A polyaniline microtube platform for direct electron transfer of glucose oxidase and biosensing applications

Polyaniline (PANI) microtubes are becoming greatly significant electrochemical materials owing to their large geometric surface area, high conductivity and ideal electrocatalytic activity. In this work, using glucose oxidase (GOx) as a model redox protein, a direct electron transfer strategy based on PANI microtubes was developed for fabricating sensitive biosensors. There is a strong electrostatic interaction between the positively charged PANI microtubes and negatively charged GOx, which promotes the immobilization of GOx on the PANI microtube surface. The immobilized GOx displayed a pair of well-defined quasi-reversible redox peaks with a potential of -0.39 V (vs. SCE) and an ideal electron transfer rate constant (k_s) of 3.0 s^-1 in PBS solution (0.1 M, pH = 5.5) on the PANI microtubes instead of a bare glass carbon electrode (GCE). The amperometric response of the GOx/PANI microtube modified electrode was linearly proportional to the concentration of glucose in the range of 4.0 μM to 0.80 mM. The glucose detection limit was 0.8 μM at a signal-to-noise ratio of 3, which was better than those reported for the GOx/PANI film (1 mM) and GOx/PANI nanowire (50 μM). The advantages might be attributed to the PANI microtubes' large geometric surface for carrying enzyme (GOx) and efficient electrocatalytic activity to facilitate the direct electron transfer of GOx, as well as an efficient GOx biocatalyst reaction on the microtube surface. A promising application of PANI microtube-based biosensors was offered.