Optimized nanospherical layered alternating metal-dielectric probes for optical sensing.

Multishell nanospheres have been proposed as a class of layered alternating metal-dielectric probes (LAMPs) that can greatly enhance sensitivity and multiplexing capabilities of optical molecular imaging . Here we theoretically demonstrate that the interplasmonic coupling within these spheres and hence their spectral responses can be tuned by a rational selection of layer thicknesses. As a proof-of-concept, layered Mie theory calculations of near- and far-field characteristics followed by a genetic algorithm-based selection are presented for gold-silica, silver-silica and copper-silica LAMPs. The results demonstrate that the optical tunability available allows for design of application (excitation wavelength)-specific probes of different sizes. The tunability further increases with number of layers and within a particular allowable probe size provides for structures with distinct resonances at longer wavelengths. The concept of scaling internal field resonances is also shown theoretically and the range over which the magnitudes can be tuned are presented.