Recently, the team led by Associate Researcher Liu Chengbo from the Center for Biomedical Optics and Molecular Imaging, Institute of Medical and Biological Engineering, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, the team led by Professor Jonathan from the Department of Chemistry, The University of Texas at Austin, and the team led by Professor Jong Seung from the Department of Chemistry, Korea University, South Korea, have collaborated to explore the photoacoustic imaging mechanism of expandable paramagnetic metalloporphyrins. They discovered that the texaphyrin derivative centered on manganese metal (manganese texaphyrin: MMn) has the synergistic effects of paramagnetism, strong absorption of texaphyrin, the characteristic of no fluorescence emission loss, and specific protein binding properties, which is beneficial for constructing a new photoacoustic molecular imaging system and strategy. They have preliminarily explored and achieved tumor-specific three-dimensional photoacoustic molecular imaging. The related research work Manganese(II) Texaphyrin: A Paramagnetic Photoacoustic Contrast Agent Activated by Near-IR Light was published in the Journal of the American Chemical Society (J. Am. Chem. Soc., 2020, DOI: 10.1021/jacs.0c04387, with an impact factor of 14.612). In this study, the first authors are Dr. Ren Yaguang and Dr. Chen Jingqin from Shenzhen Institutes of Advanced Technology and Dr. Adam C. Sedgwick from The University of Texas at Austin. Traditional texaphyrin has a long absorption wavelength, strong light absorption, and photobleaching properties. The paramagnetic cation manganese located at the center, as a fluorescence quencher, can enhance the photoacoustic effect of MMn in the near-infrared region. Based on the independently developed near-infrared photoacoustic molecular imaging technology, the research team has achieved tumor-specific photoacoustic molecular imaging at both the in vitro and in vivo levels. The metal manganese at the center of MMn can react with superoxides such as reactive oxygen species, effectively inhibiting oxidative stress damage in the body, and at the same time, the near-infrared photoacoustic characteristics change accordingly. Therefore, photoacoustic molecular imaging using MMn as a probe can also be used as an indicator and inhibitor for studying the intensity and damage of oxidative stress in the body. On this basis, the team will continue to explore the application of MMn in brain science research and study the oxidative stress responses in various neurodegenerative diseases (such as Alzheimer's disease, Parkinson's disease, cerebral ischemia, brain injury, and epilepsy). This research project is supported by major research programs of the National Natural Science Foundation of China, instrument development projects of the Chinese Academy of Sciences, and the Young Scientists Promotion Association of the Chinese Academy of Sciences.

(a) The molecular structure and photoacoustic imaging performance of manganese texaphyrin (MMn); (b) The photoacoustic molecular signal and stability of MMn within the tumors of living animals