Ultrasound-responsive phosphorescence in aqueous solution enabled by microscale rigid framework engineering of carbon nanodots.

Solid-state phosphorescent materials with stimulus-responsive properties have been widely developed for diverse applications. However, the task of generating excited states with long lifetimes in aqueous solution remains challenging due to the ultrafast deactivation of the triplet excitons and the difficulty in regulating stimulation sites in an aqueous environment. Additionally, most existing materials are primarily responsive to limited stimuli, such as light, oxygen, or temperature. Here, we present a microscale rigid framework engineering strategy that can be used to modulate the phosphorescence properties of carbon nanodots (CNDs), by brightening triplet excitons through ultrasound-enhanced rigidity in CNDs. Ultrasound-responsive phosphorescent CNDs with a lifetime of 1.25 seconds in an aqueous solution were achieved. The CNDs exhibit high sensitivity to surrounding ultrasound, showing a linear response to ultrasound exposure during the treatment period. The ultrasound-responsive phosphorescent CNDs demonstrate potential applications as sensing units in ultrasound radar detection and in vivo afterglow imaging.