Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Tiny ring laser accurately detects and counts nanoparticles

J. Zhu, L. He, S. K. Ozdemir, and L. Yang/WUSTL

Whispering-gallery microlasers can count and measure nano-scale synthetic or biological particles. As this conceptual illustration shows, a particle disturbs the lasing "mode" to split into two frequencies (shown here as two different colors) and the frequency split acts a ruler that allows the particle to be measured. The inset at the top right shows a particle landing on the microlaser (a torus supported by a pedestal). Lina He, a graduate student in electrical and systems engineering at Washington University in St. Louis, and her co-workers demonstrated that the microlasers can detect particles 10 nanometers in radius. Their resolution limit is about one nanometer.
J. Zhu, L. He, S. K. Ozdemir, and L. Yang/WUSTL

Whispering-gallery microlasers can count and measure nano-scale synthetic or biological particles. As this conceptual illustration shows, a particle disturbs the lasing "mode" to split into two frequencies (shown here as two different colors) and the frequency split acts a ruler that allows the particle to be measured. The inset at the top right shows a particle landing on the microlaser (a torus supported by a pedestal). Lina He, a graduate student in electrical and systems engineering at Washington University in St. Louis, and her co-workers demonstrated that the microlasers can detect particles 10 nanometers in radius. Their resolution limit is about one nanometer.

Abstract:
A microlaser no bigger than a pinprick can accurately detect and count individual viruses, the particles that jumpstart cloud formation or those that contaminate the air we breathe.

Tiny ring laser accurately detects and counts nanoparticles

St. Louis, MO | Posted on June 29th, 2011

A tiny doughnut-shaped laser is the latest marvel of silicon microminiaturization, but instead of manipulating bits it detects very small particles. Small particles play a big — and largely unnoticed — role in our everyday lives. Virus particles make us sick, salt particles trigger cloud formation, and soot particles sift deep into our lungs and make it harder to breathe.

The sensor belongs to a category called whispering gallery resonators, which work like the famous whispering gallery in St. Paul's Cathedral in London, where someone on the one side of the dome can hear a message spoken to the wall by someone on the other side. Unlike the dome, which has resonances or sweet spots in the audible range, the sensor resonates at light frequencies.

Light traveling round the micro-laser is disturbed by a particle that lands on the ring, changing the light's frequency. The ring can count the touch-down of as many as 800 nanoparticles before the signals begin to be lost in the noise. By exciting more than one mode in the ring, scientists can double-check the accuracy of the count. And by changing the "gain medium," they can adapt the sensor for water rather than air.

Lan Yang, PhD, assistant professor of electrical and systems engineering at Washington University in St. Louis who leads the team that fabricated the new sensor, says that there is already lively interest in its commercialization in fields ranging from biology to aerosol science. The sensor is described and characterized in the June 26 online edition of Nature Nanotechnology.

Whispering gallery resonator becomes microlaser

A whispering gallery resonator supports "frequency degenerate modes" (modes, or patterns of excitation in the ring, with the same frequency, one traveling clockwise and the other counterclockwise around the ring.

The mode fields have "evanescent tails" that penetrate the surface of the ring and probe the surrounding medium. When a particle lands on one of the "hot spots" it scatters energy from one of the modes into the other, and the modes adopt slightly different resonance frequencies. This is referred to as mode splitting.

In an earlier work, Yang team used mode splitting in a simple glass ring that functioned as a waveguide for light coupled into it from outside. Because the ring was passive, the external-laser had to be an expensive tunable laser so that it could scan a frequency range looking for the ring's resonances to measure mode splitting. (For more information on this sensor see "Tiny sensor takes measure of nanoparticles.")

The new sensor differs from earlier whispering gallery resonators in that it is itself a miniature laser rather than the resonating cavity of an external laser.

The new sensor is also glass but glass laced with atoms of the rare earth elements that serve as a "gain medium." The glass is doped with rare-earth atoms and when an external light source boosts enough of them into an excited state, the ring begins to lase at its own preferred frequency.

When a particle lands on the microlaser, a single lasing line splits into two slightly different frequencies.

A simple way of measuring the frequency splitting is to mix the split laser modes in a photodetector, which produces a "beat frequency" that corresponds to the frequency difference.

"The tiny sensors are mass produced by sol-gel method on silicon wafer, and it is easy to switch the gain medium" says Lina He, a graduate student and first author of the paper. "The resonators are made by mixing the rare-earth ions of choice into a solution of tetraethoxysilane, water and hydrochloric acid. The solution is heated until it becomes viscous and then spin-coated on a silicon wafer and annealed to remove solvents and complete the transition to amorphous glass. The thin film of glass is then etched to create silica disks supported underneath by silicon pillars. As a final step, the rough silica disks are reflowed into smooth toroids by laser annealing."

Active sensor outperforms passive one
"The light used for sensing is generated inside the resonator itself, and so it is purer than the light in the passive sensor," says Yang "When the light is not that pure, you might not be able to see small frequency changes. But the active sensor hits one frequency — it has a really narrow linewidth — and so it is much more sensitive."

The microlaser is orders of magnitude more sensitive than the passive resonator, she says. Its effective resolution limit is about one nanometer. One nanometer is to a meter, what a marble is to the Earth.

Moreover, because the laser is now in the ring rather than coupled to it, the entire system is simpler and more self contained. "Now you just need a light source to excite the optical medium," says Yang, "and you can use a cheap laser diode for that instead of an expensive tunable laser."

Detecting many particles
The effect of a particle on a lasing mode depends on the particle's "polarizability," which is a function of its size and refractive index. To cover the possibilities, the Washington University team tested the micro-laser's performance with nanoparticles of various sizes made of various materials, including polystyrene (packing peanuts), virions (virus particles) and gold.

As particles enter the "mode volume" of the micro-laser one by one, the scientists can see a discrete upward or downward jump in the beat frequency. Each discrete jump signals the binding of a particle on the ring, and the number of the jumps reflects the number of particles.

Because the "resonator field" traps the particles on the resonator, once landed, they rarely drop off. But the team found they were able to count many particles before the losses induced by the particles made the laser linewidths so broad they couldn't detect changes in frequency splitting due to the latest arrival.

For example, they were able to detect and count as many as 816 gold nanoparticles using the same laser mode.

"When the line broadening is comparable to the change in splitting, then you're done," says Yang. "However, the whole resonator is fabricated on the chip, so you could just move on to the next resonator if necessary."

Doubling up for accuracy
The micro-laser can support more than one laser mode at a time. "By controlling the overlap of the pump light with the gain medium, you can excite more than one laser line," says Sahin Kaya Ozdemir, PhD, a research associate and co-author. "Then when a particle lands on the ring, each laser line will split into two, and generate a beat frequency. So you will have two beat frequencies instead of one."

That's an advantage, he explains, because the beat frequency depends in part on where the particle lands on the ring. If there is only one laser line and the particle falls between "hot spots" it might not be detected. The second beat frequency prevents these "false negatives," ensuring that every particle produces a detectable beat frequency.

Detecting particles in water
The microlasers intended to sense particles in air had been doped with erbium, a rare-earth element whose optical properties are well matched with those of air. In a final experiment designed to see whether this technique could be used to sense particles in water or blood, the team fabricated sensors that were doped with ytterbium rather than erbium. Ytterbium lases at wavelengths with low absorption by water.

Yang's team has already begun working to make use of the enhanced sensitivity provided by the microlaser for studying various problems. In terms of applications, "the near-term use will be the monitoring of dynamic behaviors of particles in response to environmental and chemical changes at single particle resolution," says Yang.

The next step, the team see is to engineer the surface of these tiny microlasers to detect DNA and individual biological molecules. If the DNA is tagged with engineered nanoparticles, the micro-laser sensor can count individual DNA molecules or fragments of molecules.

Listening to Yang it is hard to escape the impression that you're hearing for the first time about an astonishing device that will one day be as ubiquitous — and probably as underappreciated --- as the logic gates in our microwaves, cellphones and cars.

The Washington University in St. Louis team behind these results includes: L. He, W. Kim and J. Zhu, graduate students; S. K. Ozdemir, PhD, a research associate, and L. Yang, PhD, assistant professor in electrical and systems engineering.

This work is supported by National Science Foundation.

Lina He, Sahin Kaya Ozdemir, Jiangang Zhu, Woosung Kim and Lan Yang, "Detecting single viruses and nanoparticles using whispering gallery microlasers," Nature Nanotechnology, advanced online edition, June. 26, 2011. DOI: 10.1038/NNANO.2011.99

####

For more information, please click here

Contacts:
Diana Lutz
Senior Science Editor
(314) 935-5272


EXPERTS @ WUSTL
Lan Yang
Assistant professor of electrical and systems engineering
314-935-9543

Copyright © Washington University in St. Louis

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

Imaging

New NPZ100-403 Piezo Stage from nPoint Inc. September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

News and information

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch September 17th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Recruiting bacteria to be technology innovation partners: September 17th, 2014

Nanoribbon film keeps glass ice-free: Rice University lab refines deicing film that allows radio frequencies to pass September 16th, 2014

Sensors

Nanoscience makes your wine better September 17th, 2014

Simple, Cost-Effective Method Proposed for Synthesizing Zinc Oxide Nanopigments September 15th, 2014

First Colloid and Polymer Science Lecture awarded to Orlin D. Velev: Chemical engineer honored for outstanding research in colloid science September 12th, 2014

UT Arlington research uses nanotechnology to help cool electrons with no external sources September 11th, 2014

Discoveries

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch September 17th, 2014

Recruiting bacteria to be technology innovation partners: September 17th, 2014

Announcements

New NPZ100-403 Piezo Stage from nPoint Inc. September 17th, 2014

Scientists refine formula for nanotube types: Rice University theorists determine factors that give tubes their chiral angles September 17th, 2014

New non-invasive technique could revolutionize the imaging of metastatic cancer September 17th, 2014

Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch September 17th, 2014

Tools

New NPZ100-403 Piezo Stage from nPoint Inc. September 17th, 2014

Advanced Light Source Sets Microscopy Record| Berkeley Lab Researchers Achieve Highest Resolution Ever with X-ray Microscopy September 11th, 2014

Researchers Create World’s Largest DNA Origami September 11th, 2014

Development of Algorithm for Accurate Calculation of Average Distance Travelled by Low-Speed Electrons without Energy Loss that Are Sensitive to Surface Structure September 11th, 2014

Photonics/Optics/Lasers

'Squid skin' metamaterials project yields vivid color display: Rice lab creates RGB color display technology with aluminum nanorods September 15th, 2014

Fonon at Cutting-Edge of 3D Military Printing: Live-Combat Scenarios Could See a Decisive Advantage with 3D Printing September 15th, 2014

Simple, Cost-Effective Method Proposed for Synthesizing Zinc Oxide Nanopigments September 15th, 2014

First Colloid and Polymer Science Lecture awarded to Orlin D. Velev: Chemical engineer honored for outstanding research in colloid science September 12th, 2014

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE