Optical Fano Resonance in Self-Assembled Magnetic–Plasmonic Nanostructures

We proposed a bottom-up approach for the fabrication of magnetic–plasmonic nanostructures that exhibit tunable plasmon enhanced hots spots and Fano resonance behavior. The nanostructures are formed from the self-assembly of magnetic–plasmonic core–shell nanoparticles. The magnetic core enables magnetophoretic control of particles during assembly, while the plasmonic shell provides interesting and useful optical behavior. We demonstrate proof-of-concept using a combination of Monte Carlo analysis to predict self-assembly and full-wave computational analysis to study the optical properties of the assembled structures. Our analysis demonstrates that viable structures can be assembled using a magnetic template-assisted self-assembly protocol and that flexible tunability of the optical response can be achieved due to the strong sensitivity of nanogap hot spots and Fano resonance features on distinct geometric parameters and the surrounding medium. We demonstrate the self-assembly and Fano resonance response of a heptamer nanostructure formed from Fe 3 O 4 @Au nanoparticles and discuss its performance for biosensing. The ability to fabricate such nanostructures using bottom-up methods holds potential for numerous novel applications. Moreover, the photonic modeling approach demonstrated here broadly applies to arbitrary particle geometries, material properties, and assemblies and can be used for the rational design of such applications.