Surface coordination engineering of gold nanoclusters with Sc3+ for selective fluorescent detection of pyridoxal 5'-phosphate.

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.