Measurements and monitoring of concentrations of macromolecules in live cells and sub-cellular structures is of tremendous interest in cell biology and translational medicine. In this report we demonstrate a breakthrough potential of FLIM for real-time quantitative mapping of macromolecular distribution in the cell. In our approach we exploit a correlation existing between the fluorescence lifetime of fluorophores, refractive index and local concentrations of cellular macromolecules in the of fluorophore's microenvironment. We show a value of our approach for fundamental cell science and cellular diagnostic assays.
Experimental results on laser tweezers technology application for material science researche performed at the Institute for Lasers, Photonics and Biophotonics, University at Buffalo, SUNY are presented. Computer controlled dual-beam laser tweezers for highly efficient trapping and manipulation of micron and sub-micron size objects was designed and built. A novel technique for the calibration of laser tweezers that utilize two-photon excited fluorescence of commercial dye stained microspheres has been demonstrated. Laser tweezers technology has been used to monitor the bulk solution viscosity during the sol-gel gelation process at different depths from an interface. The gelation rate is the same in depth ranges 2 - 20 microns from the bounding surface. Optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystals with small and large birefringence was also demonstrated. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. Fast scanning beam multiple trap option of laser tweezers to construct and dynamically control micro-array structures was developed and characterized. Main parameters of scanning multiple trap setups were studied and optimized. Combination of optical trapping with the hot fluorescence phenomena has been used for local temperature monitoring in liquid samples,with under micron size resolution.
Laser tweezer trapping technology has been applied to monitor the bulk local solution viscosity during the sol-gel gelation process. The gelation rate is the same in depth ranges 2 - 20 microns from the bounding surface. Simultaneously with the laser tweezer study, a micro-viscosity kinetic measurement of the sol-gel process was performed using fluorescent anisotropy and quantum yield measurements. The differences between the bulk- and micro-viscosities obtained in the experiment reflect the intrinsic differences in solution environment sensed by the laser tweezer on the macro level and by other optical techniques within the probe microscopic environment.
Laser operation of passively Q-switched Nd3+:LSB microchip laser with Cr4+:YAG saturable absorber has been investigated theoretically and experimentally. Energy and temporal characteristics of sub-nanosecond output laser pulses have been studied using different combinations of output couplers and absorbers. Generalized model of Q-switched microchip laser has been proposed which takes into consideration thermalization and recombination in laser medium, spatial inhomogeneity of pump and laser intensity, and saturable absorber recovering. Good agreement between theory and experiment has been obtained for wide range of the pump power. Thermalization times of Nd3+ ions in LSB crystal has been estimated to our best knowledge for the first time.