The effect of UV irradiation on uracil thin layer measured by optical waveguide lightmode spectroscopy

Biological sensors for solar ultraviolet radiation

Solar ultraviolet (UV) radiation is widely known as a genotoxic environmental agent that affects Earth ecosystems and the human population. As a primary consequence of the stratospheric ozone layer depletion observed over the last decades, the increasing UV incidence levels have heightened the concern regarding deleterious consequences affecting both the biosphere and humans, thereby leading to an increase in scientific efforts to understand the role of sunlight in the induction of DNA damage, mutagenesis, and cell death. In fact, the various UV-wavelengths evoke characteristic biological impacts that greatly depend on light absorption of biomolecules, especially DNA, in living organisms, thereby justifying the increasing importance of developing biological sensors for monitoring the harmful impact of solar UV radiation under various environmental conditions. In this review, several types of biosensors proposed for laboratory and field application, that measure the biological effects of the UV component of sunlight, are described. Basically, the applicability of sensors based on DNA, bacteria or even mammalian cells are presented and compared. Data are also presented showing that on using DNA-based sensors, the various types of damage produced differ when this molecule is exposed in either an aqueous buffer or a dry solution. Apart from the data thus generated, the development of novel biosensors could help in evaluating the biological effects of sunlight on the environment. They also emerge as alternative tools for using live animals in the search for protective sunscreen products.

Quasi-isotropic analysis of anisotropic thin films on optical waveguides

Thin films assembled on a substrate are often anisotropic. Nevertheless, because of experimental limitations, sufficient parameters to characterize the anisotropy, even in the simplest (and perhaps most common) case of uniaxial thin films, which are birefringent, are not usually available. This paper examines the consequences of treating them as isotropic thin films, with particular reference to their characterization via perturbation of the propagation constants (effective refractive indices) of optical waveguides. It is shown that the refractive index and geometrical thickness of a thin film thus calculated are often unrealistic (especially when the thin film is positively birefringent), but the mass per unit area may be quite precise, depending on the sign and magnitude of the birefringence.

The effect of the short wavelength ultraviolet radiation. An extension of biological dosimetry to the UV-C range

Polycrystalline uracil thin layer can be used as biological dosimeter for assessing exposure to UV radiation. The dimerization and reversion efficiency of the ultraviolet radiation in the UV-B and the UV-C range were quantified on polycrystalline uracil thin layers irradiated with quasi-monochromatic radiation using interference filters of 10nm bandwidth. The dimer formation and monomerization (reversion) dose-effect relations were determined by optical spectroscopy. The decrease of the OD value of the uracil thin layer at 288 nm was taken as a measure of the dimer formation, while the increase of the OD of a completely irradiated (until reaching the saturation level) uracil layer was taken as the sign of the monomerization. The two processes in the UV-B and the UV-C range take place simultaneously, the individual characterization of the dimerization efficiency was performed from the initial slope of the dimerization dose-effect function and an action spectrum for dimerization was constructed in the UV-C range too. The reversion efficiency was found to be practically the same with all of the investigated wavelengths: 200 nm, 210 nm, 220 nm, 230 nm, 240 nm The possible biological relevance of the reversion of dimers are discussed.