Determining trap compliances, microsphere size variations, and response linearities in single DNA molecule elasticity measurements with optical tweezers

Optical tweezers are a powerful tool in biophysics due to the ability to manipulate single biomolecules [1,2]. For dual-trap tweezers with a steerable beam and force detection via back focal plane interferometry and a position sensitive detector [3,4], calibration can be done by stretching single DNA molecules [5,6]. Typically, DNA stretching provides accurate values for 𝛼, the force scale factor that converts from bead displacement from the trap to force, and 𝛽, the conversion between rotation of the piezoelectric controlled mirror and the linear displacement of the movable trap. Determining trap compliance using this method relies on nonlinear fitting that may be sensitive to noise and drift