Tag Archives: plasmonics

Plasmonic ‘Goldfinger’: antifungal nail polish with metallic nanoparticles

A March 29,.2017 news item on Nanowerk announces a new kind of nanopolish,

Since ancient times, people have used lustrous silver, platinum and gold to make jewelry and other adornments. Researchers have now developed a new way to add the metals to nail polish with minimal additives, resulting in durable, tinted — and potentially antibacterial — nail coloring.

Using metal nanoparticles in clear nail polish makes it durable and colorful without extra additives.
Credit: American Chemical Society

A March 29, 2017 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, adds a little more detail (Note: A link has been removed),

Nail polish comes in a bewildering array of colors. Current coloring techniques commonly incorporate pigment powders and additives. Scientists have recently started exploring the use of nanoparticles in polishes and have found that they can improve their durability and, in the case of silver nanoparticles, can treat fungal toenail infections. Marcus Lau, Friedrich Waag and Stephan Barcikowski wanted to see if they could come up with a simple way to integrate metal nanoparticles in nail polish.

The researchers started with store-bought bottles of clear, colorless nail polish and added small pieces of silver, gold, platinum or an alloy to them. To break the metals into nanoparticles, they shone a laser on them in short bursts over 15 minutes. Analysis showed that the method resulted in a variety of colored, transparent polishes with a metallic sheen. The researchers also used laser ablation to produce a master batch of metal nanoparticles in ethyl acetate, a polish thinner, which could then be added to individual bottles of polish. This could help boost the amount of production for commercialization. The researchers say the technique could also be used to create coatings for medical devices.

The authors acknowledge funding from the INTERREG-Program Germany-Netherlands.

A transparent nail varnish can be colored simply and directly with laser-generated nanoparticles. This does not only enable coloring of the varnish for cosmetic purposes, but also gives direct access to nanodoped varnishes to be used on any solid surface. Therefore, nanoparticle properties such as plasmonic properties or antibacterial effects can be easily adapted to surfaces for medical or optical purposes. The presented method for integration of metal (gold, platinum, silver, and alloy) nanoparticles into varnishes is straightforward and gives access to nanodoped polishes with optical properties, difficult to be achieved by dispersing powder pigments in the high-viscosity liquids. Courtesy: Industrial and Engineering & Chemistry Research

Here’s a link to and a citation for the paper,

Direct Integration of Laser-Generated Nanoparticles into Transparent Nail Polish: The Plasmonic “Goldfinger” by Marcus Lau, Friedrich Waag, and Stephan Barcikowski. Ind. Eng. Chem. Res., 2017, 56 (12), pp 3291–3296 DOI: 10.1021/acs.iecr.7b00039 Publication Date (Web): March 7, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Multicolor, electrochromic glass

Electrochromic (changes color to block light and heat) glass could prove to be a significant market by 2020 according to a March 8, 2017 news item on phys.org,

Rice University’s latest nanophotonics research could expand the color palette for companies in the fast-growing market for glass windows that change color at the flick of an electric switch.

In a new paper in the American Chemical Society journal ACS Nano, researchers from the laboratory of Rice plasmonics pioneer Naomi Halas report using a readily available, inexpensive hydrocarbon molecule called perylene to create glass that can turn two different colors at low voltages.

“When we put charges on the molecules or remove charges from them, they go from clear to a vivid color,” said Halas, director of the Laboratory for Nanophotonics (LANP), lead scientist on the new study and the director of Rice’s Smalley-Curl Institute. “We sandwiched these molecules between glass, and we’re able to make something that looks like a window, but the window changes to different types of color depending on how we apply a very low voltage.”

Adam Lauchner, an applied physics graduate student at Rice and co-lead author of the study, said LANP’s color-changing glass has polarity-dependent colors, which means that a positive voltage produces one color and a negative voltage produces a different color.

“That’s pretty novel,” Lauchner said. “Most color-changing glass has just one color, and the multicolor varieties we’re aware of require significant voltage.”

Glass that changes color with an applied voltage is known as “electrochromic,” and there’s a growing demand for the light- and heat-blocking properties of such glass. The projected annual market for electrochromic glass in 2020 has been estimated at more $2.5 billion.

A March 8, 2017 Rice University news release (also on EurekAlert), which originated the news item, provides more detail about the research,

Lauchner said the glass project took almost two years to complete, and he credited co-lead author Grant Stec, a Rice undergraduate researcher, with designing the perylene-containing nonwater-based conductive gel that’s sandwiched between glass layers.

“Perylene is part of a family of molecules known as polycyclic aromatic hydrocarbons,” Stec said. “They’re a fairly common byproduct of the petrochemical industry, and for the most part they are low-value byproducts, which means they’re inexpensive.”

Grant Stec and Adam Lauchner

Grant Stec and Adam Lauchner of Rice University’s Laboratory for Nanophotonics have used an inexpensive hydrocarbon molecule called perylene to create a low-voltage, multicolor, electrochromic glass. (Photo by Jeff Fitlow/Rice University)

There are dozens of polycyclic aromatic hydrocarbons (PAHs), but each contains rings of carbon atoms that are decorated with hydrogen atoms. In many PAHs, carbon rings have six sides, just like the rings in graphene, the much-celebrated subject of the 2010 Nobel Prize in physics.

“This is a really cool application of what started as fundamental science in plasmonics,” Lauchner said.

A plasmon is [a] wave of energy, a rhythmic sloshing in the sea of electrons that constantly flow across the surface of conductive nanoparticles. Depending upon the frequency of a plasmon’s sloshing, it can interact with and harvest the energy from passing light. In dozens of studies over the past two decades, Halas, Rice physicist Peter Nordlander and colleagues have explored both the basic physics of plasmons and potential applications as diverse as cancer treatment, solar-energy collection, electronic displays and optical computing.

The quintessential plasmonic nanoparticle is metallic, often made of gold or silver, and precisely shaped. For example, gold nanoshells, which Halas invented at Rice in the 1990s, consist of a nonconducting core that’s covered by a thin shell of gold.

Grant Stec, Naomi Halas and Adam Lauchner

Student researchers Grant Stec (left) and Adam Lauchner (right) with Rice plasmonics pioneer Naomi Halas, director of Rice University’s Laboratory for Nanophotonics. (Photo by Jeff Fitlow/Rice University)

“Our group studies many kinds of metallic nanoparticles, but graphene is also conductive, and we’ve explored its plasmonic properties for several years,” Halas said.

She noted that large sheets of atomically thin graphene have been found to support plasmons, but they emit infrared light that’s invisible to the human eye.

“Studies have shown that if you make graphene smaller and smaller, as you go down to nanoribbons, nanodots and these little things called nanoislands, you can actually get graphene’s plasmon closer and closer to the edge of the visible regime,” Lauchner said.

In 2013, then-Rice physicist Alejandro Manjavacas, a postdoctoral researcher in Nordlander’s lab, showed that the smallest versions of graphene — PAHs with just a few carbon rings — should produce visible plasmons. Moreover, Manjavacas calculated the exact colors that would be emitted by different types of PAHs.

“One of the most interesting things was that unlike plasmons in metals, the plasmons in these PAH molecules were very sensitive to charge, which suggested that a very small electrical charge would produce dramatic colors,” Halas said.

Electrochromic glass that glass that turns from clear to black

Rice University researchers demonstrated a new type of glass that turns from clear to black when a low voltage is applied. The glass uses a combination of molecules that block almost all visible light when they each gain a single electron. (Photo by Jeff Fitlow/Rice University)

Lauchner said the project really took off after Stec joined the research team in 2015 and created a perylene formulation that could be sandwiched between sheets of conductive glass.

In their experiments, the researchers found that applying just 4 volts was enough to turn the clear window greenish-yellow and applying negative 3.5 volts turned it blue. It took several minutes for the windows to fully change color, but Halas said the transition time could easily be improved with additional engineering.

Stec said the team’s other window, which turns from clear to black, was produced later in the project.

“Dr. Halas learned that one of the major hurdles in the electrochromic device industry was making a window that could be clear in one state and completely black in another,” Stec said. “We set out to do that and found a combination of PAHs that captured no visible light at zero volts and almost all visible light at low voltage.”

Here’s a link to and a citation for the paper,

Multicolor Electrochromic Devices Based on Molecular Plasmonics by Grant J. Stec, Adam Lauchner, Yao Cui, Peter Nordlander, and Naomi J. Halas. ACS Nano, Article ASAP DOI: 10.1021/acsnano.7b00364 Publication Date (Web): February 22, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall.

Bringing multispectral imaging into daily use

Caption: Researchers tested a new technique for printing and imaging in both color and infrared with this image of a parrot. The inlay shows how a simple RGB color scheme was created by building rectangles of varying lengths for each of the colors, as well as individual nanocubes on top of a gold film that create the plasmonic element. Credit: imageBROKER / Alamy Stock Photo

That caption makes a lot more sense after reading the news item and the news release announcing the work. First, there’s the Dec. 15, 2016 news item on ScienceDaily,

Duke University researchers believe they have overcome a longstanding hurdle to producing cheaper, more robust ways to print and image across a range of colors extending into the infrared.

As any mantis shrimp will tell you, there are a wide range of “colors” along the electromagnetic spectrum that humans cannot see but which provide a wealth of information. Sensors that extend into the infrared can, for example, identify thousands of plants and minerals, diagnose cancerous melanomas and predict weather patterns, simply by the spectrum of light they reflect.

Current imaging technologies that can detect infrared wavelengths are expensive and bulky, requiring numerous filters or complex assemblies in front of an infrared photodetector. The need for mechanical movement in such devices reduces their expected lifetime and can be a liability in harsh conditions, such as those experienced by satellites.

A closeup of the colorful parrot picture printed on a thin gold wafer using the new nanocube-based technology. The colors appear off because of the underlying gold, as well as the difficulties that typical cameras have of imaging the new technology. Credit: Maiken Mikkelsen, Duke University

A Dec. 14, 2016 Duke University news release, which originated the news item, provides more detail (Note: A link has been removed),

In a new paper, a team of Duke engineers reveals a manufacturing technique that promises to bring a simplified form of multispectral imaging into daily use. Because the process uses existing materials and fabrication techniques that are inexpensive and easily scalable, it could revolutionize any industry where multispectral imaging or printing is used.

The results appear online December 14 [2016] in the journal Advanced Materials.

“It’s challenging to create sensors that can detect both the visible spectrum and the infrared,” said Maiken Mikkelsen, the Nortel Networks Assistant Professor of Electrical and Computer Engineering and Physics at Duke.

“Traditionally you need different materials that absorb different wavelengths, and that gets very expensive,” Mikkelsen said. “But with our technology, the detectors’ responses are based on structural properties that we design rather than a material’s natural properties. What’s really exciting is that we can pair this with a photodetector scheme to combine imaging in both the visible spectrum and the infrared on a single chip.”

The new technology relies on plasmonics — the use of nanoscale physical phenomena to trap certain frequencies of light.

Engineers fashion silver cubes just 100 nanometers wide and place them only a few nanometers above a thin gold foil. When incoming light strikes the surface of a nanocube, it excites the silver’s electrons, trapping the light’s energy — but only at a certain frequency.

The size of the silver nanocubes and their distance from the base layer of gold determines that frequency, while controlling the spacing between the nanoparticles allows tuning the strength of the absorption. By precisely tailoring these spacings, researchers can make the system respond to any specific color they want, all the way from visible wavelengths out to the infrared.

The challenge facing the engineers is how to build a useful device that could be scalable and inexpensive enough to use in the real world. For that, Mikkelsen turned to her research team, including graduate student Jon Stewart.

“Similar types of materials have been demonstrated before, but they’ve all used expensive techniques that have kept the technology from transitioning to the market,” said Stewart. “We’ve come up with a fabrication scheme that is scalable, doesn’t need a clean room and avoids using million-dollar machines, all while achieving higher frequency sensitivities. It has allowed us to do things in the field that haven’t been done before.”

To build a detector, Mikkelsen and Stewart used a process of light etching and adhesives to pattern the nanocubes into pixels containing different sizes of silver nanocubes, and thus each sensitive to a specific wavelength of light. When incoming light strikes the array, each area responds differently depending on the wavelength of light it is sensitive to. By teasing out how each part of the array responds, a computer can reconstruct what color the original light was.

The technique can be used for printing as well, the team showed. Instead of creating pixels with six sections tuned to respond to specific colors, they created pixels with three bars that reflect three colors: blue, green and red. By controlling the relative lengths of each bar, they can dictate what combination of colors the pixel reflects. It’s a novel take on the classic RGB scheme first used in photography in 1861.

But unlike most other applications, the plasmonic color scheme promises to never fade over time and can be reliably reproduced with tight accuracy time and again. It also allows its adopters to create color schemes in the infrared.

“Again, the exciting part is being able to print in both visible and infrared on the same substrate,” said Mikkelsen. “You could imagine printing an image with a hidden portion in the infrared, or even covering an entire object to tailor its spectral response.”

Here’s a link to and a citation for the paper,

Toward Multispectral Imaging with Colloidal Metasurface Pixels by Jon W. Stewart, Gleb M. Akselrod, David R. Smith, and Maiken H. Mikkelsen. DOI: 10.1002/adma.201602971 Version of Record online: 14 DEC 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall. (There is a free preview but it is page 1 only of the paper.)

 

Tibetan Buddhist singing bowls inspire more efficient solar cells

There’s no mention as to whether or not Dr Niraj Lal practices any form of meditation or how he came across Tibetan Buddhist singing bowls but somehow he was inspired by them when studying for his PhD at Cambridge University (UK). From a Sept. 8, 2014 news item by Niall Byrne for physorg.com,

The shape of a centuries-old Buddhist singing bowl has inspired a Canberra scientist to re-think the way that solar cells are designed to maximize their efficiency.

Dr Niraj Lal, of the Australian National University,  found during his PhD at the University of Cambridge, that small nano-sized versions of Buddhist singing bowls resonate with light in the same way as they do with sound, and he’s applied this shape to solar cells to increase their ability to capture more light and convert it into electricity.

A Sept. ?, 2014 news release from Australian science communication company, Science in Public, fills in a few more details without any mention of Lal’s meditation practices, should he have any,

“Current standard solar panels lose a large amount of light-energy as it hits the surface, making the panels’ generation of electricity inefficient,” says Niraj. “But if the cells are singing bowl-shaped, then the light bounces around inside the cell for longer”.

Normally used in meditation, music, and relaxation, Buddhist singing bowls make a continuous harmonic ringing sound when the rim of the metal bowl is vibrated with a wooden or other utensil.

During his PhD, Niraj discovered that his ‘nanobowls’ manipulated light by creating a ‘plasmonic’ resonance, which quadrupled the laboratory solar cell’s efficiency compared to a similarly made flat solar cell.

Now, Niraj and his team aim to change all that by applying his singing-bowl discovery to tandem solar cells: a technology that has previously been limited to aerospace applications.

In research which will be published in the November issue of IEEE Journal of Photonics, Niraj and his colleagues have shown that by layering two different types of solar panels on top of each other in tandem, the efficiency of flat rooftop solar panels can achieve 30 per cent—currently, laboratory silicon solar panels convert only 25 per cent of light into electricity, while commercial varieties convert closer to 20 per cent.

The tandem cell design works by absorbing a sunlight more effectively —each cell is made from a different material so that it can ‘see’ a different light wavelength.

“To a silicon solar cell, a rainbow just looks like a big bit of red in the sky—they don’t ‘see’ the blue, green or UV light—they convert all light to electricity as if it was red ,” says Niraj. “But when we put a second cell on top, which ‘sees’ the blue part of light, but allows the red to pass through to the ‘red-seeing’ cell below, we can reach a combined efficiency of more than 30 percent.”

Niraj and a team at ANU are now looking at ways to super-charge the tandem cell design by applying the Buddhist singing bowl shape to further increase efficiency.

“If we can make a solar cell that ‘sees’ more colours and  keeps the right light in the right layers, then we could increase efficiency even further,” says Niraj.

“Every extra percent in efficiency saves you thousands of dollars over the lifetime of the panel,” says Niraj. “Current roof-top solar panels have been steadily increasing in efficiency, which has been a big driver of the fourfold drop in the price for these panels over the last five years.”

More importantly, says Niraj, greater efficiency will allow solar technology to compete with fossil fuels and meet the challenges of climate change and access.

“Electricity is also one of the most enabling technologies we have ever seen, and linking people in rural areas around the world to electricity is one of the most powerful things we can do.”

At the end of the Science in Public news release there’s mention of a science communication competition,

Niraj was a 2014 national finalist of FameLab Australia. FameLab is a global science communication competition for early-career scientists. His work is supported by the Australian Research Council and ARENA – the Australian Renewable Energy Agency.

About FameLab

In 2014, the British Council and Fresh Science have joined forces to bring FameLab to Australia.

FameLab Australia will offer specialist science media training and, ultimately, the chance for early-career researchers to pitch their research at the FameLab International Grand Final in the UK at The Times Cheltenham Science Festival from 3 to 5 June 2014.

FameLab is an international communication competition for scientists, including engineers and mathematicians. Designed to inspire and motivate young researchers to actively engage with the public and with potential stakeholders, FameLab is all about finding the best new voices of science and engineering across the world.

Founded in 2005 by The Times Cheltenham Science Festival, FameLab, working in partnership with the British Council, has already seen more than 5,000 young scientists and engineers participate in over 23 different countries — from Hong Kong to South Africa, USA to Egypt.

Now, FameLab comes to Australia in a landmark collaboration with the British Council and Fresh Science — Australia’s very own science communication competition.

For more information about FameLab Australia, head to www.famelab.org.au

You can find out more about Australia’s Fresh Science here.

Getting back to Dr. Lal, here’s a video he made about his work and where he demonstrates a Tibetan Buddhist singing bowl (this is a very low tech video and the sound quality isn’t great),

Here’s a link to and a citation for Lal’s most recent paper,

Optics and Light Trapping for Tandem Solar Cells on Silicon by Lal, N.N.; White, T.P. ; and Catchpole, K.R. Photovoltaics, IEEE Journal of  (Volume:PP ,  Issue: 99) Page(s): 1 – 7 ISSN : 2156-3381 DOI: 10.1109/JPHOTOV.2014.2342491 Published online 19 August 2014

The paper is behind a paywall but there is open access to Lal’s 2012 University of Cambridge PhD thesis on his approach,

Enhancing solar cells with plasmonic nanovoids by Lal, Niraj Narsey
URI: http://www.dspace.cam.ac.uk/handle/1810/243864 Date:2012-07-03

Hap;y reading!

US Air Force wants to merge classical and quantum physics

The US Air Force wants to merge classical and quantum physics for practical purposes according to a May 5, 2014 news item on Azonano,

The Air Force Office of Scientific Research has selected the Harvard School of Engineering and Applied Sciences (SEAS) to lead a multidisciplinary effort that will merge research in classical and quantum physics and accelerate the development of advanced optical technologies.

Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, will lead this Multidisciplinary University Research Initiative [MURI] with a world-class team of collaborators from Harvard, Columbia University, Purdue University, Stanford University, the University of Pennsylvania, Lund University, and the University of Southampton.

The grant is expected to advance physics and materials science in directions that could lead to very sophisticated lenses, communication technologies, quantum information devices, and imaging technologies.

“This is one of the world’s strongest possible teams,” said Capasso. “I am proud to lead this group of people, who are internationally renowned experts in their fields, and I believe we can really break new ground.”

A May 1, 2014 Harvard University School of Engineering and Applied Sciences news release, which originated the news item, provides a description of project focus: nanophotonics and metamaterials along with some details of Capasso’s work in these areas (Note: Links have been removed),

The premise of nanophotonics is that light can interact with matter in unusual ways when the material incorporates tiny metallic or dielectric features that are separated by a distance shorter than the wavelength of the light. Metamaterials are engineered materials that exploit these phenomena, producing strange effects, enabling light to bend unnaturally, twist into a vortex, or disappear entirely. Yet the fabrication of thick, or bulk, metamaterials—that manipulate light as it passes through the material—has proven very challenging.

Recent research by Capasso and others in the field has demonstrated that with the right device structure, the critical manipulations can actually be confined to the very surface of the material—what they have dubbed a “metasurface.” These metasurfaces can impart an instantaneous shift in the phase, amplitude, and polarization of light, effectively controlling optical properties on demand. Importantly, they can be created in the lab using fairly common fabrication techniques.

At Harvard, the research has produced devices like an extremely thin, flat lens, and a material that absorbs 99.75% of infrared light. But, so far, such devices have been built to order—brilliantly suited to a single task, but not tunable.

This project, however,is focused on the future (Note: Links have been removed),

“Can we make a rapidly configurable metasurface so that we can change it in real time and quickly? That’s really a visionary frontier,” said Capasso. “We want to go all the way from the fundamental physics to the material building blocks and then the actual devices, to arrive at some sort of system demonstration.”

The proposed research also goes further. A key thrust of the project involves combining nanophotonics with research in quantum photonics. By exploiting the quantum effects of luminescent atomic impurities in diamond, for example, physicists and engineers have shown that light can be captured, stored, manipulated, and emitted as a controlled stream of single photons. These types of devices are essential building blocks for the realization of secure quantum communication systems and quantum computers. By coupling these quantum systems with metasurfaces—creating so-called quantum metasurfaces—the team believes it is possible to achieve an unprecedented level of control over the emission of photons.

“Just 20 years ago, the notion that photons could be manipulated at the subwavelength scale was thought to be some exotic thing, far fetched and of very limited use,” said Capasso. “But basic research opens up new avenues. In hindsight we know that new discoveries tend to lead to other technology developments in unexpected ways.”

The research team includes experts in theoretical physics, metamaterials, nanophotonic circuitry, quantum devices, plasmonics, nanofabrication, and computational modeling. Co-principal investigator Marko Lončar is the Tiantsai Lin Professor of Electrical Engineering at Harvard SEAS. Co-PI Nanfang Yu, Ph.D. ’09, developed expertise in metasurfaces as a student in Capasso’s Harvard laboratory; he is now an assistant professor of applied physics at Columbia. Additional co-PIs include Alexandra Boltasseva and Vladimir Shalaev at Purdue, Mark Brongersma at Stanford, and Nader Engheta at the University of Pennsylvania. Lars Samuelson (Lund University) and Nikolay Zheludev (University of Southampton) will also participate.

The bulk of the funding will support talented graduate students at the lead institutions.

The project, titled “Active Metasurfaces for Advanced Wavefront Engineering and Waveguiding,” is among 24 planned MURI awards selected from 361 white papers and 88 detailed proposals evaluated by a panel of experts; each award is subject to successful negotiation. The anticipated amount of the Harvard-led grant is up to $6.5 million for three to five years.

For anyone who’s not familiar (that includes me, anyway) with MURI awards, there’s this from Wikipedia (Note: links have been removed),

Multidisciplinary University Research Initiative (MURI) is a basic research program sponsored by the US Department of Defense (DoD). Currently each MURI award is about $1.5 million a year for five years.

I gather that in addition to the Air Force, the Army and the Navy also award MURI funds.

E-ink discovery could be a gateway to cheaper solar cells and electronic touch pads

Non-toxic, inexpensive, and durable are words which, in combination, seem downright magical and all are mentioned in a July 31, 2013 news item on Azonano,

Researchers in the University of Minnesota’s College of Science and Engineering and the National Renewable Energy Laboratory in Golden, Colo., have overcome technical hurdles in the quest for inexpensive, durable electronics and solar cells made with non-toxic chemicals. …

“Imagine a world where every child in a developing country could learn reading and math from a touch pad that costs less than $10 or home solar cells that finally cost less than fossil fuels,” said Uwe Kortshagen, a University of Minnesota mechanical engineering professor and one of the co-authors of the paper.

The July 30, 2013 University of Minnesota news release, which originated the news item, explains the discovery and the issues the researchers are addressing and it mentions, as many do these days,  a patent,

The research team discovered a novel technology to produce a specialized type of ink from non-toxic nanometer-sized crystals of silicon, often called “electronic ink.” This “electronic ink” could produce inexpensive electronic devices with techniques that essentially print it onto inexpensive sheets of plastic.

“This process for producing electronics is almost like screen printing a number on a softball jersey,” said Lance Wheeler, a University of Minnesota mechanical engineering Ph.D. student and lead author of the research.

But it’s not quite that easy. Wheeler, Kortshagen and the rest of the research team developed a method to solve fundamental problems of silicon electronic inks.

First, there is the ubiquitous need of organic “soap-like” molecules, called ligands, that are needed to produce inks with a good shelf life, but these molecules cause detrimental residues in the films after printing. This leads to films with electrical properties too poor for electronic devices. Second, nanoparticles are often deliberately implanted with impurities, a process called “doping,” to enhance their electrical properties.

In this new paper, researchers explain a new method to use an ionized gas, called nonthermal plasma, to not only produce silicon nanocrystals, but also to cover their surfaces with a layer of chlorine atoms. This surface layer of chlorine induces an interaction with many widely used solvents that allows production of stable silicon inks with excellent shelf life without the need for organic ligand molecules. In addition, the researchers discovered that these solvents lead to doping of films printed from their silicon inks, which gave them an electrical conductivity 1,000 times larger than un-doped silicon nanoparticle films. The researchers have a provisional patent on their findings.

Here’s a link to and a citation for the published paper,

Hypervalent surface interactions for colloidal stability and doping of silicon nanocrystals by Lance M. Wheeler, Nathan R. Neale, Ting Chen, & Uwe R. Kortshagen. Nature Communications 4, Article number: 2197 doi:10.1038/ncomms3197 Published 29 July 2013

The paper is open access. The researchers also offer a brief video describing the process of making the nanocrystals,

Here’s the video description provided by the researchers (from http://www.youtube.com/watch?v=5Un_HnOl6lQ&feature=youtu.be),

This video shows how silicon nanocrystals are synthesized in a plasma reactor. Inert argon gas flows from the top of the reactor through a glass tube. Fifteen watts of radio frequency power is applied to the copper ring electrodes to ionize the argon gas and produce what is called a plasma. A gas containing silicon (silane) is injected into the reactive plasma environment to produce silicon nanocrystals. Though the plasma is energetic enough to produce these tiny crystals, the glass tube remains cool enough to touch. The plasma is a reactive environment used to produce silicon nanocrystals that can be applied to inexpensive, next-generation electronics.

Unique ‘printing’ process boosts supercapacitor performance

In addition to creating energy, we also need to store some of it for future use as a July 29, 2013 news release from the University of Central Florida notes,

Researchers at the University of Central Florida have developed a technique to increase the energy storage capabilities of supercapacitors, essential devices for powering high-speed trains, electric cars, and the emergency doors of the Airbus A380.

The finding, which offers a solution to a problem that has plagued the growing multi-billion dollar industry, utilizes a unique three-step process to “print” large – area nanostructured electrodes, structures necessary to improve electrical conductivity and boost performance of the supercapacitor.

Jayan Thomas, an assistant professor in UCF’s NanoScience Technology Center, led the project which is featured in the June edition of Advanced Materials, one of the leading peer-reviewed scientific journals covering materials science in the world. Thomas’ research appears on the journal’s highly-coveted frontispiece, the illustration page of the journal that precedes the title page.

The news release goes on to describe the supercapacitor issue the researchers were addressing,

Supercapacitors have been around since the 1960’s. Similar to batteries, they store energy. The difference is that supercapacitors can provide higher amounts of power for shorter periods of time, making them very useful for heavy machinery and other applications that require large amounts of energy to start.  However, due to their innate low energy density; supercapacitors are limited in the amount of energy that they can store.

“We had been looking at techniques to print nanostructures,” said Thomas. “Using a simple spin-on nanoprinting (SNAP) technique, we can print highly-ordered nanopillars without the need for complicated development processes. By eliminating these processes, it allows multiple imprints to be made on the same substrate in close proximity.“

This simplified fabrication method devised by Thomas and his team is very attractive for the next-generation of energy storage systems. “What we’ve found is by adding the printed ordered nanostructures to supercapacitor electrodes, we can increase their surface area many times,” added Thomas. “We discovered that supercapacitors made using the SNAP technique can store much more energy than ones made without.”

Here’s a link to and a citation for the research paper abut this new technique for supercapacitors,

Energy Storage: Highly Ordered MnO2 Nanopillars for Enhanced Supercapacitor Performance (Adv. Mater. 24/2013) by Zenan Yu, Binh Duong, Danielle Abbitt, and Jayan Thomas. Article first published online: 20 JUN 2013 DOI: 10.1002/adma.201370160 Advanced Materials Volume 25, Issue 24, page 3301, June 25, 2013.

Lead researcher Thomas was recently featured in a video for his work on creating plasmonic nanocrystals from gold nanoparticles (from the news release),

Thomas, who is also affiliated with the College of Optics and Photonics (CREOL), and the College of Engineering, was recently featured on American Institute of Physics’ Inside Science TV for his collaborative research to develop a new material using nanotechnology that could potentially help keep pilots safe by diffusing harmful laser light.

Here’s the video,

You can find videos, news, and blogs featuring other research at Inside Science and you can find out more about Dr. Jayan Thomas here.

Cow blood declumps (stabilizes) gold nanoparticles in a solution

Rice University (Texas, US) researchers have discovered a means of stabilizing gold nanoparticles in a variety of solutions including one of the harshest, salt solutions. From the May 14, 2013 news item on Nanowerk (Note: A link has been removed),

A protein from cow blood has the remarkable ability to keep gold nanoparticles from clumping in a solution. The discovery could lead to improved biomedical applications and contribute to projects that use nanoparticles in harsh environments.

Bovine serum albumin (BSA) forms a protein “corona” around gold nanoparticles that keeps them from aggregating, particularly in high-salt environments like seawater. The new research by the Rice University labs of chemists Stephan Link and Christy Landes was published by the American Chemical Society journal ACS Sustainable Chemistry and Engineering (“Adsorption of a Protein Monolayer via Hydrophobic Interactions Prevents Nanoparticle Aggregation under Harsh Environmental Conditions”).

The May 13, 2012 Rice University news release by Mike Williams, which originated the news item, describes the researchers and the nature of their work,

Link’s primary interest is in the plasmonic properties of nanoparticles. Landes’ work incorporates protein binding and molecular transport. The BSA research combines their unique talents with those of Sergio Dominguez-Medina, a graduate student in Link’s lab who studied to be a physicist at Monterrey Tech and was drawn to this interdisciplinary project during an undergraduate fellowship at Link’s Rice lab.

“Initially, we wanted to look at nanoparticles in solution with something they would encounter frequently in blood: serum albumin,” Landes said. “In our first experiments, Sergio reported the very efficient, reasonably fast and irreversible binding the moment he put nanoparticles into a solution that contained serum albumin.”

“It turned out the salt is actually driving this binding,” Dominguez-Medina said.

Without BSA, gold nanoparticles in a salty solution quickly aggregate and fall to the bottom. “That by itself is undesirable for biomedical or industrial applications, because it could lead to toxicity issues,” he said. “The nanoparticles get more hydrophobic because in the presence of salts, the excess charges on the surface (which discourage clumping) are actually removed.” But if BSA is present, the proteins are drawn to the nanoparticles faster than the particles are drawn to each other.

“Once the protein is bound, it gives a super protection against any type of salt-induced aggregation. We think this could be used for the stabilization of nanoparticles in environments where, right now, it hasn’t been achieved,” Dominguez-Medina said.

He said the discovery also offers the possibility that nanoparticles might be made more compatible for treating humans by using a patient’s own albumin. “Albumin is really easy to purify and the process is well-established,” he said.

Here’s a little more about the plasmonics of the situation and how this discovery about cow blood protein might apply in biomedical and other applications (from the news release),

The ability of gold nanoparticles to absorb and redirect light is at the heart of several breakthrough technologies being developed at Rice and elsewhere. Most notable are a nanoparticle-based cancer treatment now in human testing that was developed by Professor Naomi Halas and former Rice colleague Jennifer West, and Halas’ project to convert solar energy directly into steam for sanitation and water purification.

“The only way nanoparticles exhibit their really nice optical properties in very specific optical frequencies is if they’re separated,” Landes said.

The key words in Landes comment is ‘separated’ (from the news release),

Because pure gold nanoparticles are so hydrophobic, they naturally clump together in a solution unless chemically treated. “A lot of industrial effort goes into keeping stuff off of surfaces, like contact lenses and ship hulls,” she said. “That involves chemically altering the surfaces to prevent unwanted adsorption, or in the case of nanoparticles, unwanted aggregation.”

Protecting the surface is costly, Link said. “But we found we could take nanoparticles prepared in the cheapest way, with a sodium citrate coating that stabilizes the particles by electrostatic repulsion, and add BSA, which coats the particles and makes them really stable.”

Adding the BSA seems logical when one of the scientists explains the reasoning (from the news release),

Albumin is the most common protein in blood, and the bovine version shares 98 percent of its amino acid sequence with human serum albumin. “One of its main purposes, biologically, is to take things that aren’t water-soluble, bind to them and make them soluble,” Landes said. “When you combine it with gold nanoparticles, BSA trades places with the cheap citrate, which isn’t a good protective layer, to form the monolayer corona, which is very strong and protective.”

Aside from obvious biomedical applications (e.g. implants and joint replacements), there are desalination and fuel cell applications (from the news release),

Seawater is the very definition of a harsh environment, Landes said. “One of the problems with desalination applications and, similarly, with fuel cells, is that saline or acidic conditions are very corrosive,” she said. “That’s why you have to use platinum electrodes in fuel cells – not because they’re better than cheaper materials at catalysis, but because they don’t corrode in a harsh environment.” She sees promise for BSA-treated gold nanoparticles in both applications.

The researchers have other plans as well (from the news release),

The researchers are now looking at how well gold nanoparticles retain their albumin corona with repeated use. “Gold is expensive,” Landes said. “But the beauty of it is that if you can reuse it, it only costs you once.”

They also want to use spectroscopy to see how the binding mechanism works in real time, Link said. “We want to study what’s happening at the interface of nanoparticles and biologically relevant media” that may eventually include DNA, RNA and drugs for delivery to cells, he said.

Link plans to see how BSA can be used in combination with gold nanorods. Because nanorods’ plasmonic properties can be tuned, “we can get them into the biological window, which is near-infrared light,” he said. Near-IR from lasers is used to activate, by heating, Halas’ and West’s cancer-killing nanoshells. Nanorods may also offer ways to combine BSA and other useful proteins by coating the tips and sides separately.

For interested parties, here’s a link to and a citation for the published paper,

Adsorption of a Protein Monolayer via Hydrophobic Interactions Prevents Nanoparticle Aggregation under Harsh Environmental Conditions by Sergio Dominguez-Medina, Jan Blankenburg, Jana Olson, Christy F. Landes, and Stephan Link. ACS Sustainable Chem. Eng., Article ASAP DOI: 10.1021/sc400042h
Publication Date (Web): April 3, 2013
Copyright © 2013 American Chemical Society

Unusually for the American Chemical Society (ACS), this paper appears to be open access; I was able to access the full HTML version today, May 14, 2013 at 10:10 am PDT.

Namdiatream; a European multimodal diagnostics project

I’ve written about lab-on-a-chip projects, point-of-care diagnostics, and other such initiatives on several occasions, most recently in a Mar. 1, 2013 posting about a technique where powder is used to make the diagnostic device more portable. This time it was a Europe-wide project described in a Mar. 4, 2013 news item on Nanowerk,which caught my attention (Note: A link has been removed),

The plan of the EU-funded consortium Nanotechnological toolkits for multi-modal disease diagnostics and treatment monitoring (Namdiatream) is not to cure cancer, per se, but to boost the sensitivity of diagnostics and the ability to monitor progress during treatment. They focused on three types – breast, prostate and lung cancer.

… The prototype devices being developed during the four-year project will detect common cancer cells much earlier and, with timely treatment, improve the chances of recovery.

According to the project leader, Professor Yuri Volkov of Trinity College Dublin’s School of Medicine, the portable nanodevices are based on innovative lab-on-a-chip, -bead and -wire technologies applicable in different settings – clinical, research, or point of care (i.e. hospitals). These lab-on-x technologies exploit the photo-luminescent (‘glow-in-the-dark’ light emitting), plasmonic (‘light-on-a-wire’), magnetic and unique optical properties of nanomaterials.

Volkov offers some insight into how the project started and its current state of evolution (from the news item),

This is ground-breaking work made possible thanks to advanced technology but also to EU funding for cross-border investigations. Teams across Europe were doing related but fragmented research, suggests Prof. Volkov. This risked leaving a team dangling if their approach failed or lacked funding.

“So we integrated our research and identified joint strengths to help one another develop the best technological approaches in case something didn’t work in one, or synergies were identified, thereby increasing the chances of wider success.”

At its half-way stage, notes Prof. Volkov, Namdiatream underwent a natural evolution when it became clear that by merging and refocusing work in some areas – i.e. in fluorescent nanomaterial technology and magnetic nanowire barcodes – it would speed up industrial implementation efforts.

“Now, work on the preclinical prototype devices is well under way,” he confirms. But one of the many remaining challenges is to calibrate their sensitivity, so that they do not give false readings, for instance.

The Namdiatream (Nanotechnological Toolkits for Multi-Modal Disease Diagnostics and Treatment Monitoring) home page offers more detail about the project,

Namdiatream is a truly interdisciplinary and Pan-european consortium that builds around 7 High-Tech SMEs [small to medium enterprises], 2 Multinational industries and 13 academic institutions. NAMDIATREAM will develop nanotechnology-based toolkit to enable early detection and imaging of molecular biomarkers of the most common cancer types and of cancer metastases, as well as permitting the identification of cells indicative of early-stage disease onset. The project is built on the innovative technology concepts of super-sensitive “lab-on-a-bead”, “lab-on-a-chip” and “lab-on-a-wire” nano-devices.

Interestingly, this too was on the home page,

The ETP Nanomedicine documents point out that nanotechnology has yet to deliver practical solutions for the patients and clinicians in their struggle against common, socially and economically important diseases such as cancer. Therefore NAMDIATREAM results will firstly aim to deliver to the diagnostic and medical imaging device companies involved in the consortium, and the clinical and academic partners. This could further provide the basis for cancer therapeutics as it will be possible to accurately assess the kinetics of cancer cell destruction during the course of appropriate therapy.

Mechanics of quantum kissing

“It is as if you can kiss without quite touching lips,” says Professor Jeremy Baumberg from the University of Cambridge Cavendish Laboratory in the University of Cambridge’s Nov. 7, 2012 news release about quantum electron jumps,

Even empty gaps have a colour. Now scientists have shown that quantum jumps of electrons can change the colour of gaps between nano-sized balls of gold. The new results, published today in the journal Nature, set a fundamental quantum limit on how tightly light can be trapped.

The team from the Universities of Cambridge, the Basque Country and Paris have combined tour de force experiments with advanced theories to show how light interacts with matter at nanometre sizes. The work shows how they can literally see quantum mechanics in action in air at room temperature.

As for the kissing, it all starts with metal and jumping electrons,

Because electrons in a metal move easily, shining light onto a tiny crack pushes electric charges onto and off each crack face in turn, at optical frequencies. The oscillating charge across the gap produces a ‘plasmonic’ colour for the ghostly region in-between, but only when the gap is small enough.

Team leader Professor Jeremy Baumberg from the University of Cambridge Cavendish Laboratory suggests we think of this like the tension building between a flirtatious couple staring into each other’s eyes. As their faces get closer the tension mounts, and only a kiss discharges this energy.

H/T to the Nov. 7, 2012 news item on ScienceDaily where I first learned of quantum kissing,

In the new experiments, the gap is shrunk below 1nm (1 billionth of a metre) which strongly reddens the gap colour as the charge builds up. However because electrons can jump across the gap by quantum tunnelling, the charge can drain away when the gap is below 0.35nm, seen as a blue-shifting of the colour. …

Prof Javier Aizpurua, leader of the theoretical team from San Sebastian complains: “Trying to model so many electrons oscillating inside the gold just cannot be done with existing theories.” He has had to fuse classical and quantum views of the world to even predict the colour shifts seen in experiment.

The new insights from this work suggest ways to measure the world down to the scale of single atoms and molecules, and strategies to make useful tiny devices.

Something to think about the next time you kiss.