Ultralong lifetime room-temperature phosphorescence in aqueous medium from silica confined polymer carbon dots for autoluminescence-free bioimaging and multilevel information encryption

Ultralong room-temperature phosphorescence (URTP) materials have innate superiority in eliminating autoluminescence for bioimaging, but achieving URTP in aqueous medium is a highly challenging task, especially for carbon dot-based materials. Here we present a facile one-step hydrothermal method to effectively promote RTP emission in an aqueous medium by confining polymer carbon dots (PCDs) in silica nanospheres (SNSs) with tetraethylorthosilicate as only raw material. The polymer carbon dots-silica nanosphere composites (PCDs-SNSs) exhibit ultralong lifetime up to 2.19 s (nearly 9 s to naked eye) at ambient temperature and atmosphere. To the best of our knowledge, this is the longest RTP lifetime of carbon dot-based materials in aqueous media to date. As indicated, RTP should originate from the subfluorescent C--O groups. The shielding of SNSs to all kinds of quenching in the confined space in which there are strong interactions between PCDs and SNSs, e.g, covalent bond and hydrogen bond, which enhances the rigidity of cross-linked framework and protects emitting centers from non-radiative deactive processes of triplet state, is the main reason for the URTP observed in aqueous media. Besides, the PCDs-SNSs solution exhibits outstanding stability and low cytotoxicity. Based on the distinctive properties in aqueous media, the PCDs-SNSs have been successfully used as autoluminescence-free probes for bioimaging with high sensitivity and signal-to-noise ratio, and as security ink for strong concealment and moisture-related multilevel information protection.

Automated summary

A facile one-step hydrothermal method was presented to promote ultralong room-temperature phosphorescence (URTP) emission in an aqueous medium by confining polymer carbon dots in silica nanospheres. The polymer carbon dots-silica nanosphere composites exhibited the longest RTP lifetime of carbon dot-based materials in aqueous media to date, showing potential for applications in bioimaging without autoluminescence.