Surface coordination engineering of gold nanoclusters with Sc³⁺ for selective fluorescent detection of pyridoxal...

Pyridoxal 5'-phosphate (PLP), the active coenzyme form of vitamin B₆, plays indispensable roles in multiple metabolic pathways, and its abnormal levels are closely related to a variety of diseases. Herein, we developed a rapid and sensitive fluorescent sensing platform for PLP determination based on surface coordination engineering of 6-aza-2-thiothymine-stabilized gold nanoclusters (ATT-AuNCs) through a Sc³⁺-mediated competitive coordination strategy. Among 16 screened rare-earth ions, Sc³⁺ exhibited the strongest fluorescence activation toward ATT-AuNCs, inducing an approximately 38-fold emission enhancement together with a pronounced bathochromic shift. These effects are attributable to Sc³⁺ coordination to the N/O donor sites of the ATT ligands, which stabilizes an intramolecular charge-transfer (ICT) emissive state and restricts intramolecular motions, thereby suppressing nonradiative decay. In the presence of PLP, the phosphate oxygen donors competitively bind Sc³⁺, extracting it from the nanocluster surface and reversing the Sc³⁺-induced fluorescence enhancement in a concentration-dependent manner. Under optimized conditions, the proposed assay enabled PLP quantification over a linear range of 0.1-8 μM with a detection limit of 0.04 μM. The sensor also exhibited excellent reproducibility, good selectivity against vitamin B₆ analogues and common coexisting species, and satisfactory recovery in spiked serum samples. This work presents a facile and reliable fluorescence-based strategy for PLP analysis and provides a versatile route to constructing nanocluster-based probes through coordination modulation regulated by hard Lewis acids.