Covalent immobilization of gold nanoparticles on a plastic substrate and subsequent immobilization of biomolecules

We propose a novel approach to stably immobilize gold nanoparticles (AuNPs) on a plastic substrate and demonstrate that the modified substrate is also capable of immobilizing biomolecules. To immobilize citrate-capped AuNPs, an acrylic substrate was simply dip-coated in a functional polymer solution to decorate the outermost surface with amino groups. Electrostatic interactions between AuNPs and the amino groups immobilized the AuNPs with a high density. The AuNP-modified acrylic substrate was transparent with a red tint. A heat treatment promoted the formation of amide bonds between carboxy groups on the AuNPs and amino groups on the substrate surface. These covalent bonds stabilized the immobilized AuNPs and the resulting substrate was resistant to washing with acid and thiol-containing solutions. The surface density of AuNPs was controlled by the surface density of amino groups on the substrate surface, which was in turn controlled by the dip-coating in the functional polymer solution. We attempted to immobilize functional biomolecules on the AuNPs-functionalized plastic surface by two different approaches. An enzyme (horseradish peroxidase) was successfully immobilized on the AuNPs through amide formation and 5′-thiolated DNA was also immobilized on the AuNPs through S–Au interactions. These chemistries allow for simultaneous immobilization of two different kinds of biomolecules on a plastic substrate without loss of their functional properties.