Remote control of small particles modified with azobenzene derivatives by light irradiation

Introduction: The development of remote-controllable small machines has become important for biotechnology and industrial nanotechnology. We have developed a technique to photo-control silica micro-particles by utilizing... [ view full abstract ]

Introduction: The development of remote-controllable small machines has become important for biotechnology and industrial nanotechnology. We have developed a technique to photo-control silica micro-particles by utilizing distortion of the orientational ordered structure of liquid crystalline (LC) molecules through photo-response of small amount of additive azobenzene (Azo) molecules. In this paper, we have demonstrated remote photo-manipulation of nano-/micro-sized particles (NPs) modified with Azo molecules.
Methods: Several kinds of NPs like silica particles and nanosheets of metal oxides were modified by Azo derivatives acting as molecular motor. The resultant Azo-modified NPs (Azo/NPs) were employed in LC systems and model systems of cell membranes.
Results and Discussion: UV-visible spectroscopy results reveal that trans-to-cis and cis-to-trans isomerization cycles of Azo groups (top of Figure) could occur continuously by visible light irradiation and rapid thermal reversion. Microscopic observations of the LC system indicate that the Azo/NPs could be transported a few millimeters for ca. 150 s by moving light irradiation at 33 °C (nematic LC phase), as shown in the bottom of Figure. The critical following speed under dragging for a single Azo/NP was evaluated to be at least 10 µm/s at 33 °C. Therefore, the motion behavior appears to be correlated with generation of nano-/micro-sized disorganization regions on the nematic phase caused by photo-induced continuous isomerization of Azo groups. Hence, Azo derivatives can potentially be utilized as a molecular engine in nano-/micro-sized machines by supplying Azo-absorbed light energy and are expected to expand the application of such machines in custom-designed biotechnology and industrial small technology.