Small cantilevers for force spectroscopy of single molecules

Abstract

We have used a simple process to fabricate small rectangular cantilevers out of silicon nitride. They have lengths of 9–50 μm, widths of 3–5 μm, and thicknesses of 86 and 102 nm. We have added metallic reflector pads to some of the cantilever ends to maximize reflectivity while minimizing sensitivity to temperature changes. We have characterized small cantilevers through their thermal spectra and show that they can measure smaller forces than larger cantilevers with the same spring constant because they have lower coefficients of viscous damping. Finally, we show that small cantilevers can be used for experiments requiring large measurement bandwidths, and have used them to unfold single titin molecules over an order of magnitude faster than previously reported with conventional cantilevers.