27 April 2013 | NewScientist | 19

Protractor added to nano-sized toolbox

NEED to get a handle on a minuscule angle? All you need is your trusty plasmon nano-protractor, a new tool that can be used to do things like measure how DNA twists as it replicates.

Created by Gennady Shvets and colleagues at the University of Texas at Austin, the device is a gold sphere just 150 nanometres wide with an adjacent gold rod. Shining a light on the sphere causes photons to scatter in a particular way, producing a distinctive, measurable spectrum.

The sphere sits on a flat surface, and it is nudged towards the rod until one end is alongside. Ripples of electrons on the surfaces of the two objects, known as plasmons, then become coupled. That modifies the scattered light in a way that creates a dip in the spectrum, which is linked to the alignment between the sphere and the rod (Nature Photonics, doi.org/mbc).

Placing it on, say, a DNA molecule will change the angle between the rod and the sphere, changing the position of the dip. You use the protractor by varying the light’s orientation until the dip is most pronounced and the new angle is revealed.

Bacterial ‘dirty bomb’ nukes pancreatic cancerIN THE fight against a silent killer, you’ve got to resort to dirty tactics.

Pancreatic cancer is deadly because it tends to spread, or metastasise, to other parts of the body before symptoms appear. In previous work in mice, Claudia Gravekamp of the Albert Einstein College of Medicine in New York had shown that weakened listeria bacteria colonise tumour tissue but not healthy tissue. What’s more, the bacteria seem to home in on the metastatic tumours.

To take advantage of this, her team have now armed the bacteria

with a radioactive payload. They seeded mice with human pancreatic tumours and then injected them daily with the souped-up bacteria for a week, giving them a week off before four more days of injections. A few days later, there were on average 90 per cent fewer metastatic tumours in this group than there were in untreated mice, and the average weights of original pancreatic tumours had decreased by 64 per cent. A week later, the animals’ livers and kidneys had completely cleared the radioactive bacteria

IN A cold void in space, three galaxies eke out an existence. Linked by a rope of invisible dark matter, they reveal how all galaxies evolve.

Most galaxies live in clusters of hundreds or even thousands (see picture). These clusters form the filaments of a great cosmic web. But the gaps between filaments can host galaxies too. The newly found trio, VGS 31, is the first void galaxy group to be studied in multiple wavelengths.

Burcu Beygu of the Kapteyn Astronomical Institute at the University of Groningen, the Netherlands, and colleagues, who

discovered the group, mapped a cloud of hydrogen atoms that stretches nearly 400,000 light years across its length. The cloud is moving along a path connecting the galaxies, which suggests they lie along a dark matter filament that seeded their formation – like cluster galaxies (The Astronomical Journal, doi.org/k9x).

The VGS 31 galaxies seem to grow in a similar way to cluster galaxies, feeding on gas from the hydrogen cloud, but at a slower rate. This has kept them in an early developmental stage rarely seen in cluster galaxies, which used up available gas long ago.

Void galaxies cling to dark matter

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from their systems, with no damage to either organ (PNAS, DOI: 10.1073/pnas.1211287110).

Gravekamp thinks the radioactive bacteria affected metastatic tumours most because cells there were still rapidly multiplying, leaving their chromosomes more open to damage than those in healthy tissues or in the original tumour.

If the approach progresses to clinical trials, says Gravekamp, the idea would be to cut out the original tumour, then clear the rest with radioactive listeria.

5 + yellow = 7. True or false?

COLOURS do add up, at least if you have synaesthesia, that is. Remarkably, people who associate colours with numbers can switch between the two when doing simple equations.

Synaesthesia is thought to be the result of cross-wiring in the brain enabling people to associate numbers with colours. To test this skill, Daniel McCarthy and his colleagues at the University of Nevada in Reno asked three people with synaesthesia to do a maths test.

Using their specific colour associations, each volunteer was shown equations such as 4 + white = 5 and asked whether it was true or false. All three answered just as quickly and accurately to equations where colours replaced numbers as when only numbers were used.

Brain imaging showed similar patterns of activity whether the volunteers were processing equations with numbers or colours. This suggests that colours and numbers are processed in parallel, says McCarthy, who presented the group’s results at the Cognitive Neuroscience Society meeting in San Francisco last week.

It will be interesting to study whether the colour and number link is an advantage or disadvantage when children with synaesthesia are learning maths, says Roi Cohen Kadosh of the University of Oxford.

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