3-D Au/ZnO Hierarchical Array Engineering: Unraveling Four-Stage Interfacial Adsorption Mechanism for Robust Self-Cleaning SERS With Ultrahigh Reproducibility

Abstract

Unpredictable variation of surface-enhanced Raman scattering (SERS) intensity, caused by uncontrolled interfacial adsorption, severely limits quantitative applications. To address this issue, the evolution of analyte adsorption states was systematically investigated on a 3-D Au nanoparticles/ZnO nanoflowers (Au NPs/ZnO NFs) substrate. By correlating Raman signal fluctuations with finite element method (FEM) simulations, a four-stage interfacial adsorption model consisting of direct adsorption, indirect adsorption, saturation, and crystallization was established. Spatial volume integral evaluations reveal that during initial adsorption, capillary forces drive molecules to form an optimal monolayer within extreme nanogaps, thereby maximizing the utilization of hot spots and triggering a rapid signal surge. Conversely, excessive volume induces thick crystallization, leading to severe optical shielding and a global collapse of the localized electric field. Guided by this framework, the optimal linear dynamic range was defined, overcoming false-negative interference. Furthermore, the substrate achieved a $10^{-{8}}$ M limit of detection for Rhodamine 6G (R6G) and exceptional 15-min photocatalytic self-cleaning. This study presents a high-performance, reusable SERS platform and establishes a universal physical framework that maps macroscopic sample volume to microscale adsorption dynamics, providing crucial guidelines for maximizing linearity and defining accurate dynamic ranges in practical SERS detection protocols.