Metal-Free Elemental Selenium Quantum Dots: A Novel and Robust Fluorescent Nanoprobe for Cell Imaging and the Sensitive Detection of Cr(VI)

In this paper, we present a simple solvothermal method to synthesize highly fluorescent metal-free elemental selenium quantum dots (SeQDs) using cost-effective bulk selenium powder. The SeQDs exhibit a small and uniform size, excellent aqueous dispersibility, a high photoluminescence quantum yield (PLQY) of 19.3% with stable fluorescence, and scalable production with a 7.2% yield. Owing to the inner filter effect (IFE), these SeQDs function as a highly effective nanoprobe for Cr(VI) detection, exhibiting exceptional sensitivity (detection limit: 145 nM) and selectivity over a wide linear range (5-105 μM), along with rapid response kinetics. Moreover, SeQDs show low cytotoxicity and efficient cellular uptake, enabling cell imaging and intracellular Cr(VI) monitoring. Significant fluorescence quenching in Cr(VI)-exposed cells confirms the potential of SeQDs as a viable fluorescent nanoprobe for Cr(VI) detection in complex cellular environments. This work thus not only establishes a simple method for the preparation of fluorescent SeQDs but also develops a promising fluorescent nanoprobe for cell imaging and Cr(VI) sensing.