Architecture of electrospun carbon nanofibers–hydroxyapatite composite and its application act as a platform in biosensing

A biofunctional hybrid composite was constructed by assembling hydroxyapatite (HA) onto carboxylic group-functionalized carbon nanofibers (FCNFs). The FCNFs was obtained from acid treatment of carbon nanofibers (CNFs) which were synthesized by the combination of electrospinning and thermal treatment processes. The obtained carbon nanofibers–hydroxyapatite composite (FCNFs–HA) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and FTIR spectroscopy. Cytochrome c (Cyt c) was successfully immobilized in this three-dimensional FCNFs–HA composite and the electron transfer rate constant (k_s) was evaluated to be 3.66 s⁻¹ according to Laviron's equation. And the surface coverage (Γ*) was estimated to be 8.1 × 10⁻¹⁰ mol cm⁻². Cyt c immobilized in FCNFs–HA composite exhibited a good electrocatalytic activity towards the reduction of hydrogen peroxide (H₂O₂). The catalytic current is linear to the H₂O₂ concentration in the range of 2.0 μM to 8.7 mM (r = 0.9996; n = 28), and the detection limit was 0.3 μM based on the criterion of a signal-to-noise ratio of 3.     

Conformational flexibility decreased due to Y67F and F82H mutations in cytochrome c: Molecular dynamics simulation studies

Cytochrome c (cyt c), a mitochondrial protein, has dual functions in controlling both cellular energetic metabolism and apoptosis (programmed cell death). During apoptosis, cyt c (Fe³⁺) released into the cytosol initiates caspase activation leading to apoptosis. Since, X-ray crystallography gives only the static structure, we report here the dynamic behavior of holo and apo wild type (WT), Y67F and F82H mutant cyt c's (Fe³⁺) in their apoptotic states. Four nanosecond MD simulations were run for holo WT, Y67F and F82H cyt c's with and without FeS (Met-80) bond and also for apo WT and mutated cyt c's (Y67F and F82H) in water using GROMOS96 force field. Mutations of Y67F and F82H resulted in the decrease of backbone and Cα RMSDs, and radii of gyration (backbone and protein) in both the holo and apo forms. MD and ED results revealed that the flexibility of mutated holo cyt c's decreased perhaps affecting their ability to take part in mitochondrial electron/proton transfer process. Without FeS bond, the backbone and Cα RMSD increased in holo cyt c's perhaps resulting in enhanced peroxidase activity. ED revealed that four to six eigenvectors involved in over all motions of holo cyt c's without FeS bond, and six to eight eigenvectors in apo cyt c's in comparison to three to four eigenvectors for holo cyt c's with FeS bond.     

Direct electrochemistry of cytochrome P450 6A1 in mimic bio-membrane and its application for pesticides sensing

The direct electrochemistry of house fly cytochrome P4506A1 (CYP6A1) confined in dioctadecyl dimethyl ammonium bromide (DDAB) film was achieved. The immobilized CYP6A1 displayed a pair of redox peaks with a formal potential of −0.36 mV in pH 7.0 O₂-free phosphate buffers at scan rate of 1 V s⁻¹ and the direct electron transfer of CYP6A1 was characterized by voltammetry. The CYP6A1 in the DDAB film retained its bioactivity and could catalyze the reduction of dissolved oxygen. Upon addition of its substrate aldrin or heptachlor to the air-saturated solution, the reduction peak current of dissolved oxygen increased, which indicates the catalytic behavior of CYP6A1 to its substrates. By amperometry a calibration linear range was obtained to be 9.08 × 10⁻⁶-4.54 × 10⁻⁵ mol L⁻¹ with a sensitivity of 80 μA mM⁻¹ for aldrin or 8.91 × 10⁻⁶-4.46 × 10⁻⁵ mol L⁻¹ with a sensitivity of 66 μA mM⁻¹ for heptachlor. The apparent Michaelis-Menten constant for the electrocatalytic activity of CYP6A1 was found to be 7.468 × 10⁻⁵ mol L⁻¹ for aldrin and 4.316 × 10⁻⁵ mol L⁻¹ for heptachlor. The bioelectrocatalytic products were analysed using gas chromatography (GC) and electron ionization-mass spectrometry (EI-MS). The results confirmed that epoxidation was the main pathways of CYP6A1-mediated organochlorine pesticides oxidation.     

氨气检测的聚苯胺碳纳米管复合敏感膜的研究与应用

本文介绍了基于聚苯胺及多壁碳纳米管复合材料的氨气传感器的制备与测试,使用原位聚合法使苯胺单体以碳纳米管为核心进行聚合反应,运用介电泳法制备得聚苯胺/多壁碳纳米管气敏复合膜传感器。该传感器对10×10-6氨气的响应灵敏度为3.4,响应时间15 s,而对比实验中聚苯胺膜传感器的灵敏度为1.9。实验结果表明,由于碳纳米管在介电泳过程中构建的大比表面积纳米三维结构和优良的导电率,纳米复合材料的微观结构和导电性能都得到大幅改善,从而使得复合物具有相对于纯聚苯胺膜更好的气敏特性。     

Comparing sensitivities of differently oriented multi-walled carbon nanotubes integrated on silicon wafer for electrochemical biosensors

In this study, we report on multi-walled carbon nanotubes fabricated on silicon substrate with four different orientations via chemical vapor deposition. It is well-known that chemical treatments improve the nanotube electrochemical reactivity by creating edge-like defects on their exposed sidewalls. Before use, we performed an acid treatment on carbon nanotubes. To prove the effect of the treatment on these nanostructured electrodes, contact angles were measured. Then, sensitivities and detection limits were evaluated performing cyclic voltammetry. Two target molecules were used: potassium ferricyanide, an inorganic electroactive molecule, and hydrogen peroxide that is a product of reactions catalyzed by many enzymes, such as oxidases and peroxidases. Carbon nanotubes with tilted tips become hydrophilic after the treatment showing a contact angle of 22° ± 2°. This kind of electrode has shown also the best electrochemical performance. Sensitivity and detection limit values are 110.0 ± 0.5 μA/(mM cm²) and 8 μM for potassium ferricyanide solutions and 16.4 ± 0.1 μA/(mM cm²) and 24 μM using hydrogen peroxide as target compound. Considering the results of wettability and voltammetric measurements, nanotubes with tilted tips-based electrodes are found to be the most promising for future biosensing applications.     

A sensitive nonenzymatic hydrogen peroxide sensor based on DNA–Cu complex electrodeposition onto glassy carbon electrode

In this paper, DNA–Cu²⁺ complex was electrodeposited onto the surface of glassy carbon (GC) electrode, which fabricated a DNA–Cu²⁺/GC electrode sensor to detect H₂O₂ with nonenzyme. Cyclic voltammogram of DNA–Cu²⁺/GC electrode showed a pair of well-defined redox peaks for Cu²⁺/Cu⁺. Moreover, the electrodeposited DNA–Cu²⁺ complex exhibited excellent electrocatalytic behavior and good stability for the detection of H₂O₂. The effects of Cu²⁺ concentration, electrodeposition time and determination conditions such as pH value, applied potential on the current response of the DNA–Cu²⁺/GC electrode toward H₂O₂ were optimized to obtain the maximal sensitivity. The linear range for the detection of H₂O₂ is 8.0 × 10⁻⁷ M to 4.5 × 10⁻³ M with a high sensitivity of −40.25 μA mM⁻¹, a low detection limit of 2.5 × 10⁻⁷ M and a fast response time of within 4 s. In addition, the sensor has good reproducibility and long-term stability and is interference free.     

Effect of surface defects on biosensing properties of TiO2 nanotube arrays

In this paper, highly ordered titania nanotube (TNT) arrays fabricated by anodization were annealed at different temperatures in CO to create different concentrations of surface defects. The samples were characterized by SEM, XRD and XPS. The results showed different concentrations of Ti³⁺ defects were doped in TNT arrays successfully. Furthermore, after co-immobilized with horseradish peroxidase (HRP) and thionine chloride (Th), TNT arrays was employed as a biosensor to detect hydrogen peroxide (H₂O₂) using an amperometric method. Cyclic voltammetry results and UV-Vis absorption spectra presented that with an increase of Ti³⁺ defects concentration, the electron transfer rate and enzyme adsorption amount of TNT arrays were improved largely, which could be ascribed to the creation of hydroxyl groups on TNT surface due to dissociative adsorption of water by Ti³⁺ defects. Annealing in CO at 500 °C appeared to be the most favorable condition to achieve desirable nanotube array structure and surface defects density (0.27%), thus the TNT arrays showed the largest adsorption amount of enzyme (9.16 μg/cm²), faster electron transfer rate (1.34 × 10⁻³ cm/s) and the best response sensitivity (88.5 μA/mM l⁻¹).     

A novel microbial biosensor based on Circinella sp. modified carbon paste electrode and its voltammetric application

Microbial biosensors have been developed for voltammetric determination of various substances. This paper describes the development of a new biosorption based microbial biosensor for determination of Cu²⁺. The developed biosensor is based on carbon paste electrode consisting of whole cells of Circinella sp. Cu²⁺ was preconcentrated on the electrode surface at open circuit and then cathodically detected with the reduction of Cu²⁺. The voltammetric responses were evaluated with respect to percentage cell loading in the carbon paste, preconcentration time, pH of preconcentration solution, scan rate and interferences. The optimum response was realized by biosensor constructed using 5 mg of dry cell weight per 100 mg of carbon paste in pH 5.5 preconcentration solution. Under the optimum experimental conditions, the developed microbial biosensor exhibited an excellent current response to Cu²⁺ over a linear range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M (r² = 0.9938) with a detection limit of 5.4 × 10⁻⁸ M (S/N = 3). The microbial biosensor had good sensitivity and reproducibility (R.S.D. 4.3%, n = 6). Finally, the applicability of the proposed microbial biosensor to voltammetric determination of Cu²⁺ in real sample was also demonstrated and validated with atomic absorption spectrophotometric (AAS) method.