Visible-light-driven artificiai nano/micromotors

Abstract

The design and fabrication of motors toward nano/microscale with flexible manipulation and biocompatibility have motivated substantial academic efforts over the past decades due to their invaluable potential for accomplishing various tasks in microscopic fields such as healthcare, environmental remediation as well as nano/micro-manufacturing. Therein, nano/micromotors propelled under light illumination is an attractive strategy owing its wireless, remote propagation, as well as its precise, local and facile tunability over abundant adjustable dimensions such as direction, amplitude, sequence, wavelength and polarization. However, most of the existing light-driven nano/micromotors are mainly propelled by ultraviolet (UV) light which may limits their applications. As an alternative, the visible light shows higher penetration, better biocompatibility, convenience and more obvious discrimination compared with UV light in most situations. Here, two general strategies are proposed to design and fabricate visible-light-driven nano/micromotors. The first strategy is sensitizing the TiO2 based nano/micromotors with diverse organic dyes or quantum dots to extend the absorption range from UV region to visible region. To demonstrate this strategy, three typical dyes D5, N719 and SQ2 are employed to sensitize the Janus TiO2/Si microtree micromotors. Meanwhile, as the micromotors can be coded with orthogonal spectral response, the multichannel manipulation can be readily achieved as multiple beams of light with various wavelength can be utilized as individual control signals. However, since the available species list of organic dyes is short, it is incapable for full spectra coding and response. Therefore, another strategy is developing the visible-light-driven nano/micromotors based on semiconductor alloy materials with widely tunable compositions. As typical semiconductor materials, ZnSe, CdSe and ZnXCd1-XSe alloy are used to design visible-light-driven nanomotors with continuous tunable spectra almost across the visible region from blue light to red light with the entire compositional range from x = 0 to 1. These two strategies demonstrate the superb flexibility of selecting responsive spectra and pave the way toward more multichannel manipulation. Furthermore, the orthogonal activation capability of light-driven nano/micromotors opens up a new dimension to study the highly scientific important collective behavior of the active particles.