Raman Ink for Steganography

Abstract Steganography, also known as “invisible” communication, refers to the technique of hiding information into another medium such as video, audio, image, and text. Surface‐enhanced Raman scattering (SERS) nanotags are well suited to information encoding owing to their nanoscale dimensions, fingerprint optical spectral features, and remarkable multiplexing capability. Herein, Raman ink, fabricated by doping a new type of SERS nanotags (gap‐enhanced Raman tags, GERTs) into commercial ink, is demonstrated as security ink for multiplexing steganography. A stego‐text is written using two types of Raman ink containing different GERTs with diverse Raman signals, imaged via a confocal Raman system, and processed by the classical least squares method to extract the hidden message. The Raman ink generates distinct spectral profiles with low background from pure ink upon near‐infrared laser irradiation. A multiplexing combination of seven kinds of messages extracted from the written stego‐text is demonstrated, which adds enhanced safety and flexibility to information encoding. In addition, Raman ink exhibits good photostability and long‐term stability. Therefore, GERTs‐based Raman ink is promising for steganographic use in information security.