  In this work is presented a microbalance for single microparticle sensing
based on resonating AFM cantilever. The variation of the resonator
eigenfrequency is related to the particle mass positioned at the free apex of
the cantilever. An all-digital phase locked loop (PLL) control system is
developed to detect the variations in cantilever eigenfrequency. Two particle
populations of different materials are used in the experimental test,
demonstrating a mass sensitivity of 15 Hz/pg in ambient conditions. Thereby it
is validated the possibility of developing an inexpensive, portable and
sensitive microbalance for point-mass sensing.
