Characteristic Rotational Behaviors of Rod-Shaped Cargo Revealed by Automated Five-Dimensional Single Particle Tracking

Abstract

We report an automated single particle tracking technique for tracking the x, y, z coordinates, azimuthal and elevation angles of anisotropic plasmonic gold nanorod probes in live cells. These five spatial coordinates are collectively referred to as 5D. This method overcomes a long-standing challenge in distinguishing rotational motions from translational motions in the z-axis in differential interference contrast microscopy to result in full disclosure of nanoscale motions with high accuracy. Transferrin-coated endocytic gold nanorod cargoes initially undergo active rotational diffusion and display characteristic rotational motions on the membrane. Then as the cargoes being enclosed in clathrin-coated pits, they slow down the active rotation and experience a quiet period before they restore active rotational diffusion after fission and eventually being transported away from the original entry spots. Finally, the 3D trajectories and the accompanying rotational motions of the cargoes are resolved accurately to render the intracellular transport process in live cells.

High Fluid Velocity and Narrow Channels Enhance the Influences of Particle Shape on Colloid Retention in Saturated Groundwater Systems Under Favorable Deposition Conditions

“…Retention of spheres decreased when velocity was increased from 5 to 200 m/day (Figure 3A vs. Figure 3B), as expected from filtration theories (Yao et al, 1971;Rajagopalan and Tien, 1976;Ma et al, 2009;Ma and Johnson, 2010;Nelson and Ginn, 2011;Fang et al, 2018). As shown in Figure 2C, spherical colloids tend to follow flow streamlines, higher fluid velocity caused spheres to be transported downstream faster by convection, which led to decreased retention out of the fixed number of injected spheres compared to lower velocity.…”

“…media representations such as Happel sphere-in-cell model, or hemispheres-in-cell model (Rajagopalan and Tien, 1976;Ma et al, 2009;Ma and Johnson, 2010;Nelson and Ginn, 2011;Fang et al, 2018). Also, from colloidal filtration theories, retention of small size spheres (e.g., < 1 µm in diameter) were mostly due to Brownian motions (specifically, Brownian translation only, since Brownian rotation is irrelevant for homogeneous spheres), whereas retention of large size spheres (e.g., > 1 µm in diameter) were due to gravitational settling effect.…”

“…However, the impacts of particle shape on colloidal pollutant migration in groundwater systems are not well-understood. In conjunction with particle shape, many other factors could influence particle transport and retention, such as colloid size, colloid surface property, fluid shear, direction of flow in relation to gravity, and the dimension, contour, and surface properties of flow channels (Yao et al, 1971;Johnson et al, 2007Johnson et al, , 2010Ma et al, 2011a,b;Nelson and Ginn, 2011;Trauscht et al, 2015;Fang et al, 2018). Understanding the influences of particle shape along with factors mentioned above on particle transport and deposition is important to a variety of processes, including contaminant removal from groundwater flow (Chen et al, 2017;Ta et al, 2018), tracking contaminant fate (Mendez et al, 2018), design of microfluidic devices (Gervais and Jensen, 2006;Unni and Chun, 2009;Sen Gupta, 2016), in view of the fact that the majority of natural or engineered particles encountered in these processes, such as clay particles, heavy metals, agglomerates, bacteria, or polymer molecules are often non-spherical in shape (Salerno et al, 2006;Wang and Keller, 2009;Doshi et al, 2010).…”