Aqueous-phase synthesis of dual-anion CuInSeS quaternary quantum dots for ultrasensitive D-penicillamine detection via inter filter effect.

Dual-anion CuInSeS quaternary quantum dots (QDs) were synthesized through an aqueous-phase colloidal method. By precisely controlling the Cu/In cation ratio and S/Se anion ratio, CuInSeS QDs with optimal fluorescence performance were successfully prepared. The prepared quaternary QDs exhibited an extended fluorescence lifetime of about 100 ns. The fluorescence emission peak of CuInSeS QDs was located in the near-infrared first window, which effectively reduced self-absorption interference and provided a crucial foundation for constructing high signal-to-noise ratio fluorescent probes. Consequently, a highly sensitive fluorescent probe (CuInSeS-Fe2+) was developed for detecting D-penicillamine (D-PA). Mechanistic studies revealed that the fluorescence intensity of CuInSeS QDs remained stable in the presence of Fe2+ alone. However, density functional theory (DFT) calculations demonstrated that the Fe2+ ion can form a complex with D-PA through coordination bonds with S and N atoms, exhibiting a monodentate chelation mode. The formation of the Fe2+ + D-PA complex exhibited a broad UV-Vis absorption band (400-800 nm) that partially overlapped with both the excitation and emission spectra of CuInSeS QDs, inducing fluorescence quenching via the inner filter effect (IFE). The established detection method demonstrated a linear response (R2 = 0.993) within 18-1000 µM of D-PA concentration, with a limit of detection (LOD) of 5.42 µM. Successful quantification of D-PA in human serum samples achieved spiked recoveries of 97.77%-102.8%, confirming method reliability. This study provides a novel design strategy for dual-cation and dual-anion quaternary QD-based fluorescent probes, demonstrating potential application value in clinical drug monitoring.