A near infrared triggered double-shell fluorescent probe for clinical detection of alkaline phosphatase

Alkaline phosphatase (ALP), a hydrolase commonly found in living organisms, shows significantly elevated levels in serum of patients suffering from liver metastasis. Rapid and efficient detection of ALP activity in serum is thus critical for assessing cancer prognosis. In this study, we developed a composite nanoprobe (UCNPs@ZIF@PDA) based on upconversion nanoparticles (UCNPs), specifically NaErF 4 :Tm (0.5 mol%)@NaLuF 4 , characterized by strongly correlated energy levels, for the sensitive and stable detection of ALP in complex environments. To improve stability, UCNPs were encapsulated with zeolitic imidazolate framework-8 (ZIF-8). The upconversion luminescence (UCL) of the UCNPs was subsequently quenched by polydopamine (PDA), which was formed via in-situ polymerization of dopamine on the ZIF-8 surface. ALP catalyzed the conversion of L-ascorbic acid trisodium 2-phosphate (AAP) to ascorbic acid, which in turn triggered the degradation of PDA and restored the UCL. Through this mechanism, the limits of detection for ALP in aqueous solution and serum are 0.19 and 0.42 U/L, respectively. Moreover, the probe demonstrates precise imaging of ALP in cellular environments and successfully distinguishes ALP levels in samples with and without liver metastasis. These findings highlight the strong potential of UCNP-based composite fluorescent probes as a novel and efficient tool for ALP detection in clinical applications.