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Biosynthesis of cadmium selenide quantum dots by Providencia vermicola

Cadmium selenide quantum dots (CdSe QDs) were synthesized by using Providencia vermicola BGRW, which has discriminatory ability to resist many metals such as Selenium, Cadmium, Silver, Zinc, Copper, Lead, Nickel, Cobalt and Bismuth metals. BGRW was able to grow in the presence of 6 mM of CdCl2. The best conditions for extra/intracellular CdSe QDs synthesis were 0.1 mM SeO2: 0.9 mM CdCl2, 37°C, pH 9 within 24 h. The biosynthesis of CdSe QDs was monitored by UV–Visible spectrum that showed surface plasmon resonance (SPR) peaks at 388 nm. Depending on fluorescence property of quantum dots, photoluminescence characteristics of the biogenic CdSe QDs were at 385 nm. Further characterization of synthesized CdSe QDs was carried out using the X-ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Fourier Transform Infrared (FTIR) spectroscopy. TEM and XRD analysis revealed that CdSe QDs was cubic in shape with a size range of ∼2 to 4 nm. EDS analysis confirmed the composition of QDs from cadmium and selenium ions. FTIR spectroscopy confirmed the presence of proteins as the stabilizing agent surrounding the quantum dots. 
 
   
 
 Key words: Quantum dots, cadmium selenide quantum dots, capping agent, transmission electron microscope, fluorescence spectroscopy, X-ray and FTIR analysis.