Photonic forcemicroscope calibration by thermal noise analysis

The forces of a photonic force microscope based on optical tweezers are determined using the Boltzmann distribution of thermally driven position fluctuations. As a fundamental method, only a minimum of information about the system is required, i.e. the solution's temperature. This calibration method provides detailed information about the trapping potential with nanometer resolution. In contrast to other calibration methods, no numerical hydrodynamic corrections are necessary. The lateral force constant of the optical trap was measured along the optical axis and found to decrease linearly by ≈ 8%/μm for a latex bead 600 nm in diameter. Oscillations in the lateral force constant were found along the optical axis close to the surface.