Engineering topics

Wang, Gufeng

Publications and source records attributed to Wang, Gufeng.

6 records

DOE OSTI2013

Simultaneous Single-Particle Superlocalization and Rotational Tracking

Superlocalization of single molecules and nanoparticles has become an essential procedure to bring new insights into nanoscale structures and dynamics of biological systems. In the present study, superlocalization is combined with the newly introduced differential interference contrast (DIC) microscopy-based single-particle orientation and rotational tracking. The new technique overcomes the difficulty in localization of the antisymmetric DIC point spread function by using a dual-modality microscope configuration for simultaneous rotational tracking and localization of single gold nanorods with nanometer-scale precision. The new imaging setup has been applied to study the steric hindrance induced by relatively large cargos in the microtubule gliding assay and to track nanocargos in the crowded cellular environment. This technique has great potential in the study of biological processes where both localization and rotational information are required.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Rotational dynamics of cargos at pauses during axonal transport

Direct visualization of axonal transport in live neurons is essential for our understanding of the neuronal functions and the working mechanisms of microtubule-based motor proteins. Here we use the high-speed single particle orientation and rotational tracking technique to directly visualize the rotational dynamics of cargos in both active directional transport and pausing stages of axonal transport, with a temporal resolution of 2 ms. Both long and short pauses are imaged, and the correlations between the pause duration, the rotational behaviour of the cargo at the pause, and the moving direction after the pause are established. Furthermore, the rotational dynamics leading to switching tracks are visualized in detail. These first-time observations of cargo's rotational dynamics provide new insights on how kinesin and dynein motors take the cargo through the alternating stages of active directional transport and pause.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Electrophoretic Migration and Axial Diffusion of Individual Nanoparticles in Cylindrical Nanopores

Membranes with straight, vertical nanopores have found widespread applications in chemical and biological sciences, including separation, detection, catalysis, and drug delivery. They can also serve as a model system to understand molecular behavior and fundamental mechanisms of separation, bridging the gap between conventional model systems such as flat surfaces and real chromatographic stationary phases such as micrometer-sized porous particles. We recently found that the axial motion of individual biomolecules inside nanopores can be significantly slower than in bulk solution. This suggests that either chromatographic adsorption was present and/or the viscosity inside the nanopores was unusually high. In this study, we measured the electrophoretic motion as well as the axial diffusion of individual nanoparticles in cylindrical alumina nanopores. We found that the electrophoretic mobilities and the diffusion coefficients of polystyrene nanoparticles were both substantially smaller compared to bulk solution independent of particle size or pore diameter. The results imply that the apparent solution viscosity in nanodomains is anomalous.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Determining Full Three-Dimensional Orientation of Single Anisotropic Nanoparticles by Differential Interference Contrast Microscopy

Keeping track: By combining differential interference contrast (DIC) image pattern recognition with DIC polarization anisotropy, the exact full three-dimensional angular information of individual tilted gold nanorods positioned in the focal plane of the objective lens can be readily determined. The angular rotational modes and kinetics of individual in-focus gold nanorods can thus be resolved dynamically.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Detecting and Tracking Nonfluorescent Nanoparticles Probes in Live Cells

Precisely imaging and tracking dynamic biological processes in live cells are crucial for both fundamental research in life sciences and biomedical applications. Nonfluorescent nanoparticles are emerging as important optical probes in live-cell imaging because of their excellent photostability, large optical cross sections, and low cytotoxicity. Here, we provide a review of recent development in optical imaging of nonfluorescent nanoparticle probes and their applications in dynamic tracking and biosensing in live cells. A brief discussion on cytotoxicity of nanoparticle probes is also provided.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Whole-Cell Scan using Automatic Variable-Angle and Variable-Illumination-Depth Pseudo—Total Internal Reflection Fluorescence Microscopy

An automatic calibration and angle-scanning prism-type total internal reflection fluorescence microscope (TIRFM) was modified to function in both TIRFM and pseudo-TIRFM modes. When the incident angle of the excitation laser beam was controlled to be larger than the critical angle, the instrument served as a variable-angle TIRFM. A homemade computer program automatically calibrates the laser illumination spot in the sample to overlap with the center of the microscope's field of view. Then, by measuring the fluorescence intensities at different incident angles, the z-positions of fluorescent nanospheres close to the cell basolateral membrane can be extracted. When the incident angle is reduced to be in the subcritical range, the instrument works as a pseudo-TIRFM. The whole cell body from bottom to top can be imaged in a vertical scan process. Furthermore, the illumination field depth in the pseudo-TIRFM can be controlled by changing the incident angle or the horizontal position of the laser spot.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗