Allen HJ Yang

My research centers around the development and study of optofluidic transport devices. In short, I study how we can use photonic devices in combination with microfluidics to create systems that can influence the motions of micro- and nano- particles in their natural fluid environments for useful effects. Some applications of this technology will be in increasing the performance of biosensors and devices that are geared toward single-particle and single-molecule studies.

Phase 1 Research: Microparticle manipulation on solid-core optical waveguides

The first experimental phase of our research, was working to develop and demonstrate the idea of an “Integrated Optofluidic Transport Architecture” (IOTA). An IOTA is a lab-on-a-chip platform that contains both microfluidic (fluid flow) and optical transport elements (waveguides), working actively and dynamically to trap and transport particles suspended in a liquid.

The specific system we created was based on a SU-8 cross-linked polymer waveguides using water as our transport liquid. The SU-8 waveguides were integrated with PDMS microfluidics to create the complete optofluidic system. Our results from this study were published recently in Optics Express, where we demonstrated the ability to trap flowing particles and propel them along waveguides.

Our other Phase 1 effort was an analytical and numerical study of particle trapping in similar planar waveguide systems. The focus of these studies was on analyzing the stability of particle trapping as a function of relevant experiment parameters. These results have been published in Nanotechnology. You can check out media coverage of this work on the media page here.

Phase 2 Research: Trapping nanoparticles and biomolecules in slot waveguides

The second phase of the research project focused on removing the limitation of evanescent-field only particle-waveguide interactions. Evanescent-only interaction only allows a particle access to about 10% of the available power in a waveguide. Here we use slot waveguides, developed by the Lipson group at Cornell, which uses slotted waveguides made of silicon which exhibit the unique property of confining the majority of the optical energy into the low-index slot region of the waveguide, thus allowing for hollow-core or liquid-core type particle interaction with the optical field.

The sharp optical gradients generated by the waveguide and the strong optical intensity, along with the small size of the slots made it a prime example to test the trapping and transport of smaller sized objects in the sub-100 nm regime. Our experiments here demonstrated the ability to trap and propulse using radiation pressure polystyrene nanoparticles with diameters ranging from 75 - 100 nm. Furthermore we demonstrate for the first time, direct trapping of DNA biomolecules using optical energy. This research was published in Nature in 2009, with a simulation paper detailing the effect of the forces exerted on these small objects published in Nano Letters.