Fluorescent Realgar Quantum Dots: New Life for an Old Drug

Quantum dots (QDs) possess unique properties that are expected for various applications. Herein, realgar (As4S4) QDs were synthesized via a wet chemical method in a coordinating solvent (e.g., ethanolamine (EA)) with assistance of an acid (e.g., citric acid (CA)). The asprepared realgar QDs using EA and CA have a narrow size distribution with a mean value of 5.48 nm and a relative standard deviation of similar to 20%, and exhibit bright photoluminescence (PL) in a short wavelength window (< 480 nm) with high quantum yield up to 70%. Moreover, realgar QDs can retain their high PL after one-year storage, indicating their excellent stability. Bulk realgar is a commonly used traditional medicine, however, its water-insolubility limits its broad applications. Realgar QDs could be an alternative for the bulk realgar owing to their excellent water-solubility and efficient PL. In preliminary in vivo toxic and pharmaceutical experiments, the synthesized realgar QDs at a single oral dose of 10.0 mg realgar/kg body weight for 21 days showed tolerability in healthy mice and effective against tumor-bearing nude mice, respectively. In this study, assembly of realgar QDs into specific hollow nanospheres was first constructed by introducing an acid into their original colloidal solution. Simple dissolution of such assemblies in EA can partially return them into the fluorescent QDs. Such property is desired for a variety of media-responsive luminescence materials. In addition, a flexible inorganic/organic hybrid composite film was fabricated for the first time by incorporation of realgar QDs into polyvinyl alcohol matrix. The resulting film presents excellent PL, good transparency, intense mechanical strength and facile processibility, which meet the requirements for device integration.