David Margulies and colleagues, Weizmann Institute of Science, Rehovot, Israel, have developed a chemical “ink” that encodes text messages securely. Their system relies on a molecular sensor based on proline functionalized with three fluorophores. Other functional groups (e.g., boronic acid, thiourea, or sulfonamide) bind to randomly chosen species, such as saccharides, metal ions, or others, that serve as the molecular basis for the encryption keys.

The sender measures the optical emission intensity at 20-nm intervals for a solution containing the molecular sensor and a random compound (e.g., NaHCO₃). By this, the sender generates a sequence of numbers that forms the encryption key. The sender converts each letter in a line of text to a number using an alphanumeric key and then adds the corresponding number from the encryption key to each digit.

The receiver generates the decryption key using the same agreed-upon chemical solution. He or she subtracts the sequence of emission intensities from each corresponding encrypted number. This restores the original sequence of numbers, which can then be converted back to the original text.

• Message in a molecule,
  Tanmay Sarkar, Karuthapandi Selvakumar, Leila Motiei, David Margulies,
  Nat. Commun. 2016.
  DOI: 10.1038/ncomms11374