When single-walled carbon nanotubes are made, a mixture of both metallic and semiconducting nanotubes is produced. This is a problem for those trying to make electronic devices from nanotubes, who need pure samples of either semiconducting or metallic tubes (depending upon the application), not both. Now, researchers in the US and South Korea have a developed a new and simple technique that not only efficiently separates the two types of nanotube but also allows them to be patterned onto a substrate as thin films. These films could be used to make electronic devices with desirable properties, and could even replace silicon as the material of choice for integrated circuits.

Single-walled nanotubes are essentially rolled up sheets of graphite just one atom thick and can be metallic or semiconducting depending on the direction in which the sheet has been rolled. They have enormous potential as the building blocks in nanoscale electronics, and are often touted as being the perfect alternatives to silicon thanks to their tiny size and their ability to carry large currents. Metallic tubes could function as transparent conducting leads, while semiconducting tubes could make good nanoscale transistors.

Although researchers have already proposed several techniques to separate nanotubes, most of these have proved difficult to perform on an industrial scale. However, help may be at hand: recent experiments have shown that specific molecules tend to interact selectively with metallic or semiconducting tubes in solution. Now, new work, by Zhenan Bao of Stanford University and colleagues, builds on this work by using such molecules to create a special surface that interacts selectively with nanotubes (Science abstract).

—Jim

The challenge in treating most brain disorders is overcoming the difficulty of delivering therapeutic agents to specific regions of the brain by crossing the blood-brain barrier (BBB). This barrier — a tight seal of endothelial cells that lines the blood vessels in the brain — is a physiological checkpoint that selectively allows the entry of certain molecules from blood circulation into the brain. … while the BBB naturally evolved in order to protect the brain from invasion of various circulating toxins and other harmful molecules, it also serves as a major impediment towards the brain-specific delivery of various diagnostic/therapeutic molecules needed for combating various neuronal disorders.

To date, delivery of therapeutic molecules into the brain often involves highly invasive techniques (like drilling a hole in the skull). The utter scarcity of techniques for brain-specific delivery of therapeutic molecules using non-invasive approaches has led researchers to increasingly explore the vast potential of nanotechnology toward the diagnosis and treatment of diseases/disorders incurable with present techniques.

Scientists have now reported a nanoparticle-based platform which ‘tricks’ the BBB into allowing the entry of the nanoparticle into the brain, using an approach that draws parallel to the ‘trojan horse’ concept. Certain proteins and peptides, such as the iron-transporting protein transferrin, are allowed free access across the intact BBB as they function as carriers of essential nutrients into the brain. By linking transferrin with rod-shaped semiconductor nanocrystals (quantum rods) — an up and coming diagnostic agent which can also multitask as carriers of therapeutic molecules — it was found that the transferrin helps the linked quantum rods to ’sneak’ across the BBB into the brain. This finding can have significant potential implications towards the development of brain-directed nanoparticle based diagnostic and therapeutic agents using minimally invasive procedures.

The research was published in the journal Bioconjugate Chemistry (abstract).
—Jim

Carbon nanotubes are the crucial chemical ingredient that could make artificial photosynthesis possible, say a team of Chinese researchers. The team has found that nanotubes mimic an important step in photosynthesis that chemists have been unable to copy until now.

Artificial photosynthesis has the potential to efficiently produce hydrogen that could be used as a clean fuel for vehicles. It could also be used to mop up carbon dioxide from the atmosphere.

Photosynthetic organisms use the energy from light to break down water into oxygen and hydrogen. The hydrogen then reacts with carbon dioxide to help synthesise carbohydrates, the molecules organisms use to store energy.

Chemists have long tried in vain to reproduce the process, but one key step in particular has proven impossible to copy.

Visible photons can only contribute a limited amount of energy towards a chemical reaction. This energy is absorbed by electrons involved in the reaction.

Reactions that require more energy, such as the synthesis of carbohydrates, can only proceed when several energised electrons are available to contribute. For that reason, chemists say the photosynthesis falls into a class of reactions known as multiple electron systems.

But nobody has succeeded in making artificial multiple electron systems that could provide the necessary energy for artificial photosynthesis.

…Now, a team led by Xian-Fu Zhang at the Hebei Normal University of Science and Technology in Qinhuangdao, China, has found that single-walled carbon nanotubes could act as the chemical heart of a multiple electron system.

The research was published in the journal ChemPhysChem (citation).
—Jim

For example, researchers at Rice University have been working on the use of nanoparticles to absorb arsenic from drinking water supplies.

Nanoscale iron oxide absorbs arsenic effi ciently, but in many countries implementing the process is either too expensive or technically impossible. The Rice researchers realized they could use magnetic filtration for nanosorbents, which, at the small-size range, could pull out unsafe particles with a handheld magnet…

The “recipe” to make nanoscale magnetite can be posted on the Web, allowing the technique to be distributed to many villages and used by any individual with modest means in a regular kitchen setting.

This solution might be called “open-source nanotechnology”…

So, the recipe “can” be posted on the web, but has this happened? Unclear. —Christine

Japanese scientists have made a micro-sized sewing machine to sew long threads of DNA into shape. The work published in the Royal Society of Chemistry journal Lab on a Chip [abstract] demonstrates a unique way to manipulate delicate DNA chains without breaking them.

Scientists can diagnose genetic disorders such as Down’s syndrome by using gene markers, or “probes”, which bind to only highly similar chains of DNA. Once bound, the probe’s location can be easily detected by fluorescence, and this gives information about the gene problem.

Detecting these probes is often a slow and difficult process, however, as the chains become tightly coiled. The new method presented by Kyohei Terao from Kyoto University, and colleagues from The University of Tokyo, uses micron-sized hooks controlled by lasers to catch and straighten a DNA strand with excellent precision and care.

“When a DNA molecule is manipulated and straightened by microhooks and bobbins, the gene location can be determined easily with high-spatial resolution,” says Terao.

The team use optical tweezers — tightly focused laser beams — to control the Z-shaped micro hook and pick up a single DNA “thread”. The hook is barbed like an arrow, so the thread can’t escape. When caught on the hook, the DNA can be accurately moved around by refocusing the lasers to new positions.

…It is “an excellent idea to fabricate unique microtools that enables us to manipulate a single giant DNA molecule”, says Yoshinobu Baba, who researches biologically useful microdevices at Nagoya University, Japan. The technology will also be useful for a number of other applications including DNA sequencing and molecular electronics, he adds.

—Jim

Researchers from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University have developed a new instrument that allows them to control the size of nanoclusters — groups of 10 to 100 atoms — with atomic precision. They created a model nanocatalyst of molybdenum sulfide, the first step in developing the next generation of materials to be used in hydrodesulfurization, a process that removes sulfur from natural gas and petroleum products to reduce pollution.

As reported in the July 9, 2008 online edition of the Journal of Physical Chemistry C [abstract], the scientists made size-selected molybdenum sulfide nanoclusters as gaseous ions, and then gently deposited the clusters on a gold surface. The nanoclusters interact weakly with the gold support and therefore remain intact.

“With this new instrument, we can control how many and what type of atoms are in a nanocluster,” said Brookhaven chemist Michael White, the principal author of the paper. “This knowledge enables us to make nanoclusters with predetermined size, structure and chemical composition, all which are important for the design of new catalysts.”

—Jim

The [National Cancer Institute] poured money into cancer nanotech training and research. At the time, experiments were largely restricted to animals; as of today, at least 48 clinical trials are ongoing, many already in Phase II.

…”The field has been quietly progressing,” said David Cheresh, a University of California, San Diego pathologist … “What happened is that the National Cancer Institute supported this area. They assembled teams at various universities, including my own. That money directly allowed us to do this work [see below].”

Such basic research, said Cheresh, “is not something that industry would necessarily do. They’re not going to support the kind of research that the government would for bringing this to fruition. But they’ll capitalize on the discoveries we make. Those will be taken into the private sector, because we do discovery but aren’t in a position to do a scale-up and the pre-clinical studies. That has to come from the private sector.”

One very recent example of the potential of nanotechnology for cancer therapy is the topic of another article by Keim. In experiments in mice, chemotherapy drugs encapsulated in nanoparticles targeted to the blood vessels that supply nutrients to tumor cells prevented the usually fatal spread of the cancer to additional sites. From “Drug-Infused Nanoparticles Stop Cancer From Spreading“:

By using tumor-targeting nanoparticles filled with chemotherapy drugs, scientists kept kidney and pancreas cancers from spreading through the bodies of mice.

In an experiment described today in the Proceedings of the National Academy of Sciences [abstract], researchers led by University of California, San Diego pathologist David Cheresh designed nanoparticles that selectively attached to a protein found on the surface of blood vessels that supply tumors with nutrients and oxygen.

The particles were loaded with doxorubicin, an effective but highly toxic anti-cancer drug with side effects ranging from white cell destruction to fatal heart disease. By targeting blood vessel cells, the researchers needed just one-fifteenth the amount used in a traditional, system-flooding dose.

…Such findings aren’t unique in the fast-growing field of cancer nanotech, but the researchers found something new: Although their nanoparticles didn’t affect the original tumor, they did stop the cancers from spreading through the mice. That process is known as metastasis — a word synonymous, for anyone who has experience with cancer, with doom.

…”Those trials have begun or are in the process of being finalized,” [Cheresh] said. “The day isn’t too far off.”

A press release from the University of California - San Diego, via AAAS EurekAlert, provides the additional information that the nanoparticles used were “of 100 nanometers [diameter], made of various lipid-based polymers”.

Additional coverage of this research in Discover magazine elicited a comment from someone presumably associated with the drug delivery company pSivida about a nanostructured silicon product for pancreatic cancer that is already in phase IIb clinical trials in humans.

There is also another nano-structured product that is in development for pancreatic cancer called BrachySil. This is nano-structured silicon, doped with P³² that is injected directly into the pancreas. On July 7 it was announced that a Phase IIb clinical trial in humans started in the UK at Guy’s and St. Thomas’ NHS Foundation Trust in London and University Hospital in Birmingham. In the Phase IIa trials completed last year (and the data presented at the ASCO-GI meeting in January) BrachySil in combination with standard chemotherapy (gemcitabine) was well tolerated with no clinical significant adverse events related to the device. Data showed disease control in 82% of patients and an overall median survival of 309 days.

This research from UC San Diego is the second example we’ve seen in less than two weeks of using nanoparticles to enable an otherwise-too-toxic drug to attack the blood vessels supporting a cancer (see Nanodot July 3).
—Jim

Multiwalled carbon nanotubes (MWCNTs) grown in pores on a titanium (Ti) surface are ideal for detecting bone growth, according to Thomas Webster and his team at Brown University, US [Nanotechnology abstract]. By adding the biosensing structure to the surface of orthopedic implants, the inventors hope to monitor the success of procedures such as hip replacements in situ.

Poor adhesion to the surrounding bone is the most common cause of hip replacement failure. Currently, the diagnosis of new bone growth can be problematic as today’s imaging techniques each have their own limitations and difficulties — something that Webster and his colleagues hope to overcome.

“The idea is that our sensor will communicate the status of the surrounding tissue via radio frequencies to a handheld device,” Webster told nanotechweb.org. “In fact, we’ve taken things a step further and coated our sensor with a drug-containing polymer layer that can be degraded to release bone building agents on demand.”

…Next, the team plans to begin animal studies. “It’s a big and important jump to determine if the sensors will work in an animal,” said Webster. “We’ll be using rats and analyzing whether new bone growth can be measured and then controlled.”

—Jim

Chemists in Japan report development of the world’s first DNA molecule made almost entirely of artificial parts. The finding could lead to improvements in gene therapy, futuristic nano-sized computers, and other high-tech advances, they say.

In the new study, Masahiko Inouye and colleagues point out that scientists have tried for years to develop artificial versions of DNA in order to extend its amazing information storage capabilities.

As the genetic blueprint of all life forms, DNA uses the same set of four basic building blocks, known as bases, to code for a variety of proteins used in cell functioning and development. Until now, scientists have only been able to craft DNA molecules with one or a few artificial parts, including certain bases.

The researchers used high-tech DNA synthesis equipment to stitch together four entirely new, artificial bases inside the sugar-based framework of a DNA molecule. This resulted in unusually stable, double-stranded structures resembling natural DNA.

Like natural DNA, the new structures were right-handed and some easily formed triple-stranded structures. The unique chemistry of these structures and their high stability offer unprecedented possibilities for developing new biotech materials and applications, the researchers say.

The research was published in Journal of the American Chemical Society [abstract].
—Jim

Molecular transport across cellular membranes is essential to many of life’s processes, for example electrical signaling in nerves, muscles and synapses.

In biological systems, the membranes often contain a slippery inner surface with selective filter regions made up of specialized protein channels of sub-nanometer size. These pores regulate cellular traffic, allowing some of the smallest molecules in the world to traverse the membrane extremely quickly, while at the same time rejecting other small molecules and ions.

Researchers at Lawrence Livermore National Laboratory are mimicking that process with manmade carbon nanotube membranes, which have pores that are 100,000 times smaller than a human hair, and were able to determine the rejection mechanism within the pores.

“Hydrophobic, narrow diameter carbon nanotubes can provide a simplified model of membrane channels by reproducing these critical features in a simpler and more robust platform,” said Olgica Bakajin, who led the LLNL team whose study appeared in the June 6 online edition of the journal Proceedings of the National Academy of Sciences [abstract].

In the initial discovery, reported in the May 19, 2006 issue of the journal Science [abstract], the LLNL team found that water molecules in a carbon nanotube move fast and do not stick to the nanotube’s super smooth surface, much like water moves through biological channels. The water molecules travel in chains — because they interact with each other strongly via hydrogen bonds.

…One of the most promising applications for carbon nanotube membranes is sea water desalination. These membranes will some day be able to replace conventional membranes and greatly reduce energy use for desalination.

In the recent study, the researchers wanted to find out if the membranes with 1.6 nanometer (nm) pores reject ions that make up common salts. In fact, the pores did reject the ions and the team was able to understand the rejection mechanism.

“Our study showed that pores with a diameter of 1.6nm on the average, the salts get rejected due to the charge at the ends of the carbon nanotubes,” said Francesco Fornasiero, an LLNL postdoctoral researcher, team member and the study’s first author

Fast flow through carbon nanotube pores makes nanotube membranes more permeable than other membranes with the same pore sizes. Yet, just like conventional membranes, nanotube membranes exclude ions and other particles due to a combination of small pore size and pore charge effects.

This press release includes an animation comparing movement of water molecules through an ordinary rough pipe and through a carbon nanotube. A second LLNL press release (via PhysOrg.com) announced a new tool to better understand how water is structured as it moves through the carbon nanotubes “LLNL researchers peer into water in carbon nanotubes“:

Researchers have identified a signature for water inside single-walled carbon nanotubes, helping them understand how water is structured and how it moves within these tiny channels.

This is the first time researchers were able to get a snapshot of the water inside the carbon nanotubes.

…As described in an article appearing in the July edition of Nano Letters [abstract], [LLNL and University of North Carolina researchers] used a technique called Nuclear Magnetic Resonance (NMR) to get a glimpse of the water confined inside one-nanometer diameter SWCNTs.

…Earlier Livermore studies have suggested that carbon nanotubes may be used for desalination and demineralization because of their small pore size and enhanced flow properties. Conventional desalination membranes are typically much less permeable and require large pressures, entailing high energy costs.

However, these more permeable nanotube membranes could reduce the energy costs of desalination significantly.

While the technology offers great promise, there still are important unanswered scientific questions.

“There have been many predictions about how water behaves within carbon nanotubes,” said [Jason] Holt, the principal investigator of the project… “With experiments like these, we can directly probe that water and determine how close those predictions were.”

—Jim