We present here a method to calibrate the lateral force in the atomic force microscope. This method makes use of an accurately calibrated force sensor composed of a tipless piezoresistive cantilever and corresponding signal amplifying and processing electronics. Two ways of force loading with different loading points were compared by scanning the top and side edges of the piezoresistive cantilever. Conversion factors between the lateral force and photodiode signal using three types of atomic force microscope cantilevers with rectangular geometries (normal spring constants from 0.092 to 1.24 N/m and lateral stiffness from 10.34 to 101.06 N/m) were measured in experiments using the proposed method. When used properly, this method calibrates the conversion factors that are accurate to +/-12.4% or better. This standard has less error than the commonly used method based on the cantilever's beam mechanics. Methods such of this allow accurate and direct conversion between lateral forces and photodiode signals without any knowledge of the cantilevers and the laser measuring system.

Compared with the first flexure mode, higher resonant modes of the microcantilever-based mass sensor promise enhanced sensitivities in bio/chemical mass detection due to higher quality factors. Therefore, the first torsional mode is employed in our research for improved resolution of mass detection. Aiming at accurate characterization of the first torsional mode and further detection of the multi-mass attached to the microcantilevers, a model based on the Rayleigh–Ritz method, considering the attaching positions of the micro/nanoobjects adhered to the microcantilever, is presented. A ragweed pollen, as a target mass, was located at different positions on a commercial microcantilever for the contrasting experiments of the first and second flexures and the first torsional modes of the ‘cantilever–object’ system in air. Experimental results show that the mass sensitivity of the first torsional mode is an order higher than that of the first bending mode within the realm of existing commercial microcantilevers. The proposed model was further validated by the multi-mass detection results.

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