From Golden Berry To Golden Nanoprobe: Sustainable Fluorescent Sensing of Torsemide For Doping Control in Athletes

Doping represents a critical threat to the integrity of competitive sports, with diuretics frequently misused as masking agents to facilitate the urinary excretion of other prohibited substances. Torsemide (TSD), a widely misused loop diuretic, requires a sensitive and selective method for its determination in biological matrices to support efficient doping control. Herein, a sustainable fluorescent nanosensor based on multi-self-doped carbon quantum dots was synthesized for the first time from golden berry (GBQDs) via a rapid, one-step microwave-assisted approach at 800 W in just 7 min without additional surface passivation agents. Notably, these innovative CDs outperform previous traditional methods, as their preparation relies on minimum energy consumption and green natural substrate. The fabricated GBQDs exhibited intense blue fluorescence at λ_ex/λ_em 350/423 nm, a quantum yield of 28.9%, nano-sized CDs (7.67 ± 1.02 nm), and a chemical composition of C (51.12%), N (22.8%), O (25.6%), S (0.02%), K (0.38%), Cl (0.04%), P (0.02%), and Cu (0.02%). The GBQDs demonstrated excellent aqueous solubility, remarkable photostability (3% fluorescence decrease after 60 min), and storage stability (in refrigerator) for 8 weeks. TSD selectively quenches GBQDs fluorescence via a combined inner filter effect and static quenching mechanism, forming the basis of a "turn-off" fluorescent nanosensor. Under optimized conditions, the method showed linearity over 0.5-30 μg/mL (r² = 0.9999), LOD of 0.110 μg/mL, LOQ of 0.335 μg/mL, high accuracy (99.75 ± 1.02%), precision (RSD < 1%), selectivity, and robustness. The proposed nanosensor was successfully applied for TSD determination in pharmaceutical dosage forms, human urine, and plasma with recoveries ranging from 99.43 to 100.29%. Greenness and blueness assessments using Complex-GAPI, BAGI (80), AGREE-Prep (0.79), and NAT (91) confirmed superior environmental sustainability and feasibility for on-site detection in doping regulation laboratories. This strategy offers a rapid, cost-effective, sensitive, and eco-friendly platform for anti-doping surveillance and therapeutic monitoring of TSD in biological matrices, guaranteeing fair competition and safeguarding athletes' health in the sports world.