The battery components, described in Proceedings of the National Academy of Sciences, are only four micrometers wide and could find application in labs on a chip or other small medical devices, the researchers say. Building microscopic batteries has proved difficult in the past because the proportion of electrochemically active material inside a battery decreases as its size is reduced.  As a trend in electronics is toward patterning devices onto flexible or curved surfaces, which power sources must be able to adapt to, the MIT work suggests that small, reliable batteries can be both made on the microscopic scale and embedded on a variety of surfaces.

"What's new about this research is both the size [of the battery electrodes] and the process we used to position them," says the bacteriaphage toolkit guru, Angela Belcher, (right) professor of materials science at MIT, who collaborated with colleagues Yet-Ming Chiang and Paula Hammond on the work.

They began by etching columns four micrometers wide and a few micrometers tall onto a silicon-based surface to effectively create a stamp. They then deposited alternating layers of two different polymers, which served as the solid electrolyte and battery separator, on top of these columns.

The virus, called M13, which the researchers  employed in earlier self-assembly studies, was then used to make the anode. The virus is made of proteins, which can be genetically modified to react with particular substances. In this case, it generated structured arrays of cobalt oxide nanowires on top of the solid electrolyte. Finally, the assembled electrodes were flipped over and pressed onto thin bands of platinum, which were joined to a copper contact in order to collect current from the device.

The researchers tested the performance of the device using a layer of lithium foil.
"The quality of the electrodes is exactly the same as before," says Belcher, referring to the group's earlier demonstrations of larger virus-assembled batteries.

 She adds that the cobalt oxide anode has a much higher charge storage capacity than the carbon-based electrodes typically used in lithium-ion batteries, and that it's stable throughout charging and discharging. It also has a higher density of active material than do conventional batteries.

Other advantages of virus assembly include functioning at room temperature and precise control over the size and spacing of nanomaterials, leading to uniform and easily reproducible devices. The researchers' next goal is to add a virus-assembled cathode to create a complete battery.

As they have experimented with different materials and fabricated cathodes on a larger scale, Belcher says that incorporating micro cathodes into the printing method is "definitely possible." In the future, she adds, they will work toward devices with higher energy density and creating devices that are biocompatible.

Bacteria self-sacrifice as  survival strategy
ETH Zurich biologists, led by Professors Martin Ackermann and Wolf-Dietrich Hardt, in collaboration with Michael Doebeli of the University of British Colombia in Vancouver (CN), have described how random molecular processes during cell division allow some cells to engage in a self-destructive act to generate a greater common good, thereby improving the situation of the surviving siblings.

(Right and below: Salmonella bacteria (Salmonellae typhimurium) in the mouse intestine. The bacteria are green, the intestine of the mouse show as blue and red. Courtesy: Wolf-Dietrich Hardt/ETH Zürich)

The biologists investigated this unusual biological concept using the pathogenic salmonella bacteria. Diseases caused by salmonellae are unpleasant and even life-threatening. When contaminated food is consumed the salmonella bacteria enter the gastro-intestinal tract triggering infection, with vomiting and diarrhoea lasting for days.

Normally, salmonellae grow poorly in the intestine because they are not competitive with other gut bacteria.  This  changes if salmonellae induce an inflammatory response, namely diarrhoea, which suppresses the other bacteria. The inflammation is triggered by salmonellae penetrating into the intestinal tissues. Once inside, salmonellae is killed by the immune system. This creates a conflict: salmonellae are either suppressed by the other bacteria in the gut, or die trying to eliminate these competitors.

Ackermann, Hardt and Doebeli report that salmonellae have a solution to this conflict. Inside the gut, the samonella bacteria form two groups that  job-share. The first group invades the tissue, triggers an inflammation, and dies. The second group waits inside the gut until inactivation of the normal intestinal flora gives them an opportunity to strike.The second group then multiplies unhindered.

Random processes to self-sacrifice
What determines whether an individual salmonella bacterium cell self-sacrifices, or will wait and benefit from the sacrifice of others? The two groups are clones of the same genotype. Genetic differences do not play a role. The difference between the two groups is a result of random molecular processes during cell division.

Cellular components are randomly distributed between the two daughter cells with each cell receiving a different amount. The resulting imbalance can be amplified leading to different properties of the clonal siblings. Recently it has been recognised that such random processes in a cell can have a large influence on individual cells.  The work by the ETH Zurich researchers reveals a new biological explanation for the phenomenon. The two salmonella phenotypes share their work, with the result being that they achieve what a single phenotype on its own would not be capable of doing.

This scenario is fundamentally different from the usual explanations, and presupposes that individual phenotypes interact and have an effect on one another. The self-sacrifice of phenotypes may be quite common among pathogenic bacteria, for example, among the pathogens causing diarrhoea after antibiotic treatment (clostridia) or pneumonia (streptococci).

Professor Ackermann (left) says that “Random processes could promote job-sharing in many different types of organisms.” Many bacteria manufacture substances which are toxic to their hosts, only released into the host environment if the bacteria sacrifice themselves - if this is the sole method to get the toxin out of the cell. This is why every cell makes a decision: toxin and death or no toxin.

He stresses that it would not have been possible to study this theory so thoroughly without the collaboration that took place among the three specialist groups: Professor Hardt’s group specialises in salmonella infections; Professor Doebeli is a mathematician and theoretical biologist; and Professor Ackermann’s group focuses on phenotypic noise.

Source: http://www.technologyreview.com
Web:http://dmse.mit.edu/faculty/faculty/belcher/
http://www.tb.ethz.ch/people/martinac