Alive and charging

Kollegala Sharma reports on research that turns snails into living batteries. When stuck with electrodes, snails produce as much as 0.5V of current.

What use can snails be? Some can be of plain nuisance value, devouring carefully tended gardens, while some can be delicious, exotic snacks.

But, for Evgyn Katz, a nano technologist at the Ilse Katz Institute for Nanoscale Science and Technology at the Ben-Gurion University, Israel, snails can also be inexhaustible sources of electricity - batteries that recharge themselves and do not dirty the environment.

In a report published in the Journal of American Chemical Society, Katz and colleagues show how delicately designed electrodes turn white-lipped snails (Neohelix albolabris) into live batteries.

Batteries work by producing a flow of electrons, which we call electricity. While on the one end of the battery, electrons are freed from atoms by chemical reactions; at the other end, the electrons are consumed in another chemical reaction.

The electrons are picked up at one end by an anode and delivered, or drained out of the circuit at the other end, through a cathode.

A battery remains live as long as there are free electrons. If, for any reason, electron supply stops, the battery goes dead. It usually happens because the chemicals participating in the reactions get depleted.

Katz’ ‘living’ battery, however, seems to have no such snags, as it relies on glucose for providing electrons. Glucose, as we all know, is what supplies energy for activities of all cells and is produced continuously in all living beings.

Katz’ team, which has been working for several years on the idea of developing a sustainable, ‘bio-fuel’ battery, tasted success with the designing of special bioelectrodes that use glucose.

The bioelectrodes are made of carbon nanowire – a tube made of nanocarbon with a structure that resembles a wire mesh tube – instead of the usual metal or ceramic materials. Katz’ team stuck enzymes on the tube to create the bioelectrodes. The tubular structure of nanocarbon helps more glucose to reach the enzymes.

For the anode, the team used an enzyme with a name that is mouthful, the pyrroloquinoline quinine dependent glucose dehydregenase (PQQ-GDH). PQQ-GDH converts glucose to glucoronic acid, simultaneously releasing an electron and oxygen. For the cathode, the team used laccase enzyme which converts oxygen into water. The oxygen consumed at one end is restored at the other end, but a current is produced.

Effectiveness of electrodes

Katz’ team has demonstrated the effectiveness of bioelectrodes both in test tubes and in a living animal. When stuck with electrodes, snails produced as much as 0.5 V current, about one-third of that provided by a pen-cell. Won’t draining glucose thus famish the animal?

Probably no, says Katz. “The glucose concentration decreases, but probably not too much to result in a hypoglycemic shock. In the experiment described, the glucose concentration was decreased by 18 per cent,” says Katz.

The voltage, however, drops after some use, as happens with any battery. But the snail battery is different in that if such a discharged battery is left undisturbed, it gets recharged.

The voltage drops may be because the glucose supply is drained off at the anode faster or the snail may be producing glucose at a snail’s pace.

“The activity is restored in a few minutes,” reassures Katz, and adds that “the produced electrical energy can be accumulated in a condenser and then the accumulated energy can be released as required.”

In another paper about to be published, the team used a series of electrode-implanted clams to even run a small motor.

Usefulness

What use can such live batteries be? We can’t carry them around to charge devices, did you say? There can be two uses, says the team. If not the snails, the bioelectrodes at least can be used to power implanted biomedical devices such as pace makers, using the glucose circulating in the blood of humans.

Or it can be used in “environmental monitoring, military and homeland security applications where small animals like snails, worms and insects are used to power sensors and wireless transmitters. Our work is looking at the second possibility,” says Katz.

That surely is not fantasy. “The technology for microelectronic devices is available. Such devices can be activated with the micropower produced by the “electrified snail”.

The devices may perform various sensing (video cameras, gas sensors, etc) and they can be equipped with wireless transmitters. The devices might be fixed externally on the body and connected to the implanted electrodes with some wires,” says Katz. 

Well, Katz team’s innovation may not make business hard for current battery producers. But it opens up an interesting possibility of snails snooping around corners, may be for hidden contrabands, chemical leaks or, in the worst case, radiation leaks.

And being green, the living rechargeable batteries do not need any waste disposal instructions!