Hierarchical assembly of upconversion nanoparticle–grating hybrids on flexible nanofibers for multi-level physical unclonable functions

Electrospun nanofiber-based physical unclonable functions (PUFs) offer ideal security features, positioning them as highly promising for document and packaging authentication as well as data encryption. Additionally, electrospun nanofiber membranes serve as versatile substrates for integrating functional components and nanoparticles, offering significant potential for photonic integration and enhanced optical security. In this study, we integrate plasmon-enhanced upconversion luminescence with hierarchical diffraction gratings on electrospun nanofiber membranes to create a multi-level, high-security PUF system. A novel approach is used to co-assemble silver nanocubes and upconverting nanoparticles at the oil-water interface, followed by microcontact printing to efficiently transfer the Ag/UCNP gratings onto electrospun nanofiber membranes. This hybrid structure exhibits a disorder-order-disorder pattern across multiple length scales: disordered Ag/UCNPs at the nanoscale, short-range ordered grating units at the microscale, and long-range randomness introduced by the electrospun nanofiber network at the macroscale. These structural features contribute to three distinct optical anti-counterfeiting mechanisms: plasmon-enhanced upconversion luminescence emission, achieving a fivefold increase in green luminescence intensity under 980 nm laser excitation; angle-dependent rainbow holography, generated by the ordered grating units; and physically unclonable patterns, which enable cryptographic key generation with a vast key space of 10⁶³. The integration of multi-responsive nanoparticles with electrospun nanofiber membranes opens new possibilities for lightweight, compact, and secure optical devices, providing a robust platform for next-generation authentication and encryption technologies.