The molecular-level origins of disease are being elucidated at a rapid pace, potentially ushering in a new era of personalized medicine in which a specific course of therapy is developed for each patient. To fully exploit this expanding knowledge of disease phenotype, new methods for detecting biomolecules and delivering therapeutics are required. Detection methods must be rapid, sensitive, highly parallel, and ideally, capable of diagnosing cellular phenotype in vivo. New therapeutic delivery systems are needed which target specific tissues (e.g., breast cancer tissue), and deliver payloads into the nucleus of target cells with high efficiency and cell selectivity. This lecture will describe a variety of hybrid biomolecule/gold nanoparticle composite materials that are being explored for use in new gene and protein detection schemes on chips and in living cells, and for delivering therapeutics into cell nuclei. The talk will focus on the chemical, optical, and electronic properties of gold particles that make them well suited for applications in biosensing and in vivo therapeutic delivery.