Highly Conductive Redox Protein-Carbon Nanotube Complex for Biosensing Applications

The integration of redox proteins with nanomaterials has attracted much interest in the past years, and metallic single-walled carbon nanotubes (SWNTs) have been introduced as efficient electrical wires to connect biomolecules to metal electrodes in advanced nano-biodevices. Besides preserving biofunctionality, the protein-nanotube connection should ensure appropriate molecular orientation, flexibility, and efficient, reproducible electrical conduction. In this respect, yeast cytochrome c redox proteins are connected to gold electrodes through lying-down functionalized metallic SWNTs. Immobilization of cytochromes to nanotubes is obtained via covalent bonding between the exposed protein thiols and maleimide-terminated functional chains attached to the carbon nanotubes. A single-molecule study performed by combining scanning probe nanoscopies ascertains that the protein topological properties are preserved upon binding and provides unprecedented current images of single proteins bound to carbon nanotubes that allow a detailed I-V characterization. Collectively, the results point out that the use as linkers of suitably functionalized metallic SWNTs results in an electrical communication between redox proteins and gold electrodes more efficient and reproducible than for proteins directly connected with metal surfaces.