Tag Archives: Agency for Science Technology and Research (A*STAR)

Killing bacteria on contact with dragonfly-inspired nanocoating

Scientists in Singapore were inspired by dragonflies and cicadas according to a March 28, 2018 news item on Nanowerk (Note: A link has been removed),

Studies have shown that the wings of dragonflies and cicadas prevent bacterial growth due to their natural structure. The surfaces of their wings are covered in nanopillars making them look like a bed of nails. When bacteria come into contact with these surfaces, their cell membranes get ripped apart immediately and they are killed. This inspired researchers from the Institute of Bioengineering and Nanotechnology (IBN) of A*STAR to invent an anti-bacterial nano coating for disinfecting frequently touched surfaces such as door handles, tables and lift buttons.

This technology will prove particularly useful in creating bacteria-free surfaces in places like hospitals and clinics, where sterilization is important to help control the spread of infections. Their new research was recently published in the journal Small (“ZnO Nanopillar Coated Surfaces with Substrate-Dependent Superbactericidal Property”)

Image 1: Zinc oxide nanopillars that looked like a bed of nails can kill a broad range of germs when used as a coating on frequently-touched surfaces. Courtesy: A*STAR

A March 28, 2018 Agency for Science Technology and Research (A*STAR) press release, which originated the news item, describes the work further,

80% of common infections are spread by hands, according to the B.C. [province of Canada] Centre for Disease Control1. Disinfecting commonly touched surfaces helps to reduce the spread of harmful germs by our hands, but would require manual and repeated disinfection because germs grow rapidly. Current disinfectants may also contain chemicals like triclosan which are not recognized as safe and effective 2, and may lead to bacterial resistance and environmental contamination if used extensively.

“There is an urgent need for a better way to disinfect surfaces without causing bacterial resistance or harm to the environment. This will help us to prevent the transmission of infectious diseases from contact with surfaces,” said IBN Executive Director Professor Jackie Y. Ying.

To tackle this problem, a team of researchers led by IBN Group Leader Dr Yugen Zhang created a novel nano coating that can spontaneously kill bacteria upon contact. Inspired by studies on dragonflies and cicadas, the IBN scientists grew nanopilllars of zinc oxide, a compound known for its anti-bacterial and non-toxic properties. The zinc oxide nanopillars can kill a broad range of germs like E. coli and S. aureus that are commonly transmitted from surface contact.

Tests on ceramic, glass, titanium and zinc surfaces showed that the coating effectively killed up to 99.9% of germs found on the surfaces. As the bacteria are killed mechanically rather than chemically, the use of the nano coating would not contribute to environmental pollution. Also, the bacteria will not be able to develop resistance as they are completely destroyed when their cell walls are pierced by the nanopillars upon contact.

Further studies revealed that the nano coating demonstrated the best bacteria killing power when it is applied on zinc surfaces, compared with other surfaces. This is because the zinc oxide nanopillars catalyzed the release of superoxides (or reactive oxygen species), which could even kill nearby free floating bacteria that were not in direct contact with the surface. This super bacteria killing power from the combination of nanopillars and zinc broadens the scope of applications of the coating beyond hard surfaces.

Subsequently, the researchers studied the effect of placing a piece of zinc that had been coated with zinc oxide nanopillars into water containing E. coli. All the bacteria were killed, suggesting that this material could potentially be used for water purification.

Dr Zhang said, “Our nano coating is designed to disinfect surfaces in a novel yet practical way. This study demonstrated that our coating can effectively kill germs on different types of surfaces, and also in water. We were also able to achieve super bacteria killing power when the coating was used on zinc surfaces because of its dual mechanism of action. We hope to use this technology to create bacteria-free surfaces in a safe, inexpensive and effective manner, especially in places where germs tend to accumulate.”

IBN has recently received a grant from the National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme to further develop this coating technology in collaboration with Tan Tock Seng Hospital for commercial application over the next 5 years.

1 B.C. Centre for Disease Control

2 U.S. Food & Drug Administration

(I wasn’t expecting to see a reference to my home province [BC Centre for Disease Control].) Back to the usual, here’s a link to and a citation for the paper,

ZnO Nanopillar Coated Surfaces with Substrate‐Dependent Superbactericidal Property by Guangshun Yi, Yuan Yuan, Xiukai Li, Yugen Zhang. Small https://doi.org/10.1002/smll.201703159 First published: 22 February 2018

This paper is behind a paywall.

One final comment, this research reminds me of research into simulating shark skin because that too has bacteria-killing nanostructures. My latest about the sharkskin research is a Sept, 18, 2014 posting.

Oil spill cleanup nanotechnology-enabled solution from A*STAR

A*STAR (Singapore’s Agency for Science Technology and Research) has developed a new technology for cleaning up oil spills according to an Oct. 11, 2016 news item on Nanowerk,

Oceanic oil spills are tough to clean up. They dye feathers a syrupy sepia and tan fish eggs a toxic tint. The more turbulent the waters, the farther the slick spreads, with inky droplets descending into the briny deep.

Now technology may be able to succeed where hard-working volunteers have failed in the past. Researchers at the A*STAR Institute of Bioengineering and Nanotechnology (IBN) are using nanotechnology to turn an oil spill into a floating mass of brown jelly that can be scooped up before it can make its way into the food chain.

“Nanoscience makes it possible to tailor the essential structures of materials at the nanometer scale to achieve specific properties,” says chemist Yugen Zhang at IBN, who is developing some of the technologies. “Structures and materials in the nanometer size range often take on distinctive properties that are not seen in other size ranges,” adds Huaqiang Zeng, another chemist at IBN.

An Oct. 11, 2016 A*STAR press release, which originated the news item, describes some of problematic solutions before describing the new technology,

There are many approaches to cleaning an oil spill, and none are completely effective. Fresh, thick grease can be set ablaze or contained by floating barriers for skimmers to scoop out. The slick can also be inefficiently hardened, messily absorbed, hazardously dispersed, or slowly consumed by oil-grazing bacteria. All of these are deficient on a large scale, especially in rough waters.

Organic molecules with special gelling abilities offer a cheap, simple and environmentally friendly alternative for cleaning up the mess. Zeng has developed several such molecules that turn crude oil into jelly within minutes.

To create his ‘supergelators’, Zeng designed the molecules to associate with each other without forming physical bonds. When sprayed on contaminated seawater, the molecules immediately bundle into long fibers between 40 and 800 nanometers wide. These threads create a web that traps the interspersed oil in a giant blob that floats on the water’s surface. The gunk can then be swiftly sieved out of the ocean. Valuable crude oil can later be reclaimed using a common technique employed by petroleum refineries called fractional distillation.

Zeng tested the supergelators on four types of crude oil with different densities, viscosities and sulfur levels in a small round dish. The results were impressive. “The supergelators solidified both freshly spilled crude oil and highly weathered crude oil 37 to 60 times their own weight,” says Zeng. The materials used to produce these organic molecules are cheap and non toxic, which make them a commercially viable solution for managing accidents out at sea. Zeng hopes to work with industrial partners to test the nanomolecules on a much larger scale.

Zeng and his colleagues have developed other other ‘water’ applications as well,

Unsalty water

Scientists at IBN are also using nanoscience to remove salt from seawater and heavy metals from contaminated water.

With dwindling global fresh and ground water reserves, many countries are looking to desalination as a viable source of drinking water. Desalination is expected to meet 30 per cent of the water demand of Singapore by 2060, which will mean tripling the country’s current desalination capacity. But desalination demands huge energy consumption and reverse osmosis, the mainstream technology it depends on, has a relatively high cost. Reverse osmosis works by using extreme pressures to squeeze water molecules through tightly knit membranes.

An emerging alternative solution mimics the way proteins embedded in cell membranes, known as aquaporins, channel water in and out. Some research groups have even created membranes made of fatty lipid molecules that can accommodate natural aquaporins. Zeng has developed a cheaper and more resilient replacement.

His building blocks consist of helical noodles with sticky ends that connect to form long spirals. Water molecules can flow through the 0.3 nanometer openings at the center of the spirals, but all the other positively and negatively charged ions that make up saltwater are too bulky to pass. These include sodium, potassium, calcium, magnesium, chlorine and sulfur oxide. “In water, all of these ions are highly hydrated, attached to lots of water molecules, which makes them too large to go through the channels,” says Zeng.

The technology could lead to global savings of up to US$5 billion a year, says Zeng, but only after several more years of testing and tweaking the lipid membrane’s compatibility and stability with the nanospirals. “This is a major focus in my group right now,” he says. “We want to get this done, so that we can reduce the cost of water desalination to an acceptable level.”

Stick and non-stick

Nanomaterials also offer a low-cost, effective and sustainable way to filter out toxic metals from drinking water.

Heavy metal levels in drinking water are stringently regulated due to the severe damage the substances can cause to health, even at very low concentrations. The World Health Organization requires that levels of lead, for example, remain below ten parts per billion (ppb). Treating water to these standards is expensive and extremely difficult.

Zhang has developed an organic substance filled with pores that can trap and remove toxic metals from water to less than one ppb. Each pore is ten to twenty nanometers wide and packed with compounds, known as amines that stick to the metals.

Exploiting the fact that amines lose their grip over the metals in acidic conditions, the valuable and limited resource can be recovered by industry, and the polymers reused.

The secret behind the success of Zhang’s polymers is the large surface area covered by the pores, which translates into more opportunities to interact with and trap the metals. “Other materials have a surface area of about 100 square meters per gram, but ours is 1,000 square meters per gram,” says Zhang. “It is 10 times higher.”

Zhang tested his nanoporous polymers on water contaminated with lead. He sprinkled a powdered version of the polymer into a slightly alkaline liquid containing close to 100 ppb of lead. Within seconds, lead levels reduced to below 0.2 ppb. Similar results were observed for cadmium, copper and palladium. Washing the polymers in acid released up to 93 per cent of the lead.

With many companies keen to scale these technologies for real-world applications, it won’t be long before nanoscience treats the Earth for its many maladies.

I wonder if the researchers have found industrial partners (who could be named) to bring these solutions for oil spill cleanups, desalination, and water purification to the market.

International NanoCar race: 1st ever to be held in Autumn 2016

They have a very intriguing set of rules for the 1st ever International NanoCar Race to be held in Toulouse, France in October 2016. From the Centre d’Élaboration de Matériaux et d’Études Structurales (CEMES) Molecule-car Race International page (Note: A link has been removed),

1) General regulations

The molecule-car of a registered team has at its disposal a runway prepared on a small portion of the (111) face of the same crystalline gold surface. The surface is maintained at a very low temperature that is 5 Kelvin = – 268°C (LT) in ultra-high vacuum that is 10-8 Pa or 10-10 mbar 10-10 Torr (UHV) for at least the duration of the competition. The race itself last no more than 2 days and 2 nights including the construction time needed to build up atom by atom the same identical runway for each competitor. The construction and the imaging of a given runway are obtained by a low temperature scanning tunneling microscope (LT-UHV-STM) and certified by independent Track Commissioners before the starting of the race itself.

On this gold surface and per competitor, one runway is constructed atom by atom using a few surface gold metal ad-atoms. A molecule-car has to circulate around those ad-atoms, from the starting to the arrival lines, each line being delimited by 2 gold ad-atoms. The spacing between two metal ad-atoms along a runway is less than 4 nm. A minimum of 5 gold ad-atoms line has to be constructed per team and per runway.

The organizers have included an example of a runway,

A preliminary runway constructed by C. Manzano and We Hyo Soe (A*Star, IMRE) in Singapore, with the 2 starting gold ad-atoms, the 5 gold ad-atoms for the track and the 2 gold ad-atoms had been already constructed atom by atom.

A preliminary runway constructed by C. Manzano and We Hyo Soe (A*Star, IMRE) in Singapore, with the 2 starting gold ad-atoms, the 5 gold ad-atoms for the track and the 2 gold ad-atoms had been already constructed atom by atom.

A November 25, 2015 [France] Centre National de la Recherche Scientifique (CNRS) press release notes that five teams presented prototypes at the Futurapolis 2015 event preparatory to the upcoming Autumn 2016 race,

The French southwestern town of Toulouse is preparing for the first-ever international race of molecule-cars: five teams will present their car prototype during the Futurapolis event on November 27, 2015. These cars, which only measure a few nanometers in length and are propelled by an electric current, are scheduled to compete on a gold atom surface next year. Participants will be able to synthesize and test their molecule-car until October 2016 prior to taking part in the NanoCar Race organized at the CNRS Centre d’élaboration des matériaux et d’études structurales (CEMES) by Christian Joachim, senior researcher at the CNRS and Gwénaël Rapenne, professor at Université Toulouse III-Paul Sabatier, with the support of the CNRS.

There is a video describing the upcoming 2016 race (English, spoken and in subtitles),


NanoCar Race, the first-ever race of molecule-cars by CNRS-en

A Dec. 14, 2015 Rice University news release provides more detail about the event and Rice’s participation,

Rice University will send an entry to the first international NanoCar Race, which will be held next October at Pico-Lab CEMES-CNRS in Toulouse, France.

Nobody will see this miniature grand prix, at least not directly. But cars from five teams, including a collaborative effort by the Rice lab of chemist James Tour and scientists at the University of Graz, Austria, will be viewable through sophisticated microscopes developed for the event.

Time trials will determine which nanocar is the fastest, though there may be head-to-head races with up to four cars on the track at once, according to organizers.

A nanocar is a single-molecule vehicle of 100 or so atoms that incorporates a chassis, axles and freely rotating wheels. Each of the entries will be propelled across a custom-built gold surface by an electric current supplied by the tip of a scanning electron microscope. The track will be cold at 5 kelvins (minus 450 degrees Fahrenheit) and in a vacuum.

Rice’s entry will be a new model and the latest in a line that began when Tour and his team built the world’s first nanocar more than 10 years ago.

“It’s challenging because, first of all, we have to design a car that can be manipulated on that specific surface,” Tour said. “Then we have to figure out the driving techniques that are appropriate for that car. But we’ll be ready.”

Victor Garcia, a graduate student at Rice, is building what Tour called his group’s Model 1, which will be driven by members of Professor Leonhard Grill’s group at Graz. The labs are collaborating to optimize the design.

The races are being organized by the Center for Materials Elaboration and Structural Studies (CEMES) of the French National Center for Scientific Research (CNRS).

The race was first proposed in a 2013 ACS Nano paper by Christian Joachim, a senior researcher at CNRS, and Gwénaël Rapenne, a professor at Paul Sabatier University.

Joining Rice are teams from Ohio University; Dresden University of Technology; the National Institute for Materials Science, Tsukuba, Japan; and Paul Sabatier [Université Toulouse III-Paul Sabatier].

I believe there’s still time to register an entry (from the Molecule-car Race International page; Note: Links have been removed),

To register for the first edition of the molecule-car Grand Prix in Toulouse, a team has to deliver to the organizers well before March 2016:

  • The detail of its institution (Academic, public, private)
  • The design of its molecule-vehicle including the delivery of the xyz file coordinates of the atomic structure of its molecule-car
  • The propulsion mode, preferably by tunneling inelastic effects
  • The evaporation conditions of the molecule-vehicles
  • If possible a first UHV-STM image of the molecule-vehicle
  • The name and nationality of the LT-UHV-STM driver

Those information are used by the organizers for selecting the teams and for organizing training sessions for the accepted teams in a way to optimize their molecule-car design and to learn the driving conditions on the LT-Nanoprobe instrument in Toulouse. Then, the organizers will deliver an official invitation letter for a given team to have the right to experiment on the Toulouse LT-Nanoprobe instrument with their own drivers. A detail training calendar will be determined starting September 2015.

The NanoCar Race website’s homepage notes that it will be possible to view the race in some fashion,

The NanoCar Race is a race where molecular machines compete on a nano-sized track. A NanoCar is a single molecule-car that has wheels and a chassis… and is propelled by a small electric shock.

The race will be invisible to the naked eye: a unique microscope based in Toulouse, France, will make it possible to watch the competition.

The NanoCar race is mostly a fantastic human and scientific adventure that will be broadcast worldwide. [emphasis mine]

Good luck to all the competitors.

Not the same old gold: there’s a brand new phase

A Dec. 7, 2015 news item on ScienceDaily announces a new phase for gold has been identified,

A new and stable phase of gold with different physical and optical properties from those of conventional gold has been synthesized by Agency for Science, Technology and Research (A*STAR) researchers [1], Singapore, and promises to be useful for a wide range of applications, including plasmonics and catalysis.

Many materials exist in a variety of crystal structures, known as phases or polymorphs. These different phases have the same chemical composition but different physical structures, which give rise to different properties. For example, two well-known polymorphs of carbon, graphite and diamond, arranged differently, have radically different physical properties, despite being the same element.

Gold has been used for many purposes throughout history, including jewelry, electronics and catalysis. Until now it has always been produced in one phase ― a face-centered cubic structure in which atoms are located at the corners and the center of each face of the constituent cubes.

Now, Lin Wu and colleagues at the Institute of the A*STAR Institute of High Performance Computing have modeled the optical and plasmonic properties of nanoscale ribbons of a new phase of gold — the 4H hexagonal phase (…) — produced and characterized by collaborators at other institutes in Singapore, China and the USA. The team synthesized nanoribbons of the new phase by simply heating the gold (III) chloride hydrate (HAuCl4) with a mixture of three organic solvents and then centrifuging and washing the product. This gave a high yield of about 60 per cent.

Here’s an image supplied by the researchers,

The atomic structure of the new phase of gold synthesized by A*STAR researchers. Reproduced from Ref. 1 and licensed under CC BY 4.0 © 2015 Z. Fan et al.

The atomic structure of the new phase of gold synthesized by A*STAR researchers. Reproduced from Ref. 1 and licensed under CC BY 4.0 © 2015 Z. Fan et al.

A Dec. 2, 2015 A*STAR news release, which originated the news item, provides more details,

The researchers also produced 4H hexagonal phases of the precious metals silver, platinum and palladium by growing them on top of the gold 4H hexagonal phase.

The cubic phase looks identical when viewed front on, from one side or from above. In contrast, the new 4H hexagonal phase lacks this cubic symmetry and hence varies more with direction — a property known as anisotropy. This lower symmetry gives it more directionally varying optical properties, which may make it useful for plasmonic applications. “Our finding is not only is of fundamental interest, but it also provides a new avenue for unconventional applications of plasmonic devices,” says Wu.

The team is keen to explore the potential of their new phase. “In the future, we hope to leverage the unconventional anisotropic properties of the new gold phase and design new devices with excellent performances not achievable with conventional face-centered-cubic gold,” says Wu. The synthesis method also gives rise to the potential for new strategies for controlling the crystalline phase of nanomaterials made from the noble metals.

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

Stabilization of 4H hexagonal phase in gold nanoribbons by Zhanxi Fan, Michel Bosman, Xiao Huang, Ding Huang, Yi Yu, Khuong P. Ong, Yuriy A. Akimov, Lin Wu, Bing Li, Jumiati Wu, Ying Huang, Qing Liu, Ching Eng Png, Chee Lip Gan, Peidong Yang & Hua Zhang. Nature Communications 6, Article number: 7684 doi:10.1038/ncomms8684 Published 28 July 2015

This is an open access paper.

Hydro-Québec, lithium-ion batteries, and silicate-based nanoboxes

Hydro-Québec (Canada) is making a bit of a splash these days (this is the third mention within less than a week) on my blog, if nowhere else. The latest development was announced in a Feb. 24, 2015 news item on Nanowerk (Note: A link has been removed),

Researchers from Singapore’s Institute of Bioengineering and Nanotechnology (IBN) of A*STAR and Quebec’s IREQ (Hydro-Québec’s research institute) have synthesized silicate-based nanoboxes that could more than double the energy capacity of lithium-ion batteries as compared to conventional phosphate-based cathodes (“Synthesis of Phase-Pure Li2MnSiO4@C Porous Nanoboxes for High-Capacity Li-Ion Battery Cathodes”). This breakthrough could hold the key to longer-lasting rechargeable batteries for electric vehicles and mobile devices.

A Feb. 24, 2015 Hydro-Québec press release (also on Canadian News Wire), which originated the news item, describe the research and the relationship between the two institutions,

“IBN researchers have successfully achieved simultaneous control of the phase purity and nanostructure of Li2MnSiO4 for the first time,” said Professor Jackie Y. Ying, IBN Executive Director. “This novel synthetic approach would allow us to move closer to attaining the ultrahigh theoretical capacity of silicate-based cathodes for battery applications.”

“We are delighted to collaborate with IBN on this project. IBN’s expertise in synthetic chemistry and nanotechnology allows us to explore new synthetic approaches and nanostructure design to achieve complex materials that pave the way for breakthroughs in battery technology, especially regarding transportation electrification,” said Dr. Karim Zaghib, Director – Energy Storage and Conservation at Hydro-Québec.

Lithium-ion batteries are widely used to power many electronic devices, including smart phones, medical devices and electric vehicles. Their high energy density, excellent durability and lightness make them a popular choice for energy storage. Due to a growing demand for long-lasting, rechargeable lithium-ion batteries for various applications, significant efforts have been devoted to improving the capacity of these batteries. In particular, there is great interest in developing new compounds that may increase energy storage capacity, stability and lifespan compared to conventional lithium phosphate batteries.

The five-year research collaboration between IBN and Hydro-Québec was established in 2011. The researchers plan to further enhance their new cathode materials to create high-capacity lithium-ion batteries for commercialization.

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

Synthesis of phase-pure Li2MnSiO4@C porous nanoboxes for high-capacity Li-ion battery cathodes by Xian-Feng Yang, Jin-Hua Yang, Karim Zaghib, Michel L. Trudeau, and Jackie Y. Ying. Nano Energy Volume 12, March 2015, Pages 305–313 doi:10.1016/j.nanoen.2014.12.021

This paper is behind a paywall.

Here are my two most recent mentions of Hydro-Québec and lithium-ion batteries (both Grafoid and NanoXplore have deals with Hydro-Québec),

Investment in graphene (Grafoid), the Canadian government, and a 2015 federal election (Feb. 23, 2015)

NanoXplore: graphene and graphite in Québec (Canada) (Feb. 20, 2015)

Gold nanoparticles as catalysts for clear water and hydrogen production

The research was published online May 2014 and in a July 2014 print version,  which seems a long time ago now but there’s a renewed interest in attracting attention for this work. A Dec. 17, 2014 news item on phys.org describes this proposed water purification technology from Singapore’s A*STAR (Agency for Science Technology and Research), Note: Links have been removed,

A new catalyst could have dramatic environmental benefits if it can live up to its potential, suggests research from Singapore. A*STAR researchers have produced a catalyst with gold-nanoparticle antennas that can improve water quality in daylight and also generate hydrogen as a green energy source.

This water purification technology was developed by He-Kuan Luo, Andy Hor and colleagues from the A*STAR Institute of Materials Research and Engineering (IMRE). “Any innovative and benign technology that can remove or destroy organic pollutants from water under ambient conditions is highly welcome,” explains Hor, who is executive director of the IMRE and also affiliated with the National University of Singapore.

A Dec. 17, 2014 A*STAR research highlight, which originated the news item, describes the photocatalytic process the research team developed and tested,

Photocatalytic materials harness sunlight to create electrical charges, which provide the energy needed to drive chemical reactions in molecules attached to the catalyst’s surface. In addition to decomposing harmful molecules in water, photocatalysts are used to split water into its components of oxygen and hydrogen; hydrogen can then be employed as a green energy source.

Hor and his team set out to improve an existing catalyst. Oxygen-based compounds such as strontium titanate (SrTiO3) look promising, as they are robust and stable materials and are suitable for use in water. One of the team’s innovations was to enhance its catalytic activity by adding small quantities of the metal lanthanum, which provides additional usable electrical charges.

Catalysts also need to capture a sufficient amount of sunlight to catalyze chemical reactions. So to enable the photocatalyst to harvest more light, the scientists attached gold nanoparticles to the lanthanum-doped SrTiO3 microspheres (see image). These gold nanoparticles are enriched with electrons and hence act as antennas, concentrating light to accelerate the catalytic reaction.

The porous structure of the microspheres results in a large surface area, as it provides more binding space for organic molecules to dock to. A single gram of the material has a surface area of about 100 square meters. “The large surface area plays a critical role in achieving a good photocatalytic activity,” comments Luo.

To demonstrate the efficiency of these catalysts, the researchers studied how they decomposed the dye rhodamine B in water. Within four hours of exposure to visible light 92 per cent of the dye was gone, which is much faster than conventional catalysts that lack gold nanoparticles.

These microparticles can also be used for water splitting, says Luo. The team showed that the microparticles with gold nanoparticles performed better in water-splitting experiments than those without, further highlighting the versatility and effectiveness of these microspheres.

The researchers have provided an illustration of the process,

Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water. © 2014 A*STAR Institute of Materials Research and Engineering

Improved photocatalyst microparticles containing gold nanoparticles can be used to purify water.
© 2014 A*STAR Institute of Materials Research and Engineering

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

Novel Au/La-SrTiO3 microspheres: Superimposed Effect of Gold Nanoparticles and Lanthanum Doping in Photocatalysis by Guannan Wang, Pei Wang, Dr. He-Kuan Luo, and Prof. T. S. Andy Hor. Chemistry – An Asian Journal Volume 9, Issue 7, pages 1854–1859, July 2014. Article first published online: 9 MAY 2014 DOI: 10.1002/asia.201402007

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

A rose by any other name: water pinning nanostructures and wettability

There are two items about rose petals as bioinspiration for research in this posting. The first being the most recent research where scientists in Singapore have made an ultrathin film modeled on rose petals. From an Aug. 13, 2014 news item on Nanowerk (Note: A link has been removed),

A*STAR [based in Singapore] researchers have used nanoimprinting methods to make patterned polymeric films with surface topography inspired by that of a rose petal, producing a range of transparent films with high water pinning forces (“Bioinspired Ultrahigh Water Pinning Nanostructures”).

An Aug. 13, 2014 A*STAR news highlight, which originated the news item, describes the nature of the research,

A surface to which a water droplet adheres, even when it is turned upside down, is described as having strong water pinning characteristics. A rose petal and a lotus leaf are both superhydrophobic, yet dissimilarities in their water pinning properties cause a water droplet to stick to a rose petal but roll off a lotus leaf. The two leaf types differ in their micro- and nanoscale surface topography and it is these topographical details that alter the water pinning force. The rose petal has almost uniformly distributed, conical-shaped microscale protrusions with nanoscale folds on these protrusions, while the lotus leaf has randomly distributed microscale protrusions.

The imprinted surfaces developed by Jaslyn Law and colleagues at the A*STAR Institute of Materials Research and Engineering and the Singapore University of Technology and Design have uniformly distributed patterns of nanoscale protrusions that are either conical or parabolic in shape. The researchers found that the water pinning forces on these continuously patterned surfaces were much greater than on non-patterned surfaces and surfaces composed of isolated nanopillared structures or nanoscale gratings. They could then achieve high water pinning forces by patterning the nanoprotrusions onto polymeric films with a range of different non-patterned hydrophobicities, including polycarbonate, poly(methyl methacrylate) and polydimethylsiloxane (see image).

“Other methods that recreate the water pinning effect have used actual rose petals as the mold, but unless special care is taken, there are likely to be defects and inconsistencies in the recreated pattern,” says co-author Andrew Ng. “While bottom-up approaches for making patterns — for example, laser ablation, liquid flame spray or chemical vapor deposition — are more consistent, these methods are limited in the types of patterns that can be used and the scale at which a substrate can be patterned.”

In contrast, nanoimprinting methods are capable of fabricating versatile and large-scale surfaces, and can be combined with roll-to-roll techniques, hence potentially enabling more commercial applications.

The patterned polycarbonate surfaces were also shown to reduce the ‘coffee-ring’ effect: the unevenly deposited film left behind upon the evaporation of a solute-laden droplet. This mitigation of the coffee-ring effect may assist microfluidic technologies and, more generally, the patterned surfaces could be used in arid regions for dew collection or in anti-drip applications such as in greenhouses.

The study which was published online in Dec. 2013, was featured in a Jan. 22, 2014 article by Katherine Bourzac for C&EN (Chemistry and Engineering News),

In the early morning, dew clings to rose petals; when the sun rises, the dewdrops act like tiny lenses, making diffraction patterns that attract pollinating insects, says Jaslyn Bee Khuan Law, a materials scientist at the Agency for Science, Technology, and Research (A*STAR), in Singapore. A drop of water will cling to a rose petal even when it’s tilted or held upside down. The petals can hold onto these droplets because their surfaces consist of closely packed conical structures a few micrometers across. These microscale surface patterns tweak the surface tension of the water droplets, causing them to cling to the petals.

But none of these fabrication methods are amenable to large-scale, low-cost manufacturing, preventing commercialization of the water-clinging surfaces. So Law turned to a specialty of her lab: nanoimprint lithography. This printing method utilizes metal or silicon drums molded with nanoscale features on their surfaces. When the molds are heated and pressed against sheets of plastic, the plastic is embossed with the nanoscale pattern. This roll-to-roll printing process resembles the way newspapers are printed. It’s capable of producing large-area films in a short amount of time.

Water droplets easily slid off plastic films patterned with simple nanoscale gratings; isolated nanoscale pillars hung onto water slightly better. But the films with the best properties consisted of tightly packed cones about 300 nm tall. Plastic patterned with these structures could hold onto water droplets as massive as 69 mg. The team could print a 110- by 65-mm sheet of this plastic film at a speed of 10 m per minute. Currently, the dimensions of the films are limited by the size of the premade molds, Law says.

While the Singapore group has made good progress on manufacturing these materials, very basic, vexing questions about how water clings to these surfaces remain, Hayes says. For example, very small changes in the surface’s roughness can switch it from water-pinning to super hydrophobic, and researchers don’t have a detailed understanding of why.

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

Bioinspired Ultrahigh Water Pinning Nanostructures by Jaslyn Bee Khuan Law, Andrew Ming Hua Ng, Ai Yu He, and Hong Yee Low. Langmuir, 2014, 30 (1), pp 325–331 DOI: 10.1021/la4034996 Publication Date (Web): December 20, 2013
Copyright © 2013 American Chemical Society

This paper appears to be open access (I was able to access it by clicking on the HTML option).

Finally, here’s an image supplied by the A*Star researchers to illustrate their work,

[downloaded from http://pubs.acs.org/doi/full/10.1021/la4034996]

[downloaded from http://pubs.acs.org/doi/full/10.1021/la4034996]

This second rose petal item comes from Australia and dates from Fall 2013. From a Sept. 18, 2013 news item on ScienceDaily,

A new nanostructured material with applications that could include reducing condensation in airplane cabins and enabling certain medical tests without the need for high tech laboratories has been developed by researchers at the University of Sydney [Australia].

“The newly discovered material uses raspberry particles — so-called because of their appearance — which can trap tiny water droplets and prevent them from rolling off surfaces, even when that surface is turned upside down,” said Dr Andrew Telford from the University’s School of Chemistry and lead author of the research recently published in the journal, Chemistry of Materials.

The ability to immobilise [pin] very small droplets on a surface is, according to Dr Telford, a significant achievement with innumerable potential applications.

A Sept. 17, 2013 University of Sydney news release, which originated the news item, provides more insight into the research where the scientists have focused on ‘raspberry particles’ which could also be described as the ‘conical structures’ mentioned in the A*STAR work to achieve what appear to be similar ends,

Raspberry particles mimic the surface structure of some rose petals.

“Water droplets bead up in a spherical shape on top of rose petals,” Dr Telford said. “This is a sign the flower is highly water repellent.”

The reasons for this are complex and largely due to the special structure of the rose petal’s surface. The research team replicated the rose petal by assembling raspberry particles in the lab using spherical micro- and nanoparticles.

The result is that water droplets bead up when placed on films of the raspberry particles and they’re not able to drip down from it, even when turned upside down.

“Raspberry particle films can be described as sticky tape for water droplets,” Dr Telford said.

This could be useful in preventing condensation issues in airplane cabins. It could also help rapidly process simple medical tests on free-standing droplets, with the potential for very high turnover of tests with inexpensive equipment and in remote areas.

Other exciting applications are under study: if we use this nanotechnology to control how a surface is structured we can influence how it will interact with water.

“This means we will be able to design a surface that does whatever you need it to do.

“We could also design a surface that stays dry forever, never needs cleaning or able to repel bacteria or even prevent mould and fungi growth.

“We could then tweak the same structure by changing its composition so it forces water to spread very quickly.

“This could be used on quick-dry walls and roofs which would also help to cool down houses.

“This can only be achieved with a very clear understanding of the science behind the chemical properties and construction of the surface,” he said.

The discovery is also potentially viable commercially.

“Our team’s discovery is the first that allows for the preparation of raspberry particles on an industrial scale and we are now in a position where we can prepare large quantities of these particles without the need to build special plants or equipment,” Dr Telford said.

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

Mimicking the Wettability of the Rose Petal using Self-assembly of Waterborne Polymer Particles by A. M. Telford, B. S. Hawkett, C. Such, and C. Neto. Chem. Mater., 2013, 25 (17), pp 3472–3479 DOI: 10.1021/cm4016386 Publication Date (Web): July 23, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.