Modular Protein Engineering Approach to the Functionalization of Gold Nanoparticles for Use in Clinical Diagnostics

Functional protein–gold nanoparticle (AuNP) conjugates have a wide variety of applications including biosensing and drug delivery. Correct protein orientation, which is important to maintain functionality on the nanoparticle surface, can be difficult to achieve in practice, and dedicated protein scaffolds have been used on planar gold surfaces to drive the self-assembly of oriented protein arrays. Here we use the transmembrane domain of Escherichia coli outer membrane protein A (OmpATM) to create protein–AuNP conjugates. The addition of a single cysteine residue into a periplasmic loop, to create cysOmpATM, drives oriented assembly and increased equilibrium binding. As the protein surface concentration increases, the sulfur–gold bond in cysOmpATM creates a more densely populated AuNP surface than the poorly organized wtOmpATM layer. The functionalization of AuNP improved both their stability and homogeneity. This was further exploited using multidomain protein chimeras, based on cysOmpATM, which were show...