Stable plasmonic nanogap engineering for SERS detection via COFs-constrained nanoparticles

Surface-enhanced Raman spectroscopy (SERS) relies on the formation of precise and stable plasmonic nanogaps to achieve high sensitivity and reproducibility. However, the dynamic nature of plasmonic nanoparticles often leads to uncontrolled nanogap fluctuations, limiting SERS signal stability. Here, we present a novel strategy for stable plasmonic nanogap engineering by employing covalent organic frameworks (COFs) to confine the motion of Au nanoparticles at the nanoscale. The porous and rigid structure of COFs effectively restricts nanoparticle mobility, ensuring the formation of well-defined and fixed plasmonic nanogaps. Time-resolved studies demonstrate that COFs-modified Au nanoparticles exhibit a highly stable SERS signal, with only 37.5 % intensity fluctuations, whereas bare Au nanoparticles undergo significant blinking, leading to an 82.8 % signal loss over 300 s. This confinement strategy not only contributes to enhancing SERS signal stability but also holds promise as a platform for ultrasensitive molecular detection, biosensing, and in situ chemical analysis, offering potential insights for the development of precisely engineered nano-plasmonic sensing systems.