Update Rice University – Researchers develop a method to make atom-flat sensors that seamlessly integrate with devices – technique will make active sensors or devices possible for telecommunication and bio-sensing, plasmonics


Rice U Flat Atom structure DuEfkhxWwAAfEGTRice University engineers have developed a method to transfer complete, flexible, two-dimensional circuits from their fabrication platforms to curved and other smooth surfaces. Such circuits are able to couple with near-field …more

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by  scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices to report on what they perceive.

Electronically active 2-D materials have been the subject of much research since the introduction of graphene in 2004. Even though they are often touted for their strength, they’re difficult to move to where they’re needed without destroying them.Nano Sensor 1 FANG

The Ajayan and Lou groups, along with the lab of Rice engineer Jacob Robinson, have a new way to keep the materials and their associated circuitry, including electrodes, intact as they’re moved to curved or other smooth surfaces.

The results of their work appear in the American Chemical Society journal ACS Nano.

Rice logo_rice3The Rice team tested the concept by making a 10-nanometer-thick indium selenide photodetector with gold electrodes and placing it onto an . Because it was so close, the near-field sensor effectively coupled with an evanescent field—the oscillating electromagnetic wave that rides the surface of the fiber—and accurately detected the flow of information inside.

The benefit is that these sensors can now be imbedded into such fibers where they can monitor performance without adding weight or hindering the signal flow.

“This paper proposes several interesting possibilities for applying 2-D devices in real applications,” Lou said. “For example, optical fibers at the bottom of the ocean are thousands of miles long, and if there’s a problem, it’s hard to know where it occurred. If you have these sensors at different locations, you can sense the damage to the fiber.”

Lou said labs have gotten good at transferring the growing roster of 2-D materials from one surface to another, but the addition of electrodes and other components complicates the process. “Think about a transistor,” he said. “It has source, drain and gate electrodes and a dielectric (insulator) on top, and all of these have to be transferred intact. That’s a very big challenge, because all of those materials are different.”

Raw 2-D materials are often moved with a layer of polymethyl methacrylate (PMMA), more commonly known as Plexiglas, on top, and the Rice researchers make use of that technique. But they needed a robust bottom layer that would not only keep the circuit intact during the move but could also be removed before attaching the device to its target. (The PMMA is also removed when the circuit reaches its destination.)

The ideal solution was poly-dimethyl-glutarimide (PMGI), which can be used as a device fabrication platform and easily etched away before transfer to the target. “We’ve spent quite some time to develop this sacrificial layer,” Lou said. PMGI appears to work for any 2-D material, as the researchers experimented successfully with molybdenum diselenide and other materials as well.

Nano sensors 2 electronics_vision_10-11-17

The Rice labs have only developed passive sensors so far, but the researchers believe their technique will make active  or devices possible for telecommunication, biosensing, plasmonics and other applications.

 Explore further: Fluorine flows in, makes material metal

More information: Zehua Jin et al, Near-Field Coupled Integrable Two-Dimensional InSe Photosensor on Optical Fiber, ACS Nano (2018). DOI: 10.1021/acsnano.8b07159

 

Advertisements

NIST Research Suggests Graphene Can Stretch to be a Tunable Ion Filter – Applications for nanoscale sensors, drug delivery and water purification


 

 

Researchers at the National Institute of Standards and Technology (NIST) have conducted simulations suggesting that graphene, in addition to its many other useful features, can be modified with special pores to act as a tunable filter or strainer for ions (charged atoms) in a liquid.

The concept, which may also work with other membrane materials, could have applications such as nanoscale mechanical sensors, drug delivery, water purification and sieves or pumps for ion mixtures similar to biological ion channels, which are critical to the function of living cells. The research is described in the November 26 issue of Nature Materials.

“Imagine something like a fine-mesh kitchen strainer with sugar flowing through it,” project leader Alex Smolyanitsky said. “You stretch that strainer in such a way that every hole in the mesh becomes 1-2 percent larger. You’d expect that the flow through that mesh will be increased by roughly the same amount. Well, here it actually increases 1,000 percent. I think that’s pretty cool, with tons of applications.”

If it can be achieved experimentally, this graphene sieve would be the first artificial ion channel offering an exponential increase in ion flow when stretched, offering possibilities for fast ion separations or pumps or precise salinity control. Collaborators plan laboratory studies of these systems, Smolyanitsky said.

Graphene is a layer of carbon atoms arranged in hexagons, similar in shape to chicken wire, that conducts electricity. The NIST molecular dynamics simulations focused on a graphene sheet 5.5 by 6.4 nanometers (nm) in size and featuring small holes lined with oxygen atoms. These pores are crown ethers—electrically neutral circular molecules known to trap metal ions. A previous NIST simulation study showed this type of graphene membrane might be used for nanofluidic computing.

In the simulations, the graphene was suspended in water containing potassium chloride, a salt that splits into potassium and chlorine ions. The crown ether pores can trap potassium ions, which have a positive charge. The trapping and release rates can be controlled electrically. An electric field of various strengths was applied to drive the ion current flowing through the membrane.

Researchers then simulated tugging on the membrane with various degrees of force to stretch and dilate the pores, greatly increasing the flow of potassium ions through the membrane. Stretching in all directions had the biggest effect, but even tugging in just one direction had a partial effect.

Researchers found that the unexpectedly large increase in ion flow was due to a subtle interplay of a number of factors, including the thinness of graphene; interactions between ions and the surrounding liquid; and the ion-pore interactions, which weaken when pores are slightly stretched. There is a very sensitive balance between ions and their surroundings, Smolyanitsky said.

The research was funded by the Materials Genome Initiative.


Paper: A. Fang, K. Kroenlein, D. Riccardi and A. Smolyanitsky. Highly mechanosensitive ion channels from graphene-embedded crown ethers. Nature Materials. Published online November 26, 2018. DOI: 10.1038/s41563-018-0220-4

Israeli scientists develop ‘Cancer-Sniffing Nose’ using Nanotechnology – new device can ‘smell’ 17 diseases on a person’s breath


 

Nano Nose 2 nanose2-900x497

London audience told by Israeli-Christian professor about a new device which can ‘smell’ 17 diseases on a person’s breath

Professor Hossam Haick, an Israeli Christian, delivered Technion UK’s Ron Arad lecture at the Royal College of Physicians last week.

The electronic ‘nose’ he developed can smell 17 diseases on a person’s breath, including Alzheimer’s, Parkinson’s, tuberculous, diabetes and lung cancer.Cancer Nose I 140715155737-na-nose-face-story-top

The non-intrusive medical device, which works by identifying as disease’s bio-markers, has attracted the attention of billionaires such as Bill and Melinda Gates, whose foundation focuses on the diagnostics of diseases.

“Every disease has a unique signature – a ‘breath print,’” Haick said. “The challenge is to bring the best science we have proven into reality by developing a smaller device that captures all the components of a disease appearing in the breath.”

Cancer Sniffing Nose The-Technion-Ron-Arad-Dinner-The-Technion-UK_Prof_Hosaim-Haick_Cancer-Sniffing_Nose_Lecture-2-635x357Haick works at the Department of Chemical Engineering and the Russell Berrie Nanotechnology Institute at the Technion in Israel and is an expert in the field of nanotechnology and non-invasive disease diagnosis. (Left) Professor Hossam Haick at the Technion Ron Arad Dinner Credit: John Rifkin

The University said the latest advances in his research mean that it has the potential to identify diseases though sensors in mobile phones and wearable technology, and with more analysis and data it may even be able to predict cancer in the future.

“We cannot develop this technology in Israel without developing the best science,” he said. “Integrating the software, machine learning and academic intelligence will make a critical change in the early detection and prevention of cancerous diseases.”

US Patent Granted to Grolltex for Advanced Graphene ‘Super’ Sensor


December 8, 2017

San Diego based Grolltex was granted a patent by the USPTO for a new multi-modal ‘super’ sensor design made of single layer graphene.

The patent, titled “Graphene-based multi-modal sensor” describes a one atom thick architecture and utilizes several of Grolltex’ 2D materials technologies to produce what the company internally calls ‘The smallest, most sensitive sensor in the world’.

The company is working on initial applications for these sensors that are targeting the bio-sensing and defense fields as leading-edge users of this technology.

“Our single atom thick sensor design, in the strain sensor configuration, is so sensitive that it captures a robust and repeatable signal on the contractility strength of individual ‘cardio myocytes’ or heart cells as they beat”, said Jeff Draa, company co-founder and CEO.

“This can be a holy grail for fields such as cardiotoxicity testing as it has the capacity to be a significant time and money saver in the new drug testing and approval process”.

Additionally, the single layer graphene sensor covered by this patent has a very high threshold for thermal coefficient of resistance, meaning it experiences little to no signal drift when exposed to extreme levels of heat. This makes it an ideal sensor for measuring micro strain in high speed aeronautical vehicles.

These sensors are so small and thin, they can be layered into the skins of airplanes, helicopters or other high stress vehicles to real-time measure and detect micro stress at architectures and levels not currently possible with today’s sensing technologies. These sensors could also be discreetly placed within critical structures such as bridges or buildings.

The full story is available below.

Source: The Daily Telescope

MIT: Nanosensors could help determine tumors’ ability to remodel tissue – Nanosensors that can ‘profile’ tumors


mit-nanosensorsc-093016MIT researchers have designed nanosensors that can profile tumors and may yield insight into how they will respond to certain therapies. Credit: Christine Daniloff/MIT

MIT researchers have designed nanosensors that can profile tumors and may yield insight into how they will respond to certain therapies. The system is based on levels of enzymes called proteases, which cancer cells use to remodel their surroundings.

Once adapted for humans, this type of sensor could be used to determine how aggressive a tumor is and help doctors choose the best treatment, says Sangeeta Bhatia, the John and Dorothy Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science and a member of MIT’s Koch Institute for Integrative Cancer Research.

“This approach is exciting because people are developing therapies that are protease-activated,” Bhatia says. “Ideally you’d like to be able to stratify patients based on their protease activity and identify which ones would be good candidates for these therapies.”

Once injected into the tumor site, the nanosensors are activated by a  that is harmless to healthy tissue. After interacting with and being modified by the target tumor proteins, the sensors are secreted in the urine, where they can be easily detected in less than an hour.

Bhatia and Polina Anikeeva, the Class of 1942 Associate Professor of Materials Science and Engineering, are the senior authors of the paper, which appears in the journal Nano Letters. The paper’s lead authors are Koch Institute postdoc Simone Schurle and graduate student Jaideep Dudani.

Heat and release

Tumors, especially aggressive ones, often have elevated protease levels. These enzymes help tumors spread by cleaving proteins that compose the extracellular matrix, which normally surrounds cells and holds them in place.

In 2014, Bhatia and colleagues reported using nanoparticles that interact with a type of protease known as matrix metalloproteinases (MMPs) to diagnose cancer. In that study, the researchers delivered nanoparticles carrying peptides, or short protein fragments, designed to be cleaved by the MMPs. If MMPs were present, hundreds of cleaved peptides would be excreted in the urine, where they could be detected with a simple paper test similar to a pregnancy test.

In the new study, the researchers wanted to adapt the sensors so that they could report on the traits of tumors in a known location. To do that, they needed to ensure that the sensors were only producing a signal from the target organ, unaffected by background signals that might be produced in the bloodstream. They first designed sensors that could be activated with light once they reached their target. That required the use of ultraviolet light, however, which doesn’t penetrate very far into tissue.

“We started thinking about what kinds of energy we might use that could penetrate further into the body,” says Bhatia, who is also a member of MIT’s Institute for Medical Engineering and Science.

To achieve that, Bhatia teamed up with Anikeeva, who specializes in using magnetic fields to remotely activate materials. The researchers decided to encapsulate Bhatia’s protease-sensing nanoparticles along with magnetic particles that heat up when exposed to an alternating magnetic field. The field is produced by a small magnetic coil that changes polarity some half million times per second.

The heat-sensitive material that encapsulates the particles disintegrates as the magnetic particles heat up, allowing the protease sensors to be released. However, the particles do not produce enough heat to damage nearby tissue.

“It has been challenging to examine tumor-specific protease activities from patients’ biofluids because these proteases are also present in blood and other organs,” says Ji Ho (Joe) Park, an associate professor of bio and brain engineering at the Korea Advanced Institute of Science and Technology.

“The strength of this work is the magnetothermally responsive protease nanosensors with spatiotemporal controllability,” says Park, who was not involved in the research. “With these nanosensors, the MIT researchers could assay protease activities involved more in tumor progression by reducing off-target activation significantly.”

Choosing treatments

In a study of mice, the researchers showed that they could use these particles to correctly profile different types of colon tumors based on how much protease they produce.

Cancer treatments based on proteases, now in clinical trials, consist of antibodies that target a tumor protein but have “veils” that prevent them from being activated before reaching the tumor. The veils are cleaved by proteases, so this therapy would be most effective for patients with high  levels.

The MIT team is also exploring using this type of sensor to image cancerous lesions that spread to the liver from other organs. Surgically removing such lesions works best if there are fewer than four, so measuring them could help doctors choose the best treatment.

Bhatia says this type of sensor could be adapted to other tumors as well, because the magnetic field can penetrate deep into the body. This approach could also be expanded to make diagnoses based on detecting other kinds of enzymes, including those that cut sugar chains or lipids.

Explore further: Nanoparticles amplify tumor signals, making them much easier to detect in the urine

More information: Simone Schuerle et al. Magnetically Actuated Protease Sensors for in Vivo Tumor Profiling, Nano Letters (2016). DOI: 10.1021/acs.nanolett.6b02670

 

 

University of Cambridge and IBM Collaborate on “Something Deep Within” ~ Nanocrystals grown in nanowires for new classes of high-performance, energy-efficient computing, communications, and environmental and medical sensing systems.


Deep Nanowires 081116 160729143208_1_540x360Top: High-resolution electron microscopy images of a nickel silicide rhombic nanocrystal embedded in a silicon nanowire prepared with gold silicide used as a catalyst. The images demonstrate the intimate interactions that arise at the interfaces of these nanomaterials. Bottom: The physical properties that arise from such complex nano-systems could be used in next-generation photodetectors, lasers, and transistors.
Credit: Image courtesy of Department of Energy, Office of Science
 

As any good carpenter knows, it’s often easier to get what you want if you build it yourself. An international team using resources at the Center for Functional Nanomaterials took that idea to heart. They wanted to tailor extremely small wires that carry light and electrons. They devised an approach that lets them tailor the wires through exquisite control over the structures at the nanoscale. New structures could open up a potential path to a wide range of smaller, lighter, or more efficient devices.

This development could lead to highly tailored nanowires for new classes of high-performance, energy-efficient computing, communications, and environmental and medical sensing systems. The resulting devices could lead to smaller electronics as well as improving solar panels, photodetectors, and semiconductor lasers.

Semiconducting nanowires have a wide range of existing and potential applications in optoelectronic materials, from single-electron transistors and tunnel diodes, to light-emitting semiconducting nanowires to energy-harvesting devices. An international collaboration led by the University of Cambridge and IBM has demonstrated a new method to create novel nanowires that contain nanocrystals embedded within them. They accomplished this by modifying the classic “vapor-liquid-solid” crystal growth method, wherein a liquid-phase catalyst decomposes an incoming gas-phase source and mediates the deposition of the solid, growing nanowire.

In this work, a bimetallic catalyst is used. The team showed that by appropriate thermal treatment, it is possible to crystallize a solid silicide structure within the liquid catalyst, and then attach the nanowire to the solid silicon in a controlled epitaxial fashion. The Center for Functional Nanomaterials’ Electron Microscopy Facility was employed to image the nanomaterials by high spatial-resolution, aberration-corrected transmission electron microscopy. As well, scientists used a first-of-its-kind direct electron detector to obtain high temporal-resolution images of the fabrication process. Incorporating these instruments with the expertise and insight of the scientific team led to fantastic, nanoscale control over these structures and presents notable potential for a broad range of potential devices, like photodetectors and single electron transistors.


Story Source:

The above post is reprinted from materials provided byDepartment of Energy, Office of Science. Note: Content may be edited for style and length.


Journal Reference:

  1. F. Panciera, Y.-C. Chou, M. C. Reuter, D. Zakharov, E. A. Stach, S. Hofmann, F. M. Ross. Synthesis of nanostructures in nanowires using sequential catalyst reactions. Nature Materials, 2015; 14 (8): 820 DOI:10.1038/nmat4352

Research: “Flexible ‘Nano-Skin’ for “Cloaking” Objects


Iowa Cloak Skin 110528_web

IMAGE: This flexible, stretchable and tunable “meta-skin ” can trap radar waves and cloak objects from detection. view more  Credit: Liang Dong/Iowa State University

Iowa State University engineers have developed a new flexible, stretchable and tunable “meta-skin” that uses rows of small, liquid-metal devices to cloak an object from the sharp eyes of radar.

The meta-skin takes its name from metamaterials, which are composites that have properties not found in nature and that can manipulate electromagnetic waves. By stretching and flexing the polymer meta-skin, it can be tuned to reduce the reflection of a wide range of radar frequencies.

The journal Scientific Reports recently reported the discovery online. Lead authors from Iowa State’s department of electrical and computer engineering are Liang Dong, associate professor; and Jiming Song, professor. Co-authors are Iowa State graduate students Siming Yang, Peng Liu and Qiugu Wang; and former Iowa State undergraduate Mingda Yang. The National Science Foundation and the China Scholarship Council have partially supported the project.

“It is believed that the present meta-skin technology will find many applications in electromagnetic frequency tuning, shielding and scattering suppression,” the engineers wrote in their paper.

Dong has a background in fabricating micro and nanoscale devices and working with liquids and polymers; Song has expertise in looking for new applications of electromagnetic waves.

Working together, they were hoping to prove an idea: that electromagnetic waves – perhaps even the shorter wavelengths of visible light – can be suppressed with flexible, tunable liquid-metal technologies.

What they came up with are rows of split ring resonators embedded inside layers of silicone sheets. The electric resonators are filled with galinstan, a metal alloy that’s liquid at room temperature and less toxic than other liquid metals such as mercury.

Those resonators are small rings with an outer radius of 2.5 millimeters and a thickness of half a millimeter. They have a 1 millimeter gap, essentially creating a small, curved segment of liquid wire.

The rings create electric inductors and the gaps create electric capacitors. Together they create a resonator that can trap and suppress radar waves at a certain frequency. Stretching the meta-skin changes the size of the liquid metal rings inside and changes the frequency the devices suppress.

Tests showed radar suppression was about 75 percent in the frequency range of 8 to 10 gigahertz, according to the paper. When objects are wrapped in the meta-skin, the radar waves are suppressed in all incident directions and observation angles.

“Therefore, this meta-skin technology is different from traditional stealth technologies that often only reduce the backscattering, i.e., the power reflected back to a probing radar,” the engineers wrote in their paper.

As he discussed the technology, Song took a tablet computer and called up a picture of the B-2 stealth bomber. One day, he said, the meta-skin could coat the surface of the next generation of stealth aircraft.

But the researchers are hoping for even more – a cloak of invisibility.

“The long-term goal is to shrink the size of these devices,” Dong said. “Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light. While that would require advanced nanomanufacturing technologies and appropriate structural modifications, we think this study proves the concept of frequency tuning and broadening, and multidirectional wave suppression with skin-type metamaterials.”

Nebraska Researcher Find Gold “There’s Gold in them-thare (hills) … rather Nano-Sensors”!


gold-panningInstead of a pan and a pick ax, prospectors of the future might seek gold with a hand-held biosensor that uses a component of DNA to detect traces of the element in water.

The gold sensor is the latest in a series of metal-detecting biosensors under development by Rebecca Lai, an associate professor of chemistry at the University of Nebraska-Lincoln. Other sensors at various stages of development detect mercury, silver or platinum. Similar technology could be used to find cadmium, lead, arsenic, or other metals and metalloids.

A primary purpose for the sensors would be to detect water contaminants, Lai said. She cited the August 2015 blowout of a gold mine near Silverton, Colorado, which spilled chemicals into nearby rivers, as well as the ongoing problems with lead-tainted water supplies in Flint, Michigan.

Gold NEB 021816 rd1602_gold

The photo shows the gold biosensor developed by Rebecca Lai, associate professor of chemistry at the University of Nebraska-Lincoln. The center diagram illustrates how gold ions connect two strands of adenine and hinder electron transmission. The right diagram shows the effect on current signaling the presence of gold. Source: Rebecca Lai/University of Nebraska-Lincoln

Fabricated on paper strips about the size of a litmus strip, Lai’s sensors are designed to be inexpensive, portable and reusable. Instead of sending water samples away for time-consuming tests, people might someday use the biosensors to routinely monitor household water supplies for lead, mercury, arsenic or other dangerous contaminants.

But Lai also is among scientists searching for new and better ways to find gold. Not only aesthetically appealing and financially valuable, the precious metal is in growing demand for pharmaceutical and scientific purposes, including anti-cancer agents and drugs fighting tuberculosis and rheumatoid arthritis.

“Geochemical exploration for gold is becoming increasingly important to the mining industry,” Lai said. “There is a need for developing sensitive, selective and cost-effective analytical methods capable of identifying and quantifying gold in complex biological and environmental samples.”

Scientists have employed several strategies to find gold, such as fluorescence-based sensors, nanomaterials and even a whole cell biosensor that uses transgenic E. coli. Lai was a co-author of a 2013 study that explored the use of E. coli as a gold biosensor.

DNA, the carrier of genetic information in nearly all living organisms, might seem an unlikely method to detect gold and other metals. Lai’s research, however, exploits long-observed interactions between metal ions and the four basic building blocks of DNA: adenine, cytosine, guanine and thymine.

Different metal ions have affinities with the different DNA bases. The gold sensor, for example, is based on gold ions’ interactions with adenine. A mercury sensor is based upon mercury ions’ interaction with thymine. A silver sensor would be based upon silver ions’ interaction with cytosine.

NUtech Ventures, UNL’s affiliate for technology commercialization, is pursuing patent protection and seeking licensing partners for Lai’s metal ion sensors. She applied for a patent for the sensors in 2014.

“Although these interactions have been well-studied, they have not been exploited for use in electrochemical metal ion sensing,” Lai and doctoral student Yao Wu said in a recent Analytical Chemistry article describing the gold sensor.

Lai and Wu say their article is the first report of how oligoadenines — short adenine chains — can be used in the design and fabrication of this class of electrochemical biosensors, which would be able to measure concentrations of a target metal in a water sample as well as its presence.

The DNA-based sensor detects Au(III), a gold ion that originates from the dissolution of metallic gold. The mercury and silver sensors also detect dissolved mercury and silver ions.

“The detected Au(III) has to come from metallic gold, so if gold is found in a water supply, a gold deposit is somewhere nearby,” Lai explained.

The DNA-based biosensors need more refinement before they can be made commercially available, she said.

Lai’s sensor works by measuring electric current passing from an electrode to a tracer molecule, methylene blue in this case. In the absence of Au(III), the observed current is high because the oligoadenine probes are highly flexible and the electron transfer between the electrode and the tracer molecule is efficient.

But upon binding to Au(III) in the sample, the flexibility of the oligoadenine DNA probes is hindered, resulting in a large reduction in the current from the tracer molecule. The extent of the change in current is used to determine the concentration of AU(III) in the sample.

To allow the sensor to be reused multiple times, the Au(III) is later removed from the sensor with an application of another ligand.

Lai’s research focus is on electrochemical ion sensors. Her research has been supported with grants from the National Institutes of Health and the National Science Foundation.

Source: Univ. of Nebraska – Lincoln 

Advance could aid development of nanoscale biosensors


Sensors 021616 advancecould

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 sources that deliver coherent light, which the technique normally requires. The advance could enable more versatile and more compact devices.

“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 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 . 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 . 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”.

Explore further: Periodic structures in organic light-emitters can efficiently enhance, replenish surface plasmon waves

Graphene-Coated e-Fabrics Detect Noxious Gases


S Korea Graphene Sensors fibersensorx250Scientists in Korea have developed wearable, graphene-coated fabrics that can detect dangerous gases present in the air, alerting the wearer by turning on a light-emitting diode (LED) light.

The researchers, from the Electronics and Telecommunications Research Institute and Konkuk Univ. in the Republic of Korea, coated cotton and polyester yarn with a nanoglue called bovine serum albumin (BSA). The yarns were then wrapped in graphene oxide sheets.

Graphene is an incredibly strong one-atom-thick layer of carbon, and is known for its excellent conductive properties of heat and electricity. The graphene sheets stuck very well to the nanoglue—so much so that further testing showed the fabrics retained their electrical conducting properties after 1,000 consecutive cycles of bending and straightening and ten washing tests with various chemical detergents. Finally, the graphene oxide yarns were exposed to a chemical reduction process, which involves the gaining of electrons.

The reduced-graphene-oxide-coated materials were found to be particularly sensitive to detecting nitrogen dioxide, a pollutant gas commonly found in vehicle exhaust that also results from fossil fuel combustion. Prolonged exposure to nitrogen dioxide can be dangerous to human health, causing many respiratory-related illnesses. Exposure of these specially treated fabrics to nitrogen dioxide led to a change in the electrical resistance of the reduced graphene oxide.

The fabrics were so sensitive that 30 mins of exposure to 0.25 ppm of nitrogen dioxide (just under five times above the acceptable standard set by the U.S. Environmental Protection Agency) elicited a response. The fabrics were three times as sensitive to nitrogen dioxide in air compared to another reduced graphene oxide sensor previously prepared on a flat material.

The new technology, according to the researchers, can be immediately adopted in related industries because the coating process is a simple one, making it suitable for mass production. It would allow outdoor wearers to receive relevant information about air quality. The materials could also be incorporated with air-purifying filters to act as “smart filters” that can both detect and filter harmful gas from air.

“This sensor can bring a significant change to our daily life since it was developed with flexible and widely used fibers, unlike the gas sensors invariably developed with the existing solid substrates,” says Dr. Hyung-Kun Lee, who led this research initiative. The study was published online in Scientific Reports.

Source: Electronics and Telecommunications Research Institute

%d bloggers like this: