In situ measurement of single-nanoparticle refractive index via electrically modulated optical tweezers

Accurate measurement of the refractive index of nanoparticles is a core challenge in basic science and multi-disciplinary application. The current methods usually involve statistical analysis of the particle group, which reduces the measurement accuracy and ignores the individual characteristics. Based on the photomechanical regulation mechanism, the research constructed an optical tweezers and electric field synergistic platform, and realized the in-situ dynamic measurement of the refractive index of single- nanoparticles through the composite drive of periodic electric field and direct-current field. By driving the sensing unit to change the equilibrium position, the sub-wavelength size optical field is accurately measured, and the nanoscale physical information under the force equilibrium state is measured. This method is sensitive to the refractive index of typical particles such as SiO₂ and PS. It can distinguish different types of particles and different states of particles based on real-time detection of refractive index measurement, with a maximum standard deviation of 4.9 %.