CdSe Core and CdSe@ZnSe Core–Shell QDs Decorated with Human Serum Albumin: Deciphering the Antimicrobial Properties and Sensing of Mercury Ion

In recent decades, Cd-based quantum dots (QDs) have gained tremendous interest as luminescence tags for numerous biological applications. However, chemical synthesis using organic molecules to encapsulate the QDs surface is a highly complex process, high-cost and aggressive fabrication, and less aqueous and biocompatible, which leads to restricted biological applications. In this paper, we have reported the biogenic synthesis of CdSe-HSA core and CdSe@ZnSe-HSA core–shell QDs for the first time using human serum albumin protein as a surface engineering molecule. The biosynthesized QDs were found to be smaller in size (2–3.5 nm) and highly aqueous compatible (stable for up to 150 days). The biosynthesized QDs act as ultrasensitive fluorescence probes for label-free sensing of Hg2+ with enhanced efficiency, and an LOD value of 1.3 nM for CdSe@ZnSe-HSA QDs (concentration range: 0–2 μM) was obtained and were also able to detect with the naked eye. A dynamic quenching mechanism was observed for the fluorescence quenching of the biosynthesized QDs by Hg2+ ions, and affinity toward the formation of Hg–Se or Hg–SH with the QDs provided the unique selectivity. Moreover, the smaller size and unique surface properties of the biosynthesized QDs contributed to the enhanced antibacterial properties against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria and found more effective against Gram-negative bacteria. This work implies the biogenic aqueous compatible synthesis of core and core–shell QDs for biological and environmental monitoring analytical methods for the development of bionanotechnology.