Direct measurement of thermophoretic and photophoretic force acting on hot micromotors with optical tweezers

Johannes Frueh, Sven Rutkowski, Tieyan Si, Yu Xuan Ren, Meiyu Gai, Sergei I. Tverdokhlebov, Guangyu Qiu, Jean Schmitt, Qiang He, Jing Wang

Research output: Contribution to journalArticlepeer-review


Synthetic microparticles present exciting features owing to their customizable light-matter interaction. We hereby report on the optical trapping of two artificial plasmonic microparticles: one with isotropic nanoparticles covering the surface (homogeneous particle) used as a hot Brownian particle and an anisotropic Janus microparticle, half coated with a gold nano-layer. The homogeneous particle decorated with plasmonic nanoparticles on the surface displays features of hot Brownian dynamics as well as photophoretic motion along z dimension in the optical trap. A dielectric particle was used as a reference particle because it acts as a cold particle with only the gradient force affecting it. In general, Janus particles orient in the trap with the dielectric part in the trap center. Plasmonic gold nanostructures absorb the light energy and produce heat; the photothermal forces significantly affect the optical trapping. These hot microspheres display temperature and Janus orientation dependent position distribution significantly different from cold (purely dielectric) microparticles. The developed method allows for the first time direct determination of the photophoretic (thermal force along light propagation direction) and thermophoretic force (light propagation direction independent force) acting on the respective particles, which opens new paths for analysis and control of micromachines.

Original languageEnglish
Article number149319
JournalApplied Surface Science
Publication statusPublished - 30 May 2021


  • Hot Brownian particle
  • Janus particle
  • Micromotor
  • Optical tweezers
  • Photophoresis
  • Thermophoresis

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Physics and Astronomy(all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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