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On Going Research Work at ILPB

1. CARS/SHG/SFG/TPEF imaging setup.

We showed that biocompatible zinc oxide (ZnO) NCs having non-centrosymmetric structure can be used as non-resonant nonlinear optical probes for targeting in bioimaging applications in vitro by use of the second order processes of second harmonic and sum frequency generation, as well as the third order process of four wave mixing. These non-resonant processes provide advantages above and beyond traditional two-photon bioimaging: (i) the probes do not photo-bleach; (ii) the input wavelength can be judiciously selected; and (iii) no heat is dissipated into the cells, ensuring longer cell viability and ultimately longer imaging times. ZnO NCs have been synthesized in organic media by using a non-hydrolytic sol-gel process, and subsequently dispersed in aqueous media using phospholipid micelles, and incorporated with the biotargeting molecule folic acid (FA). Sum Frequency, Second Harmonic and non-resonant four wave mixing non-linear signals from this stable dispersion of ZnO NCs, targeted to the live tumor (KB) cells were used for imaging. Robust intracellular accumulation of the targeted (FA incorporated) ZnO nanocrystals could be observed, without any indication of cytotoxicity

2. We showed that biocompatible zinc oxide (ZnO) NCs having non-centrosymmetric structure can be used as non-resonant nonlinear optical probes for targeting in bioimaging applications in vitro by use of the second order processes of second harmonic and sum frequency generation, as well as the third order process of four wave mixing. These non-resonant processes provide advantages above and beyond traditional two-photon bioimaging: (i) the probes do not photo-bleach; (ii) the input wavelength can be judiciously selected; and (iii) no heat is dissipated into the cells, ensuring longer cell viability and ultimately longer imaging times. ZnO NCs have been synthesized in organic media by using a non-hydrolytic sol-gel process, and subsequently dispersed in aqueous media using phospholipid micelles, and incorporated with the biotargeting molecule folic acid (FA). Sum Frequency, Second Harmonic and non-resonant four wave mixing non-linear signals from this stable dispersion of ZnO NCs, targeted to the live tumor (KB) cells were used for imaging. Robust intracellular accumulation of the targeted (FA incorporated) ZnO nanocrystals could be observed, without any indication of cytotoxicity.

3. We demonstrate three-dimensional vibrational imaging of director structures in liquid crystals using coherent anti-Stokes Raman scattering (CARS) microscopy. CARS signal in anisotropic fluids strongly depends on alignment of chemical bonds/molecules with respect to collinear polarizations of Stokes and pump/probe excitation beams and thus can be used for three-dimensional (3-D) imaging of director structures. This dependence allows for visualization of the bond/molecular orientations via polarized detection of the CARS signal, as we demonstrated using typical structures in nematic, cholesteric, and smectic liquid crystals. We demonstrated that CARS signal in anisotropic fluids such as thermotropic liquid crystals strongly depends on alignment of chemical bonds/molecules with respect to collinear polarizations of Stokes and pump/probe excitation beams and thus can be used for three-dimensional (3-D) imaging of director structures.

4. We applied CARS imaging technique to live and fixed cells to image 3D distribution of proteins, DNA/RNA, and lipids inside the cells. (See movie)

5. We successfully demonstrated multimodal CARS-TPEF imaging of live and fixed cells to image 3D distribution of DNA, RNA and proteins. (See movie)

6. Laser student kit

We have developed versatile laser/course materials designed to teach University students to the latest in solid-state laser technology and a wide range of physical principles.
Laboratory laser experiments included in the Laser Kit Manual

• Experiment #1: Measurement of the time relaxation of the upper laser level of Nd3+:KGd(WO4)2
• Experiment #2: Obtaining CW laser operation
• Experiment #3: Single mode laser operation and resonator stability
• Experiment #4: Measurement of laser threshold and output power at CW laser operation
• Experiment #5: Passive Q-switched regime of laser operation
• Experiment #6: Passive Q-switched regime of laser operation
• Experiment #7: Intracavity CW second harmonic generation
• Experiment #8: Intracavity second harmonic generation using Q-switched laser operation
• Experiment #9: Intracavity Raman self-conversion using Q-switched laser operation

7. Laser Tweezers/Micro-Raman Setup

• Laser tweezers trapping 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. Simultaneously with the laser tweezers study, a micro viscosity kinetic measurement of the sol-gel process was performed by fluorescent anisotropy and quantum yield methods. The large differences found between the bulk and micro viscosities obtained in the experiment reflect the intrinsic differences in solution environment sensed by the laser tweezers on the macro level and by other optical techniques on the micro levels.
• Laser tweezers trapping 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. Simultaneously with the laser tweezers study, a micro viscosity kinetic measurement of the sol-gel process was performed by fluorescent anisotropy and quantum yield methods. The large differences found between the bulk and micro viscosities obtained in the experiment reflect the intrinsic differences in solution environment sensed by the laser tweezers on the macro level and by other optical techniques on the micro levels.

8.We demonstrated optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We showed for the first time that even the inter-particles interaction between two microspheries can still be anisotropic if these particles are in an anisotropic medium which in the present instance is a liquid crystal. Also we found that laser beam in LCs can generate anisotropic optical trapping forces. Immersed colloidal particles modify the fluid’s ordered molecular structures and locally distort its optic axis. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. Using thermotropic liquid crystals and biological materials, we show that these phenomena are quite general for all anisotropic fluids and impinge broadly on their quantitative studies using laser tweezers. (In collaboration with Dr. I. Smalukh, Colorado University).

9. A multiple trap single beam scanning laser tweezers was investigated and characterized. Optimal parameters for efficient generation of complex arrays and matrices were determined. Examples of single laser beam multi-trap application were demonstrated by measuring the trap stiffness in water for our laser tweezers setup and by stretching the disclination quadrupole in liquid crystal to measure line tension. See movie.

10. We investigated intracellular processes in the blood cell under bead-cell interaction Cell (right) and bead (left) approaching shown in transmission mode, then cell and bead separating shown in fluorescence mode - fluorescence spike of dye stained cell was observed. (In collaboration with Dr. S.Neelamegham, Dept. of Chemical and Biological Engineering, UB). See movie

11. Micro-Raman spectroscopy We applied micro-Raman spectroscopy to study the organization of the cell nucleus during cell cycle.