Sixth sense: How do we sense electric fields?

A research team has found the first actual "sensor mechanism" that allows a living cell detect an electric field (stock image).

A variety of animals are able to sense and react to electric fields, and living human cells will move along an electric field, for example in wound healing. Now a team lead by Min Zhao at the UC Davis Institute for Regenerative Cures has found the first actual "sensor mechanism" that allows a living cell detect an electric field. The work is published Oct. 9 in the journal Nature Communications.

"We believe there are several types of sensing mechanisms, and none of them are known. We now provide experimental evidence to suggest one which has not been even hypothesized before, a two-molecule sensing mechanism," Zhao said.

Zhao and colleagues have been studying these "electric senses" in cells from both larger animals (fish skin cells, human cell lines) and in the soil-dwelling amoeba Dictyostelium. By knocking out some genes in Dictyostelium, they previously identified some of the genes and proteins that allow the amoeba to move in a certain direction when exposed to an electric field.

In the new work, carried out in a human cell line, they found that two elements, a protein called Kir4.2 (made by gene KCNJ15) and molecules within the cell called polyamines, were needed for signaling to occur. Kir4.2 is a potassium channel -- it forms a pore through the cell membrane that allows potassium ions to enter the cell. Such ion channels are often involved in transmitting signals into cells. Polyamines are molecules within the cell that carry a positive charge.

Zhao and colleagues found that when the cells were in an electric field, the positively-charged polyamines tend to accumulate at the side of the cell near the negative electrode. The polyamines bind to the Kir4.2 potassium channel, and regulate its activity.

He cautioned that they do not yet have definitive evidence of how "switching" of the potassium channel by polyamines translates into directional movement by the cell.

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The above post is reprinted from materials provided by University of California - Davis. Note: Materials may be edited for content and length.

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Journal Reference:

1. Ken-ichi Nakajima, Kan Zhu, Yao-Hui Sun, Bence Hegyi, Qunli Zeng, Christopher J. Murphy, J. Victor Small, Ye Chen-Izu, Yoshihiro Izumiya, Josef M. Penninger, Min Zhao. KCNJ15/Kir4.2 couples with polyamines to sense weak extracellular electric fields in galvanotaxis. Nature Communications, 2015; 6: 8532 DOI:10.1038/ncomms9532

Africa's urban waste: A valuable source of electricity

Estimated electricity production from the total waste generated in Africa could reach 122.2 TWh in 2025, or more than 20% of the electricity consumed in 2010 at continental level (661.5TWh), according to a JRC co-authored study which analysed the potential of urban solid waste for Africa's electricity needs.

This is an equivalent to the energy needed for 40 million households in 2025 in Africa. However waste management is poor -- the potential electricity of waste actually collected was estimated at 83.8 TWh in 2025. Still, this represents energy needed for 27 million families in 2025, considering the average electricity consumption in 2010 in Africa.

Many Africans do not have access to energy. Besides providing an interesting share of gross energy consumption and electricity as a renewable resource, energy recovered from waste could also help minimise the impact of municipal solid waste on the environment. The study Evaluation of energy potential of Municipal Solid Waste from African urban areas provides an estimate of the total potential of energy from waste incineration and from landfill gas (LFG) 2025 for each African country.

In 2010, there were more than 600 waste-to-energy facilities in the world, most of them in Europe (472), Japan (100) and the US (86). In Africa, a very limited share of waste is recovered and reused, and only major or capital cities have waste management systems.

In a number of countries, the use of waste to generate electricity could have a significant impact. Waste can have a very high contribution to providing electricity to citizens and alleviate energy poverty especially in countries with low access to electricity and reduced electricity consumption per capita, such as the Central African Republic, Burundi, Guinea-Bissau, Mali, Sierra Leone, Rwanda and Somalia.

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The above post is reprinted from materials provided by European Commission Joint Research Centre. Note: Materials may be edited for content and length.

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Journal Reference:

1. N. Scarlat, V. Motola, J.F. Dallemand, F. Monforti-Ferrario, Linus Mofor.Evaluation of energy potential of Municipal Solid Waste from African urban areas. Renewable and Sustainable Energy Reviews, 2015; 50: 1269 DOI: 10.1016/j.rser.2015.05.067

Just a touch of skyrmions

Ancient memory devices such as handwriting were based on mechanical energy--but in the modern world they have given way to devices based generally on electrical manipulation.

Today, scientists from the RIKEN Center for Emergent Matter Science may be about to wind back time. In a study published in Nature Communications, they have found a way to manipulate skyrmions--tiny nanometer-sized magnetic vortices found at the surface of magnetic materials--using mechanical energy.

Skyrmions have been widely touted as providing the basis for new high-density memory devices because of their small size and relative stability. However, it has proven difficult to create, delete, and move them, and skyrmion-based devices are not yet competitive with other high-tech devices based on spin.

According to Yoichi Nii of the Emergent Device Research Team, the first author of the study, "We began from the simple question of whether it would be practical to turn skyrmions on and off with mechanical force, and wondered how much force would be required. We imagined it would be substantial."

The group set out to work using a specially designed stress probe that could apply mechanical stress to the surface of manganese-silicide, a "chiral magnetic" that is known to host skyrmions, cooled to very low temperature. They found, to their surprise, that the force to create and destroy skyrmions was quite low, less than ten nanonewtons per skyrmion, which is comparable to the pressure exerted by the tip of a conventional pencil when we write in a notebook. A force applied perpendicular to the magnetic field led to the creation of skyrmions, while one parallel to the field turned the skyrmions off, making it possible to turn them on and off mechanically.

"This means," says Yoshihiro Iwasa, leader of the Emergent Device Research Team, "that we may be able to fabricate devices in which skyrmions are created and deleted by a small mechanical force. This could be an inexpensive and low-energy-consuming way to create new low-cost memory devices and open the road to skymionics."

One drawback of the current work is that it does require cooling the magnet to very low temperatures for the system to work. According to Nii, they plan to continue experiments with a variety of materials to try to identify ones that can host skyrmions that can be manipulated mechanically but at higher temperatures.

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1. Y. Nii, T. Nakajima, A. Kikkawa, Y. Yamasaki, K. Ohishi, J. Suzuki, Y. Taguchi, T. Arima, Y. Tokura, Y. Iwasa. Uniaxial stress control of skyrmion phase. Nature Communications, 2015; 6: 8539 DOI:10.1038/NCOMMS9539

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The above post is reprinted from materials provided by RIKEN. Note: Materials may be edited for content and length.

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