Reduction of nonspecific signals (noise) in electrochemical biosensors is important for the realization of enzyme‐free, point‐of‐care (POC) diagnostic devices. In this study, a simple biosensor interface that simultaneously realizes analyte signal enhancement and noise reduction to increase signal‐to‐noise ratio in a field‐effect transistor‐based potentiometric biosensor is proposed. As a proof‐of‐concept, a phytic‐acid‐doped self‐functionalized polyaniline (pAni)‐based nanostructure is designed. It is shown that the incorporation of gold nanoparticles in the nanostructure increases the signal intensity in serotonin sensing. Moreover, the phenylboronic acid moiety in the pAni backbone and porous nanostructure of the pAni nanostructure reduces the interfering noise generated by catecholamines and human serum albumin. It is believed that this study will contribute to the realization of versatile and multiplexed POC diagnostic devices in the future.