The ability of independent movement is generally considered one of the characteristics of living beings, or, in extreme cases, robots. Dr. Martin Hanczyc decided to pick this axiom to pieces, conducting an experiment at the University of Southern Denmark. He forced a drop of alcohol not just to move, but also to make its own way through the labyrinth.
"The system itself is very simple, but it displays sophisticated behavior", says Hanczyc, who is now working at the University of Trento.
The scientist used an aqueous solution of sodium decanoate (CH3 (CH2) 8COO-Na +) and decanol droplets (C10H21OH), which began to move in search of salt concentrations.
"Salt is the stimulus that makes them move," says Hanczyc. "They move because the salt gradient provides a different energy landscape. It is like taking a ball that is laying still on a flat surface and then suddenly make the surface hilly. The ball will roll to the lowest accessible point. That is what the droplet is doing. Without a salt gradient every direction in which a droplet might move looks the same (flat). But with a salt gradient coming from one direction the droplet can move energetically downhill into the salt gradient. And stronger salt concentrations will attract the droplet more."
If there is a "choice" between the salt sources of different concentration, the droplets will move toward higher concentrations. Temperature gradients may also have a similar effect.
Certainly for those who like to drink it might be more interesting if in the course of the experiment ethanol was used instead of decanol – fatty alcohol, which irritates the skin and mucous membranes. Nevertheless, Hanczyc said that such drops are able to perform useful tasks.
"The droplet can act as a carrier for chemistry that can find a target destination and release its content, such as flavoring and medicine", Hanczyc says.
The challenge remains as to how to create salty conditions where the droplets need to go, but Hanczyc has previously achieved similar feats with oil droplets and wonders whether this sort of self-moving behavior might once have been a predecessor to life .