Lună: martie 2016

Design nou al celulelor de combustibil alimentat cu nanocristale învelite în grafen ( New fuel cell design powered by graphene-wrapped nanocrystals )

au elaborat o nouă rețetă de materiale pentru baterii pile de combustie cu hidrogen – care înconjoară nanocristalele de magneziu absorbante de hidrogen cu foi grafenice atomice subțiri – pentru a-și împinge performanțele înainte în zonele cheie.
Grafenul protejează nanocristalele de oxigen, umiditate și contaminanți, în timp ce găurile naturale mici permit moleculelor de hidrogen mai mici să treacă. Acest proces de filtrare depășește problemele comune care degradează performanța hidrurilor metalice pentru stocarea de hidrogen. Într-un vehicul alimentat cu celule de combustie pe bază de hidrogen, care utilizează aceste materiale, cunoscut sub numele de „hidrură metalică legată cu metal”, gazul hidrogen pompat într-un vehicul ar fi absorbit chimic de pulberea de nanocristalină de magneziu și ar fi asigurat în condiții de presiune scăzută .

Posted: Mar 11, 2016

New fuel cell design powered by graphene-wrapped nanocrystals

(Nanowerk News) Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn’t be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers–with water as the only byproduct of combustion.
While there remain scientific challenges to making hydrogen-based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like hydrogen fuel cell–which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets–to push its performance forward in key areas.
The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for hydrogen storage.
Illustration of Graphene Sheets and Magnesium Nanocrystal
Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated nanoscale magnesium crystals (yellow) with graphene oxide sheets to produce a new formula for metal hydride fuel cells. (Image: Jeong Yun Kim)
These graphene-encapsulated magnesium crystals act as „sponges” for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall „tank” size.
„Among metal hydride-based materials for hydrogen storage for fuel-cell vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability,” said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications („Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage”).
In a hydrogen fuel cell-powered vehicle using these materials, known as a „metal hydride” (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.
Jeff Urban, a Berkeley Lab staff scientist and co-author, said, „This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity–concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials.”
The research, conducted at Berkeley Lab’s Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials–Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab’s lead scientist for that effort.
The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.
Hydrogen-fuel-cell vehicles haven’t yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.
A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that hydrogen fuel cells can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.
A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the „gravimetric energy density,” is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.
More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.
Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.
The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials’ fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.
Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.
Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective „one pan” technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals’ structure using X-rays at Berkeley Lab’s Advanced Light Source. The X-ray studies showed how hydrogen gas pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.
„It is stable in air, which is important,” Cho said.
Next steps in the research will focus on using different types of catalysts–which can improve the speed and efficiency of chemical reactions–to further improve the fuel cell’s conversion of electrical current, and in studying whether different types of material can also improve the fuel cell’s overall capacity, Cho said.
Source: Lawrence Berkeley National Laboratory

Read more: New fuel cell design powered by graphene-wrapped nanocrystals

Un material pliabil care poate schimba dimensiunea, volumul și forma (A foldable material that can change size, volume and shape )

au proiectat un nou tip de material pliabil, care este versatil, reglabil și acționat automat. Se poate schimba dimensiunea, volumul și forma; Se poate plia pentru a rezista greutatea unui elefant fără a se rupe și a ieși din nou în sus pentru a se pregăti pentru următoarea sarcină.

Posted: Mar 11, 2016

A foldable material that can change size, volume and shape

(Nanowerk News) Imagine a house that could fit in a backpack or a wall that could become a window with the flick of a switch.
Harvard researchers have designed a new type of foldable material that is versatile, tunable and self actuated. It can change size, volume and shape; it can fold flat to withstand the weight of an elephant without breaking, and pop right back up to prepare for the next task.
The research was lead by Katia Bertoldi, the John L. Loeb Associate Professor of the Natural Sciences at the John A. Paulson School of Engineering and Applied Sciences (SEAS), James Weaver, Senior Research Scientist at the Wyss Institute for Biologically Inspired Engineering at Harvard University and Chuck Hoberman, of the Graduate School of Design. It is described in Nature Communications.
3-D Material with Controllable Shape and Size
Harvard researchers have designed a new type of foldable material that is versatile, tunable and self actuated. Here a single cell is folds according to its actuation. (Image: Johannes Overvelde/SEAS)
„We’ve designed a three-dimensional, thin-walled structure that can be used to make foldable and reprogrammable objects of arbitrary architecture, whose shape, volume and stiffness can be dramatically altered and continuously tuned and controlled,” said Johannes T. B. Overvelde, graduate student in Bertoldi’s lab and first author of the paper.
The structure is inspired by an origami technique called snapology, and is made from extruded cubes with 24 faces and 36 edges. Like origami, the cube can be folded along its edges to change shape. The team demonstrated, both theoretically and experimentally, that the cube can be deformed into many different shapes by folding certain edges, which act like hinges. The team embedded pneumatic actuators into the structure, which can be programmed to deform specific hinges, changing the cube’s shape and size, and removing the need for external input.
The team connected 64 of these individual cells to create a 4x4x4 cube that can grow, and shrink, change its shape globally, change the orientation of its microstructure and fold completely flat. As the structure changes shape, it also changes stiffness – meaning one could make a material that’s very pliable or very stiff using the same design. These actuated changes in material properties adds a fourth dimension to the material.
„We not only understand how the material deforms, but also have an actuation approach that harnesses this understanding,” said Bertoldi. „We know exactly what we need to actuate in order to get the shape we want.”
3-D Origami Inspired Metamaterial
A self actuating folding structure is pictured. (Image: Johannes Overvelde/Harvard SEAS)
The material can be embedded with any kind of actuator, including thermal, dielectric or even water.
„The opportunities to move all of the control systems onboard combined with new actuation systems already being developed for similar origami-like structures really opens up the design space for these easily deployable transformable structures”, said Weaver.
„This structural system has fascinating implications for dynamic architecture including portable shelters, adaptive building facades and retractable roofs,” said Hoberman. „Whereas current approaches to these applications rely on standard mechanics, this technology offers unique advantages such as how it integrates surface and structure, its inherent simplicity of manufacture, and its ability to fold flat.”
„This research demonstrates a new class of foldable materials that is also completely scalable,” Overvelde said, ” It works from the nanoscale to the meter-scale and could be used to make anything from surgical stents to portable pop-up domes for disaster relief.”
Source: Harvard John A. Paulson School of Engineering and Applied Sciences

Read more: A foldable material that can change size, volume and shape

Acoperirea prin pulverizare ar putea fi avioane, linii electrice, parbrize rezistente la gheață ( Spray-on coating could ice-proof airplanes, power lines, windshields )

Acest lucru s-ar putea schimba în curând datorită unui înveliș rezistent la gheață durabil și ieftin dezvoltat de cercetătorii din Universitatea din Michigan. Subțire, limpede și puțin cauciuc la atingere, formula de pulverizare ar putea face ca gheața să alunece echipamentul, avioanele și parbrizele mașinii numai cu forța gravitațională sau cu o briză ușoară. Acest lucru ar putea avea implicații majore în sectoare precum energia, transportul maritim și transporturile, în cazul în care gheața este o problemă constantă în climatul rece.

Read more: Spray-on coating could ice-proof airplanes, power lines, windshields

Posted: Mar 11, 2016

Spray-on coating could ice-proof airplanes, power lines, windshields

(Nanowerk News) On your car windshield, ice is a nuisance. But on an airplane, a wind turbine, an oil rig or power line, it can be downright dangerous. And removing it with the methods that are available today–usually chemical melting agents or labor-intensive scrapers and hammers–is difficult and expensive work.
That could soon change thanks to a durable, inexpensive ice-repellent coating developed by University of Michigan researchers. Thin, clear and slightly rubbery to the touch, the spray-on formula could make ice slide off equipment, airplanes and car windshields with only the force of gravity or a gentle breeze. This could have major implications in industries like energy, shipping and transportation, where ice is a constant problem in cold climates.
The new coating could also lead to big energy savings in freezers, which today rely on complex and energy-hungry defrosting systems to stay frost-free. An ice-repelling coating could do the same job with zero energy consumption, making household and industrial freezers up to 20 percent more efficient. The coating is detailed in a new paper published in the journal Science Advances („Designing durable icephobic surfaces”).
Made of a blend of common synthetic rubbers, the formula marks a departure from earlier approaches that relied on making surfaces either very water-repellent or very slippery.
„Researchers had been trying for years to dial down ice adhesion strength with chemistry, making more and more water-repellent surfaces,” said Kevin Golovin, a doctoral student in materials science and engineering. „We’ve discovered a new knob to turn, using physics to change the mechanics of how ice breaks free from a surface.”
Led by Anish Tuteja, associate professor of materials science and engineering, the team initially experimented with water-repelling surfaces as well, but found that they weren’t effective at shedding ice. But during their experiments, they noticed something unexpected: rubbery coatings worked best for repelling ice, even when they weren’t water-repellent. Eventually, they discovered that the ability to shed water wasn’t important at all. The rubbery coatings repelled ice because of a different phenomenon, called „interfacial cavitation.”
Golovin explains that two rigid surfaces–say, ice and your car windshield–can stick tightly together, requiring a great deal of force to break the bond between them. But because of interfacial cavitation, a solid material stuck to a rubbery surface behaves differently. Even a small amount of force can deform the rubbery surface, breaking the solid free.
„Nobody had explored the idea that rubberiness can reduce ice adhesion,” Tuteja said. „Ice is frozen water, so people assumed that ice-repelling surfaces had to also repel water. That was very limiting.”
The new approach makes it possible to dramatically improve durability compared to previous icephobic coatings, which relied on fragile materials that lost their ice-shedding abilities after just a few freeze-thaw cycles. The new coatings stood up to a variety of lab tests including peel tests, salt spray corrosion, high temperatures, mechanical abrasion and hundreds of freeze-thaw cycles.
The team has also found that by slightly altering the smoothness and rubberiness of the coating, they can fine-tune its degree of ice repellency and durability. Softer surfaces tend to be more ice-repellent but less durable, while the opposite is true for harder coatings. Golovin believes that that flexibility will enable them to create coatings for a huge variety of applications.
„An airplane coating, for example, would need to be extremely durable, but it could be less ice-repellent because of high winds and vibration that would help push ice off,” Golovin said. „A freezer coating, on the other hand, could be less durable, but would need to shed ice with just the force of gravity and slight vibrations. The great thing about our approach is that it’s easy to fine-tune it for any given application.”
The team has already designed hundreds of ice-repelling formulas. Some are rough to the touch, some smooth; some shed water while others don’t.
„I think the first commercial application will be in linings for commercial frozen food packaging, where sticking is often a problem. We’ll probably see that within the next year,” Tuteja said. „Using this technology in places like cars and airplanes will be very complex because of the stringent durability and safety requirements, but we’re working on it.”
Source: University of Michigan

Read more: Spray-on coating could ice-proof airplanes, power lines, windshields

Trei dezvoltări noi pentru chips-uri inteligente senzor(Three new developments for smarter sensor chips)

Deoarece trebuie să funcționeze în fiecare zi, trebuie să-și părăsească zona de confort și să se obișnuiască cu temperaturi, umiditate, ariditate și vibrații foarte variabile

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Inginerii dezvoltă o piele flexibilă care captează undele radar, obiecte de mantale(Engineers develop flexible skin that traps radar waves, cloaks objects

au dezvoltat o nouă meta-piele flexibilă, extensibilă și adaptabilă, care utilizează rânduri de dispozitive mici, lichide și metalice pentru a acoperi un obiect din ochii ascuțiți ai radarului.
Meta-pielea ia numele din metamateriale, care sunt compozite care au proprietăți care nu sunt găsite în natură și care pot manipula undele electromagnetice. Prin întinderea și flexarea meta-pielei polimerului, aceasta poate fi reglată pentru a reduce reflexia unei game largi de frecvențe radar.

Posted: Mar 07, 2016

Engineers develop flexible skin that traps radar waves, cloaks objects

(Nanowerk News) 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 („From Flexible and Stretchable Meta-Atom to Metamaterial: A Wearable Microwave Meta-Skin with Tunable Frequency Selective and Cloaking Effects”). 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.
Meta-Skin Cloaking Device
This flexible, stretchable and tunable „meta-skin” can trap radar waves and cloak objects from detection. (Image: Liang Dong/Iowa State University)
„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.”
Source: Iowa State University

Read more: Engineers develop flexible skin that traps radar waves, cloaks objects

Dezvoltarea de senzori de imprimare respirație pentru diagnosticarea precoce și monitorizarea bolilor(Development of breath-print sensors for early diagnosis and monitoring of diseases

dezvolta senzori ultrasensitivi si selectivi de gaz pentru a diagnostica bolile prin analiza expirarii respiratiei. Profesorul Kim a condus dezvoltarea matricelor senzorilor de nanofibre pe bază de oxid de metal pe bază de oxid de metal, care sunt optimizate pentru recunoașterea modelului de amprente ale respirației ( Small , ” Detectoarele biomemarkerilor bazate pe nanofibre WO 3, activate de catalizatorul încapsulat de proteine ​​auto-asamblate pe polistiren coloid” ).Platforma senzorilor care utilizează nanofibre de oxid de metal poate fi utilizată atât în ​​domeniul diagnosticării bolilor cât și al controlului calității aerului interior / exterior

Posted: Mar 07, 2016

Development of breath-print sensors for early diagnosis and monitoring of diseases

(Nanowerk News) Professor Il-Doo Kim in the Department of Materials Science and Engineering at KAIST is developing ultrasensitive and highly selective gas sensors to diagnose diseases by exhaled breath analysis. Professor Kim has led the development of semiconductor metal oxide-based nanofiber sensor arrays, which are optimized for pattern recognition of breath prints (Small, „WO3 Nanofiber-Based Biomarker Detectors Enabled by Protein-Encapsulated Catalyst Self-Assembled on Polystyrene Colloid Templates”).
Demonstration of breath analysis using nanofibers
Demonstration of breath analysis using nanofibers functionalized with various catalysts for pattern recognition of breath components such as hydrogen sulfide, acetone, and methyl mercaptan for diagnosis of diabetes and halitosis.
Human breath contains a number of volatile organic compounds (VOCs). Accurate detection of specific VOCs in exhaled breath can provide essential information for the early diagnosis of diseases. For example, acetone, H2S, ammonia, and toluene can be used to evaluate diabetes, halitosis, kidney malfunction, and lung cancer, respectively, where the diagnosis of these diseases can be achieved by analyzing the concentration of VOCs in exhaled breath, originating from the molecular exchange between lung tissue and blood. Variations in the concentration of the exhaled VOCs that may serve as biomarkers for specific diseases can distinguish healthy people from those who are sick.
The non-invasive diagnosis of various diseases is the key advantage of exhaled breath analysis techniques over other commonly used methods. For example, conventional diagnostic methods such as MRI, CT, blood test, endoscope, and X-ray examination, which are expensive and sometimes painful, are usually implemented in hospitals. However, in the near future, inexpensive and simple diagnoses are expected to detect and examine diseases in the early stages. The use of multi-sensor arrays with nanostructured semiconductor metal oxides is essential for developing inexpensive and simple diagnostic tools by examining the concentration of VOCs in exhaled breath. The research team has been developing an array of breathing sensors consisting of a number of semiconductor metal oxide fibers, which will offer patients a real-time diagnosis of diseases.
The sensor arrays are advantageous in terms of gas adsorption, leading to large resistance changes achieved by high specific surface area and porous nanostructure. In particular, highly selective biomarker sensing was accomplished by functionalization of diverse noble metallic catalysts such as Au, Pt, Pd, and Rh, which are essential to establishing multiple sensor arrays for analysis of breath prints. These sensor arrays can be integrated with portable devices for real-time monitoring of physical conditions.
‘The sensor technology is compatible with various types of smartphones, wearable electronic gadgets, and medical devices’ Professor Kim added.
The sensor platform using metal oxide nanofibers can be utilized both in the field of disease diagnosis and indoor/outdoor air quality control. “We believe that there can be many ways to incorporate our technology based on the particular needs of industries, not just in the field of medical devices, such as detecting hazardous chemicals or gases at manufacturing factories.” Professor Kim said.
Currently, Professor Kim has filed 157 domestic and international patents. In addition, he has completed 4 technology transfers. Some of his patents were also transferred to a MEMS gas sensor company (2015). Moreover, the research team received the Grand Prize (Ph.D. candidate, Seon-Jin Choi) at the ‘9th Samsung Inside Edge Paper Competition’ from Samsung Electro-Mechanics in 2013 and the Silver Award (Ph.D. candidate, Sang-Joon Kim) at the ‘21th Samsung Human Tech Paper Competition’ from Samsung Electronics in 2015. Recently, Prof. Kim received Top Excellence Award in the KAIST EEWS Business Pan Contest 2015 (Development of Exhaled Breath Sensor for Diagnosis of Diabetes Based on Analysis of Acetone Concentration in Human Breath, Jan. 2016).
Source: Korea Advanced Institute of Science and Technology (KAIST)

Read more: Development of breath-print sensors for early diagnosis and monitoring of diseases

Noul senzor de tip galerii pentru detectarea nanoparticulelor unice (Novel whispering-gallery-type sensor for single nanoparticle detection)

Detectarea ultrasensibilă a particulelor nanometrice are aplicații în domenii importante, de la monitorizarea mediului până la analiza structurilor virale.Această metodă de detectare disipativă nu numai că oferă un nou mecanism fizic de detectare a microcavității, ci reprezintă, de asemenea, un pas semnificativ către senzorii optici practici în domeniile chimiei analitice, științei mediului și biologiei moleculare.

Posted: Mar 07, 2016

Novel whispering-gallery-type sensor for single nanoparticle detection

(Nanowerk News) Ultrasensitive detection of nanoscale particles has applications in important fields ranges from environmental monitoring to analysis of viral structures. However, it remains extremely difficult due to ultralow polarizabilities of small-sized, low-index particles.
A team led by Professor Xiao Yun-Feng at Peking University, collaborated with Yonsei University of Republic of Korea, demonstrated experimentally that the dissipative interaction in a high-Q optical microcavity allows the detection of single nanoparticles.
This work has been published in the recent issue of Physical Review Applied („Detection of Single Nanoparticles Using the Dissipative Interaction in a High-Q Microcavity”).
Schematic drawing of on-chip microcavity sensors
Schematic drawing of on-chip microcavity sensors.The probelaser light is coupled into the whisperinggallery microcavity via a fiber taper. The cavity modes can be characterized by the transmission spectrum, shown as a resonance dip. When a single nanoparticle binds to the surface of the microcavity, the linewidth change of the cavity and the mode shift are simultaneously measured, representing the dissipative and reactive sensing method, respectively.
Over the past few years, high-Q optical microcavities have shown great potential in sensing applications due to the strongly enhanced light-matter interaction therein. The conventional sensing mechanism, however, has to rely on the reactive interaction.The reactive sensing is limited by the polarizability of the particle, and will fail its sensing function when the real part of the polarizability approaches zero. In the publication, the authors pointed out that the dissipative interaction opens a channel of the cavity mode decay and results in the resonance linewidth change, which forms an effective sensing scheme even when the real part of analyte polarizability approaches zero, because the signal magnitude is determined by the absorption loss and side scattering of the particle.
In the experiment, detection of single gold nanorodsis used to assess the sensing performance.“The gold nanorod of the size of 40 nm×16 nm is a perfect candidate to test the microcavity sensor for two reasons. One is that the polarizability of this nanoparticle can be tuned by varying the probe wavelength. The other is that the surface plasmon resonance of the particle of this dimension coincides with one of our probe wavelengths in the experiment, at which the real part of the polarizability become zero, most likely invalidating the reactive sensing method, but strengthening the dissipative one,” said Dr. YanyanZhi, the post-doctor and one of the co-first authors of this work.
The researchers examined experimentally both the reactive and dissipative sensing methods, by monitoring the mode shift and the linewidth change of the high-Q cavity resonance, respectively. It is found that the reactive sensing signal cannot be recognized from the noises when the probe wavelength is on plasmonic resonance where the nanorod polarizability approaches zero, while the proposed dissipative sensing method still works well, which is consistent with the theoretical predictions.The anticipated detection limit can reach 13 nm×5 nm, which is about 12 times smaller volume than that can be detected by the reactive sensing method.
This dissipative sensing method not only provides a new physical mechanism of microcavity sensing, but also represents a significant step towards practical optical sensors in areas of analytical chemistry, environmental science, and molecular biology.
“Practically, it’s ready that both the mode shift and the linewidth change of the cavity mode can be simultaneously measured, and thus the common reactive and the proposed dissipative sensing methods are compatible to each other,” said Prof. Xiao, “The combination of those two sensing methods adds new dimensions to what can be measured using each of the two methods alone. The dissipative sensing method using a high-Q microcavityoffers a great platform for the detection of tiny single particles, such as vital virus, particles in the polluted air, lossy particles in the manufacturing process, and other nanoparticles under interest.”
Source: Peking University

Read more: Novel whispering-gallery-type sensor for single nanoparticle detection