Optical trapping

Investigating Particle Trapping in 3D

More than 40 years ago, Prof Ahskin showed that one could manipulate micro-nano objects using a tightly focused light. In 2018, Prof. Arthur Ashkin was awarded with the Nobel Prize in Physics for the discovery of this phenomenon, now referred to as optical trapping or optical tweezer. Since its discovery, researchers have used laser trapping as a technique to manipulate micro- and nano-scale materials by confining them inside the generated optical potential.


The Hofkens lab has recently introduce optical trapping on the multiplane wide field setup (see equipment section for more details on the setup). The main topic investigated with laser trapping is the interaction of nanoparticle in three-dimension under a trapping laser potential. While most groups focus on what is happening at the focus of the laser, we try to look at what is happening outside of the trapping volume. Indeed, recently, the Prof. Masuhara group (our main collaborator in this project) has reported the formation of assemblies (or swarms) of different nanoparticles (NPs), which expand outside the focal spot when the NPs are trapped close to an interface. The shape and the behavior of the generated swarm depend on the material and the shape of the NPs used as well as the polarization of the trapping laser. As an example, for Au NPs an antenna-like structure is formed at the centre of the focal spot with two large dynamically fluctuating swarms of Au NPs extending well outside the focal spot. We are now looking at this phenomenon it in 3D using our multiplane wide field setup in conjunction with particle tracking to unveil the underlying physics.


Illustration showing how our multiplane widefield setup (8 planes) can track a bead through the focus.

swarming trapping.jpg

Key Publications:

Tetsuhiro Kudo, Shang-Jan Yang, and Hiroshi Masuhara. Nano Letters 2018 18 (9), 5846-5853. https://doi.org/10.1021/acs.nanolett.8b02519