Jiang, Y. et al. Nat. Commun. 10, 2064 (2019).

Autofluorescence background can be a challenge in biomedical imaging, especially in imaging of tissues and animals. Alternatives to fluorescent probes such as luminescent and afterglow probes circumvent this issue by bypassing illumination light and emitting long after autofluorescence has occurred, respectively. Although potentially useful, afterglow probes are typically made from nanoparticles containing rare-earth metals or heavy metals, which can be toxic. Jiang et al. developed an approach to turn conventional fluorescent dyes into afterglow luminescent nanoparticles (ALNPs). ALNPs have three parts: a photosensitizer initiator that converts photoenergy into singlet oxygen, a singlet-oxygen-reactive molecule that serves as the afterglow substrate and forms an unstable chemiluminescent intermediate, and a fluorophore that serves as the afterglow relay unit to accept energy from the intermediate, gradually releasing it as photons. The researchers demonstrated that their ALNPs could be used for sensitive imaging in mice.