Reversible pH Stimulus-Response Material Based on Amphiphilic Block Polymer Self-Assembly and Its Electrochemical Application

Stimulus-responsive microporous solid thin films were successfully fabricated by simple molecular self-assembly via an amphiphilic block polymer, polystryene–b–polyacrylic acid (PS–b–PAA). The solid thin films exhibit different surface morphologies in response to external stimuli, such as environments with different pH values in aqueous solutions. The experiments have successfully applied atomic force microscope (AFM) technology to observe in-situ surface morphological changes. There is a reversible evolution of the microstructures in buffer solutions over a pH range of 2.4–9.2. These observations have been explained by positing that there is no conventional PAA swelling but that the PAA chains in the micropores stretch and contract with changes in the pH of the solution environment. The hydrophobicity of the solid thin film surface was transformed into super-hydrophilicity, as captured by optical contact angle measurements. The stimulus-responsive dynamics of pore sizes was described by a two-stage mechanism. A promising electrochemical application of this film is suggested via combination with an electrochemical impedance technique. This study is aimed at strategies for the functionalization of stimulus-responsive microporous solid thin films with reversible tunable surface morphologies, and exploring new smart materials with switch-on/switch-off behavior

Sensitive and selective xanthine amperometric sensors based on calcium carbonate nanoparticles

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A Novel Glucose Biosensor Based on Hierarchically Porous Block Copolymer Film

Enzymatic biosensors are widely used in clinical diagnostics, and electrode materials are essential for both the efficient immobilization of enzyme and the fast electron transfer between the active sites of enzyme and electrode surface. Electrode materials with a hierarchically porous structure can not only increase the specific surface area but also promote the electron transfer, facilitating the catalysis reaction. Block copolymer is a good candidate for preparation of film with a hierarchically porous structure due to its unique characteristics of self-assembly and phase separation. In the current work, hierarchically porous block copolymer film containing both micropores and nanopores was prepared by spinodal decomposition induced phase separation. The resultant copolymer film was adopted as the electrode material to immobilize glucose oxidase (GOx) for construction of an enzyme biosensor. Scanning electron microscopy (SEM), contact angle (CA) measurements, and Fourier-transform infrared (FTIR) and electrochemical impendence spectroscopy (EIS) were adopted to investigate the microstructure of the as-developed biosensor. Results demonstrated that the hierarchically porous block copolymer film offered a favorable and biocompatible microenvironment for proteins. These as-prepared glucose biosensors possessed a wide linear range (10–4500 μM), a low detection limit (0.05 μM), quick response (2 s), excellent stability, and selectivity. This work demonstrates that hierarchically porous block copolymer film is a good matrix candidate for the immobilization of the enzyme and provides a potential electrode material to construct novel biosensors with excellent performance

Porous Polystyrene-<i>Block</i>-Poly(Acrylic Acid)/Hemoglobin Membrane Formed by Dually Driven Self-Assembly and Electrochemical Application

This study demonstrated a facile method to form a porous polymeric membrane, immobilizing a biocatalyst. A polyelectrolyte-based amphiphilic diblock copolymer, i.e., polystyrene-<i>block</i>-poly­(acrylic acid) (PS-<i>b</i>-PAA), self-assembled with hemoglobin (Hb) dually driven by charge and amphiphilicity during solution-casting and evaporation. XPS and contact angle measurements suggested that the PS block enriched on the membrane surface. The PAA block pointed toward the internal membrane as well as ordered the Hb arrangement at the interface of the polymer and electrode. The obtained PS-<i>b</i>-PAA/Hb electrode showed a remarkably enhanced direct electron transfer (ET), which was revealed to be a surface-controlled process accompanied by single-proton transfer. The membrane was tested to catalyze the reduction of hydrogen peroxide, and exhibited an excellent reproducibility and stability. This method with a charge and amphiphilicity dually driven (CADD) self-assembly opened up a new way to construct a third-generation electrochemical biosensor

Direct electrochemistry of hemoglobin in poly(acrylonitrile-co-acrylic acid) and its catalysis to H2O2

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NiMn layered double hydroxide nanosheets/NiCo2O4 nanowires with surface rich high valence state metal oxide as an efficient electrocatalyst for oxygen evolution reaction

High valence transition metal oxide is significant for anode catalyst of proton membrane water electrolysis technique. Herein, we demonstrate NiMn layered double hydroxide nanosheets/NiCo 2 O 4 nanowires hierarchical nanocomposite catalyst with surface rich high valence metal oxide as an efficient catalyst for oxygen evolution reaction. A low overpotential of 310 mV is needed to drive a 10 mA cm −2 with a Tafel slope of 99 mV dec −1 , and a remarkable stability during 8 h is demonstrated in a chronoamperometry test. Theoretical calculation displays the change in the rate-determining step on the nanocomposite electrode in comparison to NiCo 2 O 4 nanowires alone. It is found high valence Ni and Mn oxide in the catalyst system can efficiently facilitate the charge transport across the electrode/electrolyte interface. The enhanced electrical conductivity, more accessible active sites and synergistic effects between NiMn layered double hydroxide nanosheets and NiCo 2 O 4 nanowires can account for the excellent oxygen evolution reaction. The catalytic performance is comparable to most of the best non-noble catalysts and IrO 2 noble catalyst, indicating the promising applications in water-splitting technology. It is an important step in the development of hierarchical nanocomposites by surface valence state tuning as an alternative to noble metals for oxygen evolution reaction