Coupling of amine-containing osmium complexes and glucose oxidase with carboxylic acid polymer and carbon nanotube matrix to provide enzyme electrodes for glucose oxidation

The immobilization methodology of enzyme and redox complex on electrode surfaces can have an impact on the magnitude and stability of amperometric current response, with implications for application as biosensor and fuel cell enzyme electrodes. Here we report on an investigation of carboxymethyl dextran (CMD) and polyacrylic acid polymers, bearing carboxylic functional groups, as chemical supports for immobilization of amine-containing osmium redox complexes and enzymes at electrode surfaces. Cross-coupling using carbodiimide reagent of the CMD polymer support, [Os (2,2′-bipyridine)₂(4-aminomethyl pyridine)Cl].PF₆ redox complex, glucose oxidase (GOx) and multiwall carbon nanotubes (MWCNT), provides a 3-dimensional matrix for catalytic electrooxidation of glucose yielding current density of 1.0 ± 0.2 mA cm^-2 and 4.5 ± 1.0 mA cm^-2 at 0.45 V vs. Ag/AgCl, in 50 mM phosphate buffer saline (pH 7.4, 37°C) containing 5 mM and saturated glucose amounts, respectively. Similar enzyme electrodes, but instead using [Os (4,4′-dimethoxy-2,2′-bipyridine)₂(4-aminomethyl pyridine)Cl].PF₆ of lower redox potential, produce current densities of 0.83 ± 0.21 mA cm^-2 in 5 mM glucose and 3.4 ± 0.7 mA cm^-2 in saturated glucose solution at 0.2 V vs. Ag/AgCl thus showing promise for application as low potential glucose oxidizing biosensors and as anodes for in-vivo enzymatic fuel cells for power generation.