Real-time particle tracking at 10,000 fps using optical fiber illumination.

We introduce optical fiber illumination for real-time tracking of optically trapped micrometer-sized particles with microsecond time resolution. Our light source is a high-radiance mercury arc lamp and a 600 μm optical fiber for short-distance illumination of the sample cell. Particle tracking is carried out with a software implemented cross-correlation algorithm following image acquisition from a CMOS camera.

Detecting DNA folding with nanocapillaries.

We demonstrate for the first time the detection of the folding state of double-stranded DNA in nanocapillaries with the resistive pulse technique. We show that glass capillaries can be pulled into nanocapillaries with diameters down to 45 nm. We study translocation of lambda -DNA which is driven by an electrophoretic force through the nanocapillary.

Helix-coil transition of gelatin: helical morphology and stability.

By combining optical rotation with thermal characterization and rheological measurements, we have studied triple helix formation in water and ethylene glycol solutions of gelatin. We find the enthalpy change per unit helix required for the transition from triple helix to random coil is independent of the concentration of helices in solution and the temperature at which the helices form. Helices formed in ethylene glycol are less stable than those formed in water solutions as, unlike water, ethylene glycol is too large a molecule to mediate interchain hydrogen bonds.

Mechanically induced helix-coil transition in biopolymer networks.

The quasi-equilibrium evolution of the helical fraction occurring in a biopolymer network (gelatin gel) under an applied stress has been investigated by observing modulation in its optical activity. Its variation with the imposed chain extension is distinctly nonmonotonic and corresponds to the transition of initially coiled strands to induced left-handed helices. The experimental results are in qualitative agreement with theoretical predictions of helices induced on chain extension.