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Alkaline Phosphatase-Triggered Self-Assembly of Near-Infrared Nanoparticles for the Enhanced Photoacoustic Imaging of Tumors.

Photoacoustic (PA) imaging is advantageous for the diagnosis of superficial cancer with high spatial resolution. However, to the best of our knowledge, using an alkaline phosphatase (ALP)-activatable probe for the enhanced PA imaging of tumors has not been reported. In this work, we rationally designed a NIR probe IR775-Phe-Phe-Tyr(H2PO3)-OH (1P) for PA imaging ALP activity in vitro and in tumor. Under the catalysis of ALP, 1P was efficiently converted to IR775-Phe-Phe-Tyr-OH (1), which self-assembled into the nanoparticles 1-NPs. The formation of 1-NPs induced a 6.4-fold enhancement of the 795 nm PA signal of 1P. In vivo tumor PA imaging results indicated that, compared to that in the ALP inhibitor-treated control group, PA contrast in the experimental group enhanced 2.3 folds at 4 h after 1P injection. By replacing the Phe-Phe-Tyr(H2PO3)-OH motif in 1P with other enzyme-cleavable ones, we hope that more PA probes could be developed for the precise diagnoses of their corresponding cancers in the near future.