Facile Synthesis of β-Lactoglobulin Capped Ag₂S Quantum Dots for In Vivo Imaging in the Second Near-Infrared Biological Window

Effective in vivo fluorescence imaging for cancer screening and diagnostics requires bright and biocompatible fluorophores whose emission can effectively penetrate biological tissues. Recent studies have confirmed that the second near-infrared window (NIR-II, 1,000-1,400 nm) is the most sensitive spectral range for in vivo imaging due to ultralow tissue absorption and autofluorescence. We report herein a facile synthesis of Ag₂S quantum dots (QDs) that emits at ~1100 nm using β-lactoglobulin (β-LG) as biological template. The β-LG protein coating improves water-solubility, faciliates rapid biodistribution and reduces in vivo toxicity of the QDs. Compared to other currently used NIR emitters, β-LG capped Ag₂S QDs exhibit superior photostablity and biocompatibility, making them a promising probe for in vivo NIR-II imaging.