Engineering the interfaces between biomolecules and nanomaterials is central to the creation of materials for diverse areas of biomedical applications, including therapy, sensing and imaging. The goal of this research has been oriented toward the tailoring of the interfaces through the atomic level control provided by the organic synthesis. By employing a synergistic approach in the research, combining colloids, surface science, organic synthesis and biology, gold nanoparticles with tailored monolayers have been developed for bio-applications. This thesis illustrates the design and synthesis of these surface functionalized gold nanoparticles and their use in protein surface recognition and delivery systems for therapeutic applications. For protein surface recognition, we have fabricated gold nanoparticles bearing a diversity of amino acids termini and studied their interactions with proteins to elucidate the parameters affecting their interactions and catalytic behavior. In therapeutic applications, we have demonstrated the use of organically tailored nanoparticles for the creation of delivery systems featuring tunable stability and regulated drug release. Additionally, gold nanoparticles functionalized with molecular recognition motif have been used to demonstrate host-guest chemistry inside the living cells for the activation of therapeutic gold nanoparticles