Photothermal modulation for oscillating mode atomic force microscopy in solution

Solution imaging using resonant techniques for atomic force microscopy is greatly simplified by driving the cantilever directly. We have taken advantage of the temperature-sensitive bending properties of metal-coated silicon nitride cantilevers to induce vibrations in the lever using a modulated laser. We demonstrate that photothermal modulation with a nominal 2 mW laser in solution produces a single resonance, typically, of 8–20 nm amplitude, that can be used for imaging. We present high-quality images of DNA on a mica surface to show the capabilities of this technique for solution imaging.