Monday, March 3, 2014

Optical nanotweezers for control of nano-objects

Trapping and moving an individual nano-object in the 3D in Nature Nanotechnology.

As science and technology go nano, scientists search for new tools to manipulate, observe and modify the “building blocks” of matter at the nanometer scale. The recent publication “Three-dimensional manipulation with scanning near-field optical nanotweezers“ in Nature Nanotechnologyby ICFO researchers Johann Berthelot, Srdjan Aćimović, Mathieu Juan (currently at Macquarie University) Mark Kreuzer, and Jan Renger, led by ICREA Prof at ICFO Romain Quidant, demonstrates for the first time the ability to use near-field optical tweezers to trap a nano-size object and manipulate it in the 3 dimensions of space.

Invented in the 80’s in Bell Labs, Optical tweezers have changed forever the fields of both biology and quantum optics. However, the technique has considerable limitations, one of them being its inability to directly trap objects smaller than a few hundreds of nanometers. This drawback prompted the pursuit of new approaches of nano-tweezers based on plasmonics, capable of trapping nano-scale objects such as proteins or nanoparticles without overheating and damaging the specimen. A few years ago the Plasmon Nano-Optics group at ICFO demonstrated that, by focusing light on a very small gold nano-structure lying on a glass surface which acts as a nano-lens, one can trap a specimen at the vicinity of the metal where the light is concentrated. This proof of concept was limited to demonstrate the mechanism but did not enable any 3D manipulation needed for practical applications.

Now they have taken a crucial step further by implementing the concept of plasmonic nano-tweezers at the extremity of a mobile optical fiber, nano-engineered with a bowtie-like gold aperture. Using this approach, they have demonstrated trapping and 3D displacement of specimens as small as a few tens of nanometers using an extremely small, non-invasive laser intensity. Central to the great potential of this technique is that both trapping and monitoring of the trapped specimen can be done through the optical fiber, performing the manipulation of nano-objects in a simple and manageable way outside of the physics research lab.