## Two dimensional mass spectroscopy

### May 15, 2007

Title: Single-molecule mass spectroscopy in solution using a solitary nanopore

Authors: Joseph W F Robertson, Claudio G Rodrigues, Vincent M Stanford, Kenneth A Rubinson, Oleg V Krasilnikov, and John J Kasianowicz

Abstract: We introduce a two-dimensional method for mass spectrometry in solution that is based on the interaction between a nanometer-scale pore and analytes. As an example, poly(ethylene glycol) molecules that enter a single {alpha}-hemolysin pore cause distinct mass-dependent conductance states with characteristic mean residence times. The conductance-based mass spectrum clearly resolves the repeat unit of ethylene glycol, and the mean residence time increases monotonically with the poly(ethylene glycol) mass. This technique could prove useful for the real-time characterization of molecules in solution.

## In Nature this week

### May 3, 2007

1. An editorial urges scientists to keep e-notebooks and share them;
2. Joseph Mazur reviews Ian Stewart’s Why beauty is truth: the history of symmetry;
3. Dirk M Guldi writes about the recent report by Simmons et al of controlling the electrical conductivity of single walled nanotubes using light; such light sensitivity is apparently achieved by filling the nano tubes with photosensitive dyes;
4. Tim D White pays his tributes to a paleoanthropologist, F Clark Howell.

## In Nature this week

### April 27, 2007

1. Of course the big story, as I blogged elsewhere, is the higher dimensional generalizations of the Neumann-Mullins rule of grain growth by MacPherson and Srolovitz:

Cellular structures or tessellations are ubiquitous in nature. Metals and ceramics commonly consist of space-filling arrays of single-crystal grains separated by a network of grain boundaries, and foams (froths) are networks of gas-filled bubbles separated by liquid walls. Cellular structures also occur in biological tissue, and in magnetic, ferroelectric and complex fluid contexts. In many situations, the cell/grain/bubble walls move under the influence of their surface tension (capillarity), with a velocity proportional to their mean curvature. As a result, the cells evolve and the structure coarsens. Over 50 years ago, von Neumann derived an exact formula for the growth rate of a cell in a two-dimensional cellular structure (using the relation between wall velocity and mean curvature, the fact that three domain walls meet at 120° and basic topology). This forms the basis of modern grain growth theory. Here we present an exact and much-sought extension of this result into three (and higher) dimensions. The present results may lead to the development of predictive models for capillarity-driven microstructure evolution in a wide range of industrial and commercial processing scenarios—such as the heat treatment of metals, or even controlling the ‘head’ on a pint of beer.

2. Henry Gee reviews The Discovery of the Hobbit: The scientific breakthrough that changed the faceof human history; and, John Hawks is not happy about the review (though he seems to have liked the book)–his review of the review is a must read, at least for sections like these:

…Gee spends several paragraphs expositing on his own role in the publication of the Homo floresiensis announcement. We learn some interesting little facts, like how the authors wanted to name the species “Sundanthropus floresianus” until a reviewer pointed out that future students would confuse the name with a flowery butt.I kid you not. Nature has a layer of reviewers to take tushie references out of taxonomy. Somehow they can’t tell a left femur from a right, but they’re on the watch for sphincter-species!

3. How does one weigh molecules, single cell virus, and bacteria whose weight are of the order of a few hundreds of femtograms (and, which are in a solution)? Liesbeth Venema describes a method that has been developed recently and reported in the same issue of Nature.
4. Martin Campbell-Kelly pays his tributes to John Backus, the inventor of FORTRAN in an obituary piece.

## Model interfaces in nanocomposites

### April 18, 2007

In a News and Views piece, Linda Schadler puts the recent work of Rittigstein et al on interfaces in model polymer nanocomposites in perspective:

Three important conclusions arise from this work. First, the size of the interfacial region (which is half the interparticle spacing or film thickness) can be as large as 250 nm, and depends on the degree of interaction between the polymer and the particle. Although this functionality remains to be quantified, this is one of the first times this behaviour has been proved and quantitatively measured in a controlled nanocomposite system. Second, they show a quantitative correlation between thin-film thickness and an ‘effective interparticle spacing’ at which changes in Tg begin to occur. Third, they find that the ageing rate — the rate at which the amorphous polymer approaches its equilibrium state — decreases dramatically in both the ‘real’ and ‘model’ nanocomposites, which implies that nanocomposite properties will be more stable than pure polymers over time.

Take a look!

## All-electrically controlled magnetic memory devices

### April 18, 2007

In a News and Views piece in the latest Nature Materials, Russell P Cowburn writes about spintroics. Here is the abstract:

The magnetization direction in the centre of a submicrometre magnetic disk can now be switched by an electrical current. This discovery demonstrates the potential of realizing all-electrically controlled magnetic memory devices.

The article begins with a discussion of magnetoresistance (change in electrical resistance due to a change in the magnetic state of the material), and its complementary effect, spin transfer (change in the magnetization of the material due to the passage of current–the spin of the electrons, while moving through regions of magnetization gradients, change and in turn also exert a torque on the magnetization of the material).  And, then it proceeds to discuss vortex cores and the recent discovery that they can be manipulated by electric fields. Finally, the article ends with a discussion as to why technologists are excited about spin transfer. A lucidly written article worth your while.

PS: The wiki page on spintronics is also a nice place to look for resources–it links to this 2002 Scientific American article for example.

## Self-assembly of nanoparticles

### April 16, 2007

Title: Plastic and moldable metals by self-assembly of sticky nanoparticle aggregates

Authors: R Klajn, K J M Bishop, M Fialkowski, M Paszewski, C J Campbell, T P Gray and B A Grzybowski

Abstract: Deformable, spherical aggregates of metal nanoparticles connected by long-chain dithiol ligands self-assemble into nanostructured materials of macroscopic dimensions. These materials are plastic and moldable against arbitrarily shaped masters and can be thermally hardened into polycrystalline metal structures of controllable porosity. In addition, in both plastic and hardened states, the assemblies are electrically conductive and exhibit Ohmic characteristics down to $\approx$20 volts per meter. The self-assembly method leading to such materials is applicable both to pure metals and to bimetallic structures of various elemental compositions.

## Ultrasound to electric energy conversion

### April 8, 2007

Title: Direct current nanogenerator driven by ultrasonic waves

Authors: X Wang, J Song, J Liu and Z L Wang

Source
: 6 April 2007, Vol. 316, No. 5821, pp. 102-105

Abstract
: We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.

Internet resources: SciAm news report