The nanotech tool kit includes a growing collection of devices for imaging, measuring, and manipulating nanoscale components. Often the devices themselves are nanoscale. Now, a double-walled carbon nanotube forms a device able to weigh a single atom of gold. Unlike other tools of comparable sensitivity, the new nanotube mass sensors are small enough to be a components of nanoscopic systems, and they do not have to ionize or destroy molecules to measure their masses. From the Lawrence Berkeley National Laboratory (credit ScienceDaily) “Golden Scales: Nanoscale Mass Sensor from Berkeley Can Be Used to Weigh Individual Atoms and Molecules“:

There’s a new “gold standard” in the sensitivity of weighing scales. Using the same technology with which they created the world’s first fully functional nanotube radio, researchers with Berkeley Lab and the University of California (UC) at Berkeley have fashioned a nanoelectromechanical system (NEMS) that can function as a scale sensitive enough to measure the mass of a single atom of gold.

Alex Zettl, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division (MSD) and UC Berkeley’s Physics Department, where he is the director of the Center of Integrated Nanomechanical Systems, led this research. Working with him were members of his research group, Kenneth Jensen and Kwanpyo Kim.

“For the past 15 years or so, the holy grail of NEMS has been to push them to a small enough size with high enough sensitivity so that they might resolve the mass of a single molecule or even single atom,” Zettl said. “This has been a challenge even at cryogenic temperatures where reduced thermal noise improves the sensitivity. We have achieved sub-single-atom resolution at room temperature!”

The new NEMS mass sensor consists of a single carbon nanotube that is double-walled to provide uniform electrical properties and increased rigidity. One tip of the carbon nanotube is free and the other tip is anchored to an electrode in close proximity to a counter-electrode. A DC voltage source, such as from a battery or a solar cell array, is connected to the electrodes. Applying a DC bias creates a negative electrical charge on the free tip of the nanotube. An additional radio frequency wave “tickles” the nanotube, causing it to vibrate at a characteristic “flexural” resonance frequency.

When an atom or molecule is deposited onto the carbon nanotube, the tube’s resonant frequency changes in proportion to the mass of the atom or molecule, much like the added mass of a diver changes the flexural resonance frequency of a diving board. Measuring this change in frequency reveals the mass of the impinging atom or molecule.

…While scientists already have the ability to measure the mass of individual atoms through a complex technique known as mass spectrometry, this new carbon nanotube NEMS mass sensor offers some distinct advantages and opens the door to new possibilities, as Jensen explained.

“Unlike mass spectrometry, our device does not require the ionization of neutral atoms or molecules that can destroy samples such as proteins. Also unlike mass spectrometers, our carbon nanotube mass sensor becomes more sensitive at higher mass ranges, which makes it more suitable for measuring large biomolecules like DNA. Finally, our device is small enough so that, in time, it could be incorporated onto a chip.”

The accomplishment has also been described in a New York Times article. The research was published in Nature Nanotechnology (abstract).
—Jim

One broad class of proposals to develop advanced nanotech (productive nanosystems) envisions engineering polymers that mimic proteins and fold into defined three-dimensional structures with enzyme-like activities. A major advance in mimicking protein function has been made by scientists working with peptoids—polymers that resemble proteins except that the polymer backbone has monomer side groups attached to nitrogen atoms rather than to alpha-carbon atoms, as in proteins. From Lawrence Berkeley National Laboratory (credit AZoNano.com) “Nanosized Jaws Perform Like Proteins“:

Berkeley Lab scientists have developed a nano-sized synthetic polymer bundle that can fold in half and trap a zinc molecule between its jaws, a first-of-its-kind feat that mimics how proteins conduct life’s vital functions.

The scientists’ success in coaxing protein-like function from a synthetic polymer is an initial step toward developing nanostructures that combine the precision of proteins with the ruggedness of non-natural materials. Although very primitive by nature’s standards, their polymer bundle could lead to highly accurate sensors capable of operating in harsh environments, or disease-targeting pharmaceuticals that last much longer than today’s therapies.

“We’re using nature as our guide to develop functional, stable nanostructures,” said Ron Zuckermann, who is the Facility Director of the Biological Nanostructures Facility in Berkeley Lab’s Molecular Foundry. Zuckermann developed the foldable polymer bundle with Byoung-Chul Lee and Tammy Chu of the Lab’s Materials Sciences Division, and Ken Dill of the Lab’s Physical Biosciences Division and the University of California at San Francisco, where he’s a professor of pharmaceutical chemistry.

“We have a long way to go, but the ultimate goal is to make useful nano-structured materials that can function over a wide range of conditions,” said Zuckermann.

…”Our goal is to take proteins’ catalysis and molecular-recognition capabilities, and add them to a material that is more rugged and less prone to degradation,” said Zuckermann. “Proteins are precisely folded linear polymer chains of amino acids. So we thought, why not make a similar polymer chain by linking together non-natural amino acids?”

Specifically, his research team works with a protein-like chain of polymers called a peptoid. Peptoids are synthetic structures that mimic peptides, which nature uses to form complex proteins. Instead of using peptides to build proteins, however, Zuckermann’s team is striving to use peptoids to build synthetic structures that behave like proteins.

The research was published in the Journal of the American Chemical Society (abstract).
—Jim

Following yesterday’s post is yet another reason why transmission electron microscopy (TEM) is becoming an increasingly useful nanotech tool. The recently demonstrated ability to visualize individual atoms of carbon and hydrogen on a graphene surface opens new avenues for studying the behavior of hydrocarbon chains. From nanotechweb.org, written by Hamish Johnston (requires free registration) “Graphene substrate reveals hydrogen atoms“:

Physicists in the US claim to have used a transmission electron microscope (TEM) to see a single hydrogen atom — the first time that a TEM has been used to image such a light atom. The breakthrough was made by supporting the atom on graphene — a sheet of carbon just one atom thick. The team has also been able to watch hydrocarbon chains move across the graphene surface, suggesting that the technique could be used to study the dynamics of biological molecules.

There is nothing new in using TEMs to see individual atoms, but until now such instruments could only be used to image heavy atoms. One reason is that a TEM creates an image by shining an electron beam on a sample and measuring how much it is deflected by atoms of interest. Lighter atoms deflect electrons less than heavier atoms, which means that only the latter show up on an image.

Another problem is that a sample in a TEM has to be supported on a substrate that is durable enough not to be damaged by the electron beam, but thin enough for most of the electrons to pass straight through. Thin metal films or semiconductor foils are usually chosen as substrates, but these are still much thicker than single atoms and contain atoms heavier than carbon or hydrogen. Scattering from the substrate therefore tends to swamp the already weak signal from lighter atoms.

Now, however, Jannik Meyer, Alex Zettl and colleagues at the University of California, Berkeley have found a way around this problem by using graphene, the thinnest and toughest known material, as a TEM substrate (Nature abstract).

The team came up with the idea while using a TEM to study defects in graphene. However, they also discovered that they could identify individual carbon and hydrogen atoms — as well as hydrocarbon chains — that had contaminated the surface of the graphene.

…Zettl told physicsworld.com that the team is particularly interested in using the technique in the development of functionalized nanostructures — tiny objects that are engineered to perform a specific function. These are often hybrid materials — say a carbon nanotube decorated with biologically active molecules — and Zettl believes that TEM could be used to understand the real-time chemical binding or molecular dynamics processes that make such materials function.

We can hope the improved ability to study hydrocarbon molecules on a surface will aid the development of diamondoid mechanosynthesis, for example as envisioned by the theoretical work of Freitas and collaborators.
—Jim