Direct electrochemistry of hemoglobin and its biosensing for hydrogen peroxide on TiO2–polystyrene nanofilms

Nanofilms of titanium dioxide (TiO₂) nanoparticles that mediate the assembly of polystyrene (PS) nanoparticles for immobilizing hemoglobin (Hb) on carbon ionic liquid electrode have been developed. Fourier transform infrared spectroscopy shows that Hb retains its native structure in TiO₂–PS nanofilms. Scanning electron microscopy reveals that the nanofilms possess uniform morphology and Hb is immobilized on the surface of the nanofilms. Electrochemical investigation of the biosensor indicates that the direct electrochemistry of hemoglobin is realized on the nanofilms, and there is a formal potential of ?0.320 V in deaerated buffer solutions; the biosensor shows good electrocatalytic activity toward the reduction of hydrogen peroxide with a linear range from 0.5 to 640 μM, a detection limit of 0.2 μM (S/N = 3) and a sensitivity of 103 μA mM^?1. Thus, the nanofilms will have potential application in the design of novel electrochemical biosensors.     

One-step fabrication of chitosan–hematite nanotubes composite film and its biosensing for hydrogen peroxide

This work reports on a novel chitosan–hematite nanotubes composite film on a gold foil by a simple one-step electrodeposition method. The hybrid chitosan–hematite nanotubes (Chi–HeNTs) film exhibits strong electrocatalytic reduction activity for H₂O₂. Interestingly, two electrocatalytic reduction peaks are observed at −0.24 and −0.56 V (vs SCE), respectively, one controlled by surface wave and the other controlled by diffusion process. The Chi–HeNTs/Au electrode shows a linear response to H₂O₂ concentration ranging from 1 × 10⁻⁶ to 1.6 × 10⁻⁵ mol L⁻¹ with a detection limit of 5 × 10⁻⁸ mol L⁻¹ and a sensitivity as high as 1859 μA μM⁻¹ cm⁻².     

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO₂–graphene (TiO₂–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO₂–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0?mM, with a sensitivity of 4.129?μA?mM^?1 and a detection limit of 1.2?×?10^?6?M under optimized conditions. The response time of the biosensor was 3?s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.     

Fc-specific biotinylation of antibody using an engineered photoactivatable Z–Biotin and its biosensing application

The development of a site-specific and covalent attachment methodology is crucial for antibody–biotin conjugates to preserve the antigen-binding ability of antibodies and yield homogeneous products. In this study, an engineered photoactivatable Z-domain variant [an UV-active amino acid benzoylphenylalanine (Bpa) was genetically incorporated into the Z-domain] carrying one biotin molecule (Z_Bpa–Biotin) was prepared by employing aminoacyl-tRNA synthetase/suppressor tRNA and Avitag/BirA techniques. The site-specific and covalent attachment of IgG–biotin conjugates, viz. photo-biotinylated IgG, was successfully achieved after UV exposure by combining the inherent Fc-binding capability of the Z-domain with the formation of covalent bond by the photo-crosslinker. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis assay showed that more than 90% of IgGs conjugated with Z_Bpa–Biotin molecules suffered 3 h UV irradiation. Further pepsin digestion analysis confirmed that the Z_Bpa–Biotin was conjugated to the Fc fragment of IgG without interference. We took the tumor biomarker carcinoembryoic antigen (CEA) as model to evaluate the detection efficiency of the site-specific photo-biotinylated IgG in biosensing application using surface plasmon resonance (SPR) technology. The photo-biotinylated IgG coated surface gave a limit of detection (LOD) of 2 ng mL^-1, is 5-fold lower than that of the randomly NHS-biotinylated IgG (10 ng mL^-1). Given that the (strept)avidin–biotin complex is extensively used in immunoassays, the proposed method for biotinylated IgG provides a powerful approach to further expand related applications.     

Construction of hyaluronan-silver nanoparticle–hemoglobin multilayer composite film and investigations on its electrocatalytic properties

In this work, hyaluronan-silver nanoparticles (HSNPs) were prepared by UV-initiated photoreduction, and protein hemoglobin (Hb) was then alternately assembled with the prepared negatively charged HSNPs into layer-by-layer (LBL) films on solid surface. The electrochemical behavior and electrocatalytic activities toward oxygen and hydrogen peroxide of the resulting films were studied. It was found that the HSNPs greatly enhanced the electron transfer reactivity of Hb as a bridge. The assembly films showed a pair of nearly reversible redox peaks with a formal potential of −0.32 V (vs. Ag/AgCl) for the heme Fe(III)/Fe(II) redox couple. The immobilized Hb in the films maintained its biological activity, showing a surface-controlled process with a heterogeneous electron transfer rate constant (k _s) of 1.0 s⁻¹ and displaying the same features of a peroxidase in the electrocatalytic reduction of oxygen and hydrogen peroxide. This work provides a novel model to fabricate LBL films with protein, polysaccharide and nanoparticles, which may establish a foundation for fabricating new type of biosensors based on the direct electron transfer of redox proteins immobilized in nanocomposite multilayer films with underlying electrodes.     

Analytical theory for ion transfer–electron transfer coupled reactions at redox layer–modified/thick film–modified electrodes

Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid–liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current–potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.     

ZnO-MWCNTs/Nafion Inorganic-organic composite film： Preparation and application in bioelectrochemistry of hemoglobin

Multi-walled carbon nanotubes(MWCNTs) were coated with ZnO by a hydrothermal method.The resulting nanocomposites were mixed with the Nafion solution to form a composite matrix for the fabrication of hemoglobin(Hb) biosensor.To prevent the leak of Hb molecules of the biosensor,silica sol-gel film was coated on the surface of the Hb/ZnO-MWCNTs/Nafion electrode.The silica sol-gel/Hb/ZnO-MWCNTs/Nafion film exhibited a pair of well-defined,quasi-reversible redox peaks.This biosensor showed excellent electroca...     

Reason for the loss of hydrophilicity of TiO_2 film and its photocatalytic regeneration

TiO2 film was prepared on soda-lime glass by sol-gel method. The water contact angle (θ) of the fresh TiO2 film is 0°. During storage in air, the surface of TiO2 film is gradually converted to the hydrophobic state. XPS and ITD results reveal that it is due to the adsorption of organic contaminants on TiO2 surface in air ambience. The lost hydrophilicity of TiO2 film can be regenerated by UV illumination.     

Synthesis of palladium–polypyrrole nanocomposite and its electrocatalytic properties in the oxidation of formaldehyde

Three alternative methods were developed for the synthesis of modifying palladium–polypyrrole layers on the surface of an inert electrode. Their electrocatalytic activity toward formaldehyde under inert atmosphere was checked. All the suggested methods are one-stage and allow synthesis of a film on the electrode surface from a solution containing a palladium salt and pyrrole in the absence of other active reagents. The electrochemical methods (potentiodynamic and double cathodic and anodic pulses techniques) in an aqueous medium give films with poorly reproducible electrocatalytic properties, while the chemical redox synthesis affords films with reproducibly high electroactivity toward methylene glycolate.     

Preparation of thorium oxalate–silica sorbent and its application for the sorption of americium from aqueous solutions

A new sorbent, thorium oxalate incorporated in silica gel matrix was prepared. This material was characterized by X-ray, Thermo-gravimetric Analysis, surface area and porosity analysis. The material was obtained in the form of granular particles in the mesh size range of 80–150 American Standard of Testing Materials, yielding good liquid flow, when packed in ion exchange column. This sorbent was investigated for the sorption of americium from various aqueous media such as nitric acid, oxalic acid and sulphuric acid by distribution coefficient studies. Column experiments were carried out to study the practical application of this sorbent for removal of americium from oxalic acid-nitric acid solutions. Elution studies were also carried out for the recovery of americium.     

Characterization and electrochemical study of hemoglobin–carbon nanoparticles–polyvinyl alcohol nanoporous hybrid film

A hybrid film is fabricated by casting hemoglobin (Hb)–carbon nanoparticles (CNPs)–polyvinyl alcohol (PVA) suspension on glassy carbon electrode (GCE). The resulting film shows a three-dimensional nanoporous structure. In the hybrid film, the ultraviolet visible (UV–Vis) absorption spectra of Hb keep almost unchanged. The organic–inorganic hybrid material can promote the direct electron transfer of Hb. A pair of well-defined and quasireversible peaks with a formal potential of −0.348 V (vs saturated calomel electrode) is obtained, which is caused by the electrochemical reaction of the Fe(III)/Fe(II) couple of Hb. The electron transfer rate constant (k _s) is estimated to be 3.9 s⁻¹. The immobilized Hb exhibits high stability and excellent electrochemical catalysis to the reduction of oxygen (O₂), hydrogen peroxide (H₂O₂), and nitrite (). The catalytic currents are linear to the concentrations of H₂O₂ and from 1.96 to 112 μM and from 0.2 to 1.8 mM, respectively. Therefore, the hybrid film may be a good matrix for protein immobilization and biosensor fabrication.     

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons and its application for the synthesis of diaryl ethers

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons support for the synthesis of diaryl ethers via Ullmann type coupling is reported. The catalyst showed excellent performance for C–O cross coupling reactions under ligand free condition. The catalyst was characterized by various techniques such as SEM, TEM, XRD, EDX, BET, TGA, and UV spectrophotometry. It was recycled several times without significant loss in its catalytic activity.     

A study on the mechanism of reaction between BNAH and chloranil:Evidence for electron transfer

The reaction between chloranil and N-benzyldihydronicotinamide(BNAH)in boratebuffer/DMF was investigated.The reaction mixture gave a strong esr signal,which is consistentwith that of chloranil anion radical,and tetrachlorohydrophenol(QH_2)and N-benzylnicotinamide(BNA~+)were obtained as the sole products.When the reaction was run in benzene solution,a greencoloured charge-transfer complex between the reactants could be isolated,which decomposed in polarsolvents to give BNA-+ and QH_2.Based on kinetic studies by esr spectroscopy by the stopped-flowtechnique,a two-step electron-transfer mechanism for the reactionis proposed in contrast to thehydride-transfer mechanism reported in the literature.     

Breakdown of the Born–Oppenheimer–Condon–Marcus approximation in long distance electron transfer

We consider the issue of how the breakdown of the Born–Oppenheimer–Condon–Marcus approximation affects the dependence of the electron-transfer rate k upon distance, as well as the dependences upon the driving force and temperature. For large distances, ca. r>10 Å, it is predicted that: (i) the slope of lnk vs r dependence decreases down to zero; (ii) the bell-shaped Marcus dependence upon the driving force is distorted, with the maximum shifting toward ΔG>0; and (iii) the apparent activation energy increases and the temperature dependence more and more declines from the Arrhenius form. These effects can be experimentally distinguished from similar effects due to other mechanisms, such as thermal activation of the electron transferred and temperature dependence of the reorganization parameters and driving force. Experimental data by Isied et al. [J. Phys. Chem. 97 (1993) 11456] on electron transfer between metal ions across rigid oligoproline bridges are well fitted using the present theory.     

Insertion of arynes into the carbon–oxygen double bond of amides and its application into the sequential reactions

The reaction of arynes, generated from ortho-(trimethylsilyl)aryl triflates, with the CO bond of formamides gave salicylaldehyde derivatives via the formation of formal [2+2] adducts. The sequential transformation of arynes into ortho-disubstituted arenes, o-aminoalkylphenols or o-hydroxyalkylphenols, was achieved by one-pot procedure using dialkylzincs.     

Fabrication of the DNA/poly(3-methylthiophene) composite film modified electrode and its application for the study on the voltammetric behavior and determination of 8-hydroxy-2′-deoxyguanosine

Science China Chemistry - A composite film of DNA/poly(3-methylthiophene) (P3MT) modified glassy carbon electrode (GCE) has been fabricated by electro-deposition method. P3MT film was first...     

LapRLSR for NIR spectral modeling and its application to online monitoring of the column separation of Salvianolate

A novel near infrared (NIR) modeling method—Laplacian regularized least squares regression (LapRLSR) was presented, which can take the advantage of many unlabeled spectra to promote the prediction performance of the model even if there are only few calibration samples. Using LapRLSR modeling, NIR spectral analysis was applied to the online monitoring of the concentration of salvia acid B in the column separation of Salvianolate. The results demonstrated that LapRLSR outperformed partial least squares (PLS) significantly, and NIR online analysis was applicable.     

A selective and sensitive off–on probe for palladium and its application for living cell imaging

A new rhodamine B derivative T1 has been rationally synthesized and displayed selective Pd(Ⅱ)-amplified absorbance and fluorescence emission above 540 nm in methanol–water. Upon the addition of Pd(Ⅱ), the spirolactam ring was unfolded and a 1:1 metal-ligand complex formed, which can be used for ‘‘naked-eyes" detection. In addition, fluorescence imaging experiments of Pd~(2+) in HepG2 living cells showed its valuable application in biological systems.