Small Cantilever AFM for Single Molecule Force Spectroscopy

AFM-based single molecule force spectroscopy has developed into a standard method to gain information about molecular elasticities, internal structural transitions and binding forces and kinetics of single (bio-)+molecules. The sensitivity and the resolution of these force spectroscopy measurements are inherently connected to the properties of the cantilevers used in these experiments. The spring constant of the cantilever determines its sensitivity, due to Hooke's law. The coefficient of viscous damping and the resonance frequency of the cantilever determine the resolution of the measurement. In case of the coefficient of viscous damping this is due to the fact, that the Nyquist theorem is valid for the thermal white noise of the cantilever. In case of high resonance frequencies, bandpassfiltering between 1/f-noise and the resonance peak reduces noise without loss of information about the force-distance-dependency of the molecule. Small cantilevers (length: < 30mm, width: < 10 mm, thickness: < 200 nm) show all necessary properties for force spectroscopy: small spring constants, low viscous damping and high resonance frequencies. We present an AFM that is capable of using small cantilevers for force spectroscopy experiments of single biomolecules and our current results.