Semiconductor nanoparticles are exciting materials because of their potential applications in medicine, engineering and biology. Size tunable emission, through the quantum confinement effect of semiconductor nanoparticles, make them useful as chromophores as biological fluorescence markers, light emitting diodes, and laser materials. These nanoparticles are stabilized by molecules bound to the surface, called capping molecules. Thiol containing molecules are the best characterized and most prevalent capping molecules to date. Although hydrophilic monothiols render the nanoparticles water soluble, they are typically degraded by light exposure. We hypothesize that peptides based on polycysteine containing metallothioneins will provide more robust, water- soluble, and biocompatible capping groups for semiconducting nanoparticles. In this research, metallothionein peptides were attached to CdSe nanoparticles. Up to eight metallothioneins were attached to each CdSe nanoparticle, as detected by an increase in fluorescence emission intensity.