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Photoswitches were incorporated into the DNA origami plates to control the locked and relaxed states of the AuNR‐bound plates by photoreaction (Figure 1.13d) [101]. Photoresponsive DNA strands containing a photoisomerizable azobenzene derivative were incorporated into the sides of the two plates. Dissociation and binding of the photo‐responsive DNA strands by UV and visible light irradiation induced the open (relaxed state) and closed (locked) states, respectively. Two AuNRs (40 nm × 10 nm) were attached to each plate via hybridization of DNA strands introduced to the AuNRs and the plates. CD bands were observed at around 740 nm in the spectrum when the two plates were locked by hybridization of photoresponsive DNA strands. When the two plates were relaxed by dissociation of the photoresponsive DNA strand, the CD signals cancelled out and became extremely weak because the angle between the two arms was not fixed. Because of the reversibility of the cis–trans photoisomerization of azobenzene, two conformations (relaxed and locked state) could be repeatedly formed by alternating UV and visible irradiation, and conformational changes could be read spectroscopically in real time. The results show that these dynamic DNA origami devices can be used for molecular memory by reading out the reversible conformational change induced by photoirradiation.

Figure 1.13 A dynamic DNA origami structure that changes the structure in response to external stimuli. (a) It consists of two units and can rotate at the central pivot. The shape of the side surfaces to be joined fits each other and close. The structure can open and close reversibly in response to temperature. (b) A molecular robot that opens and closes arms in response to salt concentration.

Source: Gerling et al. [100]/with permission of American Association for the Advancement of Science.

(c) A rotatable DNA origami structure. Two plates can rotate on the central axis. A locked state and a relaxed state are formed by addition and removal of specific DNA strands. Left‐handed and right‐handed form can be controlled by a DNA strand exchange reaction. Due to the plasmonic interaction between AuNRs and chirality, locked and relaxed state are detected by CD spectra.

Source: Kuzyk et al. [101]/Springer Nature/CC BY 4.0.

(d) A plasmonic structure that combines AuNRs that open and close in response to photoirradiation. Repeated ON/OFF of the CD signals is monitored by alternative visible and UV irradiation.

Source: Kuzyk et al. [101]/Springer Nature/CC BY 4.0.