Electrostatic Self-Assembly of Ag-NPs Mediated by Eu3+ Complexes for Physically Unclonable Function Labels

Physically unclonable functions (PUFs) are essential for anticounterfeiting. Creating high-stability, multimode, and secure labels remains challenging. Herein, we present a novel self-assembly method for modulating the optical signals of rare-earth (RE) complexes via interactions with Ag nanoparticles (Ag-NPs). Initially, we engineered a positively charged Eu³⁺ complex ([EuL₃]³⁺), which promotes the self-assembly of negatively charged Ag-NPs to form Eu/Ag-NPs composites. The assembly of Ag-NPs induces a surface plasmon effect that boosts the luminescent quantum yield and Raman signal intensities, and modifies the luminescence lifetime of the [EuL₃]³⁺. Crucially, these micron-scale Eu/Ag-NPs can be applied to substrates, facilitating high-resolution signal acquisition and diverse information encoding within limited space. Validation experiments reveal that PUF labels crafted using Eu/Ag-NPs exhibit inherent randomness and uniqueness, along with stable and repeatable signal output. The strategic self-assembly of Ag-NPs, mediated by [EuL₃]³⁺, along with the effective modulation of material properties, paves the way for advancing high-resolution, high-information-density solutions in anticounterfeiting technologies.