BSA-assisted hydrothermal conversion of MoS nanosheets into quantum dots with high yield and bright fluorescence for constructing a sensing platform via dual quenching effects.

With large surface-responsive and excitation-dependent fluorescence, two-dimensional fluorescent quantum dots (QDs) have been receiving tremendous attention to develop their facile synthetic approaches and/or expand their promising applications. Here, a two-step strategy is demonstrated for high-yield production of MoS QDs from MoS powder through first sonication-driven exfoliation and subsequent hydrothermal splitting with the assistance of bovine serum albumin (BSA). Experimentally, ∼100 nm-sized MoS nanosheets are ultrasonically exfoliated from MoS powder in a BSA solution, and further hydrothermally split into ∼ 8.2 nm-sized QDs (NQDs) at 200 °C. In addition to their excellent stability/dispersibility in aqueous solution, the resultant MoS NQDs also exhibit much brighter blue fluorescence than those synthesized by other methods. The strong fluorescence is significantly quenched by p-nitrophenol for constructing a sensitive sensor with high selectivity, which is attributed to dual quenching effects from inner filter effect (IFE) and fluorescence resonance energy transfer (FRET). Interestingly, with the increment of pH from 5 to 10, the ratio of IFE in fluorescence quenching gradually decreases accompanied by an increment of FRET ratio, resulting in the high sensitivity and responsivity for detecting p-nitrophenol at a wide range of pH. Clearly, the MoS NQD-based sensing approach demonstrates a promising potential for selective detection and fast analysis of pollutants in environment monitoring and security screening.