Multiwavelength-Steerable Visible-Light-Driven Magnetic CoO–TiO₂ Microswimmers

Abstract

While current light-driven microswimmers require high-intensity light, UV light, or toxic fuels to propel them, powering them with low-intensity UV-free visible light without fuels is essential to enable their potential high-impact applications. Therefore, in this study, a new material for light-driven microswimmers in the form of CoO is introduced. Janus CoO–TiO2 microswimmers powered with low-intensity, UV-free visible light inside water without using any toxic fuels like H2O2 is proposed. The microswimmers show propulsion under full spectrum of visible light with 17 times lower intensity than the mean solar intensity. They propel by breaking down water into oxygen and oxide radicals, which enables their potential applications for photocatalysis and drug delivery. The microswimmers are multiwavelength responsive, from the ultraviolet to the infrared region. The direction of swimming changes with the change in the illumination from the visible to UV light. In addition to being responsive, they are wavelength steerable and exhibit inherent magnetic properties enabling magnetic steering control of the CoO–TiO2 microswimmers. Thus, these microswimmers, which are propelled under low-intensity visible light, have direction-changing capability using light of different wavelengths, and have steering control capability by external magnetic fields, could be used in future potential applications, such as active and local cargo delivery, active photocatalysis, and hydrogen evolution.

Medical Micro/Nanorobots in Precision Medicine

“…[111] The later materials are of particular interest because the metallic propellant is degraded after use, leaving nontoxic byproducts behind. [112] Optical [113][114][115][116][117][118][119] and electrical fields [120][121][122][123][124][125] have also been used to enhance the reaction rate of catalytic materials to produce locomotion, although they are less commonly used in biomedical applications.…”

Carbon nitride-based light-driven microswimmers with intrinsic photocharging ability

“…So far, many photoactive molecules and materials have been adapted to serve as light-driven microswimmers by decoration with electrocatalysts ( 6 , 10 ). However, photocatalytic propulsion has mostly been realized with inorganic semiconductors, such as TiO 2 ( 1 , 11 – 27 ). A transition to nature-inspired, organic microswimmers is thus of high interest, especially regarding potential improvements in biocompatibility, tunability, and cost ( 28 ).…”

Microrobots from Toposelective Nanoparticle Attachment

“…3). Fe 2 O 3 imparts both photocatalytic and magnetic properties, and could be combined with TiO 2 P-25 for enhanced speeds (29) and controlled steering (30). SrTiO 3 is a perovskite photocatalyst widely studied for its water-splitting properties (31), and therefore is promising as the basis for a fuel-free microswimmer.…”