Gold electrodes for detection of enzyme assays with 3-indoxylphosphate as substrate

The advantageous characteristics of gold not only for its electrochemical behavior but also for the unique adsorptive protein characteristics are the basis of this paper. 3-Indoxyl phosphate (3-IP) has previously been demonstrated to be a very convenient substrate for the electrochemical detection, using carbon-based electrodes, of enzymeimmunoassays (EIAs) that employ not only alkaline phosphatase (AP) but also horseradish peroxidase (HRP) as label. Combination of both: gold electrodes and 3-IP has not been studied and it produces a very suitable detection for EIAs. The electrochemical behavior of indigo, product of the enzymatic hydrolisis of 3-IP, has been thoroughly studied for the first time on disk and band gold electrodes. The possibility of electrodepositing gold on the bands and automation has also been considered. The detection has been applied for the determination of osteocalcin with an HRP-based ELISA (enzyme-linked immunosorbent assay).