Dionne and Saleh applied plasmonic principles to design a new aperture that focuses light more effectively. The aperture is structured much like the coaxial cables that transmit television signals, Saleh said. A nanoscale tube of silver is coated in a thin layer of silicon dioxide, and those two layers are wrapped in a second outer layer of silver. When light shines through the silicon dioxide ring, it creates plasmons at the interface where the silver and silicon dioxide meet. The plasmons travel along aperture and emerge on the other end as a powerful, concentrated beam of light.
The Stanford device is not the first plasmonic trap, but it promises to trap the smallest specimens recorded to date. Saleh and Dionne have theoretically shown that their design can trap particles as small as 2 nanometers. With further improvements, their design could even be used to optically trap molecules even smaller.
An optical multi-tool
As nanoscale tools go, this new optical trap would be quite a versatile gadget. While the researchers first envisioned it in the context of materials science, its potential applications span many other fields including biology, pharmacology, and genomics.
Dionne said she would first like to trap a single protein, and try to unravel its twisted structure using visible light alone. Dionne points out that the beam of light could also be used to exert a strong pulling force on stem cells, which has been shown to change how the these important building blocks differentiate into various kinds of cells. Saleh, on the other hand, is particularly excited about moving and stacking tiny particles to explore their attractive forces and create new, "bottom-up" materials and devices.
All this is down the road, however. In the meantime, Saleh is working on turning the d
|Contact: Andrew Myers|
Stanford School of Engineering