Seminar by Dr Mondal 'Application of contactless micromanipulation using one- and two-color femtosecond lasers in force and fluorescence spectroscopy'

Speaker:
Dr Dipankar Mondal, Department of Chemistry, IIT Kharagpur, India

Talk title:
Application of contactless micromanipulation using one- and two-color femtosecond lasers in force and fluorescence spectroscopy

Abstract:

Temperature has a fundamental role in many biological activities therefore it is subject of interest to find new ways to probe bio system’s behavior under different temperature gradients. We have used Femtosecond optical tweezers (FOT) to measure temperature and microrheological properties by probing Brownian motion of micron sized polystyrene bead. In this respect we have designed and built two FOT set up with inverted microscope geometry to control and measure temperature and corresponding viscosity. We have observed convection flow due to temperature gradient that can also be used for directional drug delivery. Our newly developed a nano-viscometer works for Newtonian as well as non-Newtonian fluids. This particular method is useful for complex fluid systems (e.g. inside cell) which do not behave as simple Newtonian model due to surrounding crowding’s. Here we have performed absolute calibration using position autocorrelation and equipartition theorem that enables us to measure viscosity in complex fluids like Laponite, polyacrylamide etc. The advantage of pulsed laser based tweezers has also been explored in determining structure and dynamics of nanoparticle clusters through nonlinear optical (NLO) phenomena: two-photon fluorescence (TPF).

One other popular NLO phenomenon of femtosecond pulses is Second Harmonic generation from its fundamental wavelength. Fluorescence up-conversion techniques use this method to measure solvation dynamics inside phospholipid vesicles by observing the time dependent Stokes shift in fluorescence spectrum. Our measured solvation time has a particular interest as differential solvation control the reaction rate for proper biological function. This study reveals that molecular organization is a determining factor to control the structural aspect of the cell or cell organelles, which eventually control their functional activity.