Tag Archives: nanorods

Create gold nanoparticles and nanowires with water droplets.

For some reason it took a lot longer than usual to find this research paper despite having the journal (Nature Communications), the title (Spontaneous formation …), and the authors’ names. Thankfully, success was wrested from the jaws of defeat (I don’t care if that is trite; it’s how I felt) and links, etc. follow at the end as usual.

An April 19, 2018 Stanford University news release (also on EurekAlert) spins fascinating tale,

An experiment that, by design, was not supposed to turn up anything of note instead produced a “bewildering” surprise, according to the Stanford scientists who made the discovery: a new way of creating gold nanoparticles and nanowires using water droplets.

The technique, detailed April 19 [2018] in the journal Nature Communications, is the latest discovery in the new field of on-droplet chemistry and could lead to more environmentally friendly ways to produce nanoparticles of gold and other metals, said study leader Richard Zare, a chemist in the School of Humanities and Sciences and a co-founder of Stanford Bio-X.

“Being able to do reactions in water means you don’t have to worry about contamination. It’s green chemistry,” said Zare, who is the Marguerite Blake Wilbur Professor in Natural Science at Stanford.

Noble metal

Gold is known as a noble metal because it is relatively unreactive. Unlike base metals such as nickel and copper, gold is resistant to corrosion and oxidation, which is one reason it is such a popular metal for jewelry.

Around the mid-1980s, however, scientists discovered that gold’s chemical aloofness only manifests at large, or macroscopic, scales. At the nanometer scale, gold particles are very chemically reactive and make excellent catalysts. Today, gold nanostructures have found a role in a wide variety of applications, including bio-imaging, drug delivery, toxic gas detection and biosensors.

Until now, however, the only reliable way to make gold nanoparticles was to combine the gold precursor chloroauric acid with a reducing agent such as sodium borohydride.

The reaction transfers electrons from the reducing agent to the chloroauric acid, liberating gold atoms in the process. Depending on how the gold atoms then clump together, they can form nano-size beads, wires, rods, prisms and more.

A spritz of gold

Recently, Zare and his colleagues wondered whether this gold-producing reaction would proceed any differently with tiny, micron-size droplets of chloroauric acid and sodium borohydide. How large is a microdroplet? “It is like squeezing a perfume bottle and out spritzes a mist of microdroplets,” Zare said.

From previous experiments, the scientists knew that some chemical reactions proceed much faster in microdroplets than in larger solution volumes.

Indeed, the team observed that gold nanoparticle grew over 100,000 times faster in microdroplets. However, the most striking observation came while running a control experiment in which they replaced the reducing agent – which ordinarily releases the gold particles – with microdroplets of water.

“Much to our bewilderment, we found that gold nanostructures could be made without any added reducing agents,” said study first author Jae Kyoo Lee, a research associate.

Viewed under an electron microscope, the gold nanoparticles and nanowires appear fused together like berry clusters on a branch.

The surprise finding means that pure water microdroplets can serve as microreactors for the production of gold nanostructures. “This is yet more evidence that reactions in water droplets can be fundamentally different from those in bulk water,” said study coauthor Devleena Samanta, a former graduate student in Zare’s lab and co-author on the paper.

If the process can be scaled up, it could eliminate the need for potentially toxic reducing agents that have harmful health side effects or that can pollute waterways, Zare said.

It’s still unclear why water microdroplets are able to replace a reducing agent in this reaction. One possibility is that transforming the water into microdroplets greatly increases its surface area, creating the opportunity for a strong electric field to form at the air-water interface, which may promote the formation of gold nanoparticles and nanowires.

“The surface area atop a one-liter beaker of water is less than one square meter. But if you turn the water in that beaker into microdroplets, you will get about 3,000 square meters of surface area – about the size of half a football field,” Zare said.

The team is exploring ways to utilize the nanostructures for various catalytic and biomedical applications and to refine their technique to create gold films.

“We observed a network of nanowires that may allow the formation of a thin layer of nanowires,” Samanta said.

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

Spontaneous formation of gold nanostructures in aqueous microdroplets by Jae Kyoo Lee, Devleena Samanta, Hong Gil Nam, & Richard N. Zare. Nature Communicationsvolume 9, Article number: 1562 (2018) doi:10.1038/s41467-018-04023-z Published online: 19 April 2018

Not unsurprisingly given Zare’s history as recounted in the news release, this paper is open access.

An artificial enzyme uses light to kill bacteria

An April 4, 2018 news item on ScienceDaily announces a light-based approach to killing bacteria,

Researchers from RMIT University [Australia] have developed a new artificial enzyme that uses light to kill bacteria.

The artificial enzymes could one day be used in the fight against infections, and to keep high-risk public spaces like hospitals free of bacteria like E. coli and Golden Staph.

E. coli can cause dysentery and gastroenteritis, while Golden Staph is the major cause of hospital-acquired secondary infections and chronic wound infections.

Made from tiny nanorods — 1000 times smaller than the thickness of the human hair — the “NanoZymes” use visible light to create highly reactive oxygen species that rapidly break down and kill bacteria.

Lead researcher, Professor Vipul Bansal who is an Australian Future Fellow and Director of RMIT’s Sir Ian Potter NanoBioSensing Facility, said the new NanoZymes offer a major cutting edge over nature’s ability to kill bacteria.

Dead bacteria made beautiful,

Caption: A 3-D rendering of dead bacteria after it has come into contact with the NanoZymes.
Credit: Dr. Chaitali Dekiwadia/ RMIT Microscopy and Microanalysis Facility

An April 5, 2018 RMIT University press release (also on EurekAlert but dated April 4, 2018), which originated the news item, expands on the theme,

“For a number of years we have been attempting to develop artificial enzymes that can fight bacteria, while also offering opportunities to control bacterial infections using external ‘triggers’ and ‘stimuli’,” Bansal said. “Now we have finally cracked it.

“Our NanoZymes are artificial enzymes that combine light with moisture to cause a biochemical reaction that produces OH radicals and breaks down bacteria. Nature’s antibacterial activity does not respond to external triggers such as light.

“We have shown that when shined upon with a flash of white light, the activity of our NanoZymes increases by over 20 times, forming holes in bacterial cells and killing them efficiently.

“This next generation of nanomaterials are likely to offer new opportunities in bacteria free surfaces and controlling spread of infections in public hospitals.”

The NanoZymes work in a solution that mimics the fluid in a wound. This solution could be sprayed onto surfaces.

The NanoZymes are also produced as powders to mix with paints, ceramics and other consumer products. This could mean bacteria-free walls and surfaces in hospitals.

Public toilets — places with high levels of bacteria, and in particular E. coli — are also a prime location for the NanoZymes, and the researchers believe their new technology may even have the potential to create self-cleaning toilet bowls.

While the NanoZymes currently use visible light from torches or similar light sources, in the future they could be activated by sunlight.

The researchers have shown that the NanoZymes work in a lab environment. The team is now evaluating the long-term performance of the NanoZymes in consumer products.

“The next step will be to validate the bacteria killing and wound healing ability of these NanoZymes outside of the lab,” Bansal said.

“This NanoZyme technology has huge potential, and we are seeking interest from appropriate industries for joint product development.”

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

Visible-Light-Triggered Reactive-Oxygen-Species-Mediated Antibacterial Activity of Peroxidase-Mimic CuO Nanorods by Md. Nurul Karim, Mandeep Singh, Pabudi Weerathunge, Pengju Bian, Rongkun Zheng, Chaitali Dekiwadia, Taimur Ahmed, Sumeet Walia, Enrico Della Gaspera, Sanjay Singh, Rajesh Ramanathan, and Vipul Bansal. ACS Appl. Nano Mater., Article ASAP DOI: 10.1021/acsanm.8b00153 Publication Date (Web): March 6, 2018

Copyright © 2018 American Chemical Society

This paper is open access.

Nanorods as multistate switches

This research goes beyond the binary (0 or 1) and to an analog state that resembles quantum states. Fascinating, yes? An Oct. 10, 2016 news item on phys.org tells more,

Rice University scientists have discovered how to subtly change the interior structure of semi-hollow nanorods in a way that alters how they interact with light, and because the changes are reversible, the method could form the basis of a nanoscale switch with enormous potential.

“It’s not 0-1, it’s 1-2-3-4-5-6-7-8-9-10,” said Rice materials scientist Emilie Ringe, lead scientist on the project, which is detailed in the American Chemical Society journal Nano Letters. “You can differentiate between multiple plasmonic states in a single particle. That gives you a kind of analog version of quantum states, but on a larger, more accessible scale.”

Ringe and colleagues used an electron beam to move silver from one location to another inside gold-and-silver nanoparticles, something like a nanoscale Etch A Sketch. The result is a reconfigurable optical switch that may form the basis for a new type of multiple-state computer memory, sensor or catalyst.

An Oct. 10, 2016 Rice University news release, which originated the news item, describes the work in additional detail,

At about 200 nanometers long, 500 of the metal rods placed end-to-end would span the width of a human hair. However, they are large in comparison with modern integrated circuits. Their multistate capabilities make them more like reprogrammable bar codes than simple memory bits, she said.

“No one has been able to reversibly change the shape of a single particle with the level of control we have, so we’re really excited about this,” Ringe said.

Altering a nanoparticle’s internal structure also alters its external plasmonic response. Plasmons are the electrical ripples that propagate across the surface of metallic materials when excited by light, and their oscillations can be easily read with a spectrometer — or even the human eye — as they interact with visible light.

The Rice researchers found they could reconfigure nanoparticle cores with pinpoint precision. That means memories made of nanorods need not be merely on-off, Ringe said, because a particle can be programmed to emit many distinct plasmonic patterns.

The discovery came about when Ringe and her team, which manages Rice’s advanced electron microscopy lab, were asked by her colleague and co-author Denis Boudreau, a professor at Laval University in Quebec, to characterize hollow nanorods made primarily of gold but containing silver.

“Most nanoshells are leaky,” Ringe said. “They have pinholes. But we realized these nanorods were defect-free and contained pockets of water that were trapped inside when the particles were synthesized. We thought: We have something here.”

Ringe and the study’s lead author, Rice research scientist Sadegh Yazdi, quickly realized how they might manipulate the water. “Obviously, it’s difficult to do chemistry there, because you can’t put molecules into a sealed nanoshell. But we could put electrons in,” she said.

Focusing a subnanometer electron beam on the interior cavity split the water and inserted solvated electrons – free electrons that can exist in a solution. “The electrons reacted directly with silver ions in the water, drawing them to the beam to form silver,” Ringe said. The now-silver-poor liquid moved away from the beam, and its silver ions were replenished by a reaction of water-splitting byproducts with the solid silver in other parts of the rod.

“We actually were moving silver in the solution, reconfiguring it,” she said. “Because it’s a closed system, we weren’t losing anything and we weren’t gaining anything. We were just moving it around, and could do so as many times as we wished.”

The researchers were then able to map the plasmon-induced near-field properties without disturbing the internal structure — and that’s when they realized the implications of their discovery.

“We made different shapes inside the nanorods, and because we specialize in plasmonics, we mapped the plasmons and it turned out to have a very nice effect,” Ringe said. “We basically saw different electric-field distributions at different energies for different shapes.” Numerical results provided by collaborators Nicolas Large of the University of Texas at San Antonio and George Schatz of Northwestern University helped explain the origin of the modes and how the presence of a water-filled pocket created a multitude of plasmons, she said.

The next challenge is to test nanoshells of other shapes and sizes, and to see if there are other ways to activate their switching potentials. Ringe suspects electron beams may remain the best and perhaps only way to catalyze reactions inside particles, and she is hopeful.

“Using an electron beam is actually not as technologically irrelevant as you might think,” she said. “Electron beams are very easy to generate. And yes, things need to be in vacuum, but other than that, people have generated electron beams for nearly 100 years. I’m sure 40 years ago people were saying, ‘You’re going to put a laser in a disk reader? That’s crazy!’ But they managed to do it.

“I don’t think it’s unfeasible to miniaturize electron-beam technology. Humans are good at moving electrons and electricity around. We figured that out a long time ago,” Ringe said.

The research should trigger the imaginations of scientists working to create nanoscale machines and processes, she said.

“This is a reconfigurable unit that you can access with light,” she said. “Reading something with light is much faster than reading with electrons, so I think this is going to get attention from people who think about dynamic systems and people who think about how to go beyond current nanotechnology. This really opens up a new field.”

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

Reversible Shape and Plasmon Tuning in Hollow AgAu Nanorods by Sadegh Yazdi, Josée R. Daniel, Nicolas Large, George C. Schatz, Denis Boudreau, and Emilie Ringe. Nano Lett., Article ASAP DOI: 10.1021/acs.nanolett.6b02946 Publication Date (Web): October 5, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

The researchers have made this video available for the public,

Perovskite, nanorods, and solar energy

As the authors, Azhar Fakharuddin, Rajan Jose, and Thomas Brown, note in an Aug. 7, 2015 Nanowerk Spotlight article , securing energy sources is a global pursuit and pervoskite (a new wonder material for solar cells) has presented a challenge (Note: A link has been removed),

Energy security has been a top global concern motivating researchers to seek it from renewable and cost-effective resources. Solar cells, that convert sun light into electricity, hold the promise as a cheap energy alternative. The silicon and thin film photovoltaic industry have taken many strides to lower energy prices; however, continued research is required in order to extensively compete with fossil fuels.

The development of perovskite solar cells, first reported in 2009 (and with a record power conversion efficiency of 20.1 percent so far), is a possible route towards high efficiency photovoltaics that are also cost-effectiveness, owing to to their easy-processing from solution.

Question marks have however remained on their stability.

The authors (members of a research team) have recently published a paper about a method that could make perovskite solar cells more stable,

Now, a research team from University Malaysia Pahang, focussing on renewable energy, working in in collaboration with scientists from University of Rome ‘Tor Vergata’, Italy, has developed the world’s first nanorod-based perovskite solar module.

Among the three types of electron transport layers investigated, the nanorod-based devices retained the original efficiency values even after 2500 hours of shelf-life investigation, a protocol used to gauge initial stability and indoor lifetime performance.
The device employing a conventional TiO2 nanoparticle material showed nearly 60% of original performance, whereas planar devices employing a compact TiO2 layer showed below 5% of original performance, measured at similar experimental conditions.
A chemical analysis of the devices hinted that the peculiar conformation of nanorods facilitates a stable perovskite phase due to their inherent stability and macroporous nature.

If you want more detail, the research team’s Nanowerk Spotlight article is the place to look (it’s almost like a Reddit session except there’s no ‘ask me anything’ option). There’s also the team’s paper,

Vertical TiO2 Nanorods as a Medium for Stable and High-Efficiency Perovskite Solar Modules by Azhar Fakharuddin, Francesco Di Giacomo, Alessandro L. Palma, Fabio Matteocci, Irfan Ahmed, Stefano Razza, Alessandra D’Epifanio, Silvia Licoccia, Jamil Ismail, Aldo Di Carlo, Thomas M. Brown, and Rajan Jose. ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b03265 Publication Date (Web): July 24, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

One final note, I’ve been meaning to publish a post about perovskite-based solar cells for a while now as the material seems to be sweeping the solar energy community and, now, it’s done.

Snow reveals the truth about crystalline growth

A Jan. 24, 2014 news item on Nanowerk has a beautiful and timely (given the snowy, frigid weather in Eastern Canada and the US) opening for a story about crystals and metallic nanorods,

This time of year it’s not hard to imagine the world buried under a smooth blanket of snow. A picnic table on a flat lawn eventually vanishes as trillions of snowflakes collect around it, a crystalline sheet obscuring the normall – visible peaks and valleys of our summertime world.

This is basically how scientists understand the classical theory of crystalline growth. Height steps gradually disappear as atoms of a given material—be it snow or copper or aluminum—collect on a surface and then tumble down to lower heights to fill in the gaps. The only problem with this theory is that it totally falls apart when applied to extremely small situations—i.e., the nanoscale.

The Jan. 23, 2014 Northeastern University news release by Angela Herring, which originated the news item, goes on to provide some context and describe this work concerning nanorods,

Hanchen Huang, pro­fessor and chair of the Depart­ment of Mechan­ical and Indus­trial Engi­neering [Northeastern University located in Massachusetts, US], has spent the last 10 years revising the clas­sical theory of crystal growth that accounts for his obser­va­tions of nanorod crys­tals. His work has gar­nered the con­tinued sup­port of the U.S, Depart­ment of Energy’s Basic Energy Sci­ence Core Program.

Nanorods are minis­cule fibers grown per­pen­dic­ular to a sub­strate, each one about 100,000 times thinner than a human hair. Sur­face steps, or the minor vari­a­tions in the ver­tical land­scape of that sub­strate, deter­mine how the rods will grow.

“Even if some sur­face steps are closer and others more apart at the start, with time the clas­sical theory pre­dicts they become more equal­ized,” Huang said. “But we found that the clas­sical theory missed a pos­i­tive feed­back mechanism.”

This mech­a­nism, he explained, causes the steps to “cluster,” making it more dif­fi­cult for atoms to fall from a higher step to a lower one. So, instead of filling in the height gaps of a vari­able sur­face, atoms in a nanorod crystal localize to the highest levels.

“The taller region gets taller,” Huang said. “It’s like, if you ever play bas­ket­ball, you know the taller guys will get more rebounds.” That’s basi­cally what hap­pens with nanorod growth.

Huang’s theory, which was pub­lished in the journal Phys­ical Review Let­ters this year, rep­re­sents the first time anyone has pro­vided a the­o­ret­ical frame­work for under­standing nanorod crystal growth. “Lots of money has been spent over the past decades on nanoscience and nan­otech­nology,” Huang said. “But we can only turn that into real-​​world appli­ca­tions if we under­stand the science.”

Indeed, his con­tri­bu­tion to under­standing the sci­ence allowed him and his col­leagues to pre­dict the smallest pos­sible size for copper nanorods and then suc­cess­fully syn­the­size them. Not only are they the smallest nanorods ever pro­duced, but with Huang’s theory he can con­fi­dently say they are the smallest nanorods pos­sible using phys­ical vapor deposition.

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

Smallest Metallic Nanorods Using Physical Vapor Deposition by Xiaobin Niu, Stephen P. Stagon, Hanchen Huang, J. Kevin Baldwin, and Amit Misra. Phys. Rev. Lett. 110 (no. 13), 136102 (2013) [5 pages] DoI:

This paper is behind a paywall.

Pop and rock music lead to better solar cells

A Nov. 6, 2013 news item on Nanowerk reveals that scientists at the Imperial College of London (UK) and Queen Mary University of London (UK),

Playing pop and rock music improves the performance of solar cells, according to new research from scientists at Queen Mary University of London and Imperial College London.

The high frequencies and pitch found in pop and rock music cause vibrations that enhanced energy generation in solar cells containing a cluster of ‘nanorods’, leading to a 40 per cent increase in efficiency of the solar cells.

The study has implications for improving energy generation from sunlight, particularly for the development of new, lower cost, printed solar cells.

The Nov. 6, 2013 Imperial College of London (ICL) news release, which originated the news item, gives more details about the research,

The researchers grew billions of tiny rods (nanorods) made from zinc oxide, then covered them with an active polymer to form a device that converts sunlight into electricity.

Using the special properties of the zinc oxide material, the team was able to show that sound levels as low as 75 decibels (equivalent to a typical roadside noise or a printer in an office) could significantly improve the solar cell performance.

“After investigating systems for converting vibrations into electricity this is a really exciting development that shows a similar set of physical properties can also enhance the performance of a photovoltaic,” said Dr Steve Dunn, Reader in Nanoscale Materials from Queen Mary’s School of Engineering and Materials Science.

Scientists had previously shown that applying pressure or strain to zinc oxide materials could result in voltage outputs, known as the piezoelectric effect. However, the effect of these piezoelectric voltages on solar cell efficiency had not received significant attention before.

“We thought the soundwaves, which produce random fluctuations, would cancel each other out and so didn’t expect to see any significant overall effect on the power output,” said James Durrant, Professor of Photochemistry at Imperial College London, who co-led the study.

“The key for us was that not only that the random fluctuations from the sound didn’t cancel each other out, but also that some frequencies of sound seemed really to amplify the solar cell output – so that the increase in power was a remarkably big effect considering how little sound energy we put in.”

“We tried playing music instead of dull flat sounds, as this helped us explore the effect of different pitches. The biggest difference we found was when we played pop music rather than classical, which we now realise is because our acoustic solar cells respond best to the higher pitched sounds present in pop music,” he concluded.

The discovery could be used to power devices that are exposed to acoustic vibrations, such as air conditioning units or within cars and other vehicles.

This is not the first time that music has been shown to affect properties at the nanoscale. A March 12, 2008 article by Anna Salleh for the Australian Broadcasting Corporation featured a researcher who tested nanowire growth by playing music (Note: Links have been removed),

Silicon nanowires grow more densely when blasted with Deep Purple than any other music tested, says an Australian researcher.

But the exact potential of music in growing nanowires remains a little hazy.

David Parlevliet, a PhD student at Murdoch University in Perth, presented his findings at a recent Australian Research Council Nanotechnology Network symposium in Melbourne.

Parlevliet is testing nanowires for their ability to absorb sunlight in the hope of developing solar cells from them.

I’ve taken a look at the references cited by researchers in their paper and there is nothing from Parleviet listed, so, this seems to be one of those cases where more than one scientist is thinking along the similar lines, i.e., that sound might affect nanoscale structures in such a way as to improve solar cell efficiency.

Here’s a link to and a citation for the ICL/University of Queen Mary research paper,

Acoustic Enhancement of Polymer/ZnO Nanorod Photovoltaic Device Performance by Safa Shoaee, Joe Briscoe, James R. Durrant, Steve Dunn. Article first published online: 6 NOV 2013 DOI: 10.1002/adma.201303304
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.