Rigid, Specific, and Discrete Gold Nanoparticle/Antibody Conjugates

A general method of rigid, specific labeling of proteins with gold clusters has been devised. The method relies on the conjugation of a glutathione monolayer-protected gold cluster (MPC) with a single chain Fv antibody fragment (scFv), mutated to present an exposed cysteine residue. Efficient formation of a gold−thiolate bond between the MPC and scFv depends on activation of the gold cluster by chemical oxidation. Once formed, the MPC−scFv conjugate is treated with a reductant to quench cluster reactivity. The procedure has been performed with an MPC with an average Au₇₁ core and an scFv directed against a tetrameric protein, the influenza neuraminidase. A complex of the MPC−scFv conjugate with the neuraminidase was isolated, and the presence of four gold clusters was verified by cryoelectron microscopy.