Cadmium sulfide (CdS) nanocrystals continue to generate scientific and technological interest, owing to their valuable optical, electronic, and chemical properties. Aqueous nanocrystal syntheses rely on functional capping agents to control nanocrystal form and function. We present a series of linear and dendritic engineered peptides, rich in cysteines and aspartic acids, as CdS capping agents. The chemical composition and peptide geometry were found to significantly influence CdS nanocrystal size, optical properties, and aggregation behavior.