A misunderstanding leads to method for making nanowells

A safe, simple, and cheap method of creating perfectly etched micron and smaller size wells in a variety of substrates has been developed by researchers in Penn State's Department of Chemical Engineering. Similar patterned surfaces are currently made using complex and expensive photolithography methods and etch processes under clean room conditions and used in the fabrication of many optical, electrical, and mechanical devices.

The nanowell discovery was made in the labs of Darrell Velegol and Seong Kim by Velegol's graduate student, Neetu Chaturvedi, and Kim's graduate student, Erik Hsiao. An article detailing their research, "Maskless Fabrication of Nanowells Using Chemically Reactive Colloids," appeared in the online edition of the journal Nano Letters in January 2011. In collaboration with Chaturvedi, Hsiao was working on a project to adhere polystyrene on a silicon wafer to create nanostructures with known dimensions. When Hsiao asked her to heat one of his samples, a miscommunication led her to heat the polystyrene and silicon wafer at low temperature in water in the autoclave normally used for biological samples rather than in the vacuum furnace. When they looked at the samples under the atomic force microscope (AFM), they noticed holes had formed beneath the polystyrene particles. Further examination under the scanning electron microscope (SEM) showed them perfectly etched, pyramidal shaped holes in the substrate below the places where the amidine-functionalized polystyrene latex colloid particles had adhered to the silicon dioxide on the surface of the silicon wafer.

"We saw three holes in the sample at the first AFM imaging and didn't know what it meant since we expected pancake-like polymer patches on the sample," said Hsiao. They took the sample to their advisers, who were both surprised by the etched wafer. By going over the steps the students had taken, the researchers realized that the wells were produced when the water hydrolized the amidine group in the particle, and through a series of chemical reactions, created a hydroxide ion that etched the well into the silicon wafer. The holes were uniform and their size and depth were totally dependent on the size of the original polystyrene particle, although the orientation of the silicon crystal affected the shape of the wells. In one orientation (100), the wells were perfect four-sided inverted pyramids. In the other orientation (111), the wells were perfect hexagons. The four researchers called them nanowells, because the bottom dimension of the wells was only a couple of nanometers across. They soon realized that they had discovered a new maskless method for creating structures in silicon without the elaborate steps normally required in the clean room.

"We're delivering hydroxide ions directly to where we want to etch," Velegol explained. "It's much safer and cheaper than electron beam and X-ray lithography. It's so safe that you could practically eat these particles without any harm."

"We think this is a quite general discovery," Kim added. "It's a way to deliver chemistry locally rather than in bulk. Many metals, ceramics, and other materials can be etched with this technique."

Another potential benefit of the discovery is the ability to create patterns on curved surfaces, something that is difficult to do with conventional photolithography. Since the particles are suspended in water, they can adhere to the surface of any shape and space themselves evenly over the surface. The researchers are just beginning to come up with intriguing ideas for how to use the simple technique.

Many breakthroughs come from accidents, Velegol remarked, because once something is known, people work on it very rapidly until they have filled in all the pieces and there is less to discover. Accidents are out of the pattern. "It's one of those situations like Pasteur said where chance favors the prepared mind. We would never even have thought to try this kind of chemistry. But Neetu had been working with these colloids for several years, and Erik had experience with the AFM, so they were well prepared to take advantage of the accident," Velegol concluded.

This work was supported by the National Science Foundation (Grant Nos. IDR-1014673 and CMMI-1000021).

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Penn State Materials Research Institute, via Newswise.

Journal Reference:

Neetu Chaturvedi, Erik Hsiao, Darrell Velegol, Seong H. Kim. Maskless Fabrication of Nanowells Using Chemically Reactive Colloids. Nano Letters, 2011; 11 (2): 672 DOI: 10.1021/nl1037984

New shapes of microcompartments: Molecular shells that encapsulate cellular components

In nature and engineering, microcompartments -- molecular shells made of proteins that can encapsulate cellular components -- provide a tiny home for important reactions. In bacterial organelles, for example, microcompartments known as carboxysomes trap carbon dioxide and convert it into sugar as an energy source.

These shells naturally buckle into a specialized 20-sided shape called an icosahedron. But now researchers at Northwestern University's McCormick School of Engineering and Applied Science have discovered and explored new shapes of microcompartment shells. Understanding just how these shells form could lead to designed microreactors that mimic the functions of these cell containers or deliver therapeutic materials to cells at specific targeted locations.

The research, led by Monica Olvera de la Cruz, professor of materials science and chemical and biological engineering and chemistry, with Graziano Vernizzi, research assistant professor, and research associate Rastko Sknepnek, was recently published in the Proceedings of the National Academy of Sciences.

Olvera de la Cruz and her group knew how shells made up of just one structural unit worked -- their elasticity and rigidity cause them to naturally buckle into icosahedra. But they began considering how to create heterogenous shells by using more than one component. Using physical concepts, mathematical analysis, and running simulations, they formulated a new model for the spontaneous faceting of shells.

"The question was: if a shell is made up of components that have different rigidities or different mechanical properties, what would be the shape it takes?" Olvera de la Cruz said.

The only faceted shape previously known for molecular closed shells, such as viruses and fullerenes, was the icosahedron. But Olvera de la Cruz and her colleagues discovered that when a shell is made up of two components with different elasticities, they buckle into many different shapes, including dodecahedra (12 sides) and octahedra (8 sides) and irregular polyhedra, which surfaces are "decorated" by the natural segregation of components to yield the lowest energy conformation.

Some of these shapes had been seen in nature before -- sometimes in the bacterial organelles' carboxysomes -- but they were just called "quasi-icosahedra" because nobody knew how to characterize them and how they worked. Armed with their model, however, engineers could now potentially design shells to perform specific tasks.

"If you just want to pack something into a shell, you use a sphere," she said. "But if you want to create a shell that has intelligence and can fit somewhere perfectly because it is decorated with the right proteins, then you can use different shapes."

These designed shells could act as containers or microreactors within the body. "It's a very efficient way to deliver something," she said.

Next the group hopes to determine how general their model is and continue researching how different shapes are made.

"I think it can open a new field of research," Olvera de la Cruz said.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Northwestern University, via EurekAlert!, a service of AAAS.

Journal Reference:

G. Vernizzi, R. Sknepnek, M. Olvera de la Cruz. Platonic and Archimedean geometries in multicomponent elastic membranes. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1012872108

3-D nanoparticle in atomic resolution

In chemical terms, nanoparticles have different properties from their "big brothers and sisters:" They have a large surface area in relation to their tiny mass and at the same time a small number of atoms. This can produce quantum effects that lead to altered material properties. Ceramics made of nanomaterials can suddenly become bendy, for instance, or a gold nugget is gold-coloured while a nanosliver of it is reddish.

New method developed

The chemical and physical properties of nanoparticles are determined by their exact three-dimensional morphology, atomic structure and especially their surface composition. In a study initiated by ETH Zurich scientist Marta Rossell and Empa researcher Rolf Erni, the 3D structure of individual nanoparticles has now successfully been determined on the atomic level. The new technique could help improve our understanding of the characteristic of nanoparticles, including their reactivity and toxicity.

Gentle imaging processing

For their electron-microscopic study, which was published recently in the journal Nature, Rossell and Erni prepared silver nanoparticles in an aluminium matrix. The matrix makes it easier to tilt the nanoparticles under the electron beam in different crystallographic orientations whilst protecting the particles from damage by the electron beam. The basic prerequisite for the study was a special electron microscope that reaches a maximum resolution of less than 50 picometres. By way of comparison: the diameter of an atom measures about one Angström, i.e. 100 picometres.

To protect the sample further, the electron microscope was set up in such a way as to also yield images at an atomic resolution with a lower accelerating voltage, namely 80 kilovolts. Normally, this kind of microscope -- of which there are only a few in the world -- works at 200 -- 300 kilovolts. The two scientists used a microscope at the Lawrence Berkeley National Laboratory in California for their experiments. The experimental data was complemented with additional electron-microscopic measurements carried out at Empa.

Sharper images

On the basis of these microscopic images, Sandra Van Aert from the University of Antwerp created models that "sharpened" the images and enabled them to be quantified: the refined images made it possible to count the individual silver atoms along different crystallographic directions.

For the three-dimensional reconstruction of the atomic arrangement in the nanoparticle, Rossell and Erni eventually enlisted the help of the tomography specialist Joost Batenburg from Amsterdam, who used the data to tomographically reconstruct the atomic structure of the nanoparticle based on a special mathematical algorithm. Only two images were sufficient to reconstruct the nanoparticle, which consists of 784 atoms. "Up until now, only the rough outlines of nanoparticles could be illustrated using many images from different perspectives," says Marta Rossell. Atomic structures, on the other hand, could only be simulated on the computer without an experimental basis.

"Applications for the method, such as characterising doped nanoparticles, are now on the cards," says Rolf Erni. For instance, the method could one day be used to determine which atom configurations become active on the surface of the nanoparticles if they have a toxic or catalytic effect. Rossell stresses that in principle the study can be applied to any type of nanoparticle. The prerequisite, however, is experimental data like that obtained in the study.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Swiss Federal Laboratories for Materials Science and Technology (EMPA). The original article was written by Simone Ulmer/ETH Life.

Journal Reference:

Sandra Van Aert, Kees J. Batenburg, Marta D. Rossell, Rolf Erni, Gustaaf Van Tendeloo. Three-dimensional atomic imaging of crystalline nanoparticles. Nature, 2011; 470 (7334): 374 DOI: 10.1038/nature09741

Clay-armored bubbles may have formed first protocells: Minerals could have played a key role in the origins of life

ScienceDaily (Feb. 7, 2011) — A team of applied physicists at Harvard's School of Engineering and Applied Sciences (SEAS), Princeton, and Brandeis have demonstrated the formation of semipermeable vesicles from inorganic clay.

The research, published online in the journal Soft Matter, shows that clay vesicles provide an ideal container for the compartmentalization of complex organic molecules.

The authors say the discovery opens the possibility that primitive cells might have formed inside inorganic clay microcompartments.

"A lot of work, dating back several decades, explores the role of air bubbles in concentrating molecules and nanoparticles to allow interesting chemistry to occur," says lead author Anand Bala Subramaniam, a doctoral candidate at SEAS.

"We have now provided a complete physical mechanism for the transition from a two-phase clay-air bubble system, which precludes any aqueous-phase chemistry, to a single aqueous-phase clay vesicle system," Subramaniam says, "creating a semipermeable vesicle from materials that are readily available in the environment."

"Clay-armored bubbles" form naturally when platelike particles of montmorillonite collect on the outer surface of air bubbles under water.

When the clay bubbles come into contact with simple organic liquids like ethanol and methanol, which have a lower surface tension than water, the liquid wets the overlapping plates. As the inner surface of the clay shell becomes wet, the disturbed air bubble inside dissolves.

The resulting clay vesicle is a strong, spherical shell that creates a physical boundary between the water inside and the water outside. The translucent, cell-like vesicles are robust enough to protect their contents in a dynamic, aquatic environment such as the ocean.

Microscopic pores in the vesicle walls create a semipermeable membrane that allows chemical building blocks to enter the "cell," while preventing larger structures from leaving.

Scientists have studied montmorillonite, an abundant clay, for hundreds of years, and the mineral is known to serve as a chemical catalyst, encouraging lipids to form membranes and single nucleotides to join into strands of RNA.

Because liposomes and RNA would have been essential precursors to primordial life, Subramaniam and his coauthors suggest that the pores in the clay vesicles could do double duty as both selective entry points and catalytic sites.

"The conclusion here is that small fatty acid molecules go in and self-assemble into larger structures, and then they can't come out," says principal investigator Howard A. Stone, the Dixon Professor in Mechanical and Aerospace Engineering at Princeton, and a former Harvard faculty member. "If there is a benefit to being protected in a clay vesicle, this is a natural way to favor and select for molecules that can self-organize."

Future research will explore the physical interactions between the platelike clay particles, and between the liquids and the clay. The researchers are also interested to see whether these clay vesicles can, indeed, be found in the natural environment today.

"Whether clay vesicles could have played a significant role in the origins of life is of course unknown," says Subramaniam, "but the fact that they are so robust, along with the well-known catalytic properties of clay, suggests that they may have had some part to play."

Subramaniam and Stone's coauthors include Jiandi Wan, of Princeton University, and Arvind Gopinath, of Brandeis University.

The research was funded by the Harvard Materials Research Science and Engineering Center and supported by the Harvard Center for Brain Science Imaging Facility.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Harvard University, via EurekAlert!, a service of AAAS.

Journal Reference:

Anand Bala Subramaniam, Jiandi Wan, Arvind Gopinath, Howard A. Stone. Semi-permeable vesicles composed of natural clay. Soft Matter, 2011; DOI: 10.1039/C0SM01354D

Cheap, clean ways to produce hydrogen for use in fuel cells? A dash of disorder yields a very efficient photocatalyst

A little disorder goes a long way, especially when it comes to harnessing the sun's energy. Scientists from the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) jumbled the atomic structure of the surface layer of titanium dioxide nanocrystals, creating a catalyst that is both long lasting and more efficient than all other materials in using the sun's energy to extract hydrogen from water.

Their photocatalyst, which accelerates light-driven chemical reactions, is the first to combine durability and record-breaking efficiency, making it a contender for use in several clean-energy technologies.

It could offer a pollution-free way to produce hydrogen for use as an energy carrier in fuel cells. Fuel cells have been eyed as an alternative to combustion engines in vehicles. Molecular hydrogen, however, exists naturally on Earth only in very low concentrations. It must be extracted from feedstocks such as natural gas or water, an energy-intensive process that is one of the barriers to the widespread implementation of the technology.

"We are trying to find better ways to generate hydrogen from water using sunshine," says Samuel Mao, a scientist in Berkeley Lab's Environmental Energy Technologies Division who led the research. "In this work, we introduced disorder in titanium dioxide nanocrystals, which greatly improves its light absorption ability and efficiency in producing hydrogen from water."

Mao is the corresponding author of a paper on this research that was published online Jan. 20, 2011 in Science Express with the title "Increasing Solar Absorption for Photocatalysis with Black, Hydrogenated Titanium Dioxide Nanocrystals." Co-authoring the paper with Mao are fellow Berkeley Lab researchers Xiaobo Chen, Lei Liu, and Peter Yu.

Mao and his research group started with nanocrystals of titanium dioxide, which is a semiconductor material that is used as a photocatalyst to accelerate chemical reactions, such as harnessing energy from the sun to supply electrons that split water into oxygen and hydrogen. Although durable, titanium dioxide isn't a very efficient photocatlayst. Scientists have worked to increase its efficiency by adding impurities and making other modifications.

The Berkeley Lab scientists tried a new approach. In addition to adding impurities, they engineered disorder into the ordinarily perfect atom-by-atom lattice structure of the surface layer of titanium dioxide nanocrystals. This disorder was introduced via hydrogenation.

The result is the first disorder-engineered nanocrystal. One transformation was obvious: the usually white titanium dioxide nanocrystals turned black, a sign that engineered disorder yielded infrared absorption.

The scientists also surmised disorder boosted the photocatalyst's performance. To find out if their hunch was correct, they immersed disorder-engineered nanocrystals in water and exposed them to simulated sunlight. They found that 24 percent of the sunlight absorbed by the photocatalyst was converted into hydrogen, a production rate that is about 100 times greater than the yields of most semiconductor photocatalysts.

In addition, their photocatalyst did not show any signs of degradation during a 22-day testing period, meaning it is potentially durable enough for real-world use.

Its landmark efficiency stems largely from the photocatalyst's ability to absorb infrared light, making it the first titanium dioxide photocatalyst to absorb light in this wavelength. It also absorbs visible and ultraviolet light. In contrast, most titanium dioxide photocatalysts only absorbs ultraviolet light, and those containing defects may absorb visible light. Ultraviolet light accounts for less than ten percent of solar energy.

"The more energy from the sun that can be absorbed by a photocatalyst, the more electrons can be supplied to a chemical reaction, which makes black titanium dioxide a very attractive material," says Mao, who is also an adjunct engineering professor in the University of California at Berkeley.

The team's intriguing experimental findings were further elucidated by theoretical physicists Peter Yu and Lei Liu, who explored how jumbling the latticework of atoms on the nanocrystal's surface via hydrogenation changes its electronic properties. Their calculations revealed that disorder, in the form of lattice defects and hydrogen, makes it possible for incoming photons to excite electrons, which then jump across a gap where no electron states can exist. Once across this gap, the electrons are free to energize the chemical reaction that splits water into hydrogen and oxygen.

"By introducing a specific kind of disorder, mid-gap electronic states are created accompanied by a reduced band gap," says Yu, who is also a professor in the University of California at Berkeley's Physics Department. "This makes it possible for the infrared part of the solar spectrum to be absorbed and contribute to the photocatalysis."

This research was supported by the Department of Energy's Office of Energy Efficiency and Renewable Energy. Transmission electron microscopy imaging used to study the nanocrystals at the atomic scale was performed at the National Center for Electron Microscopy, a national user facility located at Berkeley Lab.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

X. Chen, L. Liu, P. Y. Yu, S. S. Mao. Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals. Science, 2011; DOI: 10.1126/science.1200448