An “attractive” man-machine interface

Cellular magnetism: At left, cells were pre-coated with tiny magnetic beads, each binding to a cell receptor (see arrows). When a magnetic field is applied (at right), the beads become magnets and cluster together, pulling the receptors with them. This clustering mimics what happens when drugs or other molecules bind to the receptors, triggering the same biochemical responses in the cell. Image courtesy Don Ingber, PhD, Children's Hospital Boston.

Researchers use magnetic fields, rather than drugs, to control cellular signaling Researchers at Children's Hospital Boston have developed a new "nanobiotechnology" that enables magnetic control of events at the cellular level. They describe the technology, which could lead to finely-tuned but noninvasive treatments for disease, in the January issue of Nature Nanotechnology Don Ingber, MD, PhD, and Robert Mannix, PhD, of Children's program in Vascular Biology, in collaboration with Mara Prentiss, PhD, a physicist at Harvard University, devised a way to get tiny beads--30 nanometers (billionths of a meter) in diameter--to bind to receptor molecules on the cell surface.

When exposed to a magnetic field, the beads themselves become magnets, and pull together through magnetic attraction. This pull drags the cell's receptors into large clusters, mimicking what happens when drugs or other molecules bind to them. This clustering, in turn, activates the receptors, triggering a cascade of biochemical signals that influence different cell functions.

The technology could lead to non-invasive ways of controlling drug release or physiologic processes such as heart rhythms and muscle contractions, says Ingber, the study's senior investigator. More importantly, it represents the first time magnetism has been used to harness specific cellular signaling systems normally used by hormones or other natural molecules.

"This technology allows us to control the behavior of living cells through magnetic forces rather than chemicals or hormones," says Ingber. "It may provide a new way to interface with machines or computers in the future, opening up entirely new ways of controlling drug delivery, or making detectors that have living cells as component parts. We've harnessed a biological control system, but we can control it at will, using magnetic forces."

In a demonstration involving mast cells (a kind of cell in the immune system), Ingber and Mannix showed that the beads, when bound to cell receptors and exposed to a magnetic field, were able to stimulate an influx of calcium into the cells. (Calcium influx is a fundamental signal used by nerve cells to initiate nerve conduction, by heart and muscle cells to stimulate contractions and by other cells for secretion.) Magnetic fields alone, without the beads, had no effect.

The beads--30-nm size (with an inner 5-nm particle) provides the optimal crystal geometry to make them "superparamagnetic"--able to be magnetized and demagnetized over and over, notes Mannix, who shares first authorship of the paper with Sanjay Kumar, MD, PhD of Children's. (Kumar is now a faculty member in Bioengineering at the University of California at Berkeley.) To give a sense of scale, one nanometer is to a meter (about a yard) as one blueberry is to the diameter of the Earth.

The beads were made to attach to the mast-cell receptors by pre-coating them with antigens; these antigens then bound to antibodies that coated the receptors, similar to the way antibodies bind to antigens in the immune system. "Our goal was to have one antigen coating each bead, so that each bead would bind to just one receptor," Mannix says.

As an accompanying News & Views article notes, "scaling down the interactions to single receptors demonstrates unprecedented control at the individual protein level."

Electrical stimuli have been used to influence the activity of nerve cells, but isn't effective in cells that aren't electrically excitable by nature, the researchers note. The advantage of a "nanomagnetic" control system is that it can be used in a broad range of cell types and provides a near-instantaneous on-off switch, unlike hormones and chemicals that can take minutes to hours to act and then may linger in the body. In addition, magnets can be portable and have low power requirements, allowing their use in the military and other mobile situations.
Ingber envisions a kind of pacemaker that would involve an injection of nanoparticles into the heart that could then be controlled magnetically. "You could make those cells responsive to magnetic forces that work through the skin, rather than having to do surgical implants or place wires," he speculates.

"You could also have a pacemaker for muscles in different parts of your body, or a pacemaker for producing hormones or insulin," Ingber adds. "If you're a diabetic, you could have cells that produce insulin put under your skin, and then inject nanoparticles that go to those cells. Then, when you have a meal and need more insulin, you could just use a magnet to cause the cells to produce more. So you wouldn't have to keep buying the drug and injecting it."

The nanomagnetic system could also interface with external instruments and computer controls that take in information from the body or the surrounding environment and activate the magnet as needed, Ingber adds.

A diabetic, for example, could have a transdermal glucose sensor that controls the magnet, which then controls the insulin production by itself. In the neonatal intensive care unit, sick newborns could have their heart and breathing rates monitored and their cells rigged to respond through magnetic stimulation, without a tangle of wires and probes. Or, on the battlefield, the magnet could trigger production of an antidote when a toxin or infectious agent is sensed in the environment.

But these examples are just theoretical. "The applications are hard to define because we're opening up a whole new area of control that never existed before," Ingber says.

The study was supported by a Defense Advanced Research Projects Agency (DARPA) grant from the Department of Defense and an NIH postdoctoral fellowship. (Research-Oriented #1)

Contact: James Newton James.Newton@childrens.harvard.edu 617-919-3110 Children's Hospital Boston

Technorati Tags: Nano or Nanotechnology and Nanotech or Cellular magnetism and Children's Hospital Boston or President Bush Discusses Economy, Growth Package VIDEO and Bessye J. Bearden and New nanostructured thin film shows promise for efficient solar energy conversion

New nanostructured thin film shows promise for efficient solar energy conversion

Jin Zhang is working to develop better materials for solar cells. Photo by T. Stephens.

SANTA CRUZ, CA--In the race to make solar cells cheaper and more efficient, many researchers and start-up companies are betting on new designs that exploit nanostructures -- materials engineered on the scale of a billionth of a meter. Using nanotechnology, researchers can experiment with and control how a material generates, captures, transports, and stores free electrons--properties that are important for the conversion of sunlight into electricity. Two nanotech methods for engineering solar cell materials have shown particular promise.

One uses thin films of metal oxide nanoparticles, such as titanium dioxide, doped with other elements, such as nitrogen. Another strategy employs quantum dots--nanosize crystals--that strongly absorb visible light. These tiny semiconductors inject electrons into a metal oxide film, or "sensitize" it, to increase solar energy conversion. Both doping and quantum dot sensitization extend the visible light absorption of the metal oxide materials.

Combining these two approaches appears to yield better solar cell materials than either one alone does, according to Jin Zhang, professor of chemistry at the University of California, Santa Cruz. Zhang led a team of researchers from California, Mexico, and China that created a thin film doped with nitrogen and sensitized with quantum dots. When tested, the new nanocomposite material performed better than predicted--as if the functioning of the whole material was greater than the sum of its two individual components.

"We have discovered a new strategy that could be very useful for enhancing the photo response and conversion efficiency of solar cells based on nanomaterials," said Zhang.

"We initially thought that the best we might do is get results as good as the sum of the two, and maybe if we didn't make this right, we'd get something worse. But surprisingly, these materials were much better."

The group's findings were reported in the Journal of Physical Chemistry in a paper posted online on January 4. Lead author of the paper was Tzarara Lopez-Luke, a graduate student visiting in Zheng's lab who is now at the Instituto de Investigaciones Metalurgicas, UMSNH, Morelia, Mexico.

Zhang's team characterized the new nanocomposite material using a broad range of tools, including atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy, and photoelectrochemistry techniques. They prepared films with thicknesses between 150 and 1100 nanometers, with titanium dioxide particles that had an average size of 100 nanometers. They doped the titanium dioxide lattice with nitrogen atoms. To this thin film, they chemically linked quantum dots made of cadmium selenide for sensitization.

The resulting hybrid material offered a combination of advantages. Nitrogen doping allowed the material to absorb a broad range of light energy, including energy from the visible region of the electromagnetic spectrum. The quantum dots also enhanced visible light absorption and boosted the photocurrent and power conversion of the material.

When compared with materials that were just doped with nitrogen or just embedded with cadmium selenide quantum dots, the nanocomposite showed higher performance, as measured by the "incident photon to current conversion efficiency" (IPCE), the team reported. The nanocomposite's IPCE was as much as three times greater than the sum of the IPCEs for the two other materials, Zhang said.

"We think what's happening is that it's easier for the charge to hop around in the material," he explained. "That can only happen if you have both the quantum dot sensitizing and the nitrogen doping at the same time."

The nanocomposite material could be used not only to enhance solar cells, but also to serve as part of other energy technologies. One of Zhang's long-term goals is to marry a highly efficient solar cell with a state-of-the-art photoelectrochemical cell. Such a device could, in theory, use energy generated from sunlight to split water and produce hydrogen fuel (see earlier press release at press.ucsc.edu/text). The nanocomposite material could also potentially be useful in devices for converting carbon dioxide into hydrocarbon fuels, such as methane.

The new strategy for engineering solar cell materials offers a promising path for Zhang's lab to explore for years to come.

"I'm very excited because this work is preliminary and there's a lot of optimizing we can do now," Zhang noted. "We have three materials--or three parameters--that we can play with to make the energy levels just right."

In essence, the team has been trying to manipulate materials so that when sunlight strikes them, the free electrons generated can easily move from one energy level to another--or jump across the different materials--and be efficiently converted to electricity.

"What we're doing is essentially 'band-gap engineering.' We're manipulating the energy levels of the nanocomposite material so the electrons can work more efficiently for electricity generation," Zhang said. "If our model is correct, we're making a good case for this kind of strategy." ###

Sources of funding for this research included the U.S. Department of Energy, the National Science Foundation of China, and the University of California Institute for Mexico and the United States (UC-MEXUS).

Research collaborators included Abraham Wolcott, Li-ping Xu and Shaowei Chen at UCSC; Zhenhai Wen and Jinghong Li at Tsinghua University in Beijing, China; and Elder De La Rosa of the Centro de Investigaciones en Optica, A.C., in Leon, Guanajuato, Mexico.

Contact: Tim Stephens stephens@ucsc.edu 831-459-2495 University of California - Santa Cruz

Technorati Tags: Nano or Nanotechnology and Nanotech or solar energy and University of California - Santa Cruz or John McCain TV Ad: "Michigan Endorsed" VIDEO and Garrett Augustus Morgan, Sr. and National Nanotechnology Initiative releases new strategic plan