An early way of signalling information across large distances, without needing a messenger, was through the use of beacons. Centuries before the advent of electric telegraphy, fires placed at exposed points would form successive stations of a relay to warn, for example, of enemy troops approaching. (Pictured is an illustration from Alexis Belloc's 1888 book La Télégraphie Historique showing ancient Greek warriors using smoke signals to communicate.) Even today, suggest Samuel Thomas and colleagues, combustion-based systems for information transmission might have something to offer (Proc. Natl Acad. Sci. USA 106, 9147–9150; 2009).

Credit: © SHEILA TERRY / SPL

Instead of piles of wood, Thomas et al. use flammable nitrocellulose strips on which information is encoded in the form of dots containing different alkali-metal salts. Once such an 'infofuse' is ignited, it emits a series of light pulses — at a rate of 5–20 Hz — as the flame front makes its way down the strip. Burning nitrocellulose produces hardly any smoke that would obstruct the view of the embers, and the emitted light pulses can be conveniently detected using either a colour camera or a spectrometer placed a couple of metres away from the burning fuse.

In their proof-of-principle demonstration, Thomas et al. encode an alphabet of 40 characters into pairs of pulses, each of which can have one or several colours, depending on whether the emission comes from lithium, rubidium and/or caesium. The spectra of these alkali metals consist of sharp, non-overlapping lines, making them suitable for encoding information. Parameters such as signal intensity, pulse duration and pulse spacing offer further degrees of freedom to play with.

So where could 'infochemistry' — as Thomas et al. dub this combination of information technology and chemistry — lead? They point out that infofuses are lightweight, self-powered and do not directly require electronics (the message transmitted in their first experiments was “LOOK MUM NO ELECTRICITY”). But ultimately, as these systems can interact chemically with their environment, the most interesting applications might be in the field of sensing, where the approach could be used both to detect and process chemical inputs, and to transmit the results.