Light-Powered, Fuel-Free Oscillation, Migration, and Reversible Manipulation of Multiple Cargo Types by Micromotor Swarms

Abstract

Through experiments and simulations, we show that fuel-free photoactive TiO 2 microparticles can form mobile, coherent swarms in the presence of UV light, which track the subsequent movement of an irradiated spot in a fluid-filled microchamber. Multiple concurrent propulsion mechanisms (electrolyte diffusioosmotic swarming, photocatalytic expansion, and photothermal migration) control the rich collective behavior of the swarms, which provide a strategy to reversely manipulate cargo. The active swarms can autonomously pick up groups of inert particles, sort them by size, and sequentially release the sorted particles at particular locations in the microchamber. Hence, these swarms overcome three obstacles, limiting the utility of self-propelled particles. Namely, they can (1) undergo directed, long-range migration without the addition of a chemical fuel, (2) perform diverse collective behavior not possible with a single active particle, and (3) repeatedly and controllably isolate and deliver specific components of a multiparticle "cargo". Since light sources are easily fabricated, transported, and controlled, the results can facilitate the development of portable devices, providing broader access to the diagnostic and manufacturing advances enabled by microfluidics.

Transition metal dichalcogenide micromotors with programmable photophoretic swarming motion

“…20 Photoactive TiO 2 micromotors can form swarms under irradiation with UV light in a fluid-filled microchamber due to a cooperative propulsion mechanism involving diffusioosmotic and photothermal effects. 21 TiO 2 –OH micromotors display schooling and cooperative behavior under UV light irradiation due to nonelectrolyte diffusiophoretic interactions, exhibiting also negative phototaxis. 22 Platinum nanoparticle micromotors decorated with carbon nitride can experience negative and positive phototaxis upon UV light irradiation, due to the generation of protons and hydroxyl radicals in an electrophoretic mechanism.…”

Light-powered swarming phoretic antimony chalcogenide-based microrobots with “on-the-fly” photodegradation abilities

“…19 A typical example of light-induced swarm formation are TiO 2 -based swarming photophoretic microrobots. 20 Upon light irradiation, TiO 2 microrobots show schooling behavior consisting of the expansion and contraction of the swarms that act as a microfirework or micropump system due to photophoretic properties. 21 Eventually, due to negative phototaxis, the swarms can move within the sample and transport desired substances.…”

Autonomous hydrogel locomotion regulated by light and electric fields

“…Conventional robots are typically developed to perform simple tasks, including lifting, gripping, walking, or swimming with each motion performed under direct human control or preprogrammed instruction (4)(5)(6). Self-propelled catalytic particles and lightpowered micromotors have been reported to perform persistent directional motions and collective behaviors (7,8); however, programmed stimuli are required to combine a series of motions into more complex functionalities such as cargo delivery. These robotic systems use external control units and human supervision as the feedback loop and cannot complete complex tasks involving a sequence of varying steps on their own.…”