Characterization of individual nanoparticles is a challenge due to the diffraction limit. To overcome this constraint we investigate the transfer of their optical properties to a mechanical degree of freedom of a larger object. From finite-difference time-domain computations, we estimate the mechanical frequency shift caused by metallic nanoparticles traveling through a microfluidic channel. Due to plasmonic effects we find relative shifts on the order of 1% for a 1 mW incident optical power for particles with radius ranging from 25 to 150 nm. The extreme sensitivity of this detection scheme enables real-time and in situ observation of optical dynamics at nanoscale.