The angular light scattering profile of microscopic particles significantly depends on their morphological parameters, such as size and shape. This dependency is widely used in state-of-the-art flow cytometry methods for particle classification. We recently introduced the spectrally encoded angular light scattering (SEALS) method, with potential application in scanning flow cytometry (SFC). We show that a one-to-one wavelength-to-angle mapping enables the measurement of the angular dependence of scattered light from microscopic particles over a wide dynamic range. Improvement in dynamic range is obtained by equalizing the angular scattering dependence via spectral equalization. The resulting continuous angular spectrum is obtained without mechanical scanning, enabling single-shot measurement. Using this information, particle morphology can be determined with improved accuracy. We derive and experimentally verify an analytic wavelength-to-angle mapping model, facilitating rapid data processing. As a proof of concept, we demonstrate the method’s capability of distinguishing differently sized polystyrene beads. The combination of SEALS with time-stretch dispersive Fourier transform (TS-DFT) offers real-time and high-throughput (high frame rate) measurements and renders the method suitable for integration in standard flow cytometers: By transforming the spectrum into time and slowing the time scale, using group velocity dispersion (GVD), single-shot spectra can be obtained at high throughput, using a photodiode and a real-time digitizer. The amount of group velocity dispersion is chosen to time-stretch the optical pulses, that is, to slow them down, such that they do not overlap and may be digitized in real-time.
Research in THz imaging is generally focused on three primary application areas: medical, security, and nondestructive
evaluation (NDE). While work in THz security imaging and personnel screening is populated by a number of different
active and passive system architectures, research in medical imaging in is generally performed with THz time-domain
systems. These systems typically employ photoconductive or electro-optic source/detector pairs and can acquire depth
resolved data or spectrally resolved pixels by synchronously sampling the electric field of the transmitted/reflected
waveform. While time-domain is a very powerful scientific technique, results reported in the literature suggest that
desired THz contrast in medical imaging may not require the volume of data accessible from time-resolved
measurements and that a simpler direct detection, active technique may be sufficient for specific applications. In this
talk we discuss an active direct detection reflectometer system architecture operating at a center frequency of ~ 525 GHz
that uses a photoconductive source and schottky diode detector. This design takes advantage or radar-like pulse
rectification and novel reflective optical design to achieve high target imaging contrast with significant potential for high
speed acquisition time. Results in spatially resolved hydration mapping of burn wounds are presented and future
outlooks discussed.
The delivery of extra cellular molecules into cells is essential for cell manipulation. For this purpose genetic materials
(DNA/RNA) or proteins have to overcome the impermeable cell membrane. To increase the delivery efficiency and cell
viability of common methods different nano- and micro material based approaches were applied. To manipulate the cells,
the membrane is in contact with the biocompatible material. Due to a field enhancement of the laser light at the material
and the resulting effect the cell membrane gets perforated and extracellular molecules can diffuse into the cytoplasm.
Membrane impermeable dyes, fluorescent labelled siRNA, as well as plasmid vectors encoded for GFP expression were
used as an indicator for successful perforation or transfection, respectively. Dependent on the used material, perforation
efficiencies over 90 % with a cell viability of about 80 % can be achieved. Additionally, we observed similar efficiencies
for siRNA transfection. Due to the larger molecule size and the essential transport of the DNA into the nucleus cells are
more difficult to transfect with GFP plasmid vectors. Proof of principle experiments show promising and adequate
efficiencies by applying micro materials for plasmid vector transfection. For all methods a weakly focused fs laser beam
is used to enable a high manipulation throughput for adherent and suspension cells. Furthermore, with these alternative
optical manipulation methods it is possible to perforate the membrane of sensitive cell types such as primary and stem
cells with a high viability.
In this Manuscript, we present the fabrication and spectroscopic characterization of a large-area surfaceenhanced
Raman scattering (SERS) substrate, as well as a method for improving femtomole-level trace
detection (109 molecules) using this substrate. Using multiphoton-induced exposure of a commercial
photoresist, we physically limit the available molecular adsorption sites to only the electromagnetic "hot
spots" on the substrate. This process prevents molecules from adsorbing to sites of weak SERS
enhancement, while permitting adsorption to sites of extraordinary SERS enhancement. For a randomly
adsorbed submonolayer of benzenethiol molecules the average Raman scattering cross-section of the
processed sample is 27 times larger than that of an unprocessed SERS substrate.
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