Poly(diallydimethylammonium chloride)-Induced Dispersion and Exfoliation of Tungsten Disulfide for the Sensing of Glutathione and Catalytic Hydrogenation of p-Nitrophenol

Poly(diallydimethylammonium chloride) (PDDA) has been demonstrated to be valuable in diverse fields, such as layer-by-layer assembly and material surface modification. Herein, we report a novel application of PDDA for exfoliating bulk tungsten disulfide (WS2) into few-layer WS2 nanosheets (FL-WS2-NSs) under ultrasonication treatment. Cationic PDDA molecules were capable of firmly binding to the WS2 surface to expose quaternary ammonium moieties in water, thereby creating electrostatic repulsion between each FL-WS2-NS. The formation of FL-WS2-NSs was proven by absorption spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. Additionally, PDDA molecules enable FL-WS2-NSs to be stable in 200 mM NaCl for more than six months without thermal-triggered nanosheet aggregation. Given that PDDA-stabilized FL-WS2-NSs (PDDA-FL-WS2-NSs) exhibit sulfur vacancy sites, thiolated boron–dipyrromethene (BODIPY) molecules were self-assembled onto the surface of PDDA-FL-WS2-NSs. As a result, the fluorescence of BODIPY was quenched by the mixing of static and dynamic quenching processes. The presence of glutathione (GSH) induced the liberation of BODIPY from BODIPY-conjugated PDDA-FL-WS2-NSs, thereby restoring its fluorescence. This fluorescent probe allowed for the quantitative determination of GSH in erythrocytes and the fluorescence imaging of GSH-related reactions in HeLa cells. Additionally, PDDA-FL-WS2-NSs were implemented as a platform for complexing with citrate-capped nanoparticles of Au, Pd, and Pt. The hybrids of PDDA-FL-WS2-NSs and metal nanoparticles (NPs) were more efficient for catalyzing the NaBH4-mediated reduction of 4-nitrophenol than metal NPs. It is evident that PDDA-FL-WS2-NSs are readily conjugated to thiol-terminated organic dyes and other existing nanomaterials.