In 2023, Pu and colleagues from Nanyang Technological University first explored the large penetration depth of US and the low background of afterglow luminescence for
in vivo imaging (
Fig. 1a) [
3]. For such goal, they screened a range of organic sonosensitizers as afterglow initiators and polymers or small molecules as afterglow substrates, respectively, to develop sonoafterglow nanoparticles (SNAPs). In this work, the energy flux was as follows: US → sonosenitizer → O
2 →
1O
2 → substrate → afterglow luminescence. Here, role of US was similar to that of typical photo-excitation. After receiving the US energy, the sonosensitizer experienced a regular photophysical process, namely excitation and then intersystem crossing to produce ROS, which further reacted with sonoafterglow substrates to form self-luminescence dioxetane intermediates to release sonoafterglow luminescence (
Fig. 1b). After suitable combinations of sonosensitizers and afterglow substrates, near-infrared afterglow luminescence (780 nm) with a half-life of 110 s was eventually obtained. For
in-vivo imaging, the resultant near-infrared (NIR) afterglow luminescence allowed a tissue penetration depth of 4 cm and a high signal-to-background ratio (47.4 times higher than fluorescence,
Fig. 1c).