Direct electron transfer of hemoglobin in layered α-zirconium phosphate with a high thermal stability

Determination of the total antioxidant capacity of the Chinese tea based on a novel "peroxidase/zirconium phosphonate"composite electrochemical sensor

In this work, a novel zirconium phosphonate (ZrPR1R2) was prepared by decorating both the aminoethoxy- group (R1) and the carboxypropyl- group (R2) on the zirconium phosphate layers in order to manipulate further the immobilization of the peroxidase (POD), and an antioxidant biosensor with higher sensitivity was constructed by dropping the POD/ZrPR1R2 composite onto the glassy carbon electrode surface. The activity of the POD/ZrPR1R2 composite was detected by Uv-vis spectra. The direct electrochemical behavior, the electrocatalytic response to dissolved oxygen and hydrogen peroxide, as well as the ability to detect total antioxidant capacity in tea sample were investigated by the methods of cyclic voltammetry. The results indicated that the immobilization of POD in ZrPR1R2 nanosheets matrix enhanced the enzymatic activity, and achieved the fast and direct electron transfer between POD and glassy carbon electrode. Moreover, the POD/ZrPR1R2 composite modified electrode show the electrocatalytic response to hydrogen peroxide in the linear range of 8.8×10-8 to 8.8×10-7 mol L-1, with the detection limit of 3.3×10-8 mol L-1. Attributing to the sensitive response to dissolved oxygen, the total antioxidant capacity can be detected directly in the real tea water by this POD/ZrPR1R2 composite modified electrode.

Bactericidal efficiency of porphyrin systems

Photodynamic Inactivation is an innovative technique used to combat bacterial and viral infections which involves the use of photosensitizing agents along with light to generate cytotoxic reactive oxygen species able to kill bacteria and viruses. In the first section of this minireview, porphyrin-based fluorophores are shown to be remarkable dye candidates for PDI (photodynamic inactivation) applications. The second section is dedicated to the description of porphyrin-based antimicrobial materials and their potentialities for industrial applications such as in food packaging or antimicrobial medical devices and hygiene. Finally, the failings and perspectives of PDI are analyzed to demonstrate how the PDI technique could be an efficient and ecologically friendly antimicrobial technique.

An amperometric glucose biosensor based on a MnO2/graphene composite modified electrode

In this paper, a novel composite of graphene/MnO₂ (GR/MnO₂) was successfully synthesized by a simple one-step hydrothermal method.

"Stable-on-the-Table" Biosensors: Hemoglobin-Poly (Acrylic Acid) Nanogel BioElectrodes with High Thermal Stability and Enhanced Electroactivity

In our efforts toward producing environmentally responsible but highly stable bioelectrodes with high electroactivities, we report here a simple, inexpensive, autoclavable high sensitivity biosensor based on enzyme-polymer nanogels. Met-hemoglobin (Hb) is stabilized by wrapping it in high molecular weight poly(acrylic acid) (PAA, M_W 450k), and the resulting nanogels abbreviated as Hb-PAA-450k, withstood exposure to high temperatures for extended periods under steam sterilization conditions (122 °C, 10 min, 17–20 psi) without loss of Hb structure or its peroxidase-like activities. The bioelectrodes prepared by coating Hb-PAA-450k nanogels on glassy carbon showed well-defined quasi-reversible redox peaks at −0.279 and −0.334 V in cyclic voltammetry (CV) and retained >95% electroactivity after storing for 14 days at room temperature. Similarly, the bioelectrode showed ~90% retention in electrochemical properties after autoclaving under steam sterilization conditions. The ultra stable bioelectrode was used to detect hydrogen peroxide and demonstrated an excellent detection limit of 0.5 μM, the best among the Hb-based electrochemical biosensors. This is the first electrochemical demonstration of steam-sterilizable, storable, modular bioelectrode that undergoes reversible-thermal denaturation and retains electroactivity for protein based electrochemical applications.

Direct electron transfer and electrochemical study of hemoglobin immobilized in ZnO hollow spheres

ZnO hollow spheres were firstly prepared. A new type of amperometric hydrogen peroxide biosensor was fabricated by entrapping Hemoglobin (Hb) through the ZnO hollow spheres (ZHS) nanoparticles. The composition morphology and size were studied by transmission electron microscopy. The surface topography of the prepared films was imaged by atomic force microscope (AFM). Several techniques, including UV-vis absorption spectroscopy, cyclic voltammetry, chronoamperometry were employed to characterize the performance of the biosensor. The results indicated that the ZHS nanoparticles had enhanced the performance of the hydrogen peroxide sensors. The electrochemical parameters of Hb in the ZHS were calculated by the results of the electron-transfer coefficient (α) and the apparent heterogeneous electron-transfer rate constant K (s) as 0.5 and 3.1 s(-1), respectively. The resulting biosensors showed a wide linear range from 2.1 × 10(-6) to 5.18 × 10(-3) M, with a low detection limit of 7.0 × 10(-7) M (S/N = 3) under optimized experimental conditions. The results demonstrated that the ZHS matrix may improve the protein loading with the retention of bioactivity and greatly promote the direct electron transfer, which can be attributed to its unique morphology, high specific surface area, and biocompatibility. The biosensor obtained from this study possesses high sensitivity, good reproducibility, and long-term stability.

A novel biosensor based on sol-gel poly () (PVA)/(titanium dioxide)TiO2 hybrid material

A novel hydrogen peroxide biosensor has been fabricated based on Hb entrapped poly(vinyl alcohol) (PVA)/Titanium dioxide (TiO2) hybrid material. Multi-walled carbon nanotubes (MWCNTs) were then dispersed into the composite matrix. It was found that such hybrid material could retain the native biocatalytic activity of the entrapped Hb by electrochemical experiments. In addition, MWCNTs enhanced catalytic performance of hydrogen peroxide and promoted electronic transfer. Effects of some experimental variables such as the amount of MWCNTs, concentration of enzyme, amounts of modifier on the current response of the biosensor were investigated. A linear calibration graph was obtained in the concentration range of H2O2 from 0.5 to 2.7 μM (linear regression coefficient = 0.997) with a detection limit of 0.01 μM (S/N = 3). The apparent Michaelis-Menten constant Km was 0.997 μM. The biosensor displayed excellent repeatability, high sensitivity, long-term stability, and good selectivity. The recovery of H2O2 in samples was testified with satisfactory results.

A novel mediator-free biosensor based on co-intercalation of DNA and hemoglobin in the interlayer galleries of alpha-zirconium phosphate

A novel mediator-free biosensor was constructed by the co-intercalation of negatively charged DNA and positively charged hemoglobin (Hb) in the interlayer galleries of layered alpha-zirconium phosphate (alpha-ZrP) with the delamination-assembly procedure at pH 5.5. X-ray diffraction and field-emission scanning electron microscopy results revealed the featured layered structure for the re-assembled DNA/Hb/alpha-ZrP composite. Infrared spectroscopy and circular dichroism results confirmed the coexistence of Hb and DNA in the composite and the considerably retained protein conformation of intercalated Hb. The direct electron transfer of Hb was facilitated by the co-intercalation of DNA and Hb. Because of the synergistic effect of alpha-ZrP host and co-intercalated DNA guest, the DNA/Hb/alpha-ZrP modified electrode exhibited good electrocatalytic response to H(2)O(2) with higher sensitivity of 0.79 A M(-1) cm(-2) and lower detection of 4.28x10(-7) M in the linear range of 7.28x10(-7) to 9.71x10(-5) M. Furthermore, the electrocatalytic activity of Hb in the DNA/Hb/alpha-ZrP composite retained at high temperature (85 degrees C) or in the presence of organic solvent (CH(3)CN), which could be the protection of alpha-ZrP nanosheets.