This contribution describes how de novo designed synthetic helix–loop–helix polypeptides are utilized to control the assembly of gold nanoparticles and as scaffolds for biosensing. The synthetic polypeptides are designed to fold into a four-helix bundle upon dimerization. When immobilized on gold nanoparticles, dimerization and folding occur between peptides on neighbouring particles as an effect of particle aggregation and the folded polypeptides are rigid enough to keep the particles separated at a distance corresponding to the size of the four-helix bundle. Moreover, peptide dimerization offers a convenient route to assemble nanoparticles into hybrid multilayers on planar substrates. The drastic change in the resonance conditions of the localized nanoparticle surface plasmon upon particle aggregation is shown to be useful for optical detection of biomolecular interactions.

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