Membrane ruffling is an essential process at the leading edge of the migrating cells, which contains protrusion and retraction of plasma membrane. The extension membrane determines the direction of migration. The dynamic of membrane ruffling depends on the interaction between filament actin and motor proteins. Upon the activation of motor proteins by calcium ions, the migration process starts. Therefore, it is important to study the correlation between local calcium concentration and the membrane dynamics. To study the dynamics of the membrane ruffling, we established several stable cell lines, which contain chemical and optogenetic inducible dimerization . In addition, the proteins of interest such as actin, myosin, membrane anchors and calcium indicators were labeled with fluorescence proteins. The dynamics of membrane ruffling was investigated by lattice light-sheet microscope (LLSM), which is capable of high spatial and temporal recording over three-dimensions.
Optical imaging techniques provide much important information in understanding life science especially cellular structure and morphology because “seeing is believing”. However, the resolution of optical imaging is limited by the diffraction limit, which is discovered by Ernst Abbe, i.e. λ/2(NA) (NA is the numerical aperture of the objective lens). Fluorescence super-resolution microscopic techniques such as Stimulated emission depletion microscopy (STED), Photoactivated localization microscopy (PALM), and Stochastic optical reconstruction microscopy (STORM) are invented to have the capability of seeing biological entities down to molecular level that are smaller than the diffraction limit (around 200-nm in lateral resolution). These techniques do not physically violate the Abbe limit of resolution but exploit the photoluminescence properties and labelling specificity of fluorescence molecules to achieve super-resolution imaging. However, these super-resolution techniques limit most of their applications to the 2D imaging of fixed or dead samples due to the high laser power needed or slow speed for the localization process. Extended from 2D imaging, light sheet microscopy has been proven to have a lot of applications on 3D imaging at much better spatiotemporal resolutions due to its intrinsic optical sectioning and high imaging speed. Herein, we combine the advantage of localization microscopy and light-sheet microscopy to have super-resolved cellular imaging in 3D across large field of view. With high-density labeled spontaneous blinking fluorophore and wide-field detection of light-sheet microscopy, these allow us to construct 3D super-resolution multi-cellular imaging at high speed (~minutes) by light-sheet single-molecule localization microscopy.
Self-assembly is a commonly used strategy in synthesis and fabrication. One of the most economic routes for the fabrication of large ensembles of functional nanosystem is to utilize self-assembly to assemble building blocks such as colloids, nanotubes and nanowires. However, if the functional nanostructures are to be assembled across many length scales within the integrated system, it is necessary to develop new tools for large-scale assembly of nanostructures and manipulation of individual components. Here we report a simple approach to actively control the formation of the self-assembled colloidal crystals in the two-dimensional microfluidic networks. Utilizing a combination of electrocapillary forces and evaporation induced self-assembly, it is possible to actively control the self-assembly process of the colloidal nanoparticles to form colloidal crystals inside the two-dimensional microchannel networks. Using this approach, we can not only selectively fabricate the colloidal crystals in the desired channels, but we can also build colloidal crystals with different optical properties in different channels or in the same channel. This method is not limited to the fabrication of colloidal crystals. In general, it can be configured to produce other novel functional materials using self-assembly process when it is integrated with more sophisticated microfluidic system.
Inspired by the water-repellent behavior of the micro- and nano-structured plant surfaces, superhydrophobic materials, with a water contact larger than 150 degree, have received a lot of research attentions recently. It has been suggested that contamination, oxidation and current conduction can be inhibited on such superhydrophobic surfaces, and the flow resistance in the microfluidic channels can also be reduced using super water-repellent materials. In order to prepare superhydrophobic materials, we have developed two simple approaches for fabricating tunable superhydrophobic surfaces using nanosphere lithography and plasma etching. In the first case, the polystyrene nanospheres were employed to create well-ordered rough surfaces covered by gold and alkylthiols. Using oxygen plasma treatment, the topmost surface area can be modified systematically, as the result the water contact angle on such surfaces can be tuned from 132 to 170 degree. The water contact angles measured on these surfaces can be modeled by the Cassie’s formulation without any adjustable parameter. In the second approach, thin films of Teflon were spin-coated on the substrate surfaces and treated by oxygen plasma. Superhydrophobic surfaces with water contact angle up to 170 degree were obtained by this approach. If the ITO glasses were used as the substrates, the hydrophobicity of the surface can be tuned by applying DC voltage. Water contact angle can be adjusted from 158 degree to 38 degree.
A two-dimensional Z-scan technique employing a CCD camera was used to study the nonlinear optical parameters of materials. Using the known beam distribution at the lens plane, measured by the CCD camera, and the split step beam propagation method, we simulate the evolution of the beam profile within the sample. This technique may be applied to any arbitrary beam distribution and sample thickness. We applied our two- dimensional Z-scan technique for the investigation of zinc tetraphenyltetrabenzoporphyrin and three azulene-containing donor-acceptor compounds. It was found that some samples exhibit strong nonlinear refraction while others show strong nonlinear absorption. The use of these materials in optical limiting devices is discussed.
Nanosecond x-ray pulses have been used for time resolved x- ray diffraction to measure the transient structure of Pt and GaAs crystals caused by laser pulse heating. A direct imaging x-ray CCD system with high spatial resolution allows the detection for the lattice deformations of the order of 10-4 A, induced by a laser pulse energy of a few millijoules.
Recently some phthalocynine derivatives have been reported to exhibit a strong optical limiting effect which is due
to their large reverse saturable absorption. In this report we present another close family of phthalocynine, meso-substituted
tetrabenzoporphyrins. We have employed both modified Z-scan techniques which uses a CCD camera as the detector and
picosecond transient spectroscopy to study the optical power limiting mechanism of the meso-substituted tetrabenzoporphyrin
derivatives. With the aid of a CCD detector, a two dimensional image of the beam, in the far field can be obtained directly in
the Z-scan experiments. By integrating different parts of the image, both "closed aperture" and "open aperture" information
can be calculated at the same time. In the kinetics measurements, several characteristic (ir,ir*), (,*) and (d, d) transitions
have been observed, and the absorption cross sections and the relaxation rates of each transient has been measured.
We present some of our experimental results for the generation of picosecond x-ray pulses by means of a diode driven by ultrashort ArF laser pulses. Hard x-ray pulses with duration in the range 1-100 ps have been generated at a repetition rate of 300 Hz. Some applications of this system to picosecond time resolved x-ray diffraction from laser heated crystals are reported.
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