Picoamperometric detection of glucose at ultrasmall platinum-based biosensors: Preparation and characterization

A simple method is described for the construction of a glucose biosensor with good reproducibility. After electrochemical etching, the sensing tip of an etched platinum microelectrode was insulated using a synthetic rubber dip coating. The insulating layer was then heat-cured, leading to a small exposed area at the very end of the etched Pt tip, as confirmed by scanning electron microscopy. Phenol and 2-allylphenol were electropolymerized to form an extra insulating layer that effectively retained glucose oxidase (GOX) on the sensing tip of the electrode. On the basis of cyclic voltammetry measurements, the apparent radius of the biosensor tip was estimated to be between 10 and 500 nm, depending on GOX loading. With operational and storage stabilities over 3 weeks, the glucose biosensor prepared using optimal GOX concentration (10 mg/mL) exhibited a picoamperometric current response within ∼2 s and a detection limit of 20 μM with excellent reproducibility.