The electrochemistry of a poly(anilineboronic acid)/carbon nanotube composite was studied in the presence of doparnine and ascorbic acid. To understand the binding affinity of doparnine and ascorbic acid to the boronic acid functional groups in the composite, the association constants between the diol groups in dopamine and ascorbic acid and the boronic acid were experimentally determined using a fluorescence-based binding assay. The results demonstrate that ascorbic acid could severely interfere with the detection of doparnine in nonoxidative boronic acid-binding approaches: Ascorbic acid was able to electrocatalytically reduce the fully oxidized polyaniline backbone during the electrochemical oxidation process; similarly to doparnine, ascorbic acid was also able to bind to the boronic acid groups through its planar diol group even though the binding affinity is much lower. The examination of the dopan-tine transduction mechanism and ascorbic acid interference mechanism in this nonoxidative approach will benefit the design of future boronic acid-based sensors.