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DNA Origami


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an arched shape [36] (Figure 3.2). Each tension‐adjustable module contained single‐stranded bridges containing a human telomeric repeat sequence, which forms a G‐quadruplex in the presence of K+ but dissociates into single strands in the absence of K+. Upon G‐quadruplex formation, the bridge contracted, thereby causing the bending of the module (Figure 3.2a). Through the cumulative effect of this actuation, the entire shape was deformed from the original linear shape into an arched shape (Figure 3.2a). This G‐quadruplex‐formation‐induced actuation was successfully assessed by directly visualizing morphological changes triggered by injecting a high concentration of KCl. Figure 3.2b shows a clear deformation from the relaxed linear shape into the arched shape, which was also reflected in the sudden decrease in the end‐to‐end distances at around 6–8 seconds (Figure 3.2c) and the nearly constant contour lengths of 300 nm that agreed well with the theoretical values for the structure.

      Source: Suzuki et al. [36]/with permission from John Wiley & Sons, Inc.

      A variety of DNA nanodevices capable of performing rotations have been realized by employing strand displacement reaction [19, 31,37–39], B–Z transition [40], and combination of metal ion–DNA complex with i‐motif formation [41]. However, these approaches require dilution of the system or lead to by‐product accumulation, causing decreasing yield rates during continuous manipulation. Incorporation of photochromic molecules into the DNA strands can be employed to avoid steps required to remove undesired reaction by‐products [42–44], and thus provide the possibility of manipulating nanodevices by simple photocontrol [45, 46].

      Source: Yang et al. [47]/with permission from John Wiley & Sons, Inc.

      The photoresponsive changes of the azo‐rotor on a single DNA origami stator were monitored by HS‐AFM at a time resolution of seconds. The purified sample was adsorbed onto the mica and then photoirradiated while keeping continuous AFM scanning. Successive AFM images obtained under UV irradiation revealed changes in the azo‐rotor orientation (Figure 3.3f). The azo‐rotor was initially locked in vertical orientation, but was released to rotate and was finally locked in the horizontal orientation. At 30 and 35 seconds, the azo‐rotor was not clearly imaged on the stator, yet reappeared in the frame at 40 seconds, probably due to the rapid molecular motion of the azo‐rotor after the dissociation of the OFF duplex. After the fluctuations of the rotor released by the UV‐induced dissociation of the OFF‐switching motif, it turned back to the OFF‐switch anchor position (40 seconds) probably due to failure of hybridization to the ON‐switching motif. The azo‐rotor again exhibited fluctuations in its orientation from 55 to 70 seconds and was finally locked in the horizontal orientation. Reverse change from the horizontal to vertical orientation was also monitored by scanning a pre‐UV‐irradiated sample. In the initial frame of the successive images (before Vis irradiation, Figure 3.3g), OFF‐2 and ON‐2 on the stator were clearly identified at anchorages 1 and 4, respectively, indicating the azo‐rotor was locked in the horizontal orientation at anchorage 3. After irradiation with Vis light, the azo‐rotor rotated quickly to the vertical orientation (5–10 seconds),