Unveiling Cellular Internalization Dynamics of Single Gold Nanorods by Tracking Their Orientational and Translational Motions

Abstract

Single nanoparticle tracking (SPT) is a unique and powerful tool to investigate the interaction between nanoparticles and cells, which is of considerable importance for nanotechnology applications in biomedical fields and in-depth understanding of biological activities. However, previous work typically focused on translations of single nanoparticles while they undergo both translational and rotational motions. In this study, we obtained both the translational and rotational dynamics of single gold nanorods during their cellular internalization process using dual-channel polarization microscopy. In particular, the azimuth and polar angles were integrated into a polar coordinate system to obtain three general orientation distribution patterns, found to have a close relationship with the nanoparticle cellular internalization process and time-dependent alterations. Moreover, the patterns accompanied by trajectories, translational and rotational coefficients, the azimuth and polar angles, and other parameters provided a wealth of knowledge on the nanoparticle cellular internalization dynamics with unprecedented details. We observed that the gold nanorods could initially assume a tip-first quick rotation state with partially restricted orientations, then change to a strongly confined near-vertical insertion state with slight angular fluctuations, and eventually transform into a random and fast rotation state. Our methodology opens up a new avenue for a detailed understanding of biological processes.