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“Plasmonic Cloaking” Renders Nanowires Invisible

Light detection is well known and relatively simple. Silicon generates electrical current when illuminated and is common in solar panels and light sensors today. The Stanford device, however, is a departure in that for the first time it uses a relatively new concept known as plasmonic cloaking to render the device invisible.

The field of plasmonics studies how light interacts with metal nanostructures and induces tiny oscillating electrical currents along the surfaces of the metal and the semiconductor. These currents, in turn, produce scattered light waves. By carefully designing their device — by tuning the geometries — the engineers have created a plasmonic cloak in which the scattered light from the metal and semiconductor cancel each other perfectly through a phenomenon known as destructive interference.

The rippling light waves in the metal and semiconductor create a separation of positive and negative charges in the materials — a dipole moment, in technical terms. The key is to create a dipole in the gold that is equal in strength but opposite in sign to the dipole in the silicon.

When equally strong positive and negative dipoles meet, they cancel each other and the system becomes invisible. “We found that a carefully engineered gold shell dramatically alters the optical response of the silicon nanowire,” said Fan. “Light absorption in the wire drops slightly — by a factor of just four — but the scattering of light drops by 100 times due to the cloaking effect, becoming invisible.”

“It seems counterintuitive,” said Brongersma, “but you can cover a semiconductor with metal — even one as reflective as gold — and still have the light get through to the silicon. As we show, the metal not only allows the light to reach the silicon where we can detect the current generated, but it makes the wire invisible, too.”

(via Plasmonic cloaking | KurzweilAI)

Ultra-Sensitive Biosensor Can Detect Cancer At Molecular Level

The sensor’s mechanical part is a vibrating cantilever, a sliver of silicon that resembles a tiny diving board. Located under the cantilever is a transistor, which is the sensor’s electrical part.

In other mechanical biosensors, a laser measures the vibrating frequency or deflection of the cantilever, which changes depending on what type of biomolecule lands on the cantilever. Instead of using a laser, the new sensor uses the transistor to measure the vibration or deflection.

The sensor maximizes sensitivity by biasing both the cantilever and transistor. The cantilever is biased using an electric field to pull it downward as though with an invisible string and the transistor is biased by applying a voltage. “You can make the device sensitive to almost any molecule as long as you configure the sensor properly,” Alam said.

A key innovation is the elimination of a component called a “reference electrode,” which is required for conventional electrical biosensors but cannot be miniaturized, limiting practical applications. This makes it feasible for low-cost, point-of-care applications in doctors’ offices, Alam said.

(via Ultrasensitive biosensor promising for medical diagnostics | KurzweilAI)

Hacking Spider Silk to Create Nano-Electronic Components:

As a protein-based polymer, spider silk is naturally insulating, so the researchers are exploring what happens when it’s coated with iodine, gold, or carbon nanotubes. In all three cases, the silk turned into a more conductive fiber. However, “gold really likes spider silk,” Steven told scientists at the American Physical Society’s March meeting in Boston. “Gold nanoparticles adhere to spider silk very well.”

The team started with 3.5-μm-wide silk harvested from Nephila clavipes, the golden orb-weaving spider. They placed the silk in a vacuum chamber and coated it with gold. The resulting fiber had electrical conductivity from the gold plus flexibility from the silk, and it measured only 1/25th the diameter of a human hair. That allowed the fibers to be used—even without conductive paste—as contacts on tiny organic crystals, which the lab chills to cryogenic temperatures to study their superconductivity.

Standard wires made of gold or other metals aren’t elastic enough and tend to lose contact with the soft organic crystals as temperatures change. The group found that the gold-coated silk fibers worked as contacts down to the lowest temperature they tested at, about 260 millikelvin.

The researchers also coated the silk with carbon nanotubes, creating highly sensitive strain sensors. Those could be used as heart-pulse monitors, Steven suggests.

Meanwhile, the iodine-doped silk showed changes in conductivity that depended on relative humidity. But the science didn’t stop there.

Steven heated the iodine-doped silk in an argon atmosphere to 800°C, creating a pyrolyzed, carbon-coated fiber that turned out to be a p-type semiconductor. The researchers then used those fibers to make filaments for incandescent bulbs.

Steven says the group is working on using the functionalized silk to make electronic components, such as diodes, inductors, and capacitors. It should be possible to build a field-effect transistor out of the semiconducting version of the material. (Other labs have already used silk from the silk moth, Bombyx mori, as the gate insulator in a transistor.)

Conducting and semiconducting fibers could be readily woven into fabrics to make so-called smart textiles, such as shirts that could sense temperature or other environmental changes. Combining the Florida State research with efforts under way elsewhere to create spider silk artificially might allow engineers to mass-produce fibers with tunable electrical properties, Steven says.

(via Spider Silk Weaves New Path for Electronics - IEEE Spectrum)

(Photo: Spider Silk Glands Source)

Researchers Using Bio-Engineered Viruses to Power Nano Electronics

The researchers looked to viruses as a new material to work with because they reproduce rapidly and align far better than other materials, making them good candidates to accumulate a charge on one end of the virus.

The researchers then genetically engineered the virus with proteins that enhance the buildup of charge on the ends of the rod-shaped viruses. The viruses only attack other bacteria so are considered benign.  The viruses are stacked onto thin films and then several thin films are layered to build up as much voltage as possible.

The Lawrence Berkeley Lab group isn’t the first to pursue viruses as a means for building up electric charge. Researchers at MIT in 2009 said they were able to wire a charge-building virus to a lithium ion battery. The Lawrence Berkeley Lab’s prototype was only able to generate about a quarter of the voltage of a triple A battery, but they believe that their approach to “viral electronics” can scale up.

(via Step on it: Virus could lead to motion-powered gadgets | Cutting Edge - CNET News)

DARPA Plans to Implant Diagnostic Nanochips in Soldiers

The Defense Advanced Research Projects Agency (DARPA), has announced plans to create and implant nanochips in soldiers that will monitor their health. As you might have guessed, this plan has raised a little bit of controversy with the fear that this could turn the Earth into Total Recall.

The chips would monitor soldiers’ health, especially in terms of illness in the field.

Though it seems like a simple and efficient way to keep soldiers alive and healthy, a number of opponents have come out the woodwork claiming this could be the beginning of computer chips for everyone.

Katherine Albrecht, co-author of Spychips says, “It’s never going to happen that the government at gunpoint says, ‘You’re going to have a tracking chip. It’s always in incremental steps. If you can put a microchip in someone that doesn’t track them … everybody looks and says, ‘Come on, it’ll be interesting seeing where we go.’”

But DARPA said the implants are a “truly disruptive innovation,” since most medical evacuations are the result of ordinary illness, not injuries. The chips will report to doctors and reportedly aren’t to be used for tracking.

[via] [image credit: Amal Graafstra]

(ht futurescope)

Microsubmarines Can Decontaminate Water, Deliver Drugs in Bloodstream:

The cone-machines are made from self-assembled monolayers and have special chemical properties that encourage them to pick up oil. They move quickly through the water and require very little fuel, so they could work efficiently.

In lab tests, Wang and colleagues proved the machines could move through water and pick up both olive oil and motor oil, transporting collections of droplets around. Their water-repellency could also pave the way for new drug-delivering molecules or for transferring liquids in otherwise immiscible environments, the authors say.

The devices are about 10 times thinner than a human hair, so presumably you would need epic fleets of them to make a difference in massive oil spills like the Deepwater Horizon disaster. Large-scale cleanup operations would also require different types of motors, perhaps driven by magnetic fields or electrical current, the authors note. Still, the machines could be more environmentally friendly than new types of soaps or other absorbent material.

(via In Successful Test, Microsubmarines Help Clean Up Oil Spills | Popular Science)

Using Radio Waves to Remotely Trigger Genes in Living Animals:

Rockefeller University researchers have remotely activated genes inside living animals, a proof of concept that could one day lead to medical procedures in which patients’ genes are triggered on demand.

The researchers used radio waves to switch on engineered insulin-producing genes in mice.

Jeffrey Friedman, a molecular geneticist at the Rockefeller University in New York and lead author of the study, says that in the short term, the results will lead to better tools to allow scientists to manipulate cells non-invasively. But with refinement, he thinks, clinical applications could also be possible.

Friedman and his colleagues coated iron oxide nanoparticles with antibodies that bind to a modified version of the temperature-sensitive ion channel TRPV1, which sits on the surface of cells. They injected these particles into tumors grown under the skins of mice, then used low-frequency radio waves to heat the nanoparticles. In turn, the nanoparticles heated the ion channel to its activation temperature of 42 °C. Opening the channel allowed calcium to flow into cells, triggering secondary signals that switched on an engineered calcium-sensitive gene that produces insulin. After 30 minutes of radio-wave exposure, the mice’s insulin levels had increased and their blood sugar levels had dropped.

(via Radio waves switch on genes for non-invasive treatments | KurzweilAI)