The authors present a theoretical model to predict the resonance frequency shift due to molecule adsorption on micro- and nanocantilevers. They calculate the frequency shift experienced by cantilevers made of either silicon or the polymer SU-8, when two adsorbates, myosin protein and an alkanethiol, are attached to the cantilever surface. They demonstrate that the effect of the adsorbate stiffness can be comparable or even larger than the mass effect, producing positive frequency shifts. The results provide methods for decoupling both opposite effects and routes for the design of resonators with high sensitivity to molecule adsorption based on either stiffness or mass effects.

We report the selective excitation of the flexural modes of microcantilevers in aqueous solutions, by applying the photothermal excitation technique. The experiments show that a particular vibration mode can be efficiently excited by focusing the intensity-modulated laser beam on regions of high curvature of the vibration shape. In addition, the resulting resonant peaks in liquid appear distorted by an amplitude component that decreases with the frequency. This distortion produces a shift of the resonance to lower frequencies. A theoretical model based on the transformation of optical energy into mechanical energy via an intermediate thermal stage is proposed to interpret the experimental results. The theory shows that the driven oscillation of the cantilever depends on the curvature of the eigenmode at the excitation position and the heating induced by the excitation laser, which decreases with the frequency. The results reported here set the basis for efficient excitation of high vibration modes in liquids and for optimized design of optically driven microresonators.

Resonant microcantilevers are being actively investigated as sensitive mass sensors for biological detection. By performing experiments of adsorption of the bacteria Escherichia coli on singly clamped microcantilevers, we demonstrate that the effect of the added mass is not the only and may not be the main origin of the response of these sensors. The experiments show that the magnitude and sign of resonance frequency shift both depend critically on the distribution of the adsorbed bacterial cells on the cantilever. We relate this behavior to the added mass that shifts the resonance to lower frequencies and the higher effective flexural rigidity of the cantilever due to the bacteria stiffness that shifts the resonance to higher frequencies. Both effects can be uncoupled by positioning the cells where each effect dominates, near the free cantilever end for measuring the added mass or near the clamping for measuring the increase of flexural rigidity.

An analytical model for predicting the deflection and force of a bimaterialcantilever is presented. We introduce the clamping effect characterised by an axial loadupon temperature changes. This new approach predicts a non linear thermal dependence ofcantilever strain. A profilometry technique was used to measure the thermal strain.Comparison with experimental results is used to verify the model. The concordance of theanalytical model presented with experimental measurements is better than 10%