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Abstract: Fe3O4 magnetic multilayer films were constructed on several conductive bases (glassy carbon electrode, ITO glass and Al foil) by the firstly electrodeposited chitosan/Fe3O4 nanoparticles thin film and then the layer-by-layer assembly using phytic acid and Fe3O4/chitosan. Scanning electronic microscopy (SEM), UV–vis spectra, electrochemical impedance spectroscopy (EIS) and superconducting quantum interference device (SQUID) measurements were used to characterize the multilayer films. Characteristic superparamagnetic properties of Fe3O4 nanoparticles are well remained in the film and could be controlled simply by changing the assembly layers. Moreover, the multilayer film showed good biocompatibility, the adsorbed hemoglobin (Hb) on the film realized direct electron transfer with the underlying GCE and kept high catalytic activity. This presented system avoid the complex synthesis for protecting Fe3O4 nanoparticles, and supplies a simple, universal way to construct other nanoparticles films on many conductive bases for biosensors’ development. [Copyright &y& Elsevier]

A chitosan film containing MnO2 nanoparticles was introduced to amperometric glucose biosensors for the elimination of the interference from ascorbic acid. Chitosan was mixed with MnO2 nanoparticles and electrochemically deposited on electrodes previously modified with glucose oxidase. MnO2 nanoparticles incorporated in the chitosan film was very stable and can effectively oxidize AA to electrochemical inactive product, and thus eliminate the interference of AA on the glucose biosensors based on the direct oxidation of hydrogen peroxide. The effect of the content of MnO2 nanoparticles and the deposition time on the characteristics of the film, as well as the stability of the film during continuous exposure to AA was investigated. Glucose biosensors deposited with the film containing MnO2 nanoparticles were suitable for determination of glucose in the presence of AA. [Copyright &y& Elsevier]

Humic acid (HA) films were formed on a gold electrode surface by the self-assembly method. The HA films were used as an immobilization matrix interfacing cytochrome c (cyt c) to Au electrode surface through a dip and phase inversion process. The morphologies of the films, changes of structure and properties of the electrochemistry were investigated by scanning electron microscope (SEM), UV–Vis spectroscopy (UV–Vis) and electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The results showed that the HA film acted as a good adsorption matrix for cyt c and an excellent accelerant for the redox of cyt c which gives reversible redox peaks with a formal potential of 108 mV vs SCE in pH 7.0 phosphate buffer solution. The average surface coverage of cyt c on the HA film was about 3.49 × 10−11 mol/cm2, indicating a monolayer of cyt c. The electron transfer rate constant was calculated to be 1.0 s−1. [Copyright &y& Elsevier]

Abstract: An interesting mode of reactivity of MnO2 nanoparticles modified electrode in the presence of H2O2 is reported. The MnO2 nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H2O2. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO2 nanoparticles onto a glassy carbon (GC) electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0×10−5 –2.1×10−3 M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed. [Copyright &y& Elsevier]

Abstract: A novel method for fabricating hydrogen peroxide (H2O2) sensor has been presented based on the self-assembly of ZrO2 nanoparticles with heme proteins on functional glassy carbon electrode. The immobilized proteins realized their direct electrochemistry with the formal potential of −0.032V for hemoglobin and −0.026V for myoglobin in pH 6.0 PBS, respectively. Electrochemical impedance spectroscopy and cyclic voltammetry were applied to characterize the self-assembly process and study the electrochemical behaviors of the immobilized proteins. UV–Vis spectra results suggested that proteins in ZrO2 films retained their bioactivity, hence they exhibit good electrocatalytic behaviors towards the reduction of substrate H2O2. As a result, a kind of novel third-generation biosensors for H2O2 was developed. The resultant heme-protein electrode exhibited fast amperometric response (within 10s) to H2O2, excellent stability, long-term life (more than one month) and good reproducibility. [Copyright &y& Elsevier]

Abstract: A sensitive photoelectrochemical (PEC) approach for Pb2+ sensing was achieved firstly with the coupling of G-quadruplex-based DNAzyme and biocatalytic precipitation (BCP) on a CdS quantum dots electrode. Pb2+ can induce the conformational change of K+-stabilized G-quadruplex-based DNAzyme, leading to the decrease of the catalytic activity to H2O2-mediated 4-chloro-1-naphthol oxidation (BCP reaction). From the respective BCP reaction that monitors the event of DNAzyme deactivation, a novel PEC Pb2+ sensor could be realized with a detection limit of 1.0×10−8 M. [Copyright &y& Elsevier]