Photon upconversion (UC) has drawn increasing research interest in enhancing the efficiency of solar-based technologies as well as in exploring unconventional biophotonic applications. Largely in the interests of biomedical and environmental applications where aqueous media are prevalent, the development of triplet-triplet annihilation upconversion (TTA-UC) systems that are readily suspended and functional in oxygen-rich aqueous environments is an attractive objective. Herein a strategy for the post-encapsulation of oil-phase TTA-UC into hollow mesoporous silica microcapsules (HMSMs) through its radial mesochannels is demonstrated, attaining a new materials platform for aqueous phase photon upconversion in a facile, effective, and scalable route. In-depth characterization of such upconverting oil-laden HMSMs (UC-HMSMs) showed that the mesoporous silica shells reversibly stabilized the encapsulated UC oil in water to allow efficient upconverted emission, even under aerated conditions. Together with the numerous previously reported advantages of silica nanoparticles, such as easy surface functionalization and excellent biocompatibility, the distinct advantages of UC-HMSMs were mainly exploited in the current work by demonstrating the adaptive inclusion of metal nanoparticles and the controlled encapsulation of UC-chromophores. Moving forward, an <i>in vitro</i> cell-mediated TTA-UC system using human mesenchymal stem cells (hMSCs) is described in a proof-of-concept experiment to progress our new TTA-UC platform and examine its potential for future developments in prospective biophotonic applications. Our results reveal the great promise of UC-HMSMs to serve as ideal vehicles not only for ultralow-power <i>in vivo</i> imaging, but also for stem cell labeling, to facilitate the tracking of tumor cells in animal models.

New vehicle for aqueous phase photon upconversion: Hollow/yolk-shell mesoporous silica microcapsules

2019 Fall National Meeting

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