74 research outputs found
Quantum Yield Calculations for Strongly Absorbing Chromophores
This article demonstrates that a commonly-made assumption in quantum yield
calculations may produce errors of up to 25% in extreme cases and can be
corrected by a simple modification to the analysis.Comment: 3 pages, 2 figures. Accepted by Journal of Fluorescenc
A Quantum Yield Map for Synthetic Eumelanin
The quantum yield of synthetic eumelanin is known to be extremely low and it
has recently been reported to be dependent on excitation wavelength. In this
paper, we present quantum yield as a function of excitation wavelength between
250 and 500 nm, showing it to be a factor of 4 higher at 250 nm than at 500 nm.
In addition, we present a definitive map of the steady-state fluorescence as a
function of excitation and emission wavelengths, and significantly, a
three-dimensional map of the specific quantum yield: the fraction of photons
absorbed at each wavelength that are subsequently radiated at each emission
wavelength. This map contains clear features, which we attribute to certain
structural models, and shows that radiative emission and specific quantum yield
are negligible at emission wavelengths outside the range of 585 and 385 nm (2.2
and 3.2 eV), regardless of excitation wavelength. This information is important
in the context of understanding melanin biofunctionality, and the quantum
molecular biophysics therein.Comment: 10 pages, 6 figure
Towards Structure-Property-Function Relationships for Eumelanin
We discuss recent progress towards the establishment of important
structure-property-function relationships in eumelanins - key functional
bio-macromolecular systems responsible for photo-protection and immune response
in humans, and implicated in the development of melanoma skin cancer. We focus
on the link between eumelanin's secondary structure and optical properties such
as broad band UV-visible absorption and strong non-radiative relaxation; both
key features of the photo-protective function. We emphasise the insights gained
through a holistic approach combining optical spectroscopy with first
principles quantum chemical calculations, and advance the hypothesis that the
robust functionality characteristic of eumelanin is related to extreme chemical
and structural disorder at the secondary level. This inherent disorder is a low
cost natural resource, and it is interesting to speculate as to whether it may
play a role in other functional bio-macromolecular systems.Comment: 19 pages, 8 figures, Invited highlight article for Soft Matte
Multispectral image alignment using a three channel endoscope in vivo during minimally invasive surgery.
Sequential multispectral imaging is an acquisition technique that involves collecting images of a target at different wavelengths, to compile a spectrum for each pixel. In surgical applications it suffers from low illumination levels and motion artefacts. A three-channel rigid endoscope system has been developed that allows simultaneous recording of stereoscopic and multispectral images. Salient features on the tissue surface may be tracked during the acquisition in the stereo cameras and, using multiple camera triangulation techniques, this information used to align the multispectral images automatically even though the tissue or camera is moving. This paper describes a detailed validation of the set-up in a controlled experiment before presenting the first in vivo use of the device in a porcine minimally invasive surgical procedure. Multispectral images of the large bowel were acquired and used to extract the relative concentration of haemoglobin in the tissue despite motion due to breathing during the acquisition. Using the stereoscopic information it was also possible to overlay the multispectral information on the reconstructed 3D surface. This experiment demonstrates the ability of this system for measuring blood perfusion changes in the tissue during surgery and its potential use as a platform for other sequential imaging modalities
Quantitative scattering of melanin solutions
The optical scattering coefficient of a dilute, well solubilised eumelanin
solution has been accurately measured as a function of incident wavelength, and
found to contribute less than 6% of the total optical attenuation between 210
and 325nm. At longer wavelengths (325nm to 800nm) the scattering was less than
the minimum sensitivity of our instrument. This indicates that UV and visible
optical density spectra can be interpreted as true absorption with a high
degree of confidence. The scattering coefficient vs wavelength was found to be
consistent with Rayleigh Theory for a particle radius of 38+-1nm.Comment: 23 pages, 5 figure
Imaging of Flow Patterns with Fluorescent Molecular Rotors
Molecular rotors are a group of fluorescent molecules that form twisted intramolecular charge transfer states (TICT) upon photoexcitation. Some classes of molecular rotors, among them those that are built on the benzylidene malononitrile motif, return to the ground state either by nonradiative intramolecular rotation or by fluorescence emission. In low-viscosity solvents, intramolecular rotation dominates, and the fluorescence quantum yield is low. Higher solvent viscosities reduce the intramolecular rotation rate, thus increasing the quantum yield. We recently described a different mechanism whereby the fluorescence quantum yield of the molecular rotor also depends on the shear stress of the solvent. In this study, we examined a possible application for shear-sensitive molecular rotors for imaging flow patterns in fluidic chambers. Flow chambers with different geometries were constructed from polycarbonate or acrylic. Solutions of molecular rotors in ethylene glycol were injected into the chamber under controlled flow rates. LED-induced fluorescence (LIF) images of the flow chambers were taken with a digital camera, and the intensity difference between flow and no-flow images was visualized and compared to computed fluid dynamics (CFD) simulations. Intensity differences were detectable with average flow rates as low as 0.1 mm/s, and an exponential association between flow rate and intensity increase was found. Furthermore, a good qualitative match to computed fluid dynamics simulations was seen. On the other hand, prolonged exposure to light reduced the emission intensity. With its high sensitivity and high spatial and temporal resolution, imaging of flow patterns with molecular rotors may become a useful tool in microfluidics, flow measurement, and control
Non-invasive intravital imaging of cellular differentiation with a bright red-excitable fluorescent protein
A method for non-invasive visualization of genetically labelled cells in animal disease
models with micron-level resolution would greatly facilitate development of cell-based
therapies. Imaging of fluorescent proteins (FPs) using red excitation light in the âoptical
windowâ above 600 nm is one potential method for visualizing implanted cells. However,
previous efforts to engineer FPs with peak excitation beyond 600 nm have resulted in
undesirable reductions in brightness. Here we report three new red-excitable monomeric FPs obtained by structure-guided mutagenesis of mNeptune, previously the brightest monomeric FP when excited beyond 600 nm. Two of these, mNeptune2 and mNeptune2.5, demonstrate improved maturation and brighter fluorescence, while the third, mCardinal, has a red-shifted excitation spectrum without reduction in brightness. We show that mCardinal can be used to non-invasively and longitudinally visualize the differentiation of myoblasts and stem cells into myocytes in living mice with high anatomical detail
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Haemodynamics and Oxygenation of the Tumor Microcirculation
Abnormalities of the tumor vasculature and their consequences on the microenvironment of tumor cells impact on tumor progression and response to both blood-borne anti-cancer agents and radio-therapy, as well as making tumor blood vessels a target for therapy in their own right. Intravital microscopy of experimental tumors, most commonly grown in âwindowâ chambers, such as the dorsal skin fold chamber in mice and rats, enables investigations of tumor microcirculatory function. This is needed both to understand the molecular control of tumor vascular function and to measure the response of the vasculature to treatment. In particular, intravital microscopy enables parameters associated with blood supply, vascular permeability and oxygenation to be estimated, at high spatial and temporal resolution. In this chapter, methods used for measuring a range of these parameters, specific examples of their applications, the significance of findings and some of the limitations of the techniques are described
Mapping regional oxygenation and flow in pig hearts in vivo using near-infrared spectroscopic imaging
NRC publication: Ye
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