Three-dimensional single-particle tracking by interferometric scattering microscopy with a double-helix point spread function

Abstract

Abstract Single-particle tracking (SPT) is an immensely valuable technique to study a variety of processes in the life sciences and condensed matter physics. Interferometric scattering (iSCAT) microscopy is a sensitive SPT technique that can track individual unlabeled particles with high spatial and temporal resolution. A difficulty in iSCAT is the low imaging contrast of its original image, and complicated imaging postprocessing method is necessary for deriving axial-location of the particle. Here, a planar photonic chip enhanced spin-to-orbital angular momentum conversion was introduced to the iSCAT microscopy, resulting in an axial-localization dependent double-helix point-spread-function (PSF) and high imaging contrast. This provides a new mechanism for 3D SPT over an extended axial-range in a label-free manner without use of complicated image postprocessing and optical components. The iSCAT microscopy was used to record the 3D trajectory of microbead labeled to the flagellum, facilitating precise analysis of the fluctuation in the motor dynamics. The enhanced iSCAT technique holds great promise for future applications in biological science.