Although structured illumination microscopy (SIM) demonstrates ultrahigh temporal and spatial resolution, the speed and intricacy of polarization modulation affect the speed and quality of its imaging resolution in 3D. A 3DSIM technique, developed by a team led by professor Peng Xi at Peking University, leverages digital display technology to achieve a rapid, reliable, multidimensional SIM imaging tool for investigating diverse biological phenomena. The new microscopy technique blends 3D superresolution and fast temporal resolution with polarization imaging. To do so, it combines the polarization-maintaining and modulation capabilities of a digital micromirror device (DMD) with an electro-optic modulator (EOM). A DMD uses the electromechanical rotation of micromirrors to modulate the light field reflecting off it. Since each micromirror is controlled in the binary form corresponding to “on” and “off” states, a DMD can also be used as a digital reflection grating when loading with a specific pattern, which allows it to provide a rapid switch of structured illumination patterns for 3DSIM. After loading pattern images, the DMD maintains a working state without requiring a refresh cycle, simplifying the SIM system’s timing control. The DMD has a high switching speed, making the DMD-3DSIM system suitable for fast imaging of live cells. Open-source core technology embedded inside projector hardware enables high-speed, auto-polarization-modulated, 3D structured illumination microscopy (SIM) imaging. The image shows 3DSIM reconstruction of plant and animal tissue samples: Cell walls in oleander leaves (a), hollow structures within black algal leaves (b), root tips of corn tassels (c), and actin filaments in mouse kidney tissue (d). The corresponding maximum intensity projection (MIP) images are shown respectively in the bottom row (e-h). Scale bar: 2 μm. Courtesy of Li, Cao, et al., doi 10.1117/1.APN.3.1.016001. In addition, due to the nature of the special coating on its surface, the DMD can maintain the polarization state continuity between incident and reflected light. When the DMD is paired with an EOM capable of switching speeds in the nanosecond range, the result is ultrafast imaging with minimal motion artifacts. According to the researchers, the DMD-3DSIM system provides a twofold enhancement in both lateral (133 nm) and axial (300 nm) resolution compared to traditional wide-field imaging techniques. It can acquire a data set comprising 29 sections of 1024 pixels × 1024 pixels with 15-ms exposure time and 6.75 seconds per volume. The researchers demonstrated the functionality and versatility of DMD-3DSIM by imaging various specimens, including fluorescent beads, the nuclear pore complex, microtubules, actin filaments, and mitochondria in animal cells. In a mouse kidney slice, the system revealed a pronounced polarization effect in actin filaments. The team also used the 3DSIM system to investigate highly scattering plant cell ultrastructures, examining cell walls in oleander leaves, hollow structures in black algal leaves, and features within the root tips of corn tassels. The researchers said that a computational superresolution algorithm could further improve the resolution of the DMD-based 3DSIM system. To encourage collaboration among members of the scientific community, the team has made all the hardware components and control mechanisms for DMD-3DSIM openly available on Github. By making the hardware and software components of the system accessible to the research community, the team hopes to help pave the way for the future of multidimensional imaging. The research was published in Advanced Photonics Nexus (www.doi.org/10.1117/1.APN.3.1.016001).
