Spectral imaging of the retina shows great promise for the early detection of retinal disease through retinal screening
programs. Implementation of such a program will require instrumentation capable of efficiently recording the requisite
spectral data cube. We report on the development of two candidate approaches: one employs a traditional liquid crystal
tunable filter to filter the illumination source and enable the spectral data cube to be assembled from mutually
coregistered narrow-band images recorded in time sequence: the second employs, IRIS, a novel image replicating
imaging spectrometer to record a two-dimensional spectral data cube in a single snapshot.
This study reports on current work involving the use of Surface Enhanced Raman Spectroscopy (SERS) for the intracellular detection of cell constituents in mouse fibroblast cells using gold nanoshells. Gold nanoshells were acquired from Nanospectra Biosciences that are based on a silica dielectric core and an outer gold shell layer. They
have the unique property of a tunable surface plasmon resonance wavelength from the visible through the near infrared which allows control of the electromagnetic field strength on its surface. Hence gold nanoshells can serve as SERS substrates with plasmonic properties that are not aggregation dependent and thus can be expected to overcome the reproducibility problem that is generally associated with aggregation based colloidal metal nanoparticles. These results represent the first steps in the development of a nanoshell-based SERS probe to detect cell organelles and/or intracellular biochemicals with the goal of ultimately improving the ability to monitor intracellular biological processes in real time.
We have observed a latency time of the order 10 s in the spermidine-induced condensation of YOYO-1-labelled DNA in flow. Higher flow speeds, longer DNA and higher salt all led to an increase in the latency time. We propose that two effects may be relevant to these observations (1) the competition between spermidine and YOYO-1 for DNA binding sites, and (2) the bending of DNA upon spermidine binding, so that flow-induced straightening of the DNA weakens spermidine's affinity for DNA. Moreover, literature data on the mechanical properties of condensed DNA chains suggest that the hydrodynamic drag forces in our experiments should indeed significantly perturb condensation kinetics.
Typical optical tweezers setups use high numerical aperture oil-immersion objectives to trap particles suspended in an aqueous medium. When trapping deep inside a sample or out of the imaging plane the quality of the trap in such a system deteriorates due to optical aberrations caused by the refractive index mismatch at the glass-water interface. We investigate this effect experimentally by monitoring the two-photon fluorescence of trapped dye-stained polystyrene spheres. We consider the effect of the numerical aperture on the trap quality and also partly corrected the aberrations by optimising the fluorescence signal using an adaptive deformable membrane mirror.
The stretching and unwinding of polymers under flow is important for understanding the rheological properties of dilute polymer solutions.
Scaling theory based on the blob picture of single polymer chains predicts several regimes for the overall shape of a hydrodynamically deformed macromolecule. We studied the shape of a DNA molecule stretched out by steady uniform flow at different velocities using optical trapping of single DNA molecules (tethered on polystyrene beads) and single molecule fluorescence imaging. The results show
a gradual transition from a non-draining regime at low velocities to
a free-draining regime at high velocities, thus verifying the predictions of the free draining-shell (F-shell) blob model.