Synthesis and optimization of emission characteristics of water-dispersible ag-in-s quantum dots and their bactericidal activity

Developing novel aqueous-soluble quantum dots (QDs) can create new opportunities for better biological utilization. In the present work, novel, high emissive and biocompatible N-acetyl-L-cysteine-capped Ag-In-S QDs (as an I-III-VI structure) were prepared in a facile and straightforward way. The dominance of the strong confinement regime was observed due to the very small size of nanoparticles, which was smaller than their excitonic Bohr radius. To prepare reproducible Ag-In-S QDs, their emission characteristics were improved by optimizing the experimental variables which resulted in the enhancement of their emission quantum yield to near 32% at 615 nm. The absorption and emission results support the contribution of band edge-independent radiative recombination pathways for charge carriers in the prepared Ag-In-S QDs. The possible mechanisms for such donoracceptor recombination were also discussed. To explore the antibacterial ability of the Ag-In-S QDs, their bactericidal activity was evaluated against different types of Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coil and Salmonella enterica) bacteria. Precise measurements confirmed a remarkable bactericidal activity of Ag-In-S QDs against the different pathogenic bacteria even at low concentration of QDs (15 mu g/mL). It was found that the QDs are more effective on Gram-negative bacteria. While the preparation method was simple and cost-effective, the as-synthesized QDs were highly emissive and stable with significant antibacterial activity. This demonstrates the great potential of present Ag-In-S QDs for future hygienic and medical purposes.