To start, the team built an alphabet of characters using four different monomers, or molecular building blocks with different electrochemical properties. Each character was composed of different combinations of the four monomers, which yielded a total of 256 possible characters. To test the method, they used the molecular alphabet to synthesize a chain-like polymer representing an 11-character password (‘Dh&@dR%P0W¢’), which they subsequently decoded using a method based on the molecules’ electrochemical properties.

The team’s decoding method takes advantage of the fact that certain chain-like polymers can be broken down by removing one building block at a time from the end of the chain. Since the monomers were designed to have unique electrochemical properties, this step-by-step degradation results in electrical signals that can be used to decipher the sequential identity of the monomers within the polymer.

“The voltage gives you one piece of information —the identity of the monomer currently being degraded—and so we scan through different voltages and watch this movie of the molecule being broken down, which tells us which monomer is being degraded at which point in time,” says Pasupathy. “Once we pinpoint which monomers are where, we can piece that together to get the identities of the characters in our encoded alphabet.”

One downside of the method is that each molecular message can only be read once, since decoding the polymers involves degrading them. The decoding process also takes time—around 2.5 hours for the 11-character password—but the team are working on methods to speed up the process.