A new molecular sensor that can encrypt and decode written messages by exploiting the properties of different chemicals is described in a study published in Nature Communications this week. This sensor can act as a modern day secret ink, offering users a means of communicating securely. The authors propose that, given recent concerns regarding global electronic surveillance, this sensor offers a secure means of bypassing electronic communication systems.

Although chemicals have been used as secret inks in the past, continually improving detection methods have made unauthorized reading of the hidden messages difficult to prevent.

David Margulies and colleagues developed a fluorescent molecular sensor, which can distinguish between different chemicals by generating unique fluorescence emission spectra. In order to send a message, the sender first converts the message (such as ‘open sesame’) to numbers by using a publicly-available alphanumeric code. Then, the sender adds an encryption key - a unique pattern generated by adding a randomly chosen chemical to the sensor - to the original message and sends the encrypted message to the recipient (by email, post or other means). The recipient, who must possess an identical device and must know the identity of the randomly chosen coding chemical, can decipher the message by adding the same chemical to decode it. In this manner, the message remains unreadable to someone intercepting the communication. The authors assess the efficacy and simplicity of the device by asking 12 users, including ten untrained users, to decrypt 23 messages, and show that all messages are successfully decrypted. They also find that a chemical password system whereby metal salts must be added in a defined order for decryption to occur can provide a further layer of protection.