Carbon Dot-Silica Nanoparticle Composites for Ultralong Lifetime Phosphorescence Imaging in Tissue and Cells at Room Temperature

Compared to fluorescence imaging with short-lived emissive probes, the use of phosphorescent probes conveys the advantage of long signal persistance in time and this permits one to discriminate against interference from autofluorescence. However, the realization of room temperature phosphorescence (RTP) probes that feature ultralong emission lifetimes in aqueous solution is still a challenge. Here, we present a rational strategy for realizing ultralong RTP in air-saturated aqueous media from carbon dot-based silica composites (CDs@SiO 2 ) which feature emission lifetimes as long as 1.64 s. The excellent phosphorescence properties, their small size, and their water solubility make CDs@SiO 2 a promising material for biological imaging application. We demonstrate their use as efficient reporters both in plant tissue and in animal cells where strong autofluorescence poses a severe challenge for conventional, short-lifetime probes.