A Portable Smartphone Platform for Onsite Diphenyl Phosphate Detection Enabled by Dual-Signal Molecularly Imprinted Nanozymes

Concerns regarding the environmental and health risks associated with diphenyl phosphate (DPhP) have prompted the development of sensitive, selective, and cost-effective analytical methods for its detection. In this study, we introduce a novel molecular imprinting polymer (MIP) with dual-mode detection capability for DPhP, leveraging both visual colorimetry and fluorescence. Iron–nitrogen codoped carbon dots (Fe/N-CDs) are embedded within the MIP structure, serving as the responsive signal and exhibiting peroxidase (POD)-like activity. Molecular docking simulations are used to optimize the binding ability between DPhP and the monomer. Briefly, the POD-like activity facilitates the conversion of H2O2 into ·OH, which oxidizes 3,3′,5,5′-tetramethyl-benzidine (TMB) into blue oxTMB, thereby quenching the blue fluorescence of Fe/N-CDs@MIP via the inner filter effect (IFE). This results in a decrease in the fluorescence signal, accompanied by an increase in the colorimetric signals. However, the specific binding of DPhP to the MIP’s imprinted sites hinders the access of TMB and H2O2 to the Fe/N-CDs@MIP’s catalytic center, curbing the oxidation of TMB and yielding a DPhP concentration-dependent dual-mode response in fluorescence signal enhancement and a decrease in the colorimetric signal. Utilizing a smartphone to capture dual-mode signals for analysis enables the convenient detection of environmental pollution. This dual-readout assay provides a sensitive and selective platform for DPhP detection, with detection limits of 0.016 μg/L in colorimetric mode and 0.018 μg/L in fluorescence mode, offering a straightforward visual approach to onsite monitoring of DPhP for bolstering environmental and public health safety. This innovative work provides a cost-effective, portable, and accurate platform for intelligent marine DPhP monitoring.