Positively charged sulfur quantum dots: an outstanding fluorescent nanoprobe for sensitive and selective detection of 2,4,6-trinitrophenol (picric acid).

2,4,6-Trinitrophenol (TNP), a toxic and explosive nitroaromatic industrial pollutant, necessitates low-cost, heavy-metal-free fluorescent probes with superior water dispersibility for sensitive aqueous monitoring. Herein, positively charged amine-functionalized sulfur quantum dots (A-SQDs) are fabricated via a one-pot solvothermal strategy, serving as a novel fluorescent nanoprobe for sensitive and selective TNP detection. The resultant A-SQDs exhibit a uniform particle size of about 2.47 nm, persistent positive surface charge over a wide pH window of 3-10, and a high photoluminescence quantum yield (PLQY) of 68.4%. TNP exhibits a distinct fluorescence quenching effect toward A-SQDs. This quenching is mainly caused by the pronounced spectral overlap between A-SQDs and TNP via the inner filter effect (IFE); other molecular interactions such as electrostatic interactions also participate in the fluorescence quenching process. This sensing system displays a linear response to TNP concentrations ranging from 0.27 to 45 µM with a low limit of detection of 82.6 nM, accompanied by rapid signal response, robust anti-interference against structural analogues, and satisfactory recoveries of 95.3-103.3% in river and tap water samples. Additionally, portable fluorescent test papers are constructed to enable visual on-site discrimination of TNP. This study pioneers A-SQDs-based TNP sensing probes, featuring low toxicity, simple synthetic procedures and promising prospects for practical sensing applications.