External Magnetic Field-Modulated Bi@SiO₂ NPs/Ag Nanowire Bilayers Metasurface for a Polarized Luminescence Sensing...

In this work, we developed an external magnetic field-modulated plasmonic bilayer metasurface based on localized surface plasmon resonance (LSPR) of Bi@SiO₂ NPs and surface plasmon polaritons (SPPs) of Ag nanowires (NWs) for detecting exosomal miRNA-223-3p. In the metasurface, the Bi@SiO₂ NPs converted the isotropic electrochemiluminescence (ECL) signal of MXene QDs@nanovesicles into polarized emission. By restraining light propagation through the waveguiding effect of Ag NWs array, the polarized ECL intensity was amplified by 377.5-fold. Furthermore, an external magnetic field regulated electron motion on the metal surface through the Lorentz force, dynamically adjusting the hotspot count and synergistically enhancing ECL performance. This resulted in the polarized ECL emission intensity being significantly increased to 840,000 at the 30°/210° direction. These findings demonstrated that the regulation of ECL signals by a magnetically modulated plasmonic bilayer metasurface (MPB-metasurface) strategy depended on their inherent plasmonic activity and the strength of the applied magnetic field. Finally, this MPB-metasurface strategy displayed outstanding sensing performance in detecting miRNA-223-3p in saliva exosomes. With the linear range from 100 aM to 10 nM and the detection limit reaching 29 aM, it exhibited significant potential for application in noninvasive diagnostics of childhood asthma.