We describe a method for the preparation of a polyurethane phantom to simulate the optical properties of biologic tissues at two wavelengths in the visible and near-infrared spectral range. We characterize the addition of added molecular absorbers with relatively narrow absorption bands [full width at half maximum (FWHM) 32 and 76 nm for Epolight 6084 and 4148, respectively] for independent absorption at 690 nm for absorption up to 5 cm–1, and 830 nm for absorptions up to 3 cm–1. Absorption by both dyes is linear with concentration in these respective regions and is consistent in polyurethane both before and after curing. The dyes are stable over long durations with no more than 4% change. The absorption of visible light by polyurethane decreases with time and is stable by one year with a drop of 0.03±0.003 cm–1 from 500 to 830 nm. The scattering properties are selected by the addition of TiO2 particles to the polyurethane, which we functionally describe for the 690- and 830-nm wavelengths as related to the weight per volume. We demonstrate that the variation in absorption and scattering properties for large batch fabrication (12 samples) is ±3%. The optical properties of the phantoms have not significantly changed in a period of exceeding one year, which makes them suitable for use as a reference standard.
Reactive oxygen species (ROS) are involved in the pathogenesis of many critical diseases and are also utilized as cytotoxic agents in a variety of treatments for eradication of diseased tissue, including cancer. Oxidative stress ensues when the level of ROS in a system exceeds the antioxidant capacity. Oxidative stress can have local (direct) and long-range (bystander) effects in cells and tissue and this research was carried out to determine the spatial and temporal nature of the photosensitized bystander effect using time-lapse fluorescence microscopy. By initiating photosensitization in only a portion of the microscopic imaging field it was possible to differentiate direct from bystander effects in EMT-6 murine breast cancer cells in 6-well plates. Elevated ROS levels are seen immediately following photodynamic treatment in direct cells with a delayed increase in oxidative stress observed in bystander cells. Cytotoxicity is also seen at earlier times in direct cells and occurs in bystander cells in a delayed fashion. These studies confirm the existence of a bystander effect following photosensitization and implicate mediators capable of diffusing in an intercellular manner from directly photosensitized cells to bystander cells and also implicate increased oxidative stress as a mechanistic factor in generating damage in bystander cells.
The primary absorber in dental resins is the photoinitiators, which start the photo polymerization process. We studied the quantum yield of conversion of camphorquinone (CQ), a blue light photoinitiator, using 3M FreeLight LED lamp as the light curing unit. The molar extinction coefficient, ε<sub>469</sub>, of CQ was measured to be 46±2 cm<sup>-1</sup>/(mol/L) at 469 nm. The absorption coefficient change to the radiant exposure was measured at three different irradiances. The relationship between the CQ absorption coefficient and curing lamp radiant exposure was the same for different irradiances and fit an exponential function: μ<sub>a469</sub>(H)= μ<sub>ao</sub> exp(-H/H<sub>threshold</sub>), where μ<sub>ao</sub> is 4.46±0.05 cm<sup>-1</sup>, and H<sub>threshold</sub>=43±4 J/cm<sup>2</sup>. Combining this exponential relationship with CQ molar extinction coefficient and the absorbed photon energy (i.e., the product of the radiant exposure with the absorption coefficient), we plotted CQ concentration [number of molecules/cm<sup>3</sup>] as a function of the accumulated absorbed photons per volume. The slope of the relationship is the quantum yield of the CQ conversion. Therefore, in our formulation (0.7 w% CQ with reducing agents 0.35 w% DMAEMA and 0.05 w% BHT) the quantum yield was solved to be 0.07±0.01 CQ conversion per absorbed photon.
Photo-cured dental composites are widely used in dental practices to restore teeth due to the esthetic appearance of the composites and the ability to cure in situ. However, their complex optical characteristics make it difficult to understand the light transport within the composites and to predict the depth of cure. Our previous work showed that the absorption and scattering coefficients of the composite changed after the composite was cured. The static Monte Carlo simulation showed that the penetration of radiant exposures differed significantly for cured and uncured optical properties. This means that a dynamic model is required for accurate prediction of radiant exposure in the composites. The purpose of this study was to develop and verify a dynamic Monte Carlo (DMC) model simulating light propagation in dental composites that have dynamic optical properties while photons are absorbed. The composite was divided into many small cubes, each of which had its own scattering and absorption coefficients. As light passed through the composite, the light was scattered and absorbed. The amount of light absorbed in each cube was calculated using Beer's Law and was used to determine the next optical properties in that cube. Finally, the predicted total reflectance and transmittance as well as the optical property during curing were verified numerically and experimentally. Our results showed that the model predicted values agreed with the theoretical values within 1% difference. The DMC model results are comparable with experimental results within 5% differences.
We developed a numerical model for the fluorescence output efficiency of a molecularly imprinted polymer (MIP) waveguide sensing system. A polyurethane waveguide imprinted with a polycyclic aromatic hydrocarbon (PAH) molecule was fabricated using micromolding in capillaries. The coupling of light into a 5 mm long MIP segment was verified by comparing the output transmission signals of a deuterium lamp from the MIP waveguide collected by an optical fiber with the background lamp signals collected by the same optical fiber. It was found that polyurethane MIP was an effective waveguide but absorbed much shorter wavelengths, especially in the UV region, thereby the transmission of light appeared orange/red in color. The high background absorption of polyurethane in the spectrometric regions of interest was found to be a critical problem for sensor sensitivity. Our numerical model shows that the fluorescence output is only 2x10<sup>-6</sup> of the input excitation for 25 mM anthracene for a 5 mm polyurethane waveguide. A 10 fold decrease of background absorption will increase the fluorescence output 250 times.
A Rayleigh interferometer was constructed to measure changes of concentrations in the biological solutions. With the stability tests, our Rayleigh interferometer system showed its insensitivity to environment vibrations and with the second compensating cuvette, effects on the refractive index changes other than the concentration changes of molecules in the sample solution could be compensated. A thin glass plate was inserted in the beam path and rotated to vary the optical path length to test the sensitivity of the system. With this glass plate, the detectable optical path differences of the system was Δ(<i>nl</i>) = 7 nm. Finally, the concentration of sucrose solutions were varied to change the refractive index. The refractive index changes by 1.43 × 10<sup>-4 </sup>for each gram of sucrose per liter at 20°C. With our system, the sensitivity to sucrose solution was 7mg/L. Based on this sensitivity this interferometric system can be used to detect concentrations of albumin solutions as low as 0.6mg/mL.