Covert and Multiplexed SERS QR Codes via Inkjet Printing

ABSTRACT Covert patterns have an extra layer of security protection for anti‐counterfeiting labels as compared with the traditional overt ones. To increase the complexity and security of quick response (QR) codes, it would be valuable to make covert QR codes that will be only scannable after a certain decoding process. In this work, the use of surface‐enhanced Raman spectroscopy (SERS) is explored to fabricate covert QR codes. Through developing new Raman‐active security inks, we can prepare covert QR codes using a convenient inkjet printing method. These QR codes will not be revealed directly. They can only be decoded using a confocal Raman microscope. In addition, multiplex QR codes can be accomplished using multiple Raman probes in printing. Our results showed that the printed QR codes are covert, have strong SERS signals, and can be easily recognized after the SERS decoding. It is anticipated that there is great potential for using such covert and multiplexed SERS‐based QR codes for advanced anti‐counterfeiting applications.