Aqueous synthesis of red fluorescent l-cysteine functionalized Cu₂S quantum dots with potential application as an...

Water-stable Cu₂S quantum dots were obtained by applying l-cysteine as a Cu(ii) to Cu(i) reducer and stabilizer in water and using an inert atmosphere at ambient temperature. The obtained quantum dots were characterized by STEM, XRD, FT-IR, UV-Vis, Raman, and fluorescence spectroscopy. The synthesis was optimized to achieve Cu₂S quantum dots with an average diameter of about 9 nm that show red fluorescence emission. l-cysteine stabilization mediates crystallite growth, avoids aggregation of the quantum dots, and allows water solubility through polar functional groups, improving the fluorescence. The fluorometric test in the presence of the aptamer showed a shift in fluorescence intensity when an aliquot of As(iii) with a concentration of 100 pmol l^-1 is incorporated because As(iii) and the used aptamer make a complex, leaving free the quantum dots and recovering their fluorescence response. The developed Cu₂S quantum dots open possibilities for fluorescent detection of different analytes by simply changing aptamers according to the analyte to be detected.