Endogenous Oxygen Depletion-Based Emulsion Polymerization Nanospheres for Room-Temperature Phosphorescence Bioimaging

Purely organic room-temperature phosphorescence (RTP) is easily quenched by water and oxygen in aqueous systems, severely restricting its application in bioimaging. As two main strategies for achieving aqueous RTP, nanocrystallization and supramolecular self-assembly are not applicable to chromophores that lack crystal luminescence and matrix compatibility. Here, we provide an optional strategy, endogenous oxygen depletion-based emulsion polymerization nanospheres (NSs), for achieving aqueous RTP for the aforementioned chromophores. The aqueous RTP probe is constructed by encapsulating chromophores with high reactive oxygen species (ROS) generation capabilities into poly(methyl methacrylate) (PMMA) NSs prepared via emulsion polymerization. The dense and hydrophobic structure of PMMA NSs, combined with the high ROS generation efficiency of the incorporated chromophores, effectively suppresses phosphorescence quenching by water and oxygen, thereby enabling visible aqueous RTP in an air-exposed environment. In contrast, no RTP is observed in nanocrystalline and supramolecular systems with the same chromophores. The applications of these PMMA NSs in subcutaneous, tumor, and lymphatic tissue bioimaging are successfully demonstrated, with the signal-to-background ratio reaching as high as 556. This strategy is expected to provide a feasible route for developing aqueous-phase RTP nanoprobes and to advance the broader application of organic RTP probes in bioimaging.