Background-Free Imaging of a Viral Capsid Proteins Coated Anisotropic Nanoparticle on a Living Cell Membrane with Dark-Field Optical Microscopy

Abstract

Exploring the diffusion dynamics of a viral capsid proteins (VCP)-functionalized nanocarrier on a living cell membrane could provide much kinetic information for the better understanding of their biological functionality. Gold nanoparticles are an excellent core material of nanocarriers because of the good biocompatibility as well as versatile surface chemistry. However, due to the strong scattering background from subcellular organelles, it is a grand challenge to selectively image an individual nanocarrier on a living cell membrane. In this work, we demonstrated a convenient strategy to effectively screen the scattering background from living cells for single-particle imaging with a polarization-resolved dual-channel imaging module. By taking advantage of the polarization of anisotropic gold nanoparticles (gold nanorods, GNRs), the signals from cell components could be counteracted after subtracting the sequential images one by one, while those transiently rotating GNRs on the cell membrane still exist in the processed image. In contrast to the previously reported methods, this method does not require a complicated optical setup alignment and sophisticated digital image analysis process. According to the single-particle imaging results, the majority of VCP-GNRs were anchoring on the cell membrane with confined diffusion. Interestingly, on further inspection of the diffusion trajectories, the particles displayed anomalous confined diffusion with randomly distributed large walking steps during the whole track. Non-Gaussian step distribution was noted, indicating heterogeneous binding and desorption processes on the cell membrane. As a consequence of the robust background screening capability, this approach would find broad applications for single-particle imaging under a noisy environment, e.g., living cells.

Individual Plasmonic Nanoprobes for Biosensing and Bioimaging: Recent Advances and Perspectives

“…[ 226,227 ] Ye and coworkers addressed this limitation using a polarization‐resolved dual channel imaging module. [ 228 ] The scattered signals of the interfering background from polarization‐resolved dual channels had negligible fluctuations while those of AuNRs had noticeable intensity differences, offering the opportunity to screen the interfering scattering background inside the cell by subtracting sequential images from a polarization‐resolved dual channel detector. With this strategy, the authors tracked the diffusion dynamics of viral capsid proteins (VCPs)‐coated AuNRs on living cell membrane and found that the particles displayed anomalous confined diffusion with randomly distributed large walking steps.…”

The video-rate imaging of sub-10 nm plasmonic nanoparticles in a cellular medium free of background scattering

“…Even some background scavenging reagents, background smoothing algorithms, etc., have been tried to reduce the intracellular scattering background, however, such problem has not been fully solved. [25][26][27][28] To detect small plasmonic nanoparticles, several types of photothermal imaging methods were developed based on plasmonic resonance absorption instead of scattering, since the absorption cross section of nanoparticles scales down with three power of particle size (slower than scattering). Laser scanning photothermal imaging is able to detect nanoparticles down to a few nanometers, and enable high resolution imaging of cellular structure.…”

Single-particle tracking discloses binding-mediated rocking diffusion of rod-shaped biological particles on lipid membranes

“…Particularly, for rod-like particles, comprehensive theoretical calculations illustrate that the diffusivity is much higher than that of their spherical counterparts in biological matrices 16–18. Transient adhesive interactions with the host matrix play key roles in such anomalous diffusion 19–21. Recent explorations also found that elongated rod-shaped inorganic particles exhibit a noticeable cellular translocation efficiency with size dimensions comparable to those of bacteria through carefully manipulating the surface chemistry 3.…”