18 March 2016 Reversibly switchable photoacoustic tomography using a genetically encoded near-infrared phytochrome
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Optical imaging of genetically encoded probes has revolutionized biomedical studies by providing valuable information about targeted biological processes. Here, we report a novel imaging technique, termed reversibly switchable photoacoustic tomography (RS-PAT), which exhibits large penetration depth, high detection sensitivity, and super-resolution. RS-PAT combines advanced photoacoustic imaging techniques with, for the first time, a nonfluorescent photoswitchable bacterial phytochrome. This bacterial phytochrome is the most near-infrared shifted genetically encoded probe reported so far. Moreover, this bacterial phytochrome is reversibly photoconvertible between its far-red and near-infrared light absorption states. Taking maximum advantage of the powerful imaging capability of PAT and the unique photochemical properties of the phytochrome, RS-PAT has broken through both the optical diffusion limit for deep-tissue imaging and the optical diffraction limit for super-resolution photoacoustic microscopy. Specifically, with RS-PAT we have achieved an unprecedented detection sensitivity of ~2 μM, or as few as ~20 tumor cells, at a centimeter depth. Such high sensitivity is fully demonstrated in our study by monitoring tumor growth and metastasis at whole-body level with ~100 μm resolution. Moreover, our microscopic implementation of RS-PAT is capable of imaging mammalian cells with a sub-diffraction lateral resolution of ~140 nm and axial resolution of ~400 nm, which are respectively ~2-fold and ~75-fold finer than those of our conventional photoacoustic microscopy. Overall, RS-PAT is a new and promising imaging technology for studying biological processes at different length scales.
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Junjie Yao, Junjie Yao, Andrii A. Kaberniuk, Andrii A. Kaberniuk, Lei Li, Lei Li, Daria M. Shcherbakova, Daria M. Shcherbakova, Ruiying Zhang, Ruiying Zhang, Lidai Wang, Lidai Wang, Guo Li, Guo Li, Vladislav V. Verkhusha, Vladislav V. Verkhusha, Lihong V. Wang, Lihong V. Wang, } "Reversibly switchable photoacoustic tomography using a genetically encoded near-infrared phytochrome", Proc. SPIE 9708, Photons Plus Ultrasound: Imaging and Sensing 2016, 97082U (18 March 2016); doi: 10.1117/12.2229156; https://doi.org/10.1117/12.2229156

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