Photosensitivity

About: Photosensitivity is a research topic. Over the lifetime, 764 publications have been published within this topic receiving 11742 citations. The topic is also known as: light sensitivity.

Photosensitivity in optical fiber waveguides: Application to reflection filter fabrication

Abstract: The observation of photosensitivity in Ge‐doped core optical fibers is reported. The photosensitivity is manifested by light‐induced refractive‐index changes in the core of the waveguide. Narrowband reflectors in a guide structure have been fabricated using this photosensitivity and the resulting DFB reflectors employed as laser mirrors in a cw gas laser in the visible.

Drug-induced cutaneous photosensitivity: incidence, mechanism, prevention and management.

Abstract: The interaction of sunlight with drug medication leads to photosensitivity responses in susceptible patients, and has the potential to increase the incidence of skin cancer. Adverse photosensitivity responses to drugs occur predominantly as a phototoxic reaction which is more immediate than photoallergy, and can be reversed by withdrawal or substitution of the drug. The bias and inaccuracy of the reporting procedure for these adverse reactions is a consequence of the difficulty in distinguishing between sunburn and a mild drug photosensitivity reaction, together with the patient being able to control the incidence by taking protective action. The drug classes that currently are eliciting a high level of adverse photosensitivity are the diuretic, antibacterial and nonsteroidal anti-inflammatory drugs (NSAIDs). Photosensitising chemicals usually have a low molecular weight (200 to 500 Daltons) and are planar, tricyclic, or polycyclic configurations, often with heteroatoms in their structures enabling resonance stabilisation. All absorb ultraviolet (UV) and/or visible radiation, a characteristic that is essential for the chemical to be regarded as a photosensitiser. The photochemical and photobiological mechanisms underlying the adverse reactions caused by the more photoactive drugs are mainly free radical in nature, but reactive oxygen species are also involved. Drugs that contain chlorine substituents in their chemical structure, such as hydrochlorthiazide, furosemide and chlorpromazine, exhibit photochemical activity that is traced to the UV-induced dissociation of the chlorine substituent leading to free radical reactions with lipids, proteins and DNA. The photochemical mechanisms for the NSAIDs that contain the 2-aryl propionic acid group involve decarboxylation as the primary step, with subsequent free radical activity. In aerated systems, the reactive excited singlet form of oxygen is produced with high efficiency. This form of oxygen is highly reactive towards lipids and proteins. NSAIDs without the 2-arylpropionic acid group are also photoactive, but with differing mechanisms leading to a less severe biological outcome. In the antibacterial drug class, the tetracyclines, fluoroquinolones and sulfonamides are the most photoactive. Photocontact dermatitis due to topically applied agents interacting with sunlight has been reported for some sunscreen and cosmetic ingredients, as well as local anaesthetic and anti-acne agents. Prevention of photosensitivity involves adequate protection from the sun with clothing and sunscreens. In concert with the preponderance of free radical mechanisms involving the photosensitising drugs, some recent studies suggest that diet supplementation with antioxidants may be beneficial in increasing the minimum erythemal UV radiation dose.

Hypericin and Pseudohypericin: Pharmacokinetics and Effects on Photosensitivity in Humans

Abstract: Extracts of St. John's wort (Hypericum perforatum) are used in treatment of depression. They contain various substances with the naphthodianthrones hypericin and pseudohypericin as characteristic ingredients. These compounds were shown to cause phototoxicity in cell culture and in animals. A placebo-controlled randomized clinical trial with monitoring of hypericin and pseudohypericin plasma concentration was performed to evaluate the increase in dermal photosensitivity in humans after application of high dose hypericum extracts. The study was divided into a single dose and a multiple dose part. In the single dose period, each of 13 volunteers received in a double blind fourfold complete crossover design, either placebo, or 900, 1800 or 3600 mg of a standardized hypericum extract (LI 160) containing zero, 2.81, 5.62 and 11.25 mg of total hypericin (total hypericin is the sum of hypericin and pseudohypericin). Maximum total hypericin plasma concentrations were observed about 4 h after dosage and were 0, 0.028, 0.061 and 0.159 mg/L, respectively. Before and 4 h after drug intake, the subjects were exposed at small areas of their back to increasing doses of solar simulated irradiation (SSI, with combined ultraviolet A, UV-A, and UV-B light) and another part was exposed to selective UV-A light irradiation. Minimal erythema dose was determined 5, 20 and 68 h after irradiation. Comparison of SSI sensitivity without and with hypericum extract did not show and difference and there was no dose-related trend in light sensitivity. Sensitivity to selective UV-A light was increased only after the highest dose from a minimal tanning dose of 10.8 J/ cm2 (mean) after placebo to 8.7 J/cm2 after 3600 mg extract with marginal statistical significance (p = 0.03 by one sided paired t-test). There was no correlation between total hypericin plasma concentrations and photosensitivity. In the multiple dose part, 50 volunteers received 600 mg hypericum extract t.i.d. with a daily dose of 5.6 mg of total hypericin. Comparison of UV light sensitivity before dosing with day 15 of treatment showed a slightly increased SSI sensitivity expressed by decrease of the MED from 0.17 to 0.16 J/cm2 (p = 0.005 by Wilcoxon test), and similarly, sensitivity to UV-A light increased (the mean tanning dose decreased from 9.9 to 7.8 J/cm2, p < 0.0001). This increase in cutaneous light sensitivity could be compensated by reducing irradiation time by 21%. Doses used in this study were higher than typical doses in current commercial preparations. In spite of these high doses in the double blind single dose part, frequency of side effects was equal to placebo medication and UV light sensitivity was not or only marginally increased. The study does not, however, exclude phototoxic reactions with doses above 11.25 mg of total hypericin and plasma levels above 100 micrograms/L. Furthermore, phototoxicity may be different after application of pure hypericin, since some constituents in the plant extract may exhibit protective effects.

PEG-Based Hydrogel Synthesis via the Photodimerization of Anthracene Groups

Abstract: Photo-cross-linking has received a considerable attention for the design of intelligent materials in biochemical and biomedical applications. In this report, we describe the synthesis and properties of a novel photoreversible poly(ethylene glycol)- (PEG-) based hydrogel system. 9-Anthracenecarboxylic acid was used to modify the hydroxyl groups of an eight-armed PEG polymer (molecular weight 20 000) and the degree of substitution was determined to be 87.4%. The PEG−anthracene macromers (PEG−AN) exhibited high photosensitivity at wavelengths close to visible light (absorption maxima at 366 and 380 nm) and underwent rapid and reversible photo-cross-linking upon exposure to alternating wavelengths of irradiation (365/254 nm) in the absence of photoinitiators or catalysts. Changes in light exposure and wavelength of irradiation reversibly altered the physicochemical properties of the PEG−AN hydrogel, including swellability, absorption spectrum, and topography.

Photosensitization of optical fiber and silica-on-silicon/silica waveguides.

Abstract: Localized heating with a flame is shown to be a simple and effective method for substantially augmenting the photosensitivity of high-silica optical waveguides to (UV) light. The method increases the photosensitivity of standard (Ge-doped core) telecommunications fiber by a factor greater than 10 (photoinduced ΔnUV > 10−3) and renders strongly photosensitive the cores of high-quality Ge:SiO2-on-Si and Ge:SiO2-on-SiO2 planar waveguides that were negligibly photosensitive before treatment. We have written large-modulation-depth Bragg gratings, in both fiber and planar optical waveguides photosensitized by our method, using KrF (249-nm) radiation incident upon the waveguides through a zero-order-nulled phase mask. It is noteworthy that photosensitization by our method is achieved with a negligible increase in loss at the three principal optical communication windows.