Figure 7.

Mass sensing strategies. (a) Dynamic mode: the mass adsorbed on the surface of the cantilever causes changes in both its effective mass and stiffness, resulting in a shift in the resonance frequency, $\delta f_0$, to lower or higher values, depending on which effect dominates (red and green spectra). (b) Static deflection mode: the sensor deflects by a quantity $\delta z$ due to intermolecular interactions at the surface of the sensor. In the case of a DNA biosensing experiment, the surface stress is due to the electrostatic repulsion between the molecules at the surface when complementary DNA (red strands) hybridizes with the initially immobilized DNA probes (green strands).