Picogram Mass Sensor Using Resonance Frequency Shift of Cantilever

A microsensor with a picogram mass sensitivity has been researched using the resonance frequency shift of an atomic force microscope (AFM) cantilever. The mass change of the water molecules adsorbed on the cantilever was measured by analyzing the resonance frequency shift using a laser beam deflection detection system. As experimental results, a sensitivity of about 2 pg/Hz was obtained. The mass change due to increasing humidity showed that the mechanism of water molecular growth changed from an island growth to a layer growth. The critical point of the mechanism change was a humidity of about 60%. The adsorbed mass corresponds to a water layer of about 12 monolayers.