Plasmonic Ag Nanocrystal-Patterned Metasurface with Synergistic Order/Disorder Structure for ECL Detection of miRNA-92a-3p in Extracellular Vesicles

Herein, a novel silver nanocrystal-patterned (Ag-NCP) metasurface-based electrochemiluminescence (ECL) sensor for the detection of miRNA-92a-3p in extracellular vesicles (EVs) was constructed with a luminescent 2,2′-bipyridine-5,5′-diamine (Bpy)-covalent organic framework (COF). On the basis of the soft-template and spatial confinement effects of micelles, the ordered nucleation and growth of Ag NCs finally yielded an Ag-NCP metasurface with synergistic structure characteristics of a long-range ordered arrangement and a short-range disordered morphology. Long-range order was defined as the uniform and periodic spatial arrangement of Ag NCs over macroscopic dimensions, which was characterized by a stable and regular structural organization. By comparison, short-range disorder refers to the irregularity in the size, surface morphology, and spacing of adjacent Ag NCs on the local nanoscale with random and variable features. The short-range disordered morphology of irregular Ag NCs in the metasurface generated high-density electromagnetic hotspots due to the localized surface plasmon resonance and the surface plasmon-coupling effect. It greatly enhanced the local electromagnetic field and triggered the Purcell effect, thereby accelerating the luminescence process and improving the ECL efficiency of the Bpy-COF. Moreover, the long-range-ordered arrangement of Ag NCs formed a dense electromagnetic network in the Ag-NCP metasurface to improve the stability and persistence of luminescent signals. The constructed Ag-NCP metasurface-based ECL sensor was successfully applied to the detection of miRNA-92a-3p with a linear range of 1 fM to 10 nM and a limit of detection of 0.36 fM. This biosensor was employed successfully for the detection of miRNA-92a-3p in ascites from gastric cancer patients, which can serve as an auxiliary diagnostic tool.