An effective fluorescence strategy based on xanthine oxidase catalysis and the carbon dots’ specific response to ·OH for aminophylline pharmacokinetic studies

Aminophylline (AMP), a xanthine-derived bronchodilator with a narrow therapeutic window, requires timely plasma concentration monitoring and pharmacokinetic (PK) studies for safe medication. However, efficient and sensitive detection methods remain limited. In this study, high quantum yield carbon dots (CA/EDA-CDs) were synthesized via a hydrothermal method using riboflavin as the carbon source, citric acid and ethylenediamine as functionalizing agents and dopants. The luminescent structure of CA/EDA-CDs, featuring a π-conjugated system (aromatic C=C and graphite N) and surface chromophores (C=N/C=O) connected via C-N, C-O, and hydrogen bonds, was controllably modulated by hydroxyl radical (·OH). Upon ·OH exposure, the emission band gaps of CA/EDA-CDs at 3.52 eV and 5.21 eV disappeared, while a new level at 2.63 eV emerged, leading to a quantitative and selective fluorescence quenching of CA/EDA-CDs to ·OH. Leveraging xanthine oxidase (XOD)-mediated AMP oxidation to hydrogen peroxide (H₂O₂), which subsequently reacted with Fe²⁺ to generate ·OH, a sensitive and accurate fluorescence method using CA/EDA-CDs as probe was fabricated for monitoring AMP with excellent performance. Furthermore, the developed fluorescence strategy was controllably applied to PK studies in rats administered intravenous AMP (11.25 mg/kg and 22.50 mg/kg), yielding parameters consistent with clinical data. These findings underscore the potential of CA/EDA-CDs for rapid and accurate AMP detection, addressing the clinical need for a simple and rapid monitoring method.