A new enzymatic method is reported for constructing protein- and DNA-AuNP conjugates. The strategy relies on the initial functionalization of AuNPs with phenols, followed by activation with the enzyme tyrosinase. Using an oxidative coupling reaction, the activated phenols are coupled to proteins bearing proline, thiol, or aniline functional groups. Activated phenol-AuNPs are also conjugated to a small molecule biotin and commercially available thiol-DNA. Advantages of this approach for AuNP bioconjugation include: (1) initial formation of highly stable AuNPs that can be selectively activated with an enzyme, (2) the ability to conjugate either proteins or DNA through a diverse set of functional handles, (3) site-specific immobilization, and (4) facile conjugation that is complete within 2 h at room temperature under aqueous conditions. The enzymatic oxidative coupling on AuNPs is applied to the construction of tobacco mosaic virus (TMV)-AuNP conjugates, and energy transfer between the AuNPs and fluorophores on TMV is demonstrated.