Electrocatalytic H2O2 amperometric detection using gold nanotube electrode ensembles

Arrays of nanoscopic gold tubes were prepared by electroless plating of the metal within the pores of nanoporous polycarbonate track-etched membranes. A procedure for fabricating an ensemble of enzyme-modified nanoelectrodes has been developed based on the efficient immobilization of horseradish peroxidase (HRP) to the gold nanotubes array using self-assembled monolayers (mercaptoethylamine or mercaptopropionic acid) as anchoring layers. Hydrogen peroxide (H₂O₂) was determined electrochemically by using gold nanoelectrode ensembles (NEE) functionalized or not in phosphate buffer solution (PB) with or without a mediator (hydroquinone, H₂Q). Bare NEE displays a remarkable sensitivity (14 μA mM⁻¹ in H₂Q at −0.1 V versus Ag/AgCl) compared to a classical gold macroelectrode (0.41 μA mM⁻¹). The gold nanoparticles that form the tubular structure act as excellent catalytic surfaces towards the oxidation and the reduction of H₂O₂. The HRP modified NEE presents a slightly lower sensitivity (9.5 μA mM⁻¹) than bare NEE. However, this system presents an enhanced limit of detection (up to 4 × 10⁻⁶ M) and a higher selectivity towards the detection of H₂O₂ over a wide range of potentials. The lifetime, fabrication reproducibility and measurement repeatability of the HRP enzyme electrode were evaluated with satisfactory results.