Step-by-Step Assembled Enzyme-Polymer-Carbon Nanotubes for Solution-Processed Bioreactive Composites

Protein-conjugated single-walled carbon nanotubes (SWCNTs) have received much attention for their diverse applications in molecular biology. Intrinsically water-insoluble SWCNTs avoid conjugation with proteins, which leads to limited availability of biomolecule-nanocarbon composites. Because protein functions are directly affected by assembled structures, the synthesis of heterogeneous composites with bioreactive responses is a great challenge. We demonstrate that step-by-step assembled enzyme/polymer/SWCNTs are obtained by using noncovalent-bonding methodologies in aqueous media. A multifunctional polymer containing aromatic, cationic, and redox-active units allows for a direct aqueous dispersion of SWCNTs through πinteractions and a subsequent charge attraction to the enzyme, which yields the ternary composites. The resulting composites show bioreactive responses in enzyme-conjugated SWCNT networks. The solution-processed glucose oxidase (GO_x)/polymer/SWCNT composite displays a high current density of 1420 μA cm^-2 by enzymatic oxidation of glucose. Only 2.4 μg of GO_x is shown to be necessary for the enzymatic reaction with a sensitivity of 72 μA mM^-1 cm^-2. This high sensitivity results from the assembled structure through noncovalent-bonding interactions. We demonstrate that the bioreactive composite allows energy conversion from a glucose-including beverage (cola) to electricity. Lactate oxidase-driven bioreactivity also takes place on the structurally organized composite. This step-by-step methodology would be beneficial for enzyme-assisted energy conversion nanocomposites.