Scheme 1. Schematic illustration of (A) the structures of the main building block materials and (B) the as-assembled enzymatic biofuel cell. Bioanode: GDH dimer with PQQ centers highlighted (PDB code 1c9u) and MB molecules were immobilized onto the graphene-paper electrode by π–π stacking. Biocathode: BOx with type I and type II/III (copper centers) marked (PDB code 2xll) directly adsorbed onto the graphene-paper electrode. Not drawn to scale.