Gold Nanoparticles with Gain-assisted Coating for Ultra-sensitive Biomedical Sensing

We propose and theoretically demonstrate a scheme where ultra-sensitive biomedical sensing can be realized using a gold nanosphere with gain-assisted coating. Surface plasmon resonance (SPR) enhanced optical response of this coated nanoparticle is investigated using both quasi-static approximation limit analysis and exact Mie theory calculations. It is shown that a strongly SPR-amplified scattering efficiency accompanied by an extremely high quality factor of the plasmonic resonance can be achieved by introducing a relatively low level of gain into the coating layer. The application of such a gain-assisted coated gold nanoparticle in biomedical sensing is further investigated, which proves its ability to detect even marginal change in the concentration of its surrounding medium.