Dual-substrate-based full-color fluorescent probe TPE-4PA@Tb/Eu-GMP-acac ICPs for alkaline phosphatase detection and its on-site application for algal bloom alert.

Abstract

The development of rapid, on-site analytical methods and test strips for alkaline phosphatase activity (APA) is crucial for addressing drinking water safety crises, as it enables eutrophication assessment and algal bloom warnings under phosphorus-limited conditions. In this study, we incorporate aggregation-induced emission luminogen (AIEgen) guest TPE-4PA into bimetallic lanthanide-based infinite coordination polymers (Tb/Eu-GMP ICPs). TPE-4PA exhibits unprecedented binding preference for Tb³⁺ over Eu³⁺, triggering coordination-induced emission (CIE) at 450 nm and modulating the antenna effect (AE) and the tandem energy transfer (TER) from Tb³⁺ to Eu³⁺. Subsequently, acetylacetone (acac) was further introduced to yield TPE-4PA@Tb/Eu-GMP-acac ICPs with an appropriate full-color fluoresce response capability. The addition of alkaline phosphatase (ALP) hydrolyzes GMP and TPE-4PA dual substrates, resulting in reduced characteristic emission of the bimetallic Ln-ICP host at 493, 548, 593, 619 and 703 nm, increased monomer emission of TPE-4PA at 392 nm, as well as the solvent-driven AIE of the enzymatic product TPE-4OH at 430 nm, which constitutes a novel ratiometric ALP sensing mechanism with pale-purple to blue fluorescence color shifts. Featuring high sensitivity, doubly assured selectivity, and operational simplicity, this "all-in-one" probe enables real-time APA monitoring via dual-substrate kinetics and is suitable for on-site ALP test strip development. Moreover, the unique color transition point of the dual-substrate-based TPE-4PA@Tb/Eu-GMP-acac ICPs probe can be designed to signal an APA surge prior to algal bloom onset, which holds significant potential for the development of microalgae pollution early-warning systems, thereby safeguarding drinking water safety.