Heterogeneous Electron-transfer Constants Research Articles

Electrochemical Properties Analysis of Immobilized Glucose Oxidase on Multi-Walled Carbon Nanotubes and Hydroxy-Fullerene Nanocomposites

The development of a glucose sensor that can monitor blood glucose levels is particularly important with the increasing number of diabetes patients. Here, a glucose biosensor based on Nafion (NF), glucose oxidase (GOx), multi-walled carbon nanotubes (MWCNTs), hydroxy fullerene (HFs) composite modified glassy carbon electrode (GCE) is presented. The transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), UV–visible spectroscopy (UV–vis), cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) methods are used to study the characteristics of the modification materials and to evaluate electrochemical properties of the modified electrodes. The heterogeneous electron transfer constant (ks) is calculated to be 4.49 s−1. The response to glucose is linear in the range of 0.02–0.25 mM and 0.25–4.0 mM with a sensitivity of 80.59 μA mM−1 cm−2 and detection limit (LOD) of 9.93 μM. The NF/MWCNTs-HFs-GOx/GCE biosensor demonstrate high sensitivity to glucose with excellent storage stability and anti-interference capability.

Nafion-based label-free immunosensor as a reliable warning system: The case of AFB1 detection in cattle feed

This study presents a simple method for the rapid and versatile fabrication of label-free immunosensors on Nafion-modified screen-printed platforms. Herein, Nafion is exploited both as an immobilization matrix and as a weak (unexpectedly) electrochemical enhancer for the first time. The electrochemical characteristics in terms of diffusivity and conductivity of thin cation-exchange polymer membrane-modified screen-printed electrodes were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The free electrode surface area, the diffusion coefficient, the peak-to-peak separation, the heterogeneous electron transfer constant, and the charge transfer resistance for Nafion-modified and bare SPE have been calculated and compared. Then, Nafion-SPEs were employed to develop a competitive label-free immunoassay for the quantitative detection of Aflatoxin B1. Morphological characterization of the proposed immunosensor was performed using Scanning Electron Microscopy, and its analytical performance was evaluated using square wave voltammetry as a detection technique and [Fe(CN)6]3−/4− as a redox probe. The immunosensor showed satisfactory results in spiked cattle feed in terms of limit of detection (3.8 ngmL−1), linear range (LR 10–100 ngmL−1), sensitivity (33.0 ngmL−1) and reproducibility (RSD%<10%). The comparison of performance to that of a labelled immunosensor and a conventional chromatographic technique revealed a strong correlation between the respective results, but with shorter analysis time for the proposed tool. Furthermore, The present study achieved evidence of the dependability of the proposed method, proving that its use as an early warning system for the detection of AFB1 in cattle feed is something doable and not an abstract idea.

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose.

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)+-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s-1. The heterogeneous electron transfer constant (ks) of GDH on the composite functional polymer-modified GCE was 6.5 s-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Acceptor properties of "carbon nanotubes-redox-active polymer based on bovine serum albumin modified with ferrocenecarboxaldehyde" composite for creating a BOD biosensor with Blastobotrys adeninivorans BKM Y-2677 yeast.

The possibility of using a composite material based on bovine serum albumin (BSA) covalently bonded with ferrocenecarboxaldehyde and containing carbon nanotubes (CNT) for the immobilization of Blastobotrys adeninivorans BKM Y-2677 (B. adeninivorans) yeast is discussed. The optimal ratio of ferrocenecarboxaldehyde to BSA for the redox-active polymer synthesis is 1:2, since the heterogeneous electron transfer constant is 0.45 ± 0.01s-1. When carbon nanotubes (CNTs) are added to this polymer, the heterogeneous electron transfer constant increases: at a CNT specific density of 2.5µg/mm2, it reaches a maximum value of 0.55 ± 0.01s-1. The addition of CNTs into the conducting system leads to increasing of the rate constant of interaction redox species with B. adeninivorans yeast by an order: the rate constant of interaction between B. adeninivorans yeast and electroactive particles in a redox-active polymer is 0.056 ± 0.005 dm3/g × s and in a composite material based on CNTs is 0.51 ± 0.02 dm3/g × s. The yeast specific density at the electrode of 0.1mg/mm2 and electrolyte pH of 6.2 was chosen as the working value for the receptor system operation. Immobilized in a composite material, yeast oxidizes a wider range of substrates compared with a similar receptor element based on the ferrocene mediator. The biosensors formed on the basis of hybrid polymers have a high sensitivity with a lower limit of determined concentrations of 1.5mg/dm3 with an assay time of 5min and a high correlation (R = 0.9945) with the results of the standard method for determining biochemical oxygen demand (BOD) in nine real surface water samples of the Tula region.

Nanoscale engineering to control mass transfer on carbon-based electrodes

Here we use an electrode consisting of carbon nanofibers (CNFs), the lengths and surface population density of which can be effectively controlled. It is shown that (i) a thin liquid layer forms when the thickness of the diffusion layer has a specific ratio to the dimensions of the nanostructured carbon surface. (ii) This leads to a decrease in the peak potential difference and a subsequent increase in the apparent heterogeneous electron transfer (HET) constant, both of which could be interpreted as a result of increased catalytic activity. (iii) However, we show that this explanation is not likely, as our materials are chemically identical, and we use an outer sphere redox (OSR) probe to minimize any specific chemical interactions. On the contrary, (iv) the results clearly show that the observed behavior is caused by a combination of the formation of a thin liquid layer and the increased apparent surface area of the electrodes.

Electrode Kinetics of Ion Jelly and Ion Sol-Gel Redox Materials on Screen-Printed Electrodes

Several hydrogel materials have been proposed for drug delivery systems and other purposes as interfacial materials, such as components for fuel cells and immobilization of biomolecules. In the present work, two materials, an ion sol-gel, based on 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and an ion jelly (1-ethyl-3-methylimidazolium ethylsulfate) film deposited on carbon screen-printed electrodes, were electrochemically characterized. The electrode kinetics of ion jelly and ion sol-gel materials were compared by using ferrocyanide/ferricyanide redox reaction couple as a model redox process. Diffusion coefficients were calculated and compared to those obtained with the model redox couple in non-modified electrodes. Results pointed to a decrease of two and four orders of magnitude in the diffusion coefficients, respectively, for ion jelly and ion sol-gel film modified electrodes. Heterogeneous electron transfer constants for the ferrocyanide/ferricyanide ion redox process were also determined for modified and non-modified electrodes, in which the ion sol-gel film modified electrode presented the lower values. This work sought to contribute to the understanding of these materials’ properties, with emphasis on their diffusion, conductivity, and electrochemical behavior, namely reversibility, transfer coefficients, and kinetics, and optimize the most suitable properties for different possible applications, such as drug delivery.

Powerful Electron-Transfer Screen-Printed Platforms as Biosensing Tools: The Case of Uric Acid Biosensor.

The use of carbon nanomaterials (CNMs) in sensors and biosensor realization is one of the hottest topics today in analytical chemistry. In this work, a comparative in-depth study, exploiting different nanomaterial (MWNT-CO2H, -NH2, -OH and GNP) modified screen-printed electrodes (SPEs), is reported. In particular, the sensitivity, the heterogeneous electron transfer constant (k0), and the peak-to-peak separation (ΔE) have been calculated and analyzed. After which, an electrochemical amperometric sensor capable of determining uric acid (UA), based on the nano-modified platforms previously characterized, is presented. The disposable UA biosensor, fabricated modifying working electrode (WE) with Prussian Blue (PB), carbon nanotubes, and uricase enzyme, showed remarkable analytical performances toward UA with high sensitivity (CO2H 418 μA μM−1 cm−2 and bare SPE-based biosensor, 33 μA μM−1 cm−2), low detection limits (CO2H 0.5 nM and bare SPE-based biosensors, 280 nM), and good repeatability (CO2H and bare SPE-based biosensors, 5% and 10%, respectively). Moreover, the reproducibility (RSD%) of these platforms in tests conducted for UA determination in buffer and urine samples results are equal to 6% and 15%, respectively. These results demonstrate that the nanoengineered electrode exhibited good selectivity and sensitivity toward UA even in the presence of interfering species, thus paving the way for its application in other bio-fluids such as simple point-of-care (POC) devices.

Electrochemical and morphological layer-by-layer characterization of electrode interfaces during a label-free impedimetric immunosensor build-up: The case of ochratoxin A

In this paper, we provide an in-depth electrochemical characterization of a label-free impedimetric immunosensor for rapid detection of ochratoxin A. The sensor was based on a carbodiimide-mediated amide coupling reaction to immobilize a specific ochratoxin A antibody onto 4-mercaptobenzoic acid-modified commercial screen-printed gold electrode. Different variables affecting the performance of the developed sensor were optimized. Cyclic voltammetry and electrochemical impedance spectroscopy were used to analyse modifications of the interfacial properties occurring at each step of the biosensor assembly. The free electrode surface area, the diffusion coefficient, the peak-to-peak separation, the heterogeneous electron transfer constant, and charge transfer resistance have been calculated and compared. The decrease of charge transfer resistance values was linearly proportional to the ochratoxin A concentration in the range of 0.37– 2.86 ng/mL, with a detection limit of 0.19 ng/mL, a limit of quantification of 0.40 ng/mL, very good selectivity, reproducibility, and storage stability in the absence of antifouling agents. Surface morphology and topographic data at each step of the immunosensor assembly were studied by Atomic Force Microscopy, which also provided information on the specific binding of ochratoxin A. Finally, contact angle measurements revealed the hydrophilicity evolution of the surface during sensor assembly enabling OTA binding.

3D-printed hybrid-carbon-based electrodes for electroanalytical sensing applications

In this work we present miniaturized, fully integrated, 3D-printed, hybrid-carbon-based electrodes fabricated using a Fused Deposition Modeling (FDM) 3D-printer. This work is significant because it is the first time that a hybrid carbon-nanotube/carbon black/polylactic acid (CNT/CB/PLA) filament material has been employed in the fabrication of an electrochemical sensing system. The integrated 3D-printed hybrid-carbon electrode is composed of two parts: a non-conductive acrylonitrile butadiene styrene substrate and a conductive CNT/CB/PLA three-electrode array (comprising working, counter, and pseudo-reference electrodes). The 3D-printed electrodes were activated in a simple and cost-effective two-step process, a chemical step followed by an electrochemical step, leading to a heterogeneous electron transfer constant of 5.02 × 10-4 cm s−1. As a proof of concept, the 3D-printed electrodes were used to detect dopamine with a limit of detection of 1.45 μM. The simplicity, portability, low cost (0.11 USD per electrode), and rapid fabrication (3.7 min) of these fully integrated, 3D-printed, hybrid-carbon-based electrodes indicate that they can be employed as true point-of-care 3D-printed electrochemical sensing systems. We believe that our work paves the way for the development of new conductive nanocomposite PLA filaments for the fabrication of 3D-printed hybrid electrodes with improved performance.

An inverse-designed electrochemical platform for analytical applications

Screen-printed electrodes are the most recent generation of low-cost, mass-produced, sensitive and portable devices for the measurement of analytes of interest. The responses of these platforms, in terms of current intensity and reproducibility, are strongly influenced by factors such as printing procedures, type of ink, substrates, etc. In this paper, an improved inverse-designed screen-printed electrode (IDSPE) is proposed. The electrochemical performance is compared with that obtained using classical screen printed electrodes (SEPs), showing enhanced sensitivity and signal-to-noise ratio (background current minimization 32 ± 3nA and 0.64 ± 0.01nA, for SPE and IDSPE, respectively). A full comparison between inverse and classical screen-printed electrodes is carried out using various electroactive species (potassium ferricyanide, ascorbic acid, hexaammineruthenium(III) chloride and NADH) and two different electrochemical techniques (cyclic and square-wave voltammetry). In tests conducted with potassium ferricyanide the sensitivity of the IDSPE shows a nearly four-fold improvement, and a limit of detection three times better than the values obtained employing the classical SPE. The reproducibility (RSD%) in tests conducted with ascorbic acid is 6% and 12% for IDSPE and SPE, respectively. Moreover, surface modification of both screen-printed electrodes (SPE and IDSPE) with biochar obtained from recycled brewers waste (Bio-SPEs and Bio-IDSPEs), further improves their electrochemical performance, in terms, for example, of the heterogeneous electron transfer constant (0.0024 and 0.0018 for Bio-SPE and Bio-IDSPE, respectively).

A mediator microbial biosensor for assaying general toxicity

A mediator biosensor based on Paracoccus yeei bacteria for assaying the toxicity of perfumery and cosmetics samples was developed. An approach to selecting an electron-transport mediator based on the heterogeneous electron transfer constants for investigated mediators (ks) and the mediator–biomaterial interaction constants (kinteract) was proposed. Screening of nine compounds as potential mediators showed a ferrocene mediator immobilized in graphite paste to have the highest efficiency of electron transfer to the graphite-paste electrode (the heterogeneous transfer constant, 0.4 ± 0.1 cm/s) and a high constant of interaction with P. yeei (0.023 ± 0.001 dm3/(g·s)). A biosensor for toxicity assessment based on the ferrocene mediator and P. yeei bacteria was formed. The biosensor was tested on samples of four heavy metals (Cu2+, Zn2+, Pb2+, Cd2+) and two phenols (phenol and p-nitrophenol). Proceeding from the EC50 index, it was found that the use of the ferrocene mediator made the biosensor more sensitive to investigated toxicants than most analogues described. Toxicity determination of four perfumery and cosmetics samples by the developed biosensor showed prospects of using this system for real-time toxicity monitoring of samples.

Glucose Oxidase Immobilized on a Functional Polymer Modified Glassy Carbon Electrode and Its Molecule Recognition of Glucose.

In the present study, a glucose oxidase (GluOx) direct electron transfer was realized on an aminated polyethylene glycol (mPEG), carboxylic acid functionalized multi-walled carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymer modified glassy carbon electrode (GCE). The amino groups in PEG, carboxyl groups in multi-walled carbon nanotubes, and IL may have a better synergistic effect, thus more effectively adjust the hydrophobicity, stability, conductivity, and biocompatibility of the composite functional polymer film. The composite polymer membranes were characterized by cyclic voltammetry (CV), ultraviolet-visible (UV-Vis) spectrophotometer, fluorescence spectroscopy, electrochemical impedance spectroscopy (EIS), and transmission electron microscopy (TEM), respectively. In 50 mM, pH 7.0 phosphate buffer solution, the formal potential and heterogeneous electron transfer constant (ks) of GluOx on the composite functional polymer modified GCE were −0.27 V and 6.5 s−1, respectively. The modified electrode could recognize and detect glucose linearly in the range of 20 to 950 μM with a detection limit of 0.2 μM. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 143 μM. The IL/mPEG-fMWCNTs functional polymer could preserve the conformational structure and catalytic activity of GluOx and lead to high sensitivity, stability, and selectivity of the biosensors for glucose recognition and detection.

Direct Electron Transfer of Catalase and its Biosensing for H2O2

By immobilizing catalase on a functional nanocomposites containing ion-liquid, TiO2 nano particles and carboxylic acid functionalized multi-walled carbon nanotubes, direct electron transfer of CAT was realized on the nanocomposites modified glassy carbon electrode. The electrochemical study showed that the formal potential and heterogeneous electron transfer constant of the prepared modified glassy carbon electrode were −0.163 V and 5.24 s−1, respectively. The electrocatalysis study showed that the linear response range toward H2O2 and the apparent Michaelis–Menten constant were from 5 μM to 1000 μM and 54.3 μM, respectively.

3D printing for electroanalysis: From multiuse electrochemical cells to sensors

This work presents potential applications of low-cost fused deposition modeling 3D-printers to fabricate multiuse 3D-printed electrochemical cells for flow or batch measurements as well as the 3D-printing of electrochemical sensing platforms. Electrochemical cells and sensors were printed with acrylonitrile butadiene styrene (ABS) and conductive graphene-doped polylactic acid (G-PLA) filaments, respectively. The overall printing operation time and estimated cost per cell were 6 h and $ 6.00, respectively, while the sensors were printed within minutes (16 sensor strips of 1 × 2 cm in 10 min at a cost of $ 1.00 each sensor). The cell performance is demonstrated for the amperometric detection of tert-butylhydroquinone, dipyrone, dopamine and diclofenac by flow-injection analysis (FIA) and batch-injection analysis (BIA) using different working electrodes, including the proposed 3D-printed sensor, which presented comparable electroanalytical performance with other carbon-based electrodes (LOD of 0.1 μmol L−1 for dopamine). Raman spectroscopy and scanning electron microscopy of the 3D-printed sensor indicated the presence of graphene nanoribbons within the polymeric matrix. Electrochemical impedance spectroscopy and heterogeneous electron transfer constants (k0) for the redox probe Ru(NH3)6+3 revealed that a glassy-carbon electrode presented faster electron transfer rates than the 3D-printed sensor; however, the latter presented lower LOD values for dopamine and catechol probably due to oxygenated functional groups at the G-PLA surface.

(Invited) Enhancing Electron Transfer Rates on Ultra-Thin Graphene Electrodes Using a Sub-Surface Patterning Approach

We will discuss the potential of mono- and few-layer graphene electrodes as versatile platforms for the exploration of new electrocatalyst design principles. By transferring cm2 layers of CVD-grown graphene over metal deposits patterned on insulating substrates, and following passivation of pinholes and grain boundaries, we have measured enhanced rates of outer-sphere and inner-sphere electron transfer on sites modified with the sub-surface metal. Reactive imaging of these electrodes using scanning electrochemical microscopy was used to confirm our modification strategy and to highlight the possibility of using this strategy to spatially encode reactivity on surfaces. These electrodes enable a unique opportunity to modify the reactivity and mechanism of electrochemical reactions by means of electronic interactions that operate at scales coincident with their limiting thickness. In a first study,[1] we deposited bi-layer graphene on SiO2 chips modified with thin deposits of Au and Pt. SECM imaging using reversible outer-sphere mediators (ferri/ferrocyanide and ferrocenemethanol) showed a five-fold increase in the heterogeneous electron transfer constant on sub-surface modified sites. These enhancements are likely a consequence of increased electronic density of states due to a donating effect from the substrate. Following this principle, we explored the impact on an inner-sphere process, the oxygen reduction reaction. Our results indicate that both the kinetics and mechanism of the reaction are sensitive to sub-surface modification, with the kinetics largely driven by the identity of the metal and the reaction mechanism dominated by graphene or adsorbed molecular catalysts.[2] SECM imaging in the redox competition mode and in the H2O2 collection mode confirmed observations done on macro-electrode interfaces. The design principles derived from these experiments open new opportunities in the coupling of materials with different electrocatalytic properties using graphene as a mediating surface. We will discuss our recent progress expanding this toolbox for mitigating problems associated with several electrocatalytic reactions and exploring other reactions of interest, including the electrochemical reduction of CO2. [1] Hui, J.; Zhou, X.; Bhargava, R.; Chinderle, A.; Zhang, J.; Rodríguez-López, J. Electrochim. Acta 2016, 211, 1016-1023. [2] Hui, J., et al., Rodríguez-López, J. In Preparation. Figure 1

Electrochemical behavior of reduced graphene oxide and multi-walled carbon nanotubes composites for catechol and dopamine oxidation

Glassy carbon electrodes were modified by drop casting carbon nanomaterials, graphene oxide, GO, and multi-walled carbon nanotubes, MWCNTs, alone, mixed together (Composite) or in the form of bi-layers. The reduction of GO was carried out by means of a green approach using cyclic voltammetry (CV). Two model compounds, catechol and dopamine, which can be considered representative of the polyphenols class, were taken into account to determine the modifying system giving the highest oxidation current. Furthermore, the fouling effects of the electrode surface were also taken into account. The electrochemically active areas of the tested configurations were estimated by two approaches, to highlight the various phenomena that may affect the redox processes of the two analytes at the different chemically modified electrodes (CMEs). All the CMEs were characterized by SEM, FT-IR and UV–vis spectroscopies. In addition, zeta potential and heterogeneous electron transfer constant were determined. The most performing configuration was found to be the Composite, as it is the best compromise in terms of sensitivity and resistance to fouling.

Graphene dispersed cellulose microfibers composite for efficient immobilization of hemoglobin and selective biosensor for detection of hydrogen peroxide

In the present work, we have investigated the electrochemical behavior and electrocatalysis of hemoglobin (Hb) immobilized on a glassy carbon electrode (GCE) modified with a graphene-cellulose microfiber (GR–CMF) composite. The GR–CMF composite was characterized by scanning electron microscopy, elemental analysis, and Raman and Fourier transform infrared spectroscopy. Well-defined electrochemical redox characteristics of Hb were observed for Hb immobilized on a GR–CMF composite modified GCE, with a formal potential of −0.306V and a peak to peak separation of approximately 67mV. Due to the high biocompatibility of the GR–CMF composite, the electrochemical behavior of the Hb heme redox couple (FeII/FeIII) was enhanced for Hb immobilized on the GR–CMF composite when compared to Hb immobilized on pristine GR. The heterogeneous electron transfer constant (ks) was calculated as 6.17 s−1, and is higher than previously reported for Hb immobilized GR supports. The Hb immobilized GR–CMF composite modified electrode was used for the quantification of H2O2 under optimal conditions, and shows a wider linear amperometric response ranging from 0.05 to 926μM. The limit of detection of the biosensor was 0.01μM with the sensitivity of 0.49μAμM−1cm−2. The biosensor also showed high selectivity in the presence of the range of interfering compounds and exhibits good operational stability and practicality in the detection of H2O2.

Evaluation of a Reduced Graphene Oxide Antimony Nanocomposite Horseradish Peroxidase Biosensor Matrix for Hydrogen Peroxide

An exploration of reduced graphene oxide impregnated with antimony nanoparticles to form a nanocomposite as a platform for the immobilization of horseradish peroxidase for the amperometric detection of hydrogen peroxide is presented. Electrochemical measurements revealed that the heterogeneous electron transfer constant (ks) was evaluated to be 0.37 s−1. The average surface concentration of electro-active HRP on the surface of the modified glassy carbon electrode was calculated to be 9.43 × 10−9 mol cm−2. The voltammetric results revealed that the peak current of the modified electrode increased linearly with increasing concentration of hydrogen peroxide (from 1nM to 4nM) with a detection limit of 2.88nM.

Biomimetic photoelectrocatalytic conversion of greenhouse gas carbon dioxide: Two-electron reduction for efficient formate production

Resource utilization of carbon dioxide (CO2) as alternative carbon feedstock is a promising solution to problems of both the energy supply and global warming. Herein, a biomimetic photoelectrocatalytic interface was covalently constructed utilizing cobalt-containing zeolite imidazolate framework (ZIF9) as CO2 fixation and activation substrate, and Co3O4 nanowires (NWs) as the photoelectrocatalyst. Adsorption experiments demonstrated that CO2 could be concentrated on ZIF9 modified Co3O4 NWs. The CO2 surface concentration exhibited a 3.44 fold increment on this hybrid interface than that on Co3O4 NWs. Theoretical calculation elucidated ZIF9 has the capacity for activating CO2 molecule via binding Co atom to the O atom of CO2, resulting in the onset potential of CO2 reduction 284mV positively shift on ZIF9-Co3O4 NWs than that on Co3O4 NWs. At a low overpotential of 290mV, CO2 has been photoelectrocatalytically conversion to formate with high conversion rate of 72.3μmolL−1cm−2h−1 and high selectivity of nearly 100% in liquid products. And the heterogeneous electron transfer constant was 2.096×10−3cms−1. This CO2 conversion process was confirmed to be an instantaneous proton-coupled 2-electron transfer process. This work opens the opportunity for constructing biomimetic photoelectrocatalytic interface with CO2 adsorption, activation and conversion to efficient CO2 resource utilization.

Direct electrochemistry of glucose oxidase and glucose biosensing on a hydroxyl fullerenes modified glassy carbon electrode

Direct electrochemistry of glucose oxidase (GOD) was achieved when GOD-hydroxyl fullerenes (HFs) nano-complex was immobilized on a glassy carbon (GC) electrode and protected with a chitosan (Chit) membrane. The ultraviolet–visible absorption spectrometry (UV–vis), transmission electron microscopy (TEM), and circular dichroism spectropolarimeter (CD) methods were utilized for additional characterization of the GOD, GOD-HFs and Chit/GOD-HFs. Chit/HFs may preserve the secondary structure and catalytic properties of GOD. The cyclic voltammograms (CVs) of the modified GC electrode showed a pair of well-defined quasi-reversible redox peaks with the formal potential (E°′) of 353±2mV versus Ag/AgCl at a scan rate of 0.05V/s. The heterogeneous electron transfer constant (ks) was calculated to be 2.7 ± 0.2s-1. The modified electrode response to glucose was linear in the concentrations ranging from 0.05 to 1.0mM, with a detection limit of 5±1μM. The apparent Michaelis–Menten constant (Kmapp) was 694±8μM. Thus, the modified electrode could be applied as a third generation biosensor for glucose with high sensitivity, selectivity and low detection limit.