Single microparticles mass measurement using an AFM cantilever resonator
  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. 
Marco Mauro, Raffaele Battaglia, Gianluca Ferrini, Roberto Puglisi,   Donatella Balduzzi and Andrea Galli
physics.ins-det