Ultrasensitive detection of alogliptin <i>via</i> fluorescence quenching of terbium-doped carbon quantum dots: mechanistic investigation, Box–Behnken optimization and analytical evaluation

A rapid, sensitive, and eco-friendly fluorescence-based analytical method was developed for the determination of the antidiabetic drug alogliptin using terbium-doped carbon quantum dots (Tb-CQDs) as a fluorescence probe. The Tb-CQDs were comprehensively characterized using dynamic light scattering, transmission electron microscopy, UV-vis spectroscopy, and fluorescence spectroscopy, revealing uniform spherical nanoparticles with strong blue emission at 448 nm. The sensing mechanism, investigated through Stern-Volmer analysis and thermodynamic studies, demonstrated a static quenching process involving the formation of a ground state complex between Tb-CQDs and alogliptin, with negative Δ<i>H</i> and positive Δ<i>S</i> values confirming the spontaneous interaction driven by hydrogen bonding and van der Waals forces. To maximize analytical performance, critical parameters affecting the quenching process (pH, Tb-CQDs volume, and incubation time) were systematically optimized using a Box-Behnken design of experiments. The statistical analysis through ANOVA confirmed the significance of the obtained quadratic model (<i>p</i> < 0.0001), revealing that pH and Tb-CQDs volume significantly influenced quenching efficiency both independently and synergistically. Under optimal conditions (pH 8.8, 1.34 mL Tb-CQDs, 1.2 min incubation), the developed method exhibited excellent linearity in the range of 0.01-1.5 μg mL^-1 with a limit of detection as low as 3.20 ng mL^-1. The validated method was successfully applied for alogliptin analysis in pharmaceutical formulations, spiked human plasma, and environmental water samples, with satisfactory recovery rates (95.10-103.79%). Additionally, the greenness and blueness assessments revealed the superior environmental compatibility and comparable analytical practicality of the Tb-CQDs fluorescence technique compared to conventional HPLC-UV approaches, highlighting the sustainability advantages of this nanomaterial-based sensing platform.