File this in the "useless but really cool" department. Scientists, inspired by the fact that DNA encodes information in its basic chemistry, pondered other systems that could function in an analogous manner. The system that they came up with is every science geek's dream: something that you set on fire and watch as it glows in different colors. The precise sequence of those colors is actually a code, one that they used to convey information—in their test case, the message "look mom no electricity."
The system is actually remarkably low-tech. The medium on which the message was written is nitrocellulose, bane of old-school molecular biologists, but known in the magic community as flash paper. It burns quickly and intensely, and doesn't leave behind any smoke that would interfere with imaging. The reason nitrocellulose was popular with molecular biologists is that it will absorb solutions of water, and then lock their contents in place as it dries. This would typically be used for holding DNA or proteins, but it works for simple salts, as well.
To encode information, the researchers took advantage of something I remember from a high school chemistry class: heating salts that contain members of the first column of the periodic table produces flames that glow some very specific colors. So, their system for storing the information involved running some nitrocellulose through an ink jet printer, which deposited small drops of salt solutions in a controlled pattern. Those solutions contained some combination of lithium, rubidium, and cesium, which have distinct emissions peaks when heated. If burning is started on one end of the nitrocellulose, the flames would glow different colors as each of these dots was vaporized. The researchers called their creation an "infofuse."
They demonstrated that the burning infofuse could be read either with a spectometer or a digital camera. Sodium was included in each dot to provide a register for the message, and then the specific combination of the remaining three salts provided the equivalent of a set of bits. Given three salts and the authors' decision not to include a spot with no salts present, they got seven possible combinations for each spot that burned. Add a second of these spots, and you're up to 49 potential combinations—enough for Roman letters, Arabic digits, and a few punctuation marks.
Their data looks remarkably clean. The authors say that the primary limiting issue is the fact that the infofuse burns out of the field of view of the devices that read the spectra, but they were using a pretty simple system to do the reading: the fuse was just hung vertically from a clip when it was set on fire. They also used lithium salts to show that it was possible to read different concentrations based on the intensity of the light emitted, so future improvements could see more information stuffed into a single spot.
I'd suggested at the start that this was pretty useless—when it comes to practicality, I'll take a USB stick any day—but the authors suggest that it's part of something that will be much bigger, which they're calling infochemistry. They're pitching infochemistry as a way for information to be encoded based on the chemistry of the environment, providing a bridge for things like environmental sensing and diagnostic tools. It's an argument that's frustratingly short on specifics, but one of the authors is at DARPA, and they have a tendency to think long-term.
PNAS, 2009. DOI: 10.1073/pnas.0902476106
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