  Counterfeiting threatens human health, social equity, national security and
global and local economies. Hardware-based cryptography that exploits physical
unclonable functions (PUFs) provides the means for secure identification and
authentication of products. While optical PUFs are among the hardest to
replicate, they suffer from low encoding capacity and often complex and
expensive read-out. Here we report PUF labels with nanoscale features and
optical responses that arise from the guided self-assembly of plasmonic
nanoparticles. Nanosphere lithography combined with DNA origami placement are
used to create tightly packed randomised nanoparticle assemblies. Nanoscale
variations within these assemblies define the scattering color of the
individual spots that are arranged in a hexagonal lattice with spacing down to
the optical resolution limit. Due to the nanoscale dimensions, the intrinsic
randomness of the particle assemblies and their resulting optical responses,
our PUFs are virtually impossible to replicate while they can be read-out with
economical 3D-printed hardware.
