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Iowa Cloak Skin 110528_webIMAGE: 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.”

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 

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 Sensors 111715 1-ultrasensiti

Ultrasensitive gas sensors based on the infusion of boron atoms into graphene—a tightly bound matrix of carbon atoms—may soon be possible, according to an international team of researchers from six countries.

Graphene is known for its remarkable strength and ability to transport electrons at high speed, but it is also a highly sensitive gas sensor. With the addition of atoms, the boron graphene sensors were able to detect noxious gas molecules at extremely low concentrations, parts per billion in the case of and parts per million for ammonia, the two gases tested to date. This translates to a 27 times greater sensitivity to nitrogen oxides and 10,000 times greater sensitivity to ammonia compared to pristine graphene. The researchers believe these results, reported today (Nov. 2) in the Proceedings of the National Academy of Sciences, will open a path to high-performance sensors that can detect trace amounts of many other molecules.

“This is a project that we have been pursuing for the past four years, ” said Mauricio Terrones, professor of physics, chemistry and materials science at Penn State. “We were previously able to dope graphene with atoms of nitrogen, but boron proved to be much more difficult. Once we were able to synthesize what we believed to be boron graphene, we collaborated with experts in the United States and around the world to confirm our research and test the properties of our material.”

Both boron and nitrogen lie next to carbon on the periodic table, making their substitution feasible. But boron compounds are very air sensitive and decompose rapidly when exposed to the atmosphere. One-centimeter-square sheets were synthesized at Penn State in a one-of-a-kind bubbler-assisted chemical vapor deposition system. The result was large-area, high-quality boron-doped graphene sheets.

Once fabricated, the researchers sent boron graphene samples to researchers at the Honda Research Institute USA Inc., Columbus, Ohio, who tested the samples against their own highly sensitive . Konstantin Novoselov’s lab at the University of Manchester, UK, studied the transport mechanism of the sensors. Novoselov was the 2010 Nobel laureate in physics. Theory collaborators in the U.S. and Belgium matched the scanning tunneling microscopy images to experimental images, confirmed the presence of the in the graphene lattice and their effect when interacting with ammonia or nitrogen oxide molecules. Collaborators in Japan and China also contributed to the research.

“This multidisciplinary research paves a new avenue for further exploration of ultrasensitive gas sensors,” said Avetik Harutyunyan, chief scientist and project leader at Honda Research Institute USA Inc. “Our approach combines novel nanomaterials with continuous ultraviolet light radiation in the sensor design that have been developed in our laboratory by lead researcher Dr. Gugang Chen in the last five years. We believe that further development of this technology may break the parts per quadrillion level of detection limit, which is up to six orders of magnitude better sensitivity than current state-of-the-art sensors.”

These sensors can be used for labs and industries that use ammonia, a highly corrosive health hazard, or to detect nitrogen oxides, a dangerous atmospheric pollutant emitted from automobile tailpipes. In addition to detecting toxic or flammable gases, theoretical work indicates that boron-doped graphene could lead to improved lithium-ion batteries and field-effect transistors, the authors report.

Explore further: Study opens graphene band-gap

More information: Ultrasensitive gas detection of large-area boron-doped graphene, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1505993112

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

newmaterialworkplayx250 Serendipity has as much a place in sci­ence as in love.

That’s what North­eastern Univ. physi­cists Swastik Kar and Srinivas Sridhar found during their four-year project to modify graphene, a stronger-than-steel infin­i­tes­i­mally thin lat­tice of tightly packed carbon atoms. Pri­marily funded by the Army Research Lab­o­ra­tory and Defense Advanced Research Projects Agency, or DARPA, the researchers were charged with imbuing the decade-old mate­rial with thermal sen­si­tivity for use in infrared imaging devices such as night-vision gog­gles for the military.

What they unearthed, pub­lished in Science Advances, was so much more: an entirely new mate­rial spun out of boron, nitrogen, carbon and oxygen that shows evi­dence of mag­netic, optical and elec­trical properties, as well as DARPA’s sought-after thermal ones. Its poten­tial appli­ca­tions run the gamut: from 20-megapixel arrays for cell­phone cam­eras to photo detec­tors to atom­i­cally thin tran­sis­tors that when mul­ti­plied by the bil­lions could fuel computers.

“We had to start from scratch and build every­thing,” says Kar, an assis­tant pro­fessor of physics in the Col­lege of Sci­ence. “We were on a journey, cre­ating a new path, a new direc­tion of research.”

newmaterialworkplayx250

An artistic ren¬dering of novel mag¬netism in 2D-BNCO sheets, the new mate¬rial Swastik Kar and Srinivas Sridhar cre¬ated. Image: Northeastern Univ.

The pair was familiar with “alloys,” con­trolled com­bi­na­tions of ele­ments that resulted in mate­rials with prop­er­ties that sur­passed graphene’s—for example, the addi­tion of boron and nitrogen to graphene’s carbon to con­note the con­duc­tivity nec­es­sary to pro­duce an elec­trical insu­lator. But no one had ever thought of choosing oxygen to add to the mix.

What led the North­eastern researchers to do so?

“Well, we didn’t choose oxygen,” says Kar, smiling broadly. “Oxygen chose us.”

Oxygen, of course, is every­where. Indeed, Kar and Sridhar spent a lot of time trying to get rid of the oxygen seeping into their brew, wor­ried that it would con­t­a­m­i­nate the “pure” mate­rial they were seeking to develop.

“That’s where the Aha! moment hap­pened for us,” says Kar. “We real­ized we could not ignore the role that oxygen plays in the way these ele­ments mix together.”

“So instead of trying to remove oxygen, we thought: Let’s con­trol its intro­duc­tion,” adds Sridhar, the Arts and Sci­ences Dis­tin­guished Pro­fessor of Physics and director of Northeastern’s Elec­tronic Mate­rials Research Institute.

Oxygen, it turned out, was behaving in the reac­tion chamber in a way the sci­en­tists had never antic­i­pated: It was deter­mining how the other elements—the boron, carbon and nitrogen—combined in a solid, crystal form, while also inserting itself into the lat­tice. The trace amounts of oxygen were, metaphor­i­cally, “etching away” some of the patches of carbon, explains Kar, making room for the boron and nitrogen to fill the gaps.

“It was as if the oxygen was con­trol­ling the geo­metric struc­ture,” says Sridhar.

They named the new mate­rial, sen­sibly, 2D-BNCO, rep­re­senting the four ele­ments in the mix and the two-dimensionality of the super-thin light­weight mate­rial, and set about char­ac­ter­izing and man­u­fac­turing it, to ensure it was both repro­ducible and scal­able. That meant inves­ti­gating the myriad per­mu­ta­tions of the four ingre­di­ents, holding three con­stant while varying the mea­sure­ment of the remaining one, and vice versa, mul­tiple times over.

After each trial, they ana­lyzed the struc­ture and the func­tional prop­er­ties of the product—elec­trical, optical—using elec­tron micro­scopes and spec­tro­scopic tools, and col­lab­o­rated with com­pu­ta­tional physi­cists, who cre­ated models of the struc­tures to see if the con­fig­u­ra­tions would be fea­sible in the real world.

Next they will examine the new material’s mechan­ical prop­er­ties and begin to exper­i­men­tally val­i­date the mag­netic ones con­ferred, sur­pris­ingly, by the inter­min­gling of these four non­mag­netic ele­ments. “You begin to see very quickly how com­pli­cated that process is,” says Kar.

Helping with that com­plexity were col­lab­o­ra­tors from around the globe. In addi­tion to North­eastern asso­ciate research sci­en­tists, post­doc­toral fel­lows, and grad­uate stu­dents, con­trib­u­tors included researchers in gov­ern­ment, industry, and acad­emia from the U.S., Mexico and India.

“There is still a long way to go but there are clear indi­ca­tions that we can tune the elec­trical prop­er­ties of these mate­rials,” says Sridhar. “And if we find the right com­bi­na­tion, we will very likely get to that point where we reach the thermal sen­si­tivity that DARPA was ini­tially looking for as well as many as-yet unfore­seen applications.”

Source: Northeastern Univ.

QD Spectrometer Cell Phones 070215 id40654 Instruments that measure the properties of light, known as spectrometers, are widely used in physical, chemical, and biological research. These devices are usually too large to be portable, but MIT scientists have now shown they can create spectrometers small enough to fit inside a smartphone camera, using tiny semiconductor nanoparticles called quantum dots.
Such devices could be used to diagnose diseases, especially skin conditions, or to detect environmental pollutants and food conditions, says Jie Bao, a former MIT postdoc and the lead author of a paper describing the quantum dot spectrometers in the July 2 issue of Nature (“A colloidal quantum dot spectrometer”).
In this illustration, the Quantum Dot (QD) spectrometer device is printing QD filters
In this illustration, the Quantum Dot (QD) spectrometer device is printing QD filters — a key fabrication step. Other spectrometer approaches have complicated systems in order to create the optical structures needed. Here in the QD spectrometer approach, the optical structure — QD filters — are generated by printing liquid droplets. This approach is unique and advantageous in terms of flexibility, simplicity, and cost reduction. (Image: Mary O’Reilly)
This work also represents a new application for quantum dots, which have been used primarily for labeling cells and biological molecules, as well as in computer and television screens.
“Using quantum dots for spectrometers is such a straightforward application compared to everything else that we’ve tried to do, and I think that’s very appealing,” says Moungi Bawendi, the Lester Wolfe Professor of Chemistry at MIT and the paper’s senior author.
Shrinking spectrometers
The earliest spectrometers consisted of prisms that separate light into its constituent wavelengths, while current models use optical equipment such as diffraction gratings to achieve the same effect. Spectrometers are used in a wide variety of applications, such as studying atomic processes and energy levels in physics, or analyzing tissue samples for biomedical research and diagnostics.
Replacing that bulky optical equipment with quantum dots allowed the MIT team to shrink spectrometers to about the size of a U.S. quarter, and to take advantage of some of the inherent useful properties of quantum dots.
Quantum dots, a type of nanocrystals discovered in the early 1980s, are made by combining metals such as lead or cadmium with other elements including sulfur, selenium, or arsenic. By controlling the ratio of these starting materials, the temperature, and the reaction time, scientists can generate a nearly unlimited number of dots with differences in an electronic property known as bandgap, which determines the wavelengths of light that each dot will absorb.
However, most of the existing applications for quantum dots don’t take advantage of this huge range of light absorbance. Instead, most applications, such as labeling cells or new types of TV screens, exploit quantum dots’ fluorescence — a property that is much more difficult to control, Bawendi says. “It’s very hard to make something that fluoresces very brightly,” he says. “You’ve got to protect the dots, you’ve got to do all this engineering.”
Scientists are also working on solar cells based on quantum dots, which rely on the dots’ ability to convert light into electrons. However, this phenomenon is not well understood, and is difficult to manipulate.
On the other hand, quantum dots’ absorption properties are well known and very stable. “If we can rely on these properties, it is possible to create applications that will have a greater impact in the relative short term,” Bao says.
Broad spectrum
The new quantum dot spectrometer deploys hundreds of quantum dot materials that each filter a specific set of wavelengths of light. The quantum dot filters are printed into a thin film and placed on top of a photodetector such as the charge-coupled devices (CCDs) found in cellphone cameras.
The researchers created an algorithm that analyzes the percentage of photons absorbed by each filter, then recombines the information from each one to calculate the intensity and wavelength of the original rays of light.
The more quantum dot materials there are, the more wavelengths can be covered and the higher resolution can be obtained. In this case, the researchers used about 200 types of quantum dots spread over a range of about 300 nanometers. With more dots, such spectrometers could be designed to cover an even wider range of light frequencies.
“Bawendi and Bao showed a beautiful way to exploit the controlled optical absorption of semiconductor quantum dots for miniature spectrometers. They demonstrate a spectrometer that is not only small, but also with high throughput and high spectral resolution, which has never been achieved before,” says Feng Wang, an associate professor of physics at the University of California at Berkeley who was not involved in the research.
If incorporated into small handheld devices, this type of spectrometer could be used to diagnose skin conditions or analyze urine samples, Bao says. They could also be used to track vital signs such as pulse and oxygen level, or to measure exposure to different frequencies of ultraviolet light, which vary greatly in their ability to damage skin.
“The central component of such spectrometers — the quantum dot filter array — is fabricated with solution-based processing and printing, thus enabling significant potential cost reduction,” Bao adds.
Source: By Anne Trafton, MIT

Read more: Chemists design a quantum-dot spectrometer small enough for a smartphone


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