This work reports progress towards demonstrated Raman-based optical refrigeration. Previously  we introduced Raman refrigeration and its required photonic structures. Building on the previous, the mechanisms and photonic structures are detailed and simplified proof-of-concept devices described. Three wavelength bands, two illuminated and one dark, are considered. The width of each of these bands is predicated upon the magnitude of the Raman shift of the active layer. Optimally, the first illuminated band is approximately one Raman shift (wavelength) in width. This illuminated band is capped above (at shorter wavelengths) by a dark band. At longer wavelengths a second illuminated band again one Raman shift in width is reflected by photonic structuring that forbids light propagation. The dark bands provide an exhaust through which up energy (anti-Stokes) shifted light can be emitted thereby carrying away heat. The Photonic structure prohibits the propagation of a band of long wavelength light thereby both blocking Stoke’s shifted illuminated band light and reflecting incident light having these wavelengths. The naturally occurring solar spectrum with its light and dark bands caused by atmospheric absorption is a good match to diamond-based Raman refrigeration. Diamond also has extremely low absorption and large Raman cross-section especially in small grain form. Proof-of-concept devices employing simple one-dimensional photonic structures are the focus of present experimental effort. The prospect of broadband refrigeration remains a delicate balance requiring limited absorption and increased Raman cross section through phonon engineering of the Raman active layer.
Described are the prospects for broadband optical refrigeration based on Raman scattering of incoherent light. Laser pumped rare earth fluorescence has been demonstrated and commercial applications are sure to follow. Broadband refrigeration requires strong Raman scattering and large Raman shift. Also required are spectral management and photonic patterning to offset the unfavorable anti-Stoke’s to Stoke’s shift ratio. Materials such as diamond, silicon, and a number of molecular systems are ideal and have low absorption. Optics splits the broadband spectrum into light and dark bands with width corresponding to the Raman shift. Broadband spectrums where photon flux decreases with increasing photon energy are ideal. By tailoring the incoming spectrum, by utilizing extremely transparent strong Raman shift materials and by photonic inhibition of Stoke’s shifted light the prospect become feasible. The Raman optical cross- section increases with decreasing particle size (until the particle become too small to support the Raman-phonons). Where conservation of phonon states in these truncated Brillioun-zone particles requires an increased density (number/cm<sup>3</sup>) of the allowed-states to compensate for states lost to particle size. Nonetheless, the anti-Stokes to Stokes ratio is approximately one-to-two at laboratory temperature. Thin film deposited diamond is an excellent candidate for refrigeration applications due to its high transparency small grain size and its large Raman magnitude and large shift. Simple one-dimensional photonic structures selectively inhibit the Stoke’s shifted light making refrigeration possible.
Spectral management and diffusive light transport enables plants to both survive on extremely low irradiance and also to survive long enough under extreme temperature and pressure to leave imprints in super-heated impact glasses. These properties are related to structures wherein a low density of light absorbent particles are embedded in a light scattering and spectral selective reflective matrix. This marvelous diffusive light engineering has wide-ranging applications based on bio-mimicry. Where, environmentally sensitive radiative-to-non-radiative lifetime ratios increase the photon flux to the chlorophyll molecules best positioned for favorable photochemistry and for preservation under extreme conditions. The embedding of absorptive particles within a transparent scattering matrix has far reaching intriguing applications. Included is the extreme heating of light absorbent particles within a relatively cold matrix. Interestingly, the hot absorbent particle-cold matrix condition is critical for the efficient extreme heating of small particles. Here the potential of non-equilibrium passive diffusive light collection will consider be explored using one of the most challenging application extreme particle heating for controlled nuclear fusion.
The purpose of this study was to develop targeted polymeric magnetic nanoparticle system for brain imaging. Near
infrared dye indocyanine green (ICG) or p-gycoprotein substrate rhodamine 123 (Rh123) were encapsulated along with
oleic acid coated magnetic nanoparticles (OAMNP) in a matrix of poly(lactide-co-glycolide) (PLGA) and methoxy
poly(ethyleneglycol)-poly(lactide) (Met-PEG-PLA). The nanoparticles were evaluated for morphology, particle size, dye
content and magnetite content. The in vivo biodistribution study was carried out using three groups of six male Sprague
Dawley rats each. Group I received a saline solution containing the dye, group II received dye-loaded polymeric magnetic
nanoparticles without the aid of a magnetic field, and group III received dye-loaded polymeric magnetic nanoparticles
with a magnet (8000 G) placed on the head of the rat. After a preset exposure period, the animals were sacrificed and dye
concentration was measured in the brain, liver, kidney, lungs and spleen homogenates. Brain sections were fixed,
cryotomed and visualized using fluorescence microscopy. The particles were observed to be spherical and had a mean
size of 220 nm. The encapsulation efficiency for OAMNP was 57%, while that for ICG was 56% and for Rh123 was
45%. In the biodistribution study, while the majority of the dose for all animals was found in the liver, kidneys and
spleen, group III showed a significantly higher brain concentration than the other two groups (p < 0.001). This result was
corroborated by the fluorescence microscopy studies, which showed enhanced dye penetration into the brain tissue for
group III. Further studies need to be done to elucidate the exact mechanism responsible for the increased brain uptake of
dye to help us understand if the magnetic nanoparticles actually penetrate the blood brain barrier or merely deliver a
massive load of dye just outside it, thereby triggering passive diffusion into the brain parenchyma. These results reinforce
the potential use of polymeric magnetically-targeted nanoparticles in active brain targeting and imaging.
Indocyanine green (ICG) is a near-infrared fluorescence contrast agent, which has enormous potential in early tumor diagnosis and therapy. The objective of this study is to develop biodegradable nanoparticles entrapping ICG and to characterize its intracellular uptake and photodynamic activity in different cancer cell lines. Nanoparticles entrapping ICG were engineered, characterized and the intracellular uptake of ICG was investigated in B16-F10 and C-33A cancer cell lines. The photodynamic activity of ICG-loaded nanoparticles was also investigated. The nanoparticles enhanced the intracellular uptake of ICG and showed significant photodynamic activity, especially at very low ICG concentrations. These preliminary studies indicate the potential of efficient tumor cell delivery and tumoricidal effect of ICG when incorporated in nanoparticles.
Degradation of Indocyanine green (ICG) in aqueous media, limits its application in early tumor diagnosis and therapy. Thus, the objective of this study is to develop biodegradable nanoparticles entrapping ICG and to establish its effectiveness in providing overall stability to ICG. Nanoparticles entrapping ICG were engineered and characterized. The degradation kinetics of ICG in the nanoparticles was investigated in aqueous media. The degradation of ICG in aqueous nanoparticle suspension followed first-order kinetics. Nanoparticles enhanced aqueous, photo and thermal-stability of ICG.
The objective of this study is to engineer a novel nanoparticlulate system for use in early tumor diagnosis. Indocyanine green (ICG)-loaded biodegradable nanoparticles were prepared by using biodegradable polymer, poly(DL-lactic-co-glycolic acid) (PLGA). The ICG entrapment, nanoparticle size, shape, zeta potential the release of ICG from nanoparticles was determined. Also, the effect of ICG entrapment on fluorescence spectra of ICG was measured. The engineered nanoparticles were nearly spherical in shape and efficiently entrapped ICG. The release profile of the nanoparticles was exponential. The entrapment of ICG in nanoparticles caused reduction in its peak fluorescence intensity and shifted its wavelength of peak fluorescence to higher values.
Many investigations in the literature have studied the migration of photons in fluorescent and non-fluorescent applications, both in the steady-state and time-resolved, within a tissue-simulating medium. However, none have addressed the specific issue of quantified the subsequent migration path of the emitted photons. This is important since fluorescent spectroscopy has been gaining acceptance as an important diagnostic tool. In this paper we show the migration patterns of fluorescent photons with respect to time in a scattering medium such as tissue. The images produced are of the paths of the emission photons that reach the detector. We are able to observe how they migrate at different times. We investigate the effect of the absorption and scattering coefficients on the migration patterns, and how it could give us information about methods to detect inhomogeneities in the medium. The images produced give us information about the accuracy of the estimation of the optical properties in particular medium. Finally, we study how the detector position and absorption and scattering coefficients affect the source of the photons that reach the detector. We discover that during the rising time of the temporal spectrum most of the detected fluorescent photons are being generated very close to the source and the path followed by these photons are localized near the detector. Therefore, we could explore this for the best orientation and location of the detector and source positions to locate inhomogenieties and also source of fluorescence photons within the medium.
In this paper we describe a Monte Carlo simulation for time resolved fluorescence. In the past information on steady state measurements have been reported. However we feel that a lot more information and insight could be gained by the use of time resolved fluorescence spectroscopy. We have developed a Monte Carlo simulation to study the fluorescence signal generated by fluorophores distributed in a scattering medium. The simulation uses a semi-infinite medium with a thickness of 1cm. We have used the simulation to study the effect of the change in optical properties of the medium on the TPSF (temporal point spread function) generated. We have also investigated the effect of the increased radial separation of the detector on the TPSF. We have observed a shift in the Tmax (time at which the peak intensity is reached) in accordance with diffusion theory.
We wanted to validate our simulation by seeing how well we could derive the optical properties of the medium from the TPSF produced from simulation. We fitted the TPSF to an adjusted form of the diffusion theory to find scattering coefficient, μ<sub>s</sub>, and we have used an analytical model of time resolved fluorescence to extract the absorption coefficient, μ<sub>a</sub>. The results obtained were better than previously reported.