Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Almost as sensitive as a dog's nose: New sensor for SERS Raman spectroscopy

The basis of the high-sensitivity sensor are carbon nanotubes having curved tips. The numerous gaps let through the Raman scattered light.Illustration: H.G. Park / ETH Zurich
The basis of the high-sensitivity sensor are carbon nanotubes having curved tips. The numerous gaps let through the Raman scattered light.

Illustration: H.G. Park / ETH Zurich

Abstract:
Scientists at ETH Zurich and the Lawrence Livermore National Laboratory (LLNL) in California have developed an innovative sensor for surface-enhanced Raman spectroscopy (SERS). Thanks to its unique surface properties at nanoscale, the method can be used to perform analyses that are more reliable, sensitive and cost-effective. In experiments with the new sensor, the researchers were able to detect a certain organic species (1,2bis(4-pyridyl)ethylene, or BPE) in a concentration of a few hundred femtomoles per litre. A 100 femtomolar solution contains around 60 million molecules per litre.

Almost as sensitive as a dog's nose: New sensor for SERS Raman spectroscopy

Zurich, Switzerland | Posted on August 28th, 2013

Until now, the detection limit of common SERS systems was in the nanomolar range, i.e. one billionth of a mole. The results of a study conducted by Hyung Gyu Park, Professor of Energy Technology at ETH Zurich, and Tiziana Bond, Capability Leader at LLNL, were published this week as a cover article in the scientific journal Advanced Materials.

Raman spectroscopy takes advantage of the fact that molecules illuminated by fixed-frequency light exhibit 'inelastic' scattering closely related to the vibrational and rotational modes excited in the molecules. Raman scattered light differs from common Rayleigh scattered light in that it has different frequencies than that of the irradiating light and produces a specific frequency pattern for each substance examined, making it possible to use this spectrum information as a fingerprint for detecting and identifying specific substances. To analyse individual molecules, the frequency signals must be amplified, which requires that the molecule in question either be present in a high concentration or located close to a metallic surface that amplifies the signal. Hence the name of the method: surface-enhanced Raman spectroscopy.

Amplified signals for improved reproducibility

"This technology has been around for decades," explains Ali Altun, a doctoral student in the group led by Park at the Institute of Energy Technology. With today's SERS sensors, however, the signal strength is adequate only in isolated cases and yields results with low reproducibility. Altun, Bond and Park therefore set themselves the goal of developing a sensor that massively amplifies the signals of the Raman-scattered light.

The substrate of choice turned out to be vertically arranged, caespitose, densely packed carbon nanotubes (CNT) that guarantee this high density of 'hot spots'. The group developed techniques to grow dense forests of CNTs in a uniform and controlled manner. The availability of this expertise was one of the principal motivations for using nanotubes as the basis for highly sensitive SERS sensors, says Park.

A spaghetti-like surface

The tips of the CNTs are sharply curved, and the researchers coated these tips with gold and hafnium dioxide, a dielectric insulating material. The point of contact between the surface of the sensor and the sample thus resembles a plate of spaghetti topped with sauce. However, between the strands of spaghetti, there are numerous randomly arranged holes that let through scattered light, and the many points of contact -- the 'hot spots' -- amplify the signals.

"One method of making highly sensitive SERS sensors is to take advantage of the contact points of metal nanowires," explains Park. The nano-spaghetti structure with metal-coated CNT tips is perfect for maximising the density of these contact points.

Indeed, Bond explains, the wide distribution of metallic nano-crevices in the nanometre range, well recognised to be responsible for extreme electromagnetic enhancement (or hot spots) and highly pursued by many research groups, has been easily and readily achieved by the team, resulting in the intense and reproducible enhancements.

The sensor differs from other comparable ultra-sensitive SERS sensors not only in terms of its structure, but also because of its relatively inexpensive and simple production process and the very large surface area of the 3D structures producing an intense, uniform signal.

A breakthrough on two levels

Initially, the researchers only coated the tips of the CNTs with gold. The first experiments with the BPE test molecule showed them that they were on the right track, but that the detection limit could not be reduced to quite the degree they had hoped. Eventually, they discovered that the electrons required on the gold layer surface for generating what is referred to as plasmon resonance were flowing out via the conductive carbon nanotubes. The task was then to figure out how to prevent this plasmonic energy leakage.

The researchers coated the CNTs with hafnium oxide, an insulating material, before applying a layer of gold. "This was the breakthrough," says Altun. The insulation layer increased the sensitivity of its sensor substrate by a factor of 100,000 in the molar concentration unit.

"For us as scientists, this was a moment of triumph," agrees Park, "and it showed us that we had made the right hypothesis and a rational design."

The key to the successful development of the sensor was therefore twofold: on the one hand, it was their decision to continue using CNTs, whose morphology is essential for maximising the number of 'hot spots', and on the other hand, it was the fact that these nanotubes were double-coated.

Park and Bond would now like to go one step further and bring their new principle to market, but they are still seeking an industry partner. Next, they want to continue improving the sensitivity of the sensor, and they are also looking for potential areas of application. Park envisions installation of the technology in portable devices, for example to facilitate on-site analysis of chemical impurities such as environmental pollutants or pharmaceutical residues in water. He stresses that invention of a new device is not necessary; it is simple to install the sensor in a suitable way.

Other potential applications include forensic investigations or military applications for early detection of chemical or biological weapons, biomedical application for real-time point-of-care monitoring of physiological levels, and fast screening of drugs and toxins in the area of law enforcement.

####

For more information, please click here

Contacts:
Hyung Gyu Park

41-446-329-460

Copyright © ETH Zurich

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 Links

Reference

Related News Press

News and information

Continuous roll-process technology for transferring and packaging flexible LSI August 29th, 2016

Meteorite impact on a nano scale August 29th, 2016

Designing ultrasound tools with Lego-like proteins August 29th, 2016

A nanoscale wireless communication system via plasmonic antennas: Greater control affords 'in-plane' transmission of waves at or near visible light August 27th, 2016

Laboratories

A new way to display the 3-D structure of molecules: Metal-organic frameworks provide a new platform for solving the structure of hard-to-study samples August 21st, 2016

Scientists uncover origin of high-temperature superconductivity in copper-oxide compound: Analysis of thousands of samples reveals that the compound becomes superconducting at an unusually high temperature because local electron pairs form a 'superfluid' that flows without resist August 19th, 2016

Law enforcement/Anti-Counterfeiting/Security/Loss prevention

Nanotech Security Featured by Simon Fraser University: Company's Anti-Counterfeiting Technology Developed With the Help of University's 4D LABS Materials Research Institute August 21st, 2016

Down to the wire: ONR researchers and new bacteria August 18th, 2016

Hexagonal boron nitride semiconductors enable cost-effective detection of neutron signals: Texas Tech University researchers demonstrate hexagonal boron nitride semiconductors as a cost-effective alternative for inspecting overseas cargo containers entering US ports August 17th, 2016

Sensors

A promising route to the scalable production of highly crystalline graphene films August 26th, 2016

Down to the wire: ONR researchers and new bacteria August 18th, 2016

'Sniffer plasmons' could detect explosives: Scientists have proposed a graphene-based spaser that can detect even small amounts of various substances, including explosives August 16th, 2016

Perpetual 'ice water': Stable solid-liquid state revealed in nanoparticles: Gallium nanoparticles that are both solid and liquid are stable over a range of 1000 degrees Fahrenheit August 5th, 2016

Discoveries

Continuous roll-process technology for transferring and packaging flexible LSI August 29th, 2016

Meteorite impact on a nano scale August 29th, 2016

Designing ultrasound tools with Lego-like proteins August 29th, 2016

A promising route to the scalable production of highly crystalline graphene films August 26th, 2016

Announcements

Continuous roll-process technology for transferring and packaging flexible LSI August 29th, 2016

Meteorite impact on a nano scale August 29th, 2016

Designing ultrasound tools with Lego-like proteins August 29th, 2016

A nanoscale wireless communication system via plasmonic antennas: Greater control affords 'in-plane' transmission of waves at or near visible light August 27th, 2016

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

Continuous roll-process technology for transferring and packaging flexible LSI August 29th, 2016

Meteorite impact on a nano scale August 29th, 2016

Designing ultrasound tools with Lego-like proteins August 29th, 2016

A nanoscale wireless communication system via plasmonic antennas: Greater control affords 'in-plane' transmission of waves at or near visible light August 27th, 2016

Military

New electrical energy storage material shows its power: Nanomaterial combines attributes of both batteries and supercapacitors August 25th, 2016

Nanoparticles that speed blood clotting may someday save lives August 23rd, 2016

Curbing the life-long effects of traumatic brain injury August 19th, 2016

Lab team spins ginger into nanoparticles to heal inflammatory bowel disease August 19th, 2016

Environment

Nanofur for oil spill cleanup: Materials researchers learn from aquatic ferns: Hairy plant leaves are highly oil-absorbing / publication in bioinspiration & biomimetics / video on absorption capacity August 25th, 2016

Researchers watch catalysts at work August 19th, 2016

Down to the wire: ONR researchers and new bacteria August 18th, 2016

SLAC, Stanford gadget grabs more solar energy to disinfect water faster: Plopped into water, a tiny device triggers the formation of chemicals that kill microbes in minutes August 15th, 2016

Research partnerships

New electrical energy storage material shows its power: Nanomaterial combines attributes of both batteries and supercapacitors August 25th, 2016

New theory could lead to new generation of energy friendly optoelectronics: Researchers at Queen's University Belfast and ETH Zurich, Switzerland, have created a new theoretical framework which could help physicists and device engineers design better optoelectronics August 23rd, 2016

A new way to display the 3-D structure of molecules: Metal-organic frameworks provide a new platform for solving the structure of hard-to-study samples August 21st, 2016

Researchers watch catalysts at work August 19th, 2016

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







Car Brands
Buy website traffic