Resonant cantilever sensors operated in a high-Q in-plane mode for real-time bio/chemical detection in liquids

A high quality-factor (Q-factor) in-plane-mode resonant cantilever sensor is developed for real-time bio/chemical detection in liquids. With electrothermal excitation and piezoresistive frequency read-out integrated, the proposed sensor is realized by micromachining technology. The in-plane mode cantilever resonator can substantially decrease the liquid drag force, comparing to conventional out-of-plane resonance-mode cantilever, thereby, having achieved a much higher Q-factor of 249 when the cantilever is connected with a phase-lock-loop (PLL) interface circuit in water. After the mass sensitivity is calibrated by specifically binding streptavidin-labeled Dynabeads with the biotin-immobilized cantilever in phosphate buffered saline (PBS) solution, specific-antibody immobilized cantilevers have been used in real-time detection of Escherichia coli in PBS solution. Real-time detection of Hg2+ ions in aqueous Hg(NO3)2 is also carried out by using sensing-group-modified cantilevers, resulting in a finer noise-limited resolution than 100 ppb.