A team of researchers at the National Institute of Standards and Technology (NIST) have demonstrated a new device that creates nanodroplet “test tubes” for studying individual proteins under conditions that mimic the crowded confines of a living cell. “By confining individual proteins in nanodroplets of water, researchers can directly observe the dynamics and structural changes of these biomolecules,” says physicist Lori Goldner, a coauthor of the paper* published in Langmuir.

With the flip of a switch: Nanodrop “test tubes” are created by an electronic switch that causes a micropipette to jerk back and leave behind a droplet less that 1 micron in diameter for study.
Credit: NIST

Researchers recently have turned their attention to the role that crowding plays in the behavior of proteins and other biomolecules—there is not much extra space in a cell. NIST’s nanodroplets can mimic the crowded environment in cells where the proteins live while providing advantages over other techniques to confine or immobilize proteins for study that may interfere with or damage the protein. This more realistic setting can help researchers study the molecular basis of disease and supply information for developing new pharmaceuticals. For example, misfolded proteins play a role in many illnesses including Type 2 diabetes, Alzheimer’s and Parkinson’s diseases. By seeing how proteins fold in these nanodroplets, researchers may gain new insight into these ailments and may find new therapies.

The NIST nanodroplet delivery system uses tiny glass micropipettes to create tiny water droplets suspended in an oily fluid for study under a microscope. An applied pressure forces the water solution containing protein test subjects to the tip of the micropipette as it sits immersed in a small drop of oil on the microscope stage. Then, like a magician whipping a tablecloth off a table while leaving the dinnerware behind, an electronic switch causes the pipette to jerk back, leaving behind a small droplet typically less than a micrometer in diameter.

The droplet is held in place with a laser “optical tweezer,” and another laser is used to excite fluorescence from the molecule or molecules in the droplet. In one set of fluorescence experiments, explains Goldner, “The molecules seem unperturbed by their confinement—they do not stick to the walls or leave the container—important facts to know for doing nanochemistry or single-molecule biophysics.” Similar to a previous work (see “‘Micro-boxes’ of Water Used to Study Single Molecules”, Tech Beat July 20, 2006), researchers also demonstrated that single fluorescent protein molecules could be detected inside the droplets.

Fluorescence can reveal the number of molecules within the nanodroplet and can show the motion or structural changes of the confined molecule or molecules, allowing researchers to study how two or more proteins interact. By using only a few molecules and tiny amounts of reagents, the technique also minimizes the need for expensive or toxic chemicals.

Reference:

* J. Tang, A.M. Jofre, G.M. Lowman, R.B. Kishore, J.E. Reiner, K. Helmerson, L.S. Goldner and M.E. Greene. Green fluorescent protein in inertially injected aqueous nanodroplets. Published in Langmuir, ASAP Article, Web release date: March 27, 2008.

(PITTSBURGH)

A team of University of Pittsburgh researchers have discovered that certain organic—or carbon-based—molecules exhibit the properties of atoms under certain circumstances and, in turn, conduct electricity as well as metal.  This allows a newfound ability of organic molecules to conduct electricity opens door to smaller, cheaper and more powerful technologies.

The work was detailed in the April 18 edition of Science, the finding is a breakthrough in developing nanotechnology that provides a new strategy for designing electronic materials, including inexpensive and multifunctional organic conductors that have long been considered the key to smaller, cheaper, and faster technologies.

The Pitt team found that the hollow, soccer-ball-shaped carbon molecules known as fullerenes can hold and transfer an electrical charge much like the most highly conductive atoms, explained project head Hrvoje Petek, a professor of physics and chemistry in Pitt’s School of Arts and Sciences and codirector of Pitt’s Petersen Institute for NanoScience and Engineering.  The research was performed by Pitt post-doctoral associates Min Feng and Jin Zhao.

When an electron was introduced into a fullerene molecule, the shape of the electron distribution mimicked that of a hydrogen atom or an atom from the alkali metal group, which includes lithium, sodium, and potassium.  Moreover, when two fullerenes were placed next to each other on a copper surface, they showed the electron distribution of their chemical bond and appeared as H2, a hydrogen molecule.  The assembly exhibited metal-like conductivity when the team extended it to a wire 1-molecule-wide.

“Our work provides a new perspective on what determines the electronic properties of materials,” Petek said.  “The realization that hollow molecules can have metal-like conductivity opens the way to develop novel materials with electronic and chemical properties that can be tailored by shape and size.”

Although the team worked with fullerenes, the team’s results apply to all hollow molecules, Petek added, including carbon nanotubes—rolled, 1-atom-thick sheets of graphite 100,000 times smaller than a human hair.

The team’s research shows promise for the future of electronics based on molecular conductors.  These molecule-based devices surpass the semiconductor and metal conductors of today in terms of lower cost, flexibility, and the ability to meld the speed and power of optics and electronics.  Plus, unlike such inorganic conductors as silicon, molecule-based electronics can be miniaturized to a 1-dimensional scale (1-molecule-wide), which may enable them to conduct electricity with minimal loss and thus improve the performance of an electronic device.

Traditionally, the problem has been that organic conductors have not conducted electrical current very well, Petek said.  The Pitt team’s discovery could enable scientists to finally overcome that problem, he added.

“Metal-like behavior in a molecular material—as we have found—is highly surprising and desirable in the emerging field of molecular electronics,” he said.

“Our work is a unique example of how nanoscale materials can be used as atom-sized building blocks for molecular materials that could replace silicon and copper in electronic devices, luminescent displays, photovoltaic cells, and other technologies.”