January 23, 2006
Controlling Cell and Molecule Movement Using Light-Responsive Nanoparticles
Using gold, crescent-shaped nanoparticles as a molecular tugboat, researchers at the University of California at Berkeley have developed a method for moving cells and biomolecules through microfluidics channels without the need for valves, pumps or other control elements. Instead, this novel technique uses the interaction between light and the nanoparticles to create a fluid force that drags liquid and the molecules in it along a trail that follows a moving light beam.
Writing in the journal Nature Materials, a research team headed by Luke Lee, Ph.D., describes the physical process that moves fluid using light-activated nanoparticles. The process starts when the gold nano-crescents absorb light energy and become warm. The heat from the nanoparticles causes a small amount of liquid surrounding them to vaporize, but the vapor quickly condenses into microscopic droplets just ahead of a moving front of the liquid, which almost as quickly coalesces with the droplets, which has the effect of moving the nanoparticle-containing fluid forward. As the beam of activating light moves along the path of the microfluidics channel, the fluid follows as this process repeats itself over and over again.
Because the investigators use a low-powered light source, the bulk liquid remains at the ambient temperature, an important consideration when the goal is to transport cells and biomolecules through a microfluidics device. The researchers demonstrated their new technique in a microfluidics device fashioned from the biocompatible polymer polydimethylsiloxane (PDMS), a material finding wide use among microfluidics researchers.
Using this technique, the investigators were able to move fluid through the straight channel, pick a direction of flow at the junction of multiple channels, and negotiate right angles within the microfluidics device. The researchers demonstrated the technique with both biomolecules and live cells.
This work is detailed in a paper titled, “Optofluidic control using photothermal nanoparticles.” An abstract is available through PubMed.