Femtogram mass detection using photothermally actuated nanomechanical resonators

Nanomechanical devices with very small mass and size have the potential for mass sensing at the level of individual molecules. In the present study, we designed nanomechanical mass sensors, demonstrated their operation under ambient pressure and temperature, and achieved femtogram-level mass sensitivity. Our nanomechanical resonators were gold-coated silicon cantilevers with resonance frequencies in the range of 1 to 10 MHz, characteristic thicknesses of 50-100 nm, and force constants of about 0.1 N/m. Using a cantilever with a resonant frequency of 2.2 MHz that was excited photothermally, we measured a mass change of 5.5 fg upon chemisorption of 11-mercaptoundecanoic acid. Our analysis indicates that, by decreasing the mass of the cantilever and increasing the excitation amplitude, even higher mass sensitivity can be realized in an easily accessible frequency range (<100 MHz). (C) 2003 American Institute of Physics.