is that microbial contamination in food processing plants can be assessed rapidly (<4 h) by measuring growth rate on piezoelectric-excited millimeter-sized glass cantilevers. Further, we compare its performance with QCM and find that PEMC is 1000 times more sensitive and 10 times quicker in establishing growth of bacteria.