posted on 2024-01-10, 13:04authored byPedro Mena-Giraldo, Mannu Kaur, Steven L. Maurizio, Gabrielle A. Mandl, John A. Capobianco
External
stimuli can trigger changes in temperature, concentration,
and momentum between micromotors and the medium, causing their propulsion
and enabling them to perform different tasks with improved kinetic
efficiencies. Light-activated micromotors are attractive systems that
achieve improved motion and have the potential for high spatiotemporal
control. Photophoretic swarming motion represents an attractive means
to induce micromotor movement through the generation of temperature
gradients in the medium, enabling the micromotors to move from cold
to hot regions. The micromotors studied herein are assembled with
Fe3O4 nanoparticles, and NaGdF4:Yb3+,Er3+/NaGdF4:Yb3+ and LiYF4:Yb3+,Tm3+ upconverting nanoparticles.
The Fe3O4 nanoparticles were localized to one
hemisphere to produce a Janus architecture that facilitates improved
upconversion luminescence with the upconverting nanoparticles distributed
throughout. Under 976 nm excitation, Fe3O4 nanoparticles
generate the temperature gradient, while the upconverting nanoparticles
produce visible light that is used for micromotor motion tracking
and triggering of reactive oxygen species generation. As such, the
motion and application of the micromotors are achieved using a single
excitation wavelength. To demonstrate the practicality of this system,
curcumin was adsorbed to the micromotor surface and degradation of
Rhodamine B was achieved with kinetic rates that were over twice as
fast as the static micromotors. The upconversion luminescence was
also used to track the motion of the micromotors from a single image
frame, providing a convenient means to understand the trajectory of
these systems. Together, this system provides a versatile approach
to achieving light-driven motion while taking advantage of the potential
applications of upconversion luminescence such as tracking and detection,
sensing, nanothermometry, particle velocimetry, photodynamic therapy,
and pollutant degradation.