Feliciano Crespo, Raquel

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    Diffracted light contrast: A chemical application
    (2010) Feliciano Crespo, Raquel; Castro Rosario, Miguel E.; College of Arts and Sciences - Sciences; Irizarry, Roberto; Mina Camilde, Nairmen; Department of Chemistry; Suárez, O. Marcelo
    There is a tremendous interest in the development of microscopy tools that can provide important information at a cost significantly smaller than those offered by traditional electron microscopes. With the purpose of learning about a new microscopy tool and at the same time contribute to the current body of understanding related to the chemistry of explosives, we report here on spectroscopy and microscopy measurements performed on trinitrotoluene (TNT). Crystals and non-crystalline TNT samples were characterized with diffracted light microscopy (DLC), near IR spectroscopy and UV visible absorption spectroscopy. DLC is an optical microscopy tool under development elsewhere claimed to allow 3 dimensional observations of materials. The technique was employed in the characterization of crystalline and non crystalline TNT particles, exposed and non-exposed to sunlight. A colored solution is observed upon sunlight exposure to TNT in the presence of a protic solvent. The solution exhibit light absorption in the visible region of the spectra: no absorption is observed in TNT solutions not exposed to sunlight. New bands are observed in the near IR spectra of TNT deposits exposed to sunlight. The advantages and limitations of the DLC to the characterization of this system as well as the chemistry of sunlight exposed TNT based on our results will be discussed.
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    Pathogenic bacteria detection by coupled water-soluble Cd- and Zn-based fluorescent nanocrystals
    (2019-05-15) Feliciano Crespo, Raquel; Perales Pérez, Oscar J.; College of Arts and Sciences - Sciences; Román Velázquez, Félix R.; Rivera Portalatín, Nilka M.; Meléndez Martínez, Enrique; Department of Chemistry; Santana Morant, Dámaris
    Semiconductors quantum dots are considered very promising candidates for bio-imaging, microorganism detection and diagnosis applications, among others, because of their tunable optical properties and good optical stability in aqueous phase. Any practical application of these materials will rely on the viability of their simple and direct synthesis in aqueous phase with no need for toxic and unstable organic media. The optical properties that can be found in Cd and Zn-based quantum dots, for example, are desirable in bio-imaging, pathogen detection and cell sorting application because of their tunable photoluminescence at the visible range. The present work addresses the synthesis of Cd-based and Zn-based water soluble quantum dots via an optimized, simple and scalable aqueous processing route at low temperatures to be applied as bio markers for bacteria that may cause serious illness to human body. The tuning of the optical properties was achieved by a suitable control of the citrate/Cd mole ratios, temperature of synthesis (20-90°C) and reaction time (0-1hour). Nanocrystals were characterized by X-Ray Diffraction, Fourier Transform Infrared (FT-IR), Near Infrared Spectroscopy (NIR), UV-VIS Spectroscopy and Photoluminescence (PL) spectroscopy techniques. The effect of the synthesis conditions on the crystal size and the corresponding functional properties of synthesized quantum dots are presented and discussed. The coupling interaction between QDs and bacteria strains were analyzed and detected by Fluorescence spectroscopy. The correlation between QDs-bacteria interaction were analyzed with fluorescence spectroscopy as a rapid detection method for Escherichia coli, Staphylococcus aureus, Salmonella thyphimurium and Listeria monocytogenes are presented and the mechanisms involved, discussed.