A fluorescence sensor utilizing 3D COF photonic crystals for enhanced detection of TNP

Driven by the growing global demand for public safety and environmental protection, there is an urgent need to develop efficient and accurate methods for detecting trace explosives such as 2,4,6-trinitrophenol (TNP). This study presents a fluorescence-enhanced sensing platform leveraging the intrinsic slow-light effect in covalent organic framework photonic crystals (COF PhCs). This strategy overcomes the low porosity limitations of polymer-based PhCs and significantly improves the detection sensitivity of fluorescent poly(tannic acid) nanoparticles (FPTA NPs), enabling selective and environmentally benign monitoring of TNP. Specifically, three-dimensional COF PhCs were fabricated via evaporation-induced self-assembly, with their diffraction wavelengths meticulously aligned with the emission profiles of fluorescent FPTA NPs. Experimental results reveal that the PL signal exhibits a remarkable enhancement by a factor of up to 10.34 when the blue edge of the photonic band gap is aligned with the emission peak of the FPTA NPs. Furthermore, the imine-based conformationally locked polymers facilitate efficient accumulation of TNP molecules through strong intermolecular interactions, thereby significantly enhancing the sensitivity for trace TNP detection and achieving a detection limit as low as 20.7 nM. This research underscores the considerable potential of PhCs for enhancing luminescence signals to enable sensitive detection of trace environmental pollutants.