Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Advance could aid development of nanoscale biosensors

16.02.2016

Imagine a hand-held environmental sensor that can instantly test water for lead, E. coli, and pesticides all at the same time, or a biosensor that can perform a complete blood workup from just a single drop. That's the promise of nanoscale plasmonic interferometry, a technique that combines nanotechnology with plasmonics--the interaction between electrons in a metal and light.

Now researchers from Brown University's School of Engineering have made an important fundamental advance that could make such devices more practical. The research team has developed a technique that eliminates the need for highly specialized external light sources that deliver coherent light, which the technique normally requires. The advance could enable more versatile and more compact devices.


Plasmonic interferometers that have light emitters within them could make for better, more compact biosensors.

Credit: Pacifici Lab / Brown University

"It has always been assumed that coherent light was necessary for plasmonic interferometry," said Domenico Pacifici, a professor of engineering who oversaw the work with his postdoctoral researcher Dongfang Li, and graduate student Jing Feng. "But we were able to disprove that assumption."

The research is described in Nature Scientific Reports.

Plasmonic interferometers make use of the interaction between light and surface plasmon polaritons, density waves created when light energy rattles free electrons in a metal. One type of interferometer looks like a bull's-eye structure etched into a thin layer of metal. In the center is a hole poked through the metal layer with a diameter of about 300 nanometers--about 1,000 times smaller than the diameter of a human hair. The hole is encircled by a series of etched grooves, with diameters of a few micrometers. Thousands of these bulls-eyes can be placed on a chip the size of a fingernail.

When light from an external source is shown onto the surface of an interferometer, some of the photons go through the central hole, while others are scattered by the grooves. Those scattered photons generate surface plasmons that propagate through the metal inward toward the hole, where they interact with photons passing through the hole. That creates an interference pattern in the light emitted from the hole, which can be recorded by a detector beneath the metal surface.

When a liquid is deposited on top of an interferometer, the light and the surface plasmons propagate through that liquid before they interfere with each other. That alters the interference patterns picked up by the detector depending on the chemical makeup of the liquid or compounds present in it. By using different sizes of groove rings around the hole, the interferometers can be tuned to detect the signature of specific compounds or molecules. With the ability to put many differently tuned interferometers on one chip, engineers can hypothetically make a versatile detector.

Up to now, all plasmonic interferometers have required the use of highly specialized external light sources that can deliver coherent light--beams in which light waves are parallel, have the same wavelength, and travel in-phase (meaning the peaks and valleys of the waves are aligned). Without coherent light sources, the interferometers cannot produce usable interference patterns. Those kinds of light sources, however, tend to be bulky, expensive, and require careful alignment and periodic recalibration to obtain a reliable optical response.

But Pacifici and his group have come up with a way to eliminate the need for external coherent light. In the new method, fluorescent light-emitting atoms are integrated directly within the tiny hole in the center of the interferometer. An external light source is still necessary to excite the internal emitters, but it need not be a specialized coherent source.

"This is a whole new concept for optical interferometry," Pacifici said, "an entirely new device."

In this new device, incoherent light shown on the interferometer causes the fluorescent atoms inside the center hole to generate surface plasmons. Those plasmons propagate outward from the hole, bounce off the groove rings, and propagate back toward the hole after. Once a plasmon propagates back, it interacts with the atom that released it, causing an interference with the directly transmitted photon. Because the emission of a photon and the generation of a plasmon are indistinguishable, alternative paths originating from the same emitter, the process is naturally coherent and interference can therefore occur even though the emitters are excited incoherently.

"The important thing here is that this is a self-interference process," Pacifici said. "It doesn't matter that you're using incoherent light to excite the emitters, you still get a coherent process."

In addition to eliminating the need for specialized external light sources, the approach has several advantages, Pacifici said. Because the surface plasmons travel out from the hole and back again, they probe the sample on top of the interferometer surface twice. That makes the device more sensitive.

But that's not the only advantage. In the new device, external light can be projected from underneath the metal surface containing the interferometers instead of from above. That eliminates the need for complex illumination architectures on top of the sensing surface, which could make for easier integration into compact devices.

The embedded light emitters also eliminate the need to control the amount of sample liquid deposited on the interferometer's surface. Large droplets of liquid can cause lensing effects, a bending of light that can scramble the results from the interferometer. Most plasmonic sensors make use of tiny microfluidic channels to deliver a thin film of liquid to avoid lensing problems. But with internal light emitters excited from the bottom surface, the external light never comes in contact with the sample, so lensing effects are negated, as is the need for microfluidics.

Finally, the internal emitters produce a low intensity light. That's good for probing delicate samples, such as proteins, than can be damaged by high-intensity light.

More work is required to get the system out of the lab and into devices, and Pacifici and his team plan to continue to refine the idea. The next step will be to try eliminating the external light source altogether. It might be possible, the researchers say, to eventually excite the internal emitters using tiny fiber optic lines, or perhaps electric current.

Still, this initial proof-of-concept is promising, Pacifici said.

"From a fundamental standpoint, we think this new device represents a significant step forward," he said, "a first demonstration of plasmonic interferometry with incoherent light".

###

The work was supported by National Science Foundation (CBET-1159255).

Note to Editors:

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

Kevin Stacey | EurekAlert!

More articles from Physics and Astronomy:

nachricht Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>