PCN-224-based fluorescent nanozymes with dual enzyme-like activities for heavy metal ions detection

Building upon the newly discovered phosphatase (PPA)-like activity of Zr(IV)-based PCN-224, a ratiometric fluorescence probe was developed for the sensitive Cd(II) detection, achieving a wide detection range of 0.05-40 μM. Furthermore, a composite nanomaterial (CeO₂/PCN-224) that integrates the multiple enzyme-like properties of cerium dioxide (CeO₂) with the luminescence of PCN-224 was innovatively engineered and applied for As(V) and Pb(II) detection. The composite exhibits enhanced PPA-like activity, catalyzing the hydrolysis of 4-methylumbelliferyl phosphate disodium salt (4-MUP) to generate the blue fluorescent product (4-MU, λ_em = 450 nm). As(V) detection was achieved through specific As-O-Ce binding that can induce noncompetitive inhibition of 4-MUP hydrolysis, showing a linear response from 0.5 to 70 μM. Additionally, the peroxidase-like (POD-like) activity and intrinsic fluorescence of CeO₂/PCN-224 facilitate Pb(II) quantification via a dual-response system. Specifically, Pb(II) simultaneously enhances the catalytic generation of reactive oxygen species (O₂^•-) while inducing both static and dynamic fluorescence quenching effects through distinct coordination pathways. Therefore, a precise ratiometric fluorescence probe of I_{565 nm}/I_{650 nm} was developed for Pb(II) detection from 0.05 to 5 μM and 5 to 9 μM. In addition, the validation studies confirm accurate detection of both As(V) and Pb(II) in real water and soil samples.