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Unprecedented 3D images of living cells plus details of molecules inside

 The University of Tokyo, Osaka University and Japan Science and Technology Agency (JST) announced on 20 April 2020, that researchers have developed a new technique to observe the insides of living cells in their natural state in greater detail than ever before. It requires no strong light and no artificial fluorescent tags,which will help reveal the complex and fragile biological interactions occurring inside cells. The work was supported by JST and Japan Society for the Promotion of Science(JSPS)and details were published in Optica by Associate Professor Takuro Ideguchi from the University of Tokyo Research Institute for Photon Science and Laser Technology as the lead author(*).

 In order to obtain high resolution image inside the living cell, fluorescence microscope is commonly used but biomolecules in the cell must be labeled with fluorescent functional groups which may affect the activities of the biomolecule. Furthermore, labeling process is apt to cause damages to the cell. For these reasons, label-free and non-destructive imaging techniques have been demanded. Although quantitative phase imaging (QPI) and molecular vibrational imaging (MVI) have been known as successful label-free and non-destructive imaging techniques, their images are inherently complementary to provide morphology by QPI and biochemistry by MVI. In this work, researchers unified MVI into the framework of QPI by realising simultaneous and in-situ acquisition of MV-fingerprint contrasts of single cells using the mid-infrared photothermal effect. By irradiating cells with mid-infrared light with scanning the wavenumber, resonated particular biomolecules raise the temperature of the surrounding water. QPI can detect the temperature change as the change in refractive index and produce the optical image of the location of the biomolecule. When the mid-infrared light is turned off, QPI gives the 3D image of the inside structure of the cell. With these information, cell structures and distribution of targeted biomolecules are both revealed in one 3D image.

 The method of this study is expected to be used in various fields of life science as a tool for observing living cells.

*Miu Tamamitsu, Keiichiro Toda, Hiroyuki Shimada, Takaaki Honda, Kohki Okabe, Yu Nagashima, Ryoichi Horisaki, and Takuro Ideguchi, "Label-free biochemical quantitative phase imaging with mid-infrared photothermal effect", Optica, Vol. 7, Issue 4, pp. 359-366 (2020), odoi: 10.1364/OPTICA.390186; Published: April 20, 2020