Aqueous synthesis of biocompatible and photoluminescent Mn-, Gd- or Fe-doped Ag-In-Zn-S quantum dots for cell imaging

We report a facile three-step aqueous synthesis of highly luminescent Ag-In-Zn-S (AIZS) quantum dots (QDs) doped with Mn, Gd, or Fe ions using glutathione (GSH) as biocompatible stabilizer. Conducted entirely in aqueous media at mild temperatures (100 °C) under ambient conditions, this environmentally sustainable approach avoids the need for toxic organic solvents typically required in organic syntheses. The doped AIZS QDs exhibit narrow size distributions (2.2–2.5 nm) and exceptional optical properties, achieving photoluminescence quantum yields (PL QYs) up to 69.3% for Gd-doped QDs. Comprehensive characterization revealed successful dopant incorporation with varying efficiencies. Magnetic measurements demonstrated tunable paramagnetic behavior with magnetization values ranging from 0.175 to 10 emu/g, though these values remain below clinical MRI requirements. Surface functionalization with poly(ethylenimine) (PEI) and folic acid (FA) used as targeting ligand enabled specific cellular uptake while maintaining excellent biocompatibility (>76% cell viability). The QDs displayed remarkable colloidal stability across physiological pH ranges and demonstrated efficient cellular labeling with predominantly cytoplasmic localization. These combined properties position the synthesized AIZS QDs as promising candidates for fluorescence-based biomedical imaging applications, with preliminary magnetic sensitivity providing a foundation for future dual-modal optimization.