Rivera Vázquez, Daniel

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    Synthesis and characterization of calcium sulfide nanoparticles
    (2014) Rivera Vázquez, Daniel; Castro-Rosario, Miguel E.; College of Arts and Sciencies - Sciences; Cádiz, Mayra E.; Santana, Alberto; Uwakweh, Oswald N.C.; Department of Chemistry; Gutiérrez, Gustavo
    Calcium sulfide (CaS) nanoparticles are cadmium free fluorescent nanostructures with potential applications in nanomedicine and as a sensing material. We employed different methods for the synthesis of CaS nanoparticles, including (1) the reaction of calcium acetate (Ca(CH₃CO₂)₂) and sodium sulfide (Na₂S) in dimethyl sulfoxide (DMSO), (2) the reaction of Ca(CH₃CO₂)₂ and DMSO in a microwave and (3) dissolving bulk quantities of CaS in DMSO. UV-Vis spectroscopy was used to determine the optical properties of the CaS nanostructures. The absorption spectra of CaS prepared from these methods consists of a well-defined peak in the UV and a long wavelength tail that extends above 700 nm. Emission bands centered around 500 nm with a long wavelength tail that extends above 600 nm are observed upon excitation at 405 nm. Scanning tunneling microscopy (STM) was used for determining the average diameter of CaS nanostructures of (3.3 ± 0.7) nm. The direct and indirect band gaps are estimated to be (0.403 ± 0.003) eV and (4.135 ± 0.006) eV. Configuration interaction singles (CIS) calculations were used to determine the electronic transition spectra of small CaS clusters. Unique to CaS nanostructures is the absorption of light at wavelengths longer that in the bulk material instead of the blue shift associated with quantum confinement effects in semiconductors. Indeed, the strong absorption bands in the visible region of the spectra of the CaS nanostructures do not have a counterpart in the gas or solid phases, with implications in the field of sensing using semiconducting nanoparticles. Density functional theory (DFT) calculations on small CaS clusters are used to establish the vibrational properties of calcium sulfide nanoclusters. Naked CaS nanostructures are found to limit the survival rate and inhibit the growth rate of carcinoma cancer cell lines (ATCC CRL-2124). A single dose of a dispersion containing (3.3 ± 0.7) nm CaS nanoparticles (total calcium content of 3.8 x10⁻⁸ moles) results in a sharp decrease in the density of live cells and a sharp increase in the number of dead cells 96 hours following the dose. No changes are observed in adenocarcinoma control cell lines. CaS do not have any effect on the survival and growth rate of normal fibroblasts as compared to control cell cultures of normal fibroblasts, which suggests that CaS nanostructures are cancer specific. The small size of the nanostructures allows them to have access to the normal and newly developed blood vessels-due to angiogenesis and elimination by the human body. The results encourage further research to establish the mechanisms of action of CaS in cancer cell cultures and laboratory animals.