Mass-produced multiscale unclonable plasmonic security labels by a robotic wet-chemical system

Plasmonic physical unclonable function (PUF) labels have been proven to be an effective anti-counterfeiting strategy, but their high tunability and multi-encoded capabilities remain to be explored for higher encoding capacity (EC). Herein, the PUF labels with high security level are prepared, which are constructed by the micro-domains of plasmonic nanostructures. The micro-domains are formed by mask-assisted ultraviolet (UV) exposure and 50 nm gold nanoparticles (Au NPs) electrostatic adsorbed on the unexposed area. And a robotic wet-chemical system is invented to modulate the in situ epitaxial growth of Au NPs by programming the growth conditions for human-free preparation and mass production. Three random processes, including mask-assisted UV photochemical reaction, electrostatic self-assembly, and in situ epitaxial growth, make sure multiscale random features. Thus, two-dimensional views with different resolutions can be obtained by three random optical imaging signals-bright field (BF), Raman imaging (RI), and dark field (DF), and the random signals will change with the modulation methods, leading to higher EC. Through analyzing the random features, a robust image authentication system is built, and the EC is calculated as 1.8 × 104966 in a 50 × 50 μm2 domain for each modulation method.