A V-Shaped Microcantilever Sensor Based on a Gap Method for Real-Time Detection of E. coli Bacteria

This paper presents a dynamic-mode microcantilever sensor based on a gap method. The sensor has a V-shaped microcantilever and a fixed structure at a distance of 2 µm from its free end. The microcantilever is excited by applying an ac electric potential (3 V(p)) to its piezoelectric pads and vibrates at its fundamental resonant frequency. An independent ac electric potential (200 kHz, 15 V(pp)) is applied to the fixed structure. This creates a non-uniform electric field with its maxima at the gap and exerts a dielectrophoresis (DEP) force. The DEP force attracts and adsorbs the E. coli bacteria to the cantilever edge at the gap. The binding of the bacteria to the cantilever creates a shift in the resonant frequency of the microcantilever sensor, which is detected by a laser vibrometer. The real-time detection of E. coli bacteria samples, diluted in distilled water, was performed for concentrations of 10(5)–10(3) cells/mL and the real-time frequency shifts were −2264.3 to −755 Hz in 4 min, respectively. The tests were expanded to study the effect of the electric potential amplitude (10, 12, 15 V(pp)) and higher frequency shifts were observed for higher amplitudes.