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 π interactions 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 (GOx)/polymer/SWCNT composite displays a high current density of 1420 μA cm–2 by enzymatic oxidation of glucose. Only 2.4 μg of GOx 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.