A method for measuring mass of a micro- and nano-sized particle. The method includes placing the micro- or nano-sized particle on a resonator having an oscillator and a first and second cantilevered arms with interdigitating finger, energizing the oscillator at a selective frequency thereby causing mechanical vibration in the first and second cantilevered arms, directing a light beam from a light source onto the interdigitating fingers, sensing intensity of light of the reflected diffraction pattern by at least one photodetector positioned about at least one of the modes, varying the frequency by sweeping a range of frequencies and correlating the sensed intensity to mass to thereby determine the mass of the micro- or nano-sized particle.