Won-Yong Jeon

Hydrophilic osmium(Os)-based redox polymers were designed as electron-transfer mediators for fungal flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH)-based glucose sensors. Poly(vinylimidazole-co-hydroxyethyl acrylate) (PVI-HEA) copolymers with different HEA compositions were synthesized and coordinated with Os(dmo-bpy)₂Cl₂ to prepare PVI-HEA-Os(dmo-bpy)₂Cl₂ redox mediators. The synthesized mediator systems were characterized using ¹H-nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, field emission scanning electron microscopy/energy dispersive spectroscopy, zeta potential analysis, cyclic voltammetry, and electrochemical impedance spectroscopy. The results confirmed the successful formation of Os redox polymer structures and their immobilization on the electrode surface. The electrochemical behavior and glucose sensing performance strongly depended on the PVI-HEA composition. Among the compositions tested, PVI-HEA(3.5:1)-Os(dmo-bpy)₂Cl₂ showed the strongest redox current response, stable aqueous dispersion behavior, and relatively low interfacial charge-transfer resistance. Glucose-sensing measurements using FAD-GDH/mediator-modified electrodes showed linear current responses over the glucose concentration range of 1.25–20 mM. The PVI-HEA(3.5:1)-Os(dmo-bpy)₂Cl₂-based electrode showed the highest sensitivity of 16.18 μA cm⁻² mM⁻¹, which was significantly higher than those observed at lower-HEA compositions. The optimized mediator system also showed selective glucose responses against representative biological interferents, including ascorbic acid, uric acid, dopamine, and serotonin. Stable catalytic current responses were maintained under Human Plasma-Like Medium conditions, suggesting improved matrix tolerance compared to conventional PVI-based Os redox polymers. The improved sensing performance was attributed to the hydrophilic polymer environment introduced by the HEA units, which may facilitate favorable interfacial charge-transfer behavior within the enzyme–mediator layer. The results show that the hydrophilic copolymer composition plays an important role in the electrochemical behavior and glucose sensing performance of Os redox polymer mediators. The proposed PVI-HEA-Os(dmo-bpy)₂Cl₂ system may be a promising candidate for future enzymatic glucose sensing and continuous glucose monitoring-related applications.

Hydrophilic polymer–osmium complexes enhance electron transfer between enzymes and electrodes in biosensors. In this study, hydrophobic poly(4-vinylpyridine) (PVP) was quaternized with 2-bromoethanol to synthesize water-soluble PVP(Q)-C₂H₄OH polymers (MW 60,000 and 160,000). The resulting PVP(Q)-C₂H₄OH-Os(dmo-bpy)₂Cl complexes were verified by UV-Vis, FT-IR, 1H NMR, SEM-EDS, and zeta potential analyses, confirming successful quaternization and osmium coordination with good dispersion stability. Electrochemical tests (cyclic voltammetry, multi-potential step, amperometry) demonstrated that electrodes with quaternized mediators showed greatly enhanced catalytic currents for glucose (0–20 mM), with sensitivities of 6.9791 (MW 60,000) and 6.6279 μA·mM⁻¹·cm⁻² (MW 160,000), respectively, which were 6.6–10.3 times higher than those of non-quaternized polymers. Selectivity tests showed negligible interference from common species such as ascorbic acid, dopamine, uric acid, and serotonin. Continuous glucose monitoring (CGM) electrodes were fabricated by immobilizing the mediator and glucose dehydrogenase on silanized Au electrodes. SEM, scan rate, and impedance analyses confirmed stable binding. The modified electrodes showed strong linearity (R² = 0.992) and high sensitivity (2.56 μA·mM⁻¹·cm⁻²), and good stability, maintaining ~82% activity for seven days. Human plasma testing validated accurate glucose detection (6.05 mM), consistent with physiological levels. Overall, quaternized PVP(Q) mediators significantly improved solubility and electron transfer, enabling the development of a stable, selective glucose sensor suitable for CGM applications.

A PAAc-PVI(4:1)@MWCNT hybrid was synthesized for the selective electrochemical detection of serotonin. Multi-walled carbon nanotubes (MWCNT) enhanced electrode conductivity, while the hydrophilic polymer Poly(Acrylic Acid-co-Vinyl imidazole) (PAAc-PVI) facilitated serotonin recognition. At pH 7.4, the carboxyl (-COO⁻) groups in PAAc-PVI interacted with the amine (-NH₃⁺) groups of serotonin, enabling oxidation and electron transfer for signal detection. Additionally, π-π interactions between vinylimidazole and MWCNT improved dispersion and stability. The hybrid materials enhanced electron transfer efficiency, increasing sensitivity and reliability. Structural and electrochemical properties were characterized using FT-IR, HR-TEM, TGA, Raman spectroscopy, impedance analysis, and differential pulse voltammetry (DPV). Serotonin detection using the fabricated electrode demonstrated high selectivity (LOD 0.077 μM and LOQ 0.26 μM), reproducibility (%RSD 1X PBS condition (4.63%) and human serum condition (4.81%)), and quantitative capability (dynamic range 1.2 μM to 10.07 μM) without interference (potential shift from +0.40 V to −0.15 V) from blood-based substances, confirming its potential for electrochemical biosensing applications.

Blood glucose monitoring (BGM) using disposable electrodes is commonly used in healthcare diagnosis. The BGM method is not suitable for people with diabetes requiring real-time monitoring who might experience sudden hypoglycemia or hyperglycemia owing to a single measurement at a specific moment. This study aimed to achieve an enhanced stability of glucose diagnosis for continuous glucose measurement systems (CGMs). A representative mediator of a second-generation glucose sensor was synthesized and coordinated with a polymer for immobilization on an indium tin oxide (ITO) electrode. For electrode immobilization, an electrode for enhanced stability was fabricated using the silanization method. The morphological properties of the electrodes were confirmed via cyclic voltammetry (CV), impedance spectroscopy, and SEM. The loss rate of the current density was only 10.11% of the initial current after 8 d. The electrode exhibited a coefficient of determination of R² = 0.9924, sensitivity of 1.5454 μA/cm²·mM, limit of quantitation (LOQ) of 7.604 μM, and limit of detection (LOD) of 2.509 μM for glucose concentrations between 0.1 and 20.0 mM. The electrode system developed in this study is applicable to the CGM healthcare industry and is expected to be applicable to biofuel cells.

There is extensive interest in developing real-time biosensing strategies to characterize the membrane-disruptive properties of antimicrobial lipids and surfactants. Currently used biosensing strategies mainly focus on tracking membrane morphological changes such as budding and tubule formation, while there is an outstanding need to develop a label-free biosensing strategy to directly evaluate the molecular-level mechanistic details by which antimicrobial lipids and surfactants disrupt lipid membranes. Herein, using electrochemical impedance spectroscopy (EIS), we conducted label-free biosensing measurements to track the real-time interactions between three representative compounds—glycerol monolaurate (GML), lauric acid (LA), and sodium dodecyl sulfate (SDS)—and a tethered bilayer lipid membrane (tBLM) platform. The EIS measurements verified that all three compounds are mainly active above their respective critical micelle concentration (CMC) values, while also revealing that GML induces irreversible membrane damage whereas the membrane-disruptive effects of LA are largely reversible. In addition, SDS micelles caused membrane solubilization, while SDS monomers still caused membrane defect formation, shedding light on how antimicrobial lipids and surfactants can be active in, not only micellar form, but also as monomers in some cases. These findings expand our mechanistic knowledge of how antimicrobial lipids and surfactants disrupt lipid membranes and demonstrate the analytical merits of utilizing the EIS sensing approach to comparatively evaluate membrane-disruptive antimicrobial compounds.

There is broad interest in fabricating cell-membrane-mimicking, hybrid lipid bilayer (HLB) coatings on titanium oxide surfaces for medical implant and drug delivery applications. However, existing fabrication strategies are complex, and there is an outstanding need to develop a streamlined method that can be performed quickly at room temperature. Towards this goal, herein, we characterized the room-temperature deposition kinetics and adlayer properties of one- and two-tail phosphonic acid-functionalized molecules on titanium oxide surfaces in various solvent systems and identified optimal conditions to prepare self-assembled monolayers (SAMs), upon which HLBs could be formed in select cases. Among the molecular candidates, we identified a two-tail molecule that formed a rigidly attached SAM to enable HLB fabrication via vesicle fusion for membrane-based biosensing applications. By contrast, vesicles adsorbed but did not rupture on SAMs composed of one-tail molecules. Our findings support that two-tail phosphonic acid SAMs offer superior capabilities for rapid HLB coating fabrication at room temperature, and these streamlined capabilities could be useful to prepare durable lipid bilayer coatings on titanium-based materials.

The electrochemical-based detection of glucose is widely used for diagnostic purposes and is mediated by enzyme-mediated signal transduction mechanisms. For such applications, recent attention has focused on utilizing the oxygen-insensitive glucose dehydrogenase (GDH) enzyme in place of the glucose oxidase (GOx) enzyme, which is sensitive to oxygen levels. Currently used Ru-based redox mediators mainly work with GOx, while Ru(dmo–bpy)₂Cl₂ has been proposed as a promising mediator that works with GDH. However, there remains an outstanding need to improve Ru(dmo–bpy)₂Cl₂ attachment to electrode surfaces. Herein, we report the use of polydopamine-functionalized multi-walled carbon nanotubes (PDA-MWCNTs) to effectively attach Ru(dmo–bpy)₂Cl₂ and GDH onto screen-printed carbon electrodes (SPCEs) without requiring a cross–linker. PDA-MWCNTs were characterized by Fourier transform infrared (FT–IR) spectroscopy, Raman spectroscopy, and thermal gravimetric analysis (TGA), while the fabrication and optimization of Ru(dmo–bpy)₂Cl₂/PDA-MWCNT/SPCEs were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The experimental results demonstrate a wide linear range of glucose-concentration-dependent responses and the multi-potential step (MPS) technique facilitated the selective detection of glucose in the presence of physiologically relevant interfering species, as well as in biological fluids (e.g., serum). The ease of device fabrication and high detection performance demonstrate a viable pathway to develop glucose sensors based on the GDH enzyme and Ru(dmo–bpy)₂Cl₂ redox mediator and the sensing strategy is potentially extendable to other bioanalytes as well.