Aryl diazonium chemistry generates a covalently attached thin film on various materials. This chemistry has diverse applications owing to the stability, ease of functionalization, and versatility of the film. However, the uncontrolled growth into a polyaryl film has limited the controllability of the film’s beneficial properties. In this study, we developed a multistep grafting protocol to densify the film while maintaining a thickness on the order of nanometers. This simple protocol enabled the full passivation of a nitrophenyl polyaryl film, completely eliminating the electrochemical reactions at the surface. We then applied this protocol to the grafting of phenylphosphorylcholine films, with which the densification significantly enhanced the antifouling property of the film. Together with its potential to precisely control the density of functionalized surfaces, we believe this grafting procedure will have applications in the development of bioelectrical interfaces.

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.

In this study, we examined the fundamental surface characteristics of a polyserotonin (pST) film, which is attractive as a bioelectrical and biocompatible interface of biosensors. The pST film can easily be modified on electrode materials such as Au by self-polymerization and electropolymerization. By a simple cytotoxicity test using nonadhesive living cells, we found that the pST film is biocompatible for culturing cells on it. This finding is also supported by the fact that the surface tension of the pST film is moderate for protein adsorptions. The pST film is thinner and smoother than a poly-dopamine film, the chemical structure of which is similar to that of the pST film, depending on the polymerization time, cycle, and temperature; thus, ST as the main monomer can facilitate the precise control of the thickness and roughness of functional polymer membranes on the nanometer order. In addition, the pST film is useful as a relatively insulative interface for preventing interfering species from approaching electrode surfaces without their nonspecific adsorption, depending on the surface charges of the pST film in solutions of different pHs. The formation of the pST film selfpolymerized on electrode materials is derived from the adsorption of pST nanoparticles formed by oxidative polymerization under basic conditions; therefore, the process of pST film formation should be considered in the functionalization of the pST film as a bioelectrical interface that allows biomolecular recognition (e.g., molecularly imprinted polymer membrane) for its application to wearable and biocompatible biosensors.

In this study, redox-labeled molecularly imprinted polymer nanoparticles (nano-MIPs) were synthesized using a solid-phase approach, templated with biomarkers for diabetes such as human serum albumin (HSA). The purpose of this research was to develop enzyme-/antibody-free electrochemical biosensors with the nano-MIP-coated Au electrodes. The synthesized HSA–nano-MIP (HNM) was analyzed for its chemical composition, size, affinity, and electrochemical property, and was tethered on gold via a coupling chemistry. The results of cyclic voltammetry analysis revealed that electron transfer occurred on the HNM-immobilized Au electrode through physical displacement of the redox centers within HNM, which hopped from one redox center to an adjacent redox center, a process known as bounded diffusion. In this paper, we present a promising approach to developing sensitive and selective electrochemical biosensors for diabetes detection.