l-cysteine capped MoS2 QDs for dual-channel imaging and superior Fe3+ ion sensing in biological systems†

MoS₂ quantum dots (MQDs) with an average size of 1.9 ± 0.7 nm were synthesized using a microwave-assisted method. Absorbance studies confirmed characteristic transitions of MoS₂, with absorption humps at 260–280 nm and 300–330 nm, and a band gap of 3.6 ± 0.1 eV. Fluorescence emission studies showed dominant blue and some green emissions under 315 nm excitation, with an absolute quantum yield of ∼9%. The MQDs exhibited fluorescence stability over time after repeated quenching cycles across various pH and media systems. In vitro toxicity tests indicated cytocompatibility, with around 80% cell survival at 1000 mg L⁻¹. Confocal imaging demonstrated significant uptake and vibrant fluorescence in cancerous and non-cancerous cell lines. The MQDs showed strong selectivity towards Fe³⁺ ions, with a detection limit of 27.61 ± 0.25 nM. Recovery rates for Fe³⁺ in phosphate buffer saline (PBS) and simulated body fluid (SBF) systems were >97% and >98%, respectively, with a relative standard deviation (RSD) within 3%, indicating precision. These findings suggest that MQDs have high potential for diagnostic applications involving Fe³⁺ detection due to their fluorescence stability, robustness, enhanced cell viability, and dual-channel imaging properties.