'Zombie' Cells May Outperform Live Ones as Catalysts and Conductors

Feb. 7, 2013 — "Zombie" mammalian cells that may function better after they die have been created by researchers at Sandia National Laboratories and the University of New Mexico (UNM).

Zombie cell, first stage -- only moderately heated, the cell is now pure silica and needed a gold coating for a scanning electron microscope to image it. (Credit: Bryan Kaehr)

The simple technique coats a cell with a silica solution to form a near-perfect replica of its structure. The process may simplify a wide variety of commercial fabrication processes from the nano- to macroscale.

The work, reported in theProceedings of the National Academy of Sciences (PNAS), uses the nanoscopic organelles and other tiny components of mammalian cells as fragile templates on which to deposit silica. The researchers then heat the cell to burn off its protein. The resultant hardened silica structures are faithful to the exterior and interior features of the formerly living cell, can survive greater pressures and temperatures than flesh ever could, and can perform some functions better than when they were alive, said lead researcher Bryan Kaehr, a Sandia materials scientist.

"It's very challenging for researchers to build structures at the nanometer scale," said Kaehr. "We can make particles and wires, but 3-D arbitrary structures haven't been achieved yet. With this technique, we don't need to build those structures -- nature does it for us. We only need to find cells that possess the machinery we want and copy it using our technique. And, using chemistry or surface patterning, we can program a group of cells to form whatever shape seems desirable."

UNM professor and Sandia Fellow Jeff Brinker added, "The process faithfully replicates features from the nanoscale to macroscale in a robust, three-dimensionally stable form that resists shrinkage even upon heating to over 500 degrees Centigrade [932 degrees Fahrenheit]. The refractoriness of these delicate structures is amazing."

The unusual but simple procedure may serve as a model for creating hardier classes of nanoscopic products.

Because a cell is populated by a vast range of proteins, lipids and scaffolding, its interior is ready-made to model catalysts, funnels, absorbents and other useful nanomachinery, said Kaehr, a former Sandia Truman Fellow.

Catalysts that evolve in cells are enzymes that have to retain a certain shape for their chemistry to work. Since structure is important to function, stabilizing a catalyst in the shape it evolved is important, Kaehr said. Heat-hardened silica would stabilize and protect the still-present protein as it did its work.

UNM post-doctoral student Jason Townson said the most immediate use for silicification may be as a simple way to preserve the structure of organic materials for imaging.

"Formerly, for internal preservation and subsequent imaging, a cell would be fixed in formaldehyde or some other preservative. But many of these methods are labor-intensive," Townson said. "This method is simple. The preserved cells will never get sloppy in decay. And when we cracked open the resulting structure, we were blown away by how well the cell was preserved, down to the minor groove of the cell's DNA."

Heating the cell to still higher temperatures (greater than 400 degrees C) evaporates the organic material of the cell -- its protein -- and leaves the silica in a kind of three-dimensional Madame Tussauds wax replica of a formerly living being. The difference is that instead of modeling the face, say, of a famous criminal, the hardened silica-based cells display internal mineralized structures with intricate features ranging from nano- to millimeter-length scales.

The construction process is relatively simple: Take some free-floating mammalian cells, put them in a petri dish and add silicic acid.

Through the action of methanol, a byproduct of the acid, the cell's lipid layers -- the protective casings that keep the cell intact -- are softened and made porous enough for the silica to flow in at about the temperature of the human body.

The silicic acid, for reasons still partially obscure, enters without clogging and in effect embalms every organelle in the cell from the micro- to the nanometer scale.

If the cell isn't heated, the silica forms a kind of permeable armor around the protein of the living cell. This may support it enough to act as a catalyst at temperatures and pressures undreamed of by nature.

"Once we've used silica to stabilize the cellular structure, it can still carry out reactions and, more importantly, that reaction is stable enough to work at high temperatures," Kaehr said. "The method is also a means to take a soft, potentially valuable biological material and convert it to a fossil that will stay on our shelves indefinitely."

Ordinarily, preserving something organic means freezing it, which is energy-intensive, he said. Instead, "We're doing rapid fossilization: quickly converting a protoplasmic cell into a hard structure that will stand the test of time."

Experiments showed the cell can be used as a reverse mold from which, at 900 degrees C, a porous carbonized structure results from heating cell protein in a vacuum. In other words, in the same way that burning wood in air leaves a residue of structureless soot, the zombie heating method results in a high-quality carbon structure. Subsequent dissolution of the underlying silica support decreased the cell's electrical resistance by approximately 20 times. Such materials would have substantial utility in fuel cells, decontamination and sensor technologies.

That such extraordinary results can be achieved by silicifying cells indicates many soft cellular architectures could be "feedstock for most materials processing procedures, including those requiring high temperatures and pressures," according to the technical paper.

Other porous material structures, relying on titanium instead of silica, have been formed using the organic template technique. Other metal oxides, said Kaehr, are a possibility. These would have more complex structural functions or could serve as catalysts.

The work follows the efforts of a number of scientific groups, including Kaehr's, that have built gel-like structures, copied them with silica and then burned off the gel to create, in effect, large sponges.

"Now we can change the biological shape and calcify (heat) it, so for the first time we get new irregular structures," Kaehr said.

Summing up, Kaehr offers what may be the first distinction in scientific literature between a mummy cell and a zombie cell: "King Tut was mummified," he said, "to approximately resemble his living self, but the process took place without mineralization [a process of fossilization]. Our zombie cells bridge chemistry and biology to create forms that not only near-perfectly resemble their past selves but can do future work."

The work was supported by DOE's Office of Science. Co-authors are Brinker, Brian Swartzentruber of Sandia and the Center for Integrated Nanotechnologies, and, from UNM, Robin Kalinich, Darren Dunphy and student Yasmine Awad.

source:sciencedaily

Using Single Quantum Dots to Probe Nanowires

Feb. 5, 2013 — Modern telecommunications happens because of fast electrons and fast photons. Can it get better? Can Moore's law -- the doubling of computing power ever 18 months or so -- be sustained? Can the compactness (nm-scale components) of electronics be combined with the speed of photonics? Well, one such hybrid approach is being explored at the Joint Quantum Institute, where scientists bring together three marvelous physics research fields: microfluidics, quantum dots, and plasmonics to probe and study optical nanostructures with spatial accuracy as fine as 12 nm.

(a) This is an optical image of the microfluidic crossed-channel device. Flow in the center control region (dashed circle) is manipulated in two dimensions by 4 external electrodes (not shown). Scale bar is 500 μm. (b) This is a schematic of the positioning and imaging technique. A single QD is driven along a trajectory close to the wire by flow control. The inset shows a microcope image of a typical nanowire with 1 μm scale bar. (Credit: JQI)

Plasmonics

When light strikes a strip of metal an electron wave can be excited in the surface. Is this "surface plasmon" a bit of light or electricity. Well, it's a bit of both. The wavelength of this electromagnetic wave is shorter and the energy density higher than that of the incoming laser light; the plasmon is thus tightly localized light constrained to propagate along the meal surface. The science of "plasmonics" has arisen to capitalize on various imaging, sensing, and processing abilities inherent in plasmons. To start with, though, one needs to know exactly what happens at that laser-excited metallic surface. That light is converted into the plasmonic wave; later the energy can be reconverted into light.

Here's where the JQI experiment comes in. The main result of the work, published February 5 in the journal Nature Communications, is to provide a map showing how the metal strip, in this case a silver wire 4 microns long and 100 nm wide, lights up.

Microfluidics and Quantum Dots

The other two chief components of the experiment, in addition to plasmonics, are microfluidics and quantum dots. Microfluidics, a relatively new science all by itself, features the movement of nanoliter volumes of fluids through channels defined on microchips, analogous to the conducting paths strung across microprocessors for carrying electrical currents. Quantum dots, nanometer-sized semiconductor balls, are tailored to possess a specified set of allowed energy states; in effect the dots are artificial atoms that can be moved around. In the JQI experiment the 10-nm-wide dots (the important cadmium-selenide layer is only 3 nm thick) float in a fluid whose flow can be controlled by varying an applied voltage. The dots are drawn up close to the nanowire as if they were mines next to a submarine.

Indeed the dot is there precisely to excite the wire. The dot is fluorescence machine -- in a loose sense a nanoscopic lightbulb. Striking it with green laser light, it quickly re-emits red light (one photon at a time), and it is this radiation which excites waves in the nearby wire, which acts like an antenna. But the interaction is a two-way street; the dot's emissions will vary depending on where along the length of the wire it is; the end of the wire (like any pointy lightning rod on a barn) is where electrical fields are highest and this attracts the most emission from the dot.

A CCD camera captures light coming from the dots and from the wire. The camera qualities, the optical properties of the dot, the careful positioning of the dot, and the shape and purity of the nanowire combine to provide an image of the electric field intensity of the nanowire with 12-nm accuracy. The intensity map shows that the input red light from the quantum dot (wavelength of 620 nm) has effectively been transformed into a plasmonic wavelength of 320 nm.

Chad Ropp is a graduate student working on the project and the lead author on the paper. "Plasmonic maps have been resolved before, but the quantum mechanical interactions with a single emitter have not, and not with this degree of accuracy," said Ropp.

Possible Applications

In an actual device, the quantum dot could be replaced by a bio-particle which could be identified through the nanowire's observed effect on particle's emissions. Or the dot-wire duo could be combined in various configurations as plasmonic equivalents of electronic circuit components. Other uses for this kind of nanowire setup might exploit the high energy density in the plasmonic state to support nonlinear effects. This could enable the nanowire-dot combination to operate as an optical transistor.

:source:sciencedaily.

Stem Cell Breakthrough Could Lead to New Bone Repair

Stem Cell Breakthrough Could Lead to New Bone Repair Therapies On Nanoscale Surfaces

Feb. 11, 2013 — Scientists at the University of Southampton have created a new method to generate bone cells which could lead to revolutionary bone repair therapies for people with bone fractures or those who need hip replacement surgery due to osteoporosis and osteoarthritis.

Stem cell breakthrough could lead to new bone repair therapies. (Credit: Image courtesy of University of Southampton)

The research, carried out by Dr Emmajayne Kingham at the University of Southampton in collaboration with the University of Glasgow and published in the journal Small, cultured human embryonic stem cells on to the surface of plastic materials and assessed their ability to change.

Scientists were able to use the nanotopographical patterns on the biomedical plastic to manipulate human embryonic stem cells towards bone cells. This was done without any chemical enhancement.

The materials, including the biomedical implantable material polycarbonate plastic, which is a versatile plastic used in things from bullet proof windows to CDs, offer an accessible and cheaper way of culturing human embryonic stem cells and presents new opportunities for future medical research in this area.

Professor Richard Oreffo, who led the University of Southampton team, explains: "To generate bone cells for regenerative medicine and further medical research remains a significant challenge. However we have found that by harnessing surface technologies that allow the generation and ultimately scale up of human embryonic stem cells to skeletal cells, we can aid the tissue engineering process. This is very exciting.

"Our research may offer a whole new approach to skeletal regenerative medicine. The use of nanotopographical patterns could enable new cell culture designs, new device designs, and could herald the development of new bone repair therapies as well as further human stem cell research," Professor Oreffo adds.

This latest discovery expands on the close collaborative work previously undertaken by the University of Southampton and the University of Glasgow. In 2011 the team successfully used plastic with embossed nanopatterns to grow and spread adult stem cells while keeping their stem cell characteristics; a process which is cheaper and easier to manufacture than previous ways of working.

Dr Nikolaj Gadegaard, Institute of Molecular, Cell and Systems Biology at the University of Glasgow, says: "Our previous collaborative research showed exciting new ways to control mesenchymal stem cell -- stem cells from the bone marrow of adults -- growth and differentiation on nanoscale patterns.

"This new Southampton-led discovery shows a totally different stem cell source, embryonic, also respond in a similar manner and this really starts to open this new field of discovery up. With more research impetus, it gives us the hope that we can go on to target a wider variety of degenerative conditions than we originally aspired to. This result is of fundamental significance."

The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC)..

source:sciencedaily