Metal nanoshells possess plasmon resonances that are controlled by the geometry of the nanoparticle. Because nanoshell plasmon resonances can be readily predicted by the plasmon hybridization model or Mie scattering theory, it is possible to design a nanoshell to possess specifically chosen plasmonic properties. This thesis examines how to optimize the nanoshell geometry for various sensing applications. Although the nanoshell plasmon can be described within the quasistatic limit using plasmon hybridization, experimentally feasible nanoshell plasmons are also influenced by finite size effects. It is thus important to gain insight into the properties of the nanoshell plasmon in this mesoscopic regime in order to optimize the nanoshell geometry for applications such as the plasmon enhanced fluorescence. We examine the roles of the nanoparticle plasmon resonance energy and nanoparticle scattering cross-section on the fluorescent emission of indocyanine green (ICG). We find that enhancement of the molecular fluorescence is optimized when the nanoshell exhibits a large scattering cross section and a plasmon resonance energy which corresponds to the emission frequency of ICG. Another potential biomedical application for nanoshell is their use as surface plasmon resonance (SPR) sensors. We investigate the geometrical parameters that determine the sensitivity of an Au-nanoshell SPR sensor. It was found that the sensitivity of the nanoshell plasmon to its embedding medium depends primarily on total nanoshell size and less sensitively on core/shell ratio. It is clear from these studies that the efficacy of a nanoshell used in a particular application depends on more parameters than just the plasmon resonance energy.