Spectral physical unclonable functions: downscaling randomness with multi-resonant hybrid particles.

Optical physical unclonable functions (PUFs) are state-of-the-art in advanced security applications. Fabricated with inherent randomness, they generate fingerprint-like responses, serving as trust anchors for material assets. However, the existing PUFs, typically reliant on microscopic spatial features, face increasing threats from rapidly advancing microscale manipulation techniques. Here, we present novel PUFs based on random nanoscale variations within multi-resonant gold-silicon particles. These inevitable structural differences, coupled with strong optical resonances, provide unique spectral features in particles' photoluminescence (PL), which we encode as unclonable keys. Our approach surpasses the shortcomings of diffraction-limited designs, additionally offering a multi-functional platform for robust authentication of goods and verification of individuals. We demonstrate two security label models based on PL mapping and direct PL imaging, as well as a concept for the first all-optical one-time password verification token with an exceptionally high storage density of unique information. This work paves the way toward nanoscale-enabled unclonability, bringing enhanced security for hardware-based cryptography, personalized access control, and cutting-edge anti-counterfeiting.