Nitrogen-Doped Carbon Dots-Eu³⁺-Tetracycline as a Ratiometric Fluorescence Probe for Turn "Off-On" Determination of...

The monitoring of alkaline phosphatase (ALP) activity and pyrophosphate (PPi) concentration is critical for assessing phosphorus dynamics and eutrophication in aquatic ecosystems. However, on-site, rapid detection of these dual targets in complex water matrices remains a challenge. In this work, a nitrogen-doped carbon dots (N-CDs)-Eu³⁺-tetracycline (TC)-based ratiometric fluorescence probe was constructed for turn "off-on" determination of PPi and ALP based on the strong binding interaction between PPi and Eu³⁺ and PPi hydrolyzed by ALP. In the N-CDs-Eu³⁺-TC system, with the addition of PPi, PPi could replace the N-CDs to form the PPi-Eu³⁺-TC multicomplex, and N-CDs were released, resulting in the fluorescence quenching of Eu³⁺ and fluorescence recovery of N-CDs. ALP could hydrolyze PPi to PO₄ ^3-, which could destroy the PPi-Eu³⁺-TC multicomplex and form the N-CDs-Eu³⁺-TC multicomplex again, and the fluorescence of Eu³⁺ at 617 nm was recovered. The N-CDs-Eu³⁺-TC-based ratiometric fluorescent probe possesses a quick fluorescence response, obvious fluorescence color variance, and excellent selectivity and sensitivity with LOD of 40 nM for PPi and 0.03 U/L for ALP. The proposed probe was successfully applied for the detection of PPi and ALP in the actual environmental water samples or serum samples.