237 / 2024-08-19 10:12:19

One-dimensional photonic crystal enhancing spin-to-orbital angular momentum conversion for single-particle tracking

Single-particle tracking,one-dimensional photonic crystal,interferometric scattering imaging,double-helix point spread function

Single-particle tracking (SPT) is a valuable technique for investigating a range of processes in life sciences and physics. It can help researchers better understand the positions, trajectories, and interactions of individual objects within highly dynamic systems or over prolonged imaging periods. Here, we propose an all-dielectric one-dimensional photonic crystal (1D PC) that significantly enhances the conversion of spin to orbital angular momentum for three-dimensional (3D) SPT applications. This well-designed 1D PC can serve as a substrate for optical microscopy. We integrate this enhancement effect into the interferometric scattering imaging (iSCAT) technique, resulting in a double-helix point spread function (DH-PSF). The DH-PSF offers more uniform Fisher information for 3D positional estimation compared to traditional microscopy point spread function. Specifically, it encodes the axial position of a single particle into the angular orientation of the DH-PSF lobes, thus providing a means for 3D SPT. This method addresses the challenge in iSCAT for 3D tracking: the issue of multiple contrast inversions when a particle moves along the axial direction. In addition, due to the inherent coaxial interference properties, it also has the advantages of high sensitivity and high temporal resolution of iSCAT technique. By employing DH-PSF in iSCAT microscopy, we successfully tracked the 3D trajectory of a single microbead attached to a flagellum, enabling detailed analysis of motor dynamics fluctuations. Additionally, we demonstrated the capability to track single nanoparticles, such as the 3D diffusion trajectories of 20 nm gold nanoparticles in a glycerol solution. The DH-PSF iSCAT technique, facilitated by a 1D PC, shows great promise for future applications across physical, biological, and chemical sciences.