Nanoporous Gold for Enzyme Immobilization

Nanoporous gold (NPG) is a material of emerging interest for the immobilization of biomolecules and especially enzymes. The material provides a high surface area form of gold that is suitable for physisorption or covalent modification by self-assembled monolayers. The material can be used as a high surface area electrode and with immobilized enzymes can be used for the development of amperometric biosensors. NPG can be prepared in a variety of formats from alloys containing between 20% and 50% atomic composition of gold and less noble element(s) by dealloying procedures. NPG can be prepared in a variety of shapes (e.g., wire, rod, sphere, plate, and supported film) and dimensions (e.g., 0-3D). Colloidal 0D NPG nanoparticles possess a higher surface area-to-volume ratio and enhanced optical properties. Materials resembling NPG can be prepared by hydrothermal and electrodeposition methods. Related high surface area gold structures have been prepared using templating approaches. Hierarchical bimodal nanoporous gold (hb-NPG) structures containing both macropores and mesopores have been engineered. NPG with a bimodal porous structure has the advantage of a large specific surface area for functionalization combined with rapid transport pathways for molecules into and out of the structure. Materials with porous architectures are potential candidates for achieving covalent enzyme immobilization by first forming a self-assembled monolayer bearing a terminal reactive functional group followed by conjugation to the enzyme through amide linkages to lysine residues. Enzymes can also be entrapped by physisorption or immobilized by electrostatic interactions.