Recent advances in NIR-II fluorescence/photoacoustic dual-modality imaging probes

The second near-infrared (NIR-II) fluorescence imaging (FLI) has been widely studied for its advantages of low self-fluorescence, strong tissue penetration, and high resolution. In recent years, photoacoustic imaging (PAI), an emerging imaging modality that combines the advantages of both optics and acoustics, has become a hot research topic that has attracted much attention. On this basis, the NIR-II probes, which is capable of simultaneous fluorescence (FL) and photoacoustic (PA) dual-modality imaging, was developed, opening a new path for the development of probe technology. At the same time, it also provides new ideas for the multimodal joint application of other imaging methods. On the one hand, this review details the current status of the development of NIR-II FL/PA dual-modality imaging probes, including probe design strategies, classification of probes, development of activatable probes, and applications in biomedicine. On the other hand, the development of such probes is summarized and future prospects and challenges are envisioned. We hope that this review can stimulate readers' thinking and help them better apply NIR-II FL/PA dual-modality imaging probes in the biomedical field.