Computational nanotech studies have shown that deliberate introduction of structural defects at specific sites in carbon nanotubes can guide electrons along specific paths, providing a way to fabricate complex electronic circuits from nanotubes. Although this research was theoretical, the researchers are quoted as saying focused electron beams could be used to create the defects where they would be needed to make complicated networks. An item on KurzweilAI.net led to this article on New Scientist Tech, written by Colin Barras. From “Flawed nanotubes could be perfect silicon replacement“:

The paradox of perfection — that flaws make things perfect — could be the key to designing nanoelectronic circuits from carbon nanotubes, according to US scientists.

They have discovered that a circuit of nanotubes can only guide a current if some of the tubes carry structural defects.

Individual carbon nanotubes are exceptionally good conductors because they are essentially a single carbon molecule. They can even outdo silicon at transmitting charge, which means nanotube circuits could boost computing speeds while reducing chip size…

But connecting nanotubes into such circuits is not easy, says Vincent Meunier at Oak Ridge National Laboratory in Tennessee. “The connections between individual nanotubes do not conduct well,” he says.

Instead of jumping easily into an adjacent nanotube, as they would between metal wires, electrons are more likely to bounce back when they reach the end of a tube, says Meunier. Electrons treat junctions between nanotubes as barriers — what scientists call “opaque”.

Now Meunier’s team has discovered that it could improve the transparency of the junctions by adding flaws to the connecting ends of nanotubes.

The carbon atoms within a nanotube are normally arranged in a hexagonal lattice similar to chicken wire. But the researchers used detailed simulations to see what happens when a few pentagons and heptagons are added to the otherwise regular structure.

The research was published in ACS Nano (abstract).
—Jim

Specially designed small RNA molecules have proven very effective in decreasing the expression of specific genes that cancer cells need to survive; however, getting these RNA molecules inside cancer cells in living animals is difficult. Using a promising nanotech approach to deliver the RNA molecules, a type of nanoparticle described as a neutral liposome was administered to mice bearing melanoma tumors and found to cause a significant decrease in tumor growth and in the number of metastatic tumor colonies. From the National Cancer Institute’s Alliance for Nanotechnology in Cancer “Nanoparticle Targets Melanoma With siRNA“:

Research has shown that a particular receptor for the blood protein thrombin is overexpressed by highly metastatic melanoma cells. When activated, this receptor triggers a wide range of biochemical changes that increase the metastatic activity of melanoma cells. To prevent those biochemical changes from occurring, a team of investigators at The University of Texas M.D. Anderson Cancer Center has developed a small interfering RNA (siRNA) agent designed to prevent melanoma cells from making this receptor, which is known as PAR-1, and used a lipid-based nanoparticle to deliver this agent to melanoma cells.

Reporting its findings in the journal Cancer Research [abstract], a team of investigators led by Menashe Bar-Eli, Ph.D., Anil Sood, M.D., and Gabriel Lopez-Berestein, M.D., describes its work in designing a neutral liposome nanoparticle to carry its siRNA agent to melanoma cells. Unlike viruses and positively charged liposomes that other investigators have used to deliver siRNA in animal models, the investigators reasoned that neutral liposomes would produce far few adverse reactions while escaping elimination from the body by macrophages.

Using this formulation to treat mice with melanoma, the researchers demonstrated that the nanoparticle was taken up by the tumors and that PAR-1 production dropped dramatically. As a result, twice-weekly injections of this formulation significantly inhibited melanoma growth and dramatically reduced the incidence of metastasis as measured by the number of metastatic lesions in the animals’ lungs. The researchers also noted that the PAR-1 siRNA was able to significantly reduce the amount of tumor-triggered angiogenesis in the treated animals.

—Jim

Previously unknown spectral properties of carbon nanotubes functionalized with DNA have been exploited to create nanotech sensors that can simultaneously detect several different substances, in real time, within living cells, to single molecule sensitivity. From “Nanotubes Track Cellular Toxins“, by Courtney Humphries, on the Technology Review web site:

Researchers at MIT have found that carbon nanotubes can serve as highly sensitive biological sensors for detecting single molecules in living cells in real time. The study, published online in Nature Nanotechnology [abstract], is the first demonstration that nanoscale sensors can be used to detect and image multiple types of molecules in cells at the same time, at a sensitivity that far exceeds that of fluorescent dyes, the standard tool for molecular imaging. The researchers used the sensors to detect substances that damage DNA, including certain cancer drugs and toxins. The sensors could eventually be used to monitor the effectiveness of chemotherapy drugs, track molecular interactions in cells, and test for low levels of toxins in the environment.

Michael Strano, an author of the paper and associate professor of chemical engineering at MIT, says that the work represents a leap forward in his goal to develop a nanoscale sensor for detecting molecules inside living cells. The tiny structures have recently shown promise for optical detection and imaging because they fluoresce when exposed to near-infrared light. This property is useful for biological imaging because near-infrared light can penetrate tissues more deeply than visible light can. And because cells do not fluoresce when exposed to near-infrared light, an near-infrared light-emitting sensor is easier to spot.

The sensors developed in Strano’s lab are single-wall carbon nanotubes wrapped with a small piece of DNA. When a target molecule binds to the DNA, it causes a change in the light emitted by the nanotube; the change in the light signal can be detected by a microscope. The researchers used the sensors to detect molecules that damage DNA, including chemotherapy drugs, free radicals, and hydrogen peroxide.

Strano says that the sensors offer several important advantages over fluorescent dyes. Not only can they detect and locate molecules, but different types of molecules will affect the properties of the emitted light differently. “When a molecule binds to it, it can change the wavelength or intensity of light that comes out,” Strano says. “Every toxin has a unique signature. So you’re not just detecting it; you can say something about what kind of toxin it is or what kind of drug it is.” In this study, the researchers used two different types of carbon nanotubes to distinguish between four different classes of toxins in living cells, but Strano believes that the sensors could be configured to detect many molecules within a sample or cell at once.

—Jim

How well prepared is the FDA to regulate nanotech products? Perhaps not very well, at least in the area of dietary supplements. The Project on Emerging Nanotechnologies will release a report on FDA regulation of nanotechnology-based dietary supplements at an event to be held and webcast on January 14, 2009. For more information and to register to attend the event (No RSVP is required to view the webcast) see “Nanotech and Your Daily Vitamins“:

Historically, the regulation of dietary supplements has been a significant challenge for the U.S. Food and Drug Administration (FDA), and the fact that some of these products are now being manufactured using nanotechnology creates an additional layer of complexity.

A new report to be released at this event will address the question: Is FDA equipped to meet the emerging regulatory challenge of dietary supplements that use engineered nanomaterials? The short answer is no.

The FDA’s ability to regulate the safety of dietary supplements using nanomaterials is severely limited by lack of information, lack of resources and the agency’s lack of statutory authority in certain critical areas, according to a new Project report: A Hard Pill to Swallow: Barriers to Effective FDA Regulation of Nanotechnology-Based Dietary Supplements.

—Jim

Molecular dynamics simulations show that electron tunneling through nanoscale rotary motors based on carbon nanotube shafts may enable nanotech motors to rotate more than a million times faster than their biological counterparts—the proton-driven molecular motors that propel some bacteria. From nanotechweb.org, written by Belle Dumé (requires free registration) “Tunnelling electrons could drive nanomotors“:

Researchers in the US have used computer simulations to show that nanometre-sized rotary motors could be driven by electron tunnelling. Although their design has not been confirmed experimentally, the team says that it is very similar to how naturally occurring biological motors work.

Sometime in the future, tiny autonomous “nanorobots” could be used to perform a wide range of tasks such as assembling electronic circuits or delivering drugs to specific parts of the body. But before this becomes a reality, nanotechnologists must come up with practical ways to propel such devices — something that has proven to be very difficult because conventional motors cannot simply be shrunk to nanometre dimensions.

Nature, however, contains a wide range of nanomotors — for example, some bacteria and other tiny organisms propel themselves using whip-like structures that are driven by biomolecular motors. Not surprisingly, researchers are looking at such “biomotors” for inspiration.

The quantum-mechanical tunnelling of protons is believed to be at the heart of some biomotors, and now Petr Král and colleagues that the University of Illinois at Chicago have shown that electron tunnelling could be used to drive manmade nanomotors.

The team used molecular-dynamics computer simulations to model nanomotors that comprise a carbon nanotube shaft with molecular “stalks” terminated by conducting “blades” …. The rotor resembles a water wheel, except that one electron at a time tunnels between stationary electrodes and moving blades.

…These artificial systems would surpass their biological counterparts in many ways, adds Král. For one, they could rotate a million or more times faster.

The research was published in Physical Review Letters [abstract].

—Jim