Immobilization and Electrochemistry of Negatively Charged Proteins on Modified Nanocrystalline Metal Oxide Electrodes

The immobilization of two acidic, low isoelectric point proteins, green fluorescence protein and ferredoxin (FRD) is investigated on nanocrystalline, mesoporous TiO2 and SnO2 electrodes. Modification of these electrodes with a cationic polypeptide (poly‐L‐lysine) or an aminosilane prior to protein immobilization is found to enhance protein binding at least ten fold, attributed to more favorable protein/electrode electrostatic interactions. Cyclic voltammetry studies of FRD‐modified SnO2 electrodes indicate reversible protein electrochemistry with a midpoint potential of −0.59 V (vs. Ag/AgCl) and an interfacial electron transfer rate constant of 0.45 s−1.