Dual-emissive polystyrene@zeolitic imidazolate framework-8 composite for ratiometric detection of singlet oxygen.

This work demonstrated the potential of zeolitic imidazolate framework-8 (ZIF-8) as a host for the co-encapsulation of multiple fluorescent cargos to fabricate fluorescent composites for ratiometric sensing. The one-pot self-assembly of 2-methylimidazole, zinc nitrate, 9-anthracenecarboxylic acid (AnC), and polystyrene sphere doped with europium chelate (EuPS) in methanol solution can lead to the formation of dual-emissive EuPS@AnC/ZIF-8 with excellent fluorescent activity. Based on the distinct fluorescent responses of Eu and AnC to singlet oxygen (O), EuPS@AnC/ZIF-8 can be developed as a ratiometric sensor for O detection. In this ratiometric sensor, Eu fluorescence was employed as a reference signal for providing built-in correction to avoid environmental effects, while AnC fluorescence served as a response signal to detect O because of its turn-off behavior upon reacting with O. Benefiting from the confinement effect of the ZIF-8 host, the presented sensor showed high sensitivity toward O with a detection limit of 43 nM and excellent selectivity over other reactive oxygen species. More attractively, the target responsive fluorescent color change of EuPS@AnC/ZIF-8 allowed O to be easily identified by the naked eye under a UV lamp. We hope that this study will provide a new insight into the design and application of multifunctional composites based on metal-organic frameworks.