The persistence of multidrug resistance among microorganisms has directed a mandate towards a hunt for the development of alternative therapeutic modalities. In this context, antimicrobial photodynamic therapy (aPDT) is sprouted as a novel strategy to mitigate biofilms and planktonic cells of pathogens. Nanoparticles (NPs) are reported with unique intrinsic and antimicrobial properties. Therefore, silver NPs (AgNPs) were investigated in this study to determine their ability to potentiate the aPDT of photosensitizer against Staphylococcus aureus and Pseudomonas aeruginosa. Biologically synthesized AgNPs were surface coated with methylene blue (MB) and studied for their aPDT against planktonic cells and biofilms of bacteria. The nano-conjugates (MB-AgNPs) were characterized for their size, shape and coated materials. MB-AgNPs showed significant phototoxicity against both forms of test bacteria and no toxicity was observed in the dark. Moreover, activity of MB-AgNPs was comparatively higher than that of the free MB, which concludes that MB-AgNPs could be an excellent alternative to combat antibiotic resistant bacteria.
Stokes Mueller formalism is used to measure the optical properties of materials by probing the sensitive changes in the polarization state of light after scattering from the medium. The formalism can be extended to nonlinear scattering processes involving two and three photon processes also. In this paper, we derive the Stokes vector, viz. triple Stokes vector analytically from quantum theory of light for a three photon process. The state of polarization of light, with three simultaneous photons, incident on a material is described by triple Stokes vector, and has 16 components involving cubes of intensities dependence. The response of a material for the scattered light in a three photon process is described by 4 × 16 Mueller matrix. Polarization in Polarization out (PIPO) experiments can be carried out to determine the elements of Mueller matrix. We identify 16 independent points on Poincare sphere and construct triple Stokes vector for each point. Four measurements are done to determine the linear Stokes vector of scattered light, where the 16 polarization states are represented by triple Stokes vector and this determines the Mueller matrix of the sample.
An affordable kit which helps to understand some of the optical phenomena qualitatively and quantitatively is presented in this paper. It supplements optics taught in classes. The kit consists of equipments which are available in the market at nominal cost such as laser pointer, lenses, glass plates, razor blades, coins, ball bearing etc. Experiments which come under wave optics (interference and diffraction) and ray optics (reflection and refraction) are explained using this kit.
We report the significance of the double Stokes Mueller polarimetry (DSMP) technique, to characterize a large size (3 × 3 × 5mm) KTP (Potassium titanyl phosphate) crystal. The crystal undergoes second harmonic generation with type II phase matching. The study of standard KTP crystal using the DSMP technique helps to validate the efficiency of this technique. We were able to extract the crystal's double Mueller matrix, relative contribution of the susceptibility tensor components, the phase difference between the susceptibility tensor components, etc. We could determine the crystal axes orientation using this optical technique, which was not possible through a single crystal X-Ray diffraction technique for such a large size crystal for which both optic axes and crystallographic axes are the same. Axes direction determined from polarization microscope measurements and Laue diffraction measurements on KTP crystal is compared with those obtained from DSMP measurements.
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