A 2D-to-3D morphology transitions of gold in organic acid electrolytes: Characterization and application in bioanode design

The inexpensive, relatively fast and scalable production of nanostructured electrodes may benefit future disposable biosensor technology. In this research, nanoporous gold (NPG) surfaces were successfully fabricated by anodizing the gold in different organic acid, and further used for glucose dehydrogenase (GDH)-based bioanode design. The porosity of NPG layers was manipulated by changing the anodization time, and the dependency of relative electrochemical surface area (rESA) on the bioanode performances was systematically examined. The X-ray photoelectron spectroscopy (XPS) studies of NPG formed in oxalic acid (NPGox) and their depth profiles of Au 4f and O 1s evidenced the chemical state of pure metallic gold (Au0), whereas NPG formed in glycolic acid (NPGgly) has appreciable content of gold oxide and hydroxides. The NPGgly/4-ATP/GDH bioanodes exhibited direct electron transfer (DET-type) bioelectrocatalytic activity, while the highest current densities of 0.35 mA cm- 2 and low onset potential of - 0.189 V (vs. Ag/AgCl) were observed. The electrodes showed longterm stability and, up to three weeks, retained 76 % of their initial value. Furthermore, the biofuel cell possessed the maximum power densities of 31.8 μW cm−2 and open-circuit potential (OCP) differences of 0.441 V, thus evidencing that NPGgly layers could be encouraging for developing biosensors and biofuel cells