Pathogenic bacteria detection by coupled water-soluble Cd- and Zn-based fluorescent nanocrystals

Abstract

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.