'Optical spring' detects single molecules

This drawing illustrates the sensing mechanism used by researchers at the universities of Rochester and Victoria, in which an ‘optical spring’ effect enhances the detection of particles and molecules.

A team of engineering researchers from the University of Rochester and the University of Victoria has demonstrated for the first time how a so-called “optical spring” effect can be used to measure individual molecules, in greater detail and at higher resolutions than is possible with conventional sensing methods.

Described in a study published in Nature Communications, the new technology has potential applications in medical diagnostics, drug development, security screening, environmental science and other fields.

The optical spring effect comes into play when light is circulated within a miniaturized resonator. The light causes the resonator to vibrate in a periodic fashion. When a particle or biomolecule lands on the resonator’s surface, the “optical spring” effect changes the vibration in a way that significantly enhances the detection of particles and molecules.

“This is the first time the sensing capability of the optical spring force has been realized, although the optical spring effect has been known for more than a decade,” says coauthor Wei Jiang, a Rochester PhD student in optics. The team also includes Qiang Lin, assistant professor of electrical and computer engineering at Rochester, and PhD student Wenyan Lu and Assistant Professor Tao Lu at Victoria.

The optical resonator used by the team – a whispering gallery micro-resonator -- was inspired by the acoustic "whispering gallery” effect first discovered in London's iconic St. Paul's Cathedral, where a voice whispered against one wall travels around the chamber’s circular rim and is clearly audible over 40 meters away on the other side.. The team’s micro-resonator – which uses light instead -- is only about 100 microns in diameter, about the width of a human hair.

“The ability to detect a single molecule or nanoparticle is essential for many applications,” note Yu and Lu. “To date, many approaches have been used to observe single particles. Our discovery may allow scientists to detect particles as miniscule as a single atom, or a single base pair of DNA.”

“The sensing principle is so universal that it can be applied to many sensing applications beyond molecule sensing itself, such as inertial sensing, electromagnetic field sensing, gas sensing, etc., that we are going to explore in the near future,” added Lin. “We proved the sensing principle in a whispering gallery resonator. The next step is to transfer our technology to a more practical and fully integrated chip-scale device platform that could be used in our daily lives in the future. This technological development will be well in line with AIM Photonics.”

The American Institute for Manufacturing Integrated Photonics (AIM Photonics), announced last year, will be headquartered in Rochester, and will bring the nation’s leading talent from companies, universities, and federal research institutions together under one entity to develop the next generation of integrated photonics.

The work represented in this paper is supported by the National Science Foundation, the Defense Advanced Research Projects Agency, and the National Sciences and Engineering Research Council of Canada.