Diffraction limit. Biomolecules below the size of mitochondria, for example the SARS-CoV-2 virus, and green fluorescent proteins and small molecules cannot be observed due to the diffraction limit.|@|~(^,^)~|@|Development of super-resolution microscope. (a) stimulated emission depletion (STED). The left side shows an E. coli image with a conventional microscope and the right side shows a super-resolution image with a STED microscope. Scale bar: 2 μm. Adapted from T. A. Klar et al. Proc. Natl. Acad. Sci. U.S.A. 2020; 97; 8206–8210 Copyright © 2020 National Academy of Science [7]. (b) Photo-activated localization microscope (PALM). The left side shows a total internal reflection fluorescence (TIRF) image and the right side shows a PALM image of the lysosomal transmembrane protein in a COS-7 cell. Scale bar: 1 μm. Adapted from E. Betzig et al. Science 2006; 313; 1642–1645 Copyright © 2006, Reprinted with permission from AAAS [23]. (c) Stochastic optical reconstruction microscope (STORM). Microtubule images by STORM in BS-C-1 cells. Scale bar: 5 μm. Adapted from B. Huang et al. Science 2008; 319; 810–813 Copyright © 2008, Reprinted with permission from AAAS [31]. (d) DNA point accumulation for imaging in nanoscale topography (DNA-PAINT). Two-color images for microtubules and mitochondria could be obtained by the multiplexed DNA-PAINT technique. Scale bar: 5 μm (left) or 1 μm (right). Adapted from R. Jungmann et al. Nat. Methods 2014; 11; 313–318 [56]. (e) FRET-based DNA-PAINT (FRET-PAINT). The time to obtain a super-resolution image was also reduced to a few seconds with FRET-PAINT. Scale bar: 5 μm (top) or 1 μm (second, third, and fourth rows). Adapted from J. Lee et al. Mol. Brain 2018; 11; 70 [64]. (f) Structured-illumination microscopy (SIM). The upper panel shows a microtubule image in a S2 cell with conventional TIRF microscope and the lower panel shows an image with TIRF-SIM. Scale bar: 2 μm. Adapted from P. Kner et al. Nat. Methods 2019; 6; 339–342 [15].|@|~(^,^)~|@|Super-resolution microscope for volumetric imaging. (a) highly inclined and laminated optical sheet (HILO). Single-molecule images of the nuclear pore complexes in cells with HILO microscopy. Scale bar: 5 μm. Adapted from M. Tokunaga et al. Nat. Methods 2008; 5; 159–161 [80]. (b) Lattice light sheet. Photo-activated localization microscope (PALM) images with a lattice light sheet show the chromosomal passenger protein GFP–AIR-2 (green) and the plasma membranes and histones (red) in embryos of C. elegans. Scale bar: 5 μm. Adapted from B.-C. Chen et al. Science 2014; 346; 1257998 Copyright © 2014, Reprinted with permission from AAAS. (c) Point spread function (PSF) engineering. Three-dimensional super-resolution image of microtubule with the self-bending point spread function. Scale bar: 500 nm. Adapted from S. Jia et al. Nat. Photonics 2014; 8; 302–306 [84]. (d) Spinning disk confocal microscope. Super-resolution image of microtubules and mitochondria using a spinning disk confocal microscope. Scale bar: 5 μm or 500 nm (inset). Adapted from F. Schueder et al. Nat. Commun. 2017; 8; 2090 [85]. (e) PSF engineering + Deep learning. Super-resolution 3D image of mitochondria over a 4 μm axial range with convolutional neural network. Scale bar: 5 μm. Adapted from E. Nehme et al. Nat. Methods 2020; 17, 734–740 [86]. (f) PSF engineering + Large axial range (2–3 μm) with deformable mirror. Three-dimensional image of mitochondria in a COS-7 cell with Zernike optimized localization approach in 3D (ZOLA-3D). Scale bar: 5 μm. Adapted from A. Aristov et al. Nat. Commun. 2018; 9; 2409 [87]. (g) Line-scan confocal microscope. The line-scan confocal microscope could be applied to obtain three-dimensional images in 100 μm mouse brain tissue. The presynapse is targeted by the Bassoon protein (green) and the postsynapse is targeted by the Homer1 protein (red). Adapted from S. Park et al. Mol. Brain 2018; 11; 17 [90]. (h) PSF engineering + Tilted light sheet. Three-dimensional super-resolution image of the nuclear lamina (Lamin B1) of a HeLa cell with a tilted light sheet microscope. Scale bar: 5 μm. Adapted from A.-K. Gustavsson et al. Nat. Commun. 2018; 9; 123 [91].|@|~(^,^)~|@|Concepts of adaptive optics and wavefront shaping. (a) The sensor-based direct adaptive optics. In the direct sensing method, the backscattered wave from the guide star is measured by the wavefront sensor. The wavefront shaping device is used to play back the phase conjugation of the measured wavefront. (b) The sensorless indirect adaptive optics. In the indirect sensing method, the wavefront is iteratively corrected by the wavefront shaping device to optimize the image metrics while the signal is detected by camera or photo multiplier tube (PMT).|@|~(^,^)~|@|Super-resolution microscope with single-molecule localization and stimulated emission depletion (STED) with adaptive optics for volumetric imaging. (a) Volumetric super-resolution image for the synaptonemal complexes in a whole-mouse spermatocyte with an interferometric photoactivated localization microscopy (iPALM) technique with two deformable mirrors. Adapted from F. Huang et al. Cell 2016; 166; 1028–1040 [95]. (b) Amyloid plaque in a 30-μm section of mouse cortex. Scale bar: 5 μm (left) or 500 nm (inset). Adapted from M. J. Mlodzianoski et al. Nat. Methods 2018; 15; 583–586 [96]. (c) Adaptive optics (AO) STED. Super-resolution image of a vesicular glutamate transporter in Drosophila melanogaster brains with AO STED microscope. Arrows: direction and length of 1 μm. Adapted from B. R. Patton et al. Opt. Express 2016; 24; 8862–8876 [98].|@|~(^,^)~|@|Super-resolution microscope of structured illumination microscope (SIM) with adaptive optics for volumetric imaging. (a) Adaptive optics (AO) SIM. Images of dendrites at a depth of 25 μm in a cortical slice of a Thy1-GFP mouse without and with AO SIM. Scale bar: 5 μm, 3 μm (top two insets) or 2 μm (bottom two insets). Adapted from R. Turcotte et al. Proc. Natl. Acad. Sci. U. S. A. 2019; 116; 9586–9591 Copyright © 2019 National Academy of Science [101]. (b) SR, AO-SIM (zebrafish in vivo). Scale bar: 20 μm or 3 μm (insets). Adapted from Sci. Adv. 2020; 6; eaaz3870 [102]. (c) SR, AO-SIM (C. Elegans, in vivo). Scale bar: 20 μm (left top), 2 μm (left inset), 5 μm (left bottom), 0.8 μm (right four panels). Adapted from R. Lin et al. Nat. Commun. 2021; 12; 3148 [103].

Curr. Opt. Photon. 2022;6:550~564 https://doi.org/10.3807/COPP.2022.6.6.550