Functionalized WS₂ Quantum Dots as Fluorescent Nanoprobes for In Vivo Bioimaging

The strong fluorescence and high photostability of inorganic quantum dots (QDs) have envisaged them as superior fluorescent probes for biomedical imaging applications compared to organic dyes that are highly prone to photobleaching. However, earlier reports suggest that the potential use of inorganic QDs can be ensured only if they remain fluorescent and stably dispersed in water and other biological fluids under a wide pH range. In the present work, we address in detail the influence of pH (range 1.0-13.0) on the photophysical properties of functionalized tungsten disulfide QDs (f-WS2-QDs) synthesized using a facile, eco-friendly, and single-step hydrothermal approach. Experimental findings suggest that the fluorescence nature of as-produced f-WS2-QDs remains highly stable in harsh acidic to basic media. The PL stability and dispersion of f-WS2-QDs in aqueous media are explained in terms of various functional groups present over the QDs' surface, which causes surface passivation of the QDs during hydrothermal growth leading to the high solubility and stable fluorescence of QDs in aqueous media. Furthermore, as a proof of concept, we have also demonstrated that the f-WS2-QDs could be potentially used as a fluorescent probe for high-contrast in vivo imaging of Drosophila third instar larvae. Thus, we anticipate that the present investigation may provide insight into the scientific community for the development of pH-universal inorganic QDs for biological applications.