Picogram mass sensor using microcantilever

A microsensor with a picogram mass sensitivity has been developed using a harmonic vibration of microcantilever. The mass change of the adsorbed molecules on the cantilever was measured by the resonance frequency shift. We constructed a prototype vibrator sensor using a piezoresistive cantilever. A detection system of the resonance frequency shift was formed by Wheatstone bridge circuits, positive feedback controller, a piezoactuator and a phase-locked loop (PLL) demodulator. As experimental results, a mass sensitivity of 0.32 pg/Hz was obtained from water molecular adsorption on the cantilever in air. We confirmed that the mechanism of water molecular growth has 2 modes of island growth and layer growth.