Novel SQDs synthesized using L-cysteine bottom-up strategy based on FRET and second-order scattering for ratiometric...

A novel bottom-up green approach is presented for synthesizing blue fluorescent sulfur quantum dots (SQDs) utilizing L-cysteine as the sulphur source and the unique structure of carboxymethyl cellulose macromolecule as the passivating agent. The method accomplishes synthesis within a shortened reaction time of only 4 h. The formation of SQDs involves three steps: heating of L-cysteine to produce H₂S, which then reacts with H₂O₂ to form elemental sulphur, eventually assembling into SQDs. The prepared SQDs exhibit favorable water dispersibility and photostability, rendering them highly suitable for fluorescent sensors. Notably, fluorescence detection experiments reveal that fluorescence resonance energy transfer (FRET) between the SQDs and curcumin (Cur) results in diminished fluorescence of the SQDs (F₄₃₅) and an increase in scattered light signal (S₆₉₀). In addition, it shows promising ratiometric linearity of the Cur concentration in the range 0.10-12.00 µM with an impressive limit of detection of 19 nM. This work not only provides valuable insights into the green and convenient sustainable preparation of SQDs but also opens up avenues for their versatile applications.