Optically trapped particle dynamic responses under varying frequency sinusoidal stimulus

Abstract

Optical tweezers have become indispensable and powerful micro-manipulation tools and acute force probes in biomedical fields. Therefore, calibrating the optical trap is essential for precise force measurements in biomolecular interactions. Currently, however, mainstream calibration methods mainly focus on analyzing nanometer level Brownian motions of trapped particles. There is thus an urgent need to investigate trapped particle dynamic processes in slightly large range to address practical situations for the biological application of optical tweezers. This paper proposes a varying frequency sinusoidal excitation method to probe trapped particle responses and develops a mathematical model to extract trap stiffness. Experimental results revealed that the proposed method achieved significantly lower relative error ( < 5%) even when particle size or laser power varied, and that the excitation frequency didn’t have much impact on trap stiffness. Thanks to its simplicity, effectiveness and robustness, our method provides an ideal candidate for further picoNewton force measurement studies for dynamic interactions in biomedical applications.