Optical, Electrical, and Morphologic Characterization of Chromium-Impurified CdS Thin Films Elaborated by the Chemical Bath Deposition.

In this research work, a material system formed of cadmium sulfide combined with chromium atoms was developed to evaluate the influence of chromium concentration on the optical, electrical, structural, and morphological properties of a precursor layer of CdS. It is possible to observe that the transmission spectra increased for all chromium concentrations analyzed. From X-ray diffractograms, we conclude more accurately that CdS presents a mixture of phases, including orthorhombic, hexagonal, and cubic. Furthermore, the impact of adding chromium results in variations in the intensity of two major peaks in the diffractograms and an anomalous shift in the CdS pattern. The calculated resistivities show an invariable behavior of 4.5 × 106 Ω cm. In addition, the bandgap values remain practically constant, with values of approximately 2.43-2.44 eV. The addition of chromium at different concentrations leads to surface morphology changes, as observed in SEM images.

Effect of Physiological Fluid on the Photothermal Properties of Gold Nanostructured.

Colloidal gold particles have been extensively studied for their potential in hyperthermia treatment due to their ability to become excited in the presence of an external laser. However, their light-to-heat efficiency is affected by the physiologic environment. In this study, we aimed to evaluate the ability of gold sphere, rod, and star-shaped colloids to elevate the temperature of blood plasma and breast cancer-simulated fluid under laser stimulation. Additionally, the dependence of optical properties and colloid stability of gold nanostructures with physiological medium, particle shape, and coating was determined. The light-to-heat efficiency of the gold particle is shape-dependent. The light-to-heat conversion efficiency of a star-shaped colloid is 36% higher than that of sphere-shaped colloids. However, the raised temperature of the surrounding medium is the lowest in the star-shaped colloid. When gold nanostructures are exited with a laser stimulation in a physiological fluid, the ions/cations attach to the surface of the gold particles, resulting in colloidal instability, which limits electron oscillation and diminishes the energy generated by the plasmonic excitation. Fluorescein (Fl) and polyethylene glycol (PEG) attached to gold spheres enhances their colloidal stability and light-to-heat efficiency; post-treatment, they remand their optical properties.

Bio-synthesis of gold nanoparticles by human epithelial cells, in vivo.

Healthy epithelial cells, in vivo, have the ability to synthesize gold nanoparticles when aqueous tetrachloroauric acid is made to react with human skin. Neither a reducing agent nor a protecting chemical is needed for this bio-synthesis method. The first indication of gold nanoparticle formation is the staining of the skin, which turns deep purple. Stereoscopic optical micrographs of human skin tissue in contact with aqueous tetrachloroauric acid clearly show the staining of the epithelial cells. The UV-Vis spectrum of these epithelial cells shows an absorption band with a maximum at 553 nm. This absorption peak is within the wavelength region where the surface plasmon resonance (SPR) band of aqueous colloidal gold exhibits a maximum. Transmission electron micrographs show that gold nanoparticles synthesized by epithelial cells have sizes between 1 and 100 nm. The electron diffraction pattern of these nanoparticles reveals a crystalline structure whose interplanar distances correspond to fcc metallic gold. Transmission electron micrographs of ultra-thin (70 nm thick) slices of epithelial cells clearly and undoubtedly demonstrate that gold nanoparticles are inside the cell. According to high resolution transmission electron micrographs of intracellular single gold nanoparticles, they have the shape of a polyhedron.