Electrochemical Grafting Research Articles

Electrochemical modification at multiwalled carbon nanotube electrodes with Azure A for FAD- glucose dehydrogenase wiring: structural optimization to enhance catalytic activity and stability

Electrochemical grafting is a suitable technology for fabricating electrode surfaces with new chemical functionalities whilst maintaining the bulk properties of the electrode, and electrochemical amine oxidation and diazonium salt reduction are two widely used techniques to achieve this end. Herein, we report the electrochemical reductive grafting of Azure A onto multiwalled carbon nanotube (MWCNT) electrodes for the efficient wiring of flavin adenine dinucleotide (FAD) dependent glucose dehydrogenase. The diazonium salt of Azure A is formed in situ and subsequently grafted onto the electrode surface through electrochemical reduction. The formal potential of the resultant Azure-A-modified electrode shifted to −0.05 V vs. Ag/AgCl upon radical coupling to the MWCNT electrode. Electron transfer from FAD buried in the protein shell to the electrode via Azure A was then observed in the presence of glucose in the buffer solution. This study focused on the important effect of CNT mass loading on Azure-A loading as well as bioelectrocatalytic activity and storage stability. The three-dimensional porous structure of the MWCNT electrode was determined to be favorable for the immobilization of flavin adenine dinucleotide dependent glucose dehydrogenase and efficient electron transfer via the Azure-A functionalities. The optimized 300 µg CNT-loaded modified electrode on glassy carbon (3 mm diameter) retains its initial activity for 3 d and 25% of its initial activity after 10 d. Furthermore, we show that grafted Azure A is stably immobilized on the MWCNTs for 1 month; therefore, the limiting stability factor is enzyme leaching and/or deactivation.

A novel approach toward attachment of graphene oxide on copper using electrochemical grafting of an organic interlayer with enhanced corrosion performance

This paper proposes a novel approach for attaching a graphene oxide (GO) film to a Cu substrate using diazonium chemistry. For this purpose, Cu was covalently modified using electrochemical grafting of p-phenylenebis(diazonium) salt (p-PBDS) followed by immersion in a basic GO suspension. The presence of the p-PBDS interlayer facilitated the assembling of GO in a multilayered film instead of a single layer as for the bare Cu substrate. The corrosion performance of the modified Cu was evaluated in 3.5% NaCl aqueous solution using potentiodynamic polarization and electrochemical impedance spectroscopy. The results inferred that the coupling of GO with p-PBDS interlayer protects effectively Cu against corrosion. Due to a low porosity percentage (0.003%), the corrosion current density is decreased by a factor of ∼ 5. It means that the coupling of GO multilayer with p-PBDS considerably prolongs the diffusion pathways for an oxidant toward the substrate. In this way, the polarization resistance of the film was increased by a factor of ∼ 4.5 (to 10.9 kΩ cm2) compared with that of a bare Cu substrate.

Controlled covalent functionalization of a graphene-channel of a field effect transistor as an ideal platform for (bio)sensing applications.

The controlled covalent functionalization of the graphene channel of a field effect transistor, based on interdigitated gold electrodes (source and drain), via electrochemical grafting, using specifically designed aryl diazonium species is demonstrated to allow the simple fabrication of a general platform for (bio)sensing applications. The electrochemical grafting of a protected ethynylphenyl diazonium salt leads to the deposition of only a monolayer on the graphene channel. This controlled covalent functionalization of the graphene channel results in a charge mobility of the GFET of 1739 ± 376 cm2 V-1 s-1 and 1698 ± 536 cm2 V-1 s-1 for the holes and electrons, respectively, allowing their utilization as (bio)sensors. After deprotection, a dense and compact ethynylphenyl monolayer is obtained and allows the immobilization of a wide range of (bio)molecules by a "click" chemistry coupling reaction (Huisgen 1,3-dipolar cycloaddition). This finding opens promising options for graphene-based (bio)sensing applications.

Synergy of electrochemical grafting and crosslinkable crystalline sizing agent to enhance the interfacial strength of carbon fiber/PEEK composites

Carbon fiber/PEEK composites have gained significant attention in the field of continuous carbon fiber reinforced polymers (CFRPs). However, it remains challenging to improve the weak interfacial strength between carbon fiber (CF) and PEEK matrix. In this paper, strong interactions at the interface of sizing agent and carbon fiber were effectively achieved by introducing chemical bonds. Specifically, a soluble PEEK sizing agent where aniline served as pendant group and phenylacetylene served as blocking agent was synthesized. In the meantime, the phenylacetylene group was grafted on the carbon fiber surface through electroreduction. Then, the soluble sizing agent was used to size the electrochemical treated carbon fiber. After the heat treatment, chemical bonds were established by the crosslinking reaction of phenylacetylene groups existed in both the surface of carbon fiber and sizing agent. Meanwhile, the crystalline structure in the sizing layer was remained, which could improve the toughness of the interphase. As a result, the interfacial shear strength (IFSS) increased by 137.5% from 43.4 MPa of the untreated carbon fiber (U-CF) to 103.1 MPa of the reductive electrografted and coated carbon fiber (E-C-CF). The interlaminar shear strength (ILSS) also increased by 66.8% from 58.4 MPa of untreated CF/PEEK composites (U-CF/PEEK) to 97.4 MPa of reductive electrografted and coated CF/PEEK composites (E-C-CF/PEEK). The outstanding performances could be attributed to better compatibility of sizing agent and most importantly, the existence of chemical bonds between the carbon fiber and sizing agent.

Diazonium based surface functionalization of graphite by electrochemical grafting

In this respect, a combination of cyclic voltammetry (CV), Raman spectroscopy, and Atomic Force Microscopy (AFM) is employed to characterize the structural, electrochemical and electronic properties of diazonium thin layers covalently functionalized highly oriented pyrolytic graphite (HOPG) surface. As a consequence, a grafted layer thin film of 4-nitro-benzene-diazonium tetrafluoroborate (4-NBD) is formed on HOPG surface with an average thickness of about 3.5 ± 0.2 nm. A D-band peak appearrance at the wave length of 1336 cm-1 on the Raman spectrum indicates an enhancing of defects caused by covalent C-C bonds. A tentative model illustrating the formation of 4-NBD grafted multilayer governed by the dendritic mechanism is also proposed. This finding opens a new approach to control the degree of functionalization of graphitic surfaces and other 2D materials.

Electrochemical Investigation of Interfacial Properties of Ti3C2T x MXene Modified by Aryldiazonium Betaine Derivatives.

For efficient and effective utilization of MXene such as biosensing or advanced applications, interfacial modification of MXene needs to be considered. To this end, we describe modification of Ti3C2Tx MXene by aryldiazonium-based grafting with derivatives bearing a sulfo- (SB) or carboxy- (CB) betaine pendant moiety. Since MXene contains free electrons, betaine derivatives could be grafted to MXene spontaneously. Kinetics of spontaneous grafting of SB and CB toward MXene was electrochemically examined in two different ways, and such experiments confirmed much quicker spontaneous SB grafting compared to spontaneous CB grafting. Moreover, a wide range of electrochemical methods investigating non-Faradaic and Faradaic redox behavior also in the presence of two redox probes together with contact-angle measurements and secondary ion mass spectrometry (SIMS) confirmed substantial differences in formation and interfacial presentation of betaine layers, when spontaneously grafted on MXene. Besides spontaneous grafting of CB and SB toward MXene, also electrochemical grafting by a redox trigger was performed. Results suggest that electrochemical grafting provides a denser layer of SB and CB on the MXene interface compared to spontaneous grafting of SB and CB. Moreover, an electrochemically grafted SB layer offers much lower interfacial resistance and an electrochemically active surface area compared to an electrochemically grafted CB layer. Thus, by adjusting the SB/CB ratio in the solution during electrochemical grafting, it is possible to effectively tune the redox behavior of an MXene-modified interface. Finally, electrochemically grafted CB and SB layers on MXene were evaluated against non-specific protein binding and compared to the anti-fouling behavior of an unmodified MXene interface.

Assisted lipid deposition by reductive electrochemical aryldiazonium grafting and insertion of the antiport NhaA protein in this stable biomimetic membrane

Quartz crystal microbalance studies have been carried out to monitor the fusion of lipid vesicles (pure 1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC) and mixed vesicles (DMPC and 4-decylaniline). In order to increase the stability of the lipid deposits onto the electrodes, we have developed an original approach involving electrografting of adsorbed mixed vesicles. Aryldiazonium salts generated in situ from 4-decylaniline (4DA) present in adsorbed and fused mixed vesicles at the electrode surface allow their cathodic reduction and subsequent grafting. The stability of the supported lipid deposit has been shown to significantly increase from less than one day for pure DMPC to about two weeks with the lipid deposition assisted by electrochemical grafting. In this stable lipid deposit, the insertion of the sodium/proton antiporter membrane protein (NhaA) or its inactive mutant has been carried out by fusion of proteoliposomes. This has been followed by characterization of the inserted protein activity by cyclic voltammetry onto an electrode previously modified by an adsorbed pH sensor (2-anthraquinone sulfonate). Activation of the protein function by sodium ions leads to a shift of the interfacial pH and confirms the integrity of the immobilized NhaA.

Photogenerated charge collection on diamond electrodes with covalently linked chromophore monolayers

Encouraged by its rich surface chemistry and excellent electrochemical properties, boron-doped nanocrystalline diamond (B:NCD) is a promising p-type photoelectrode in dye-sensitized solar cells. One method of diamond surface functionalization using stable carbon-carbon bonds involves the electrochemical grafting of diazonium salts. However, this method typically leads to multilayers that may complicate the transport of photogenerated charges. Here, we establish functionalization of B:NCD electrodes by a monolayer of ethynylphenyl molecules using sterically hindered 4-(trimethylsilyl)ethynylbenzenediazonium tetrafluoroborate. Both the density and structural orientation of the grafted layer are investigated by angular resolved X-ray photoelectron spectroscopy, confirming the presence of covalently grafted monolayers. After removal of the trimethylsilyl protective groups, the resulting ethynyl functionalities are employed to immobilize organic donor-acceptor chromophores via Sonogashira cross-coupling reactions. Homogenous surface coverage is achieved even on the B:NCD electrode. Atomic scale DFT computing reveals that for the chromophore with the strongest acceptor unit, efficient charge separation of 20 Å is obtained where photogenerated holes move directly into diamond. Yet, photocurrent and photovoltage measurements suggest competitive electron recombination to the diamond electrode via the redox electrolyte. Correlation between the density of the molecular layer and photocurrents/photovoltage provides better understanding of the charge generation and recombination pathways in diamond-organic photoelectrochemical cells.

Electrochemical grafting of poly(glycidyl methacrylate) on a carbon-fibre surface.

In this work, glycidyl methacrylate (GMA) was polymerised and grafted onto the surface of carbon fiber (CF) by using electrochemical grafting to improve the interfacial properties between the fibre and epoxy resin. The optimised conditions for electrochemical grafting and the reaction mechanism were also investigated. Results showed that GMA was covalently grafted to the CF surface by the assistance of aluminium chloride, which is a good electrolyte for electrochemical grafting. The GMA grafting ratio on the CF surface increased with electrolyte concentration and reaction time, and an optimal current intensity for the electropolymerisation was determined. On the basis of the strong correlation between the grafting ratio and the carboxyl content in the CF, a two-step mechanism of electrochemical grafting on the CF surface was proposed: first, the surface of CF was anodised to produce oxygen-containing functional groups, mainly including COOH, OH and C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O. Next, when CF was used as the anode in the electrical grafting reaction, the COOH on the surface of CF would lose electrons and then remove carbon dioxide to generate carbon radicals on the surface of CF. The carbon radical would attack the carbon–carbon double bond in GMA to initiate the radical polymerisation of GMA monomers and graft polymers would be formed on the CF surface. Compared with untreated CF, the interfacial shear strength (IFSS) test proved the improvement of the interface adhesion of the modified carbon fibre (mCF) composites. This work provided a controllable electrochemical approach that could simply and quickly graft poly(glycidyl methacrylate) (PGMA) on the surface of CF.

Enhancing the interfacial properties of high-modulus carbon fiber reinforced polymer matrix composites via electrochemical surface oxidation and grafting

Surface modification of carbon fiber is a traditional research field and many techniques have been developed to improve the adhesion force between fiber and the polymer matrix. However, most studies were focused on the carbon fibers with standard modulus. The surface of high-modulus carbon fiber (HMCF) is difficult to be activated due to the highly inert structure after graphitization. A convenient and effective surface modification method that can simultaneously improve the content of function groups with containing oxygen and nitrogen on the surface of HMCF was developed in this paper. The surface of HMCF was first anodized to be activated by electrochemical oxidation, and then the diethylenetriamine (DETA) was grafted by electrochemical grafting. The effect of the type of electrolyte on the electrochemical grafting of DETA was studied by the addition of NH4HCO3 and (NH4)2SO4, respectively. The results indicated that the addition of NH4HCO3 electrolyte in DETA solution will promote the grafting and increase the grafted amount on HMCF surface. Moreover, the addition of (NH4)2SO4 electrolyte can not only promote the grafting, but also oxidize the surface of the fibers further to generate more oxygen-containing groups. In addition, the interfacial performance of HMCF composites was significantly improved after modification by this method. Especially, when (NH4)2SO4 was added to DETA solution, the inter-laminar shear strength (ILSS) of HMCF/epoxy composites reached 97.5 MPa, which was 257.1% higher than that of untreated HMCF.

Single-Walled Carbon Nanotubes Decorated with Dendrimer-Encapsulated Platinum Nanoparticles as Catalytic Immobilization Matrix for Amperometric Sensing of Glutamate.

Herein, we report the functional decoration of single-walled carbon nanotubes (swCNTs) with Pt dendrimer-encapsulated nanoparticles (Pt DENs) (dia. (1.78 ± 0.18) nm) for the amperometric sensing of glutamate. The functional decoration of swCNTs was carried out via electrochemical grafting of Pt DENs onto swCNTs, and subsequent cross-linking of glutamate oxidase (GluOx) enzymes to the grafted Pt DENs on swCNT surfaces. The critical role of Pt DENs as catalytic immobilization matrix allowed both the immobilization of GluOx enzymes while maintaining the enzymatic activity of GluOx, and the electrocatalytic oxidation of H₂O₂ generated enzymatically in the presence of glutamate. Taking advantage of Pt DENs as catalytic immobilization matrix, the resulting swCNTs films, denoted as GluOx/Pt DEN/swCNTs, were applied as amperometric sensing platforms that display superior analytical characteristics, including sensitivity, selectivity, stability, and reproducibility, to the non-catalytic counterpart (i.e., GluOx/swCNTs), which led to the promising application of GluOx/Pt DEN/swCNTs to the practical analysis of glutamate in real samples.

Preparation oaf polyaniline/diazonium salt/TiO2 nanotube arrays as supercapacitor electrode by electrochemical grafting and deposition

Polyaniline/diazonium salt/TiO2 nanotube arrays (PANI/DZ/TiO2 NAs), as a supercapacitor electrode material, are fabricated by two-step anodic oxidation of titanium foils, electrochemical grafting and reduction of diazonium salts, and electrochemical deposition of polyaniline. Surface morphology, crystallization, and chemical compositions of nanocomposites are characterized by SEM, EDX, XRD, and Raman. Electrochemical tests indicate that PANI/DZ/TiO2 NAs have excellent capacitance of 1108.5 F g−1 when the current density is 0.6 A g−1. With the current density increasing 20 times to 12 A g−1, the capacitance remains about 77.5%, demonstrating its good rate performance. Moreover, after 2000 charge–discharge cycles at 12 A g−1, the capacitance retains 83.7% of the initial value, showing its good cycling stability.

Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions

AbstractThe electrochemical grafting of the “in-situ” prepared diazopyridinium salt have permitted the attachment of pyridine moieties onto platinum and glassy carbon surfaces. The modification of the electrode surfaces is observed by a redox probe. The ability of the film for the complexation of copper (II) ions is demonstrated by square wave voltammetry. After 45 min accumulation of copper (II) ions onto the grafted electrode surfaces, the electrode signal obtained by square wave voltammetry measurement served to discriminate the adsorbed heavy metal ions. Such measurements showed that the grafted pyridine has the ability to display complexing behavior toward some heavy metal ions. DFT calculations support a strong binding of the pyridine moieties onto the Pt surface. The most favorable complexation mode of copper (II) ions as suggested from DFT is the bidentate complex. This strategy is vital in constructing a wide range of different electrochemical sensors.

Engineering Functional Enzyme Bioelectrodes with Conductive Polymeric Films for Sensing Applications

Immobilization of enzymes is a key strategy for the development of point-of care diagnostics such as biosensors and biofuel cells. Conductive polymeric films have been proposed as excellent signal transducers for biomedical applications due to their high electrical conductivity and biocompatibility. In this context, we report a highly innovative, while simple and robust, surface chemistry approach for the covalent immobilization of enzymes onto conductive polymeric nanostructures. In particular, an electrochemical grafting approach is proposed, according to which, polypyrrole (PPy) films on gold surfaces on-chip are modified with b-alanine (Ala) as a linker, bearing free carboxylate groups, for further probe immobilization. As a case study and considering its clinical relevance for glucose monitoring systems, the enzyme Glucose Oxidase (GOx) is used. The fabricated GOx/Ala/PPy/Au electrode exhibited excellent performance for glucose detection, with a linear response within the range of 0.1 mM - 10 mM, and a sensitivity of 3.75 µA mM-1 cm-2. The observed low limit of detection is 0.1 mM; a value that lies below the normal glucose concentration in blood and non-conventional physiological fluids, such as interstitial fluid or saliva. The fabricated glucose sensor also demonstrates an excellent reproducibility with a relative standard deviation of 4 %. The methodology proposed paves the way for rapid manufacturing of effective enzyme-based polymeric electrodes, which, contrary to other PPy-based sensors previously suggested, does not involve any chemical pre-treatments of the monomer used. Figure 1

Fine growth control of electrografted homogeneous thin films on patterned gold electrodes

Electrochemical grafting of two different diazonium salts was performed on patterned gold electrodes of micrometric size. One of the molecules, a tris-bipyridine iron (II) derivative (TBPFe) enables a fine control over the final thickness of the electrografted layer thanks to its redox centers that acts as intermediate for charge transfers between the solution and the working electrode. The other one, an aromatic cycle with a fluorinated carbon chain (DzF8), forms an insulating layer that stops the charge transfer from the working electrode to the solution and thus limits the thickness of the resulting organic layer. Grafting parameters (concentration, time, tip passivation, etc.) were investigated in details. Their precise control leads to compact and homogeneous thin films. Smooth TBPFe layers with an adjustable thickness in the 5–100 nm range are obtained, while the thickness is limited to 2–6 nm in the DzF8 case. With the achieved film quality, direct metal evaporation on top of these electrodes is possible and yields 85% of working devices. Electrical measurements for the two molecules are compared for different thicknesses.

Modification of fluorine-doped tin oxide surface: Optimization of the electrochemical grafting of diazonium salt

Fluorine-doped tin oxide (FTO) electrodes were functionalized by electro reduction of in situ generated 4-carboxyphenyl diazonium salt. Several grafting potentials and times were investigated in order to find the optimal grafting conditions. The electrochemical behavior of bare FTO electrodes in the presence of the diazonium, together with Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) characterization of the grafted electrodes in the presence of redox probes ferricyanide and ferrocene allowed us to conclude that 10 min grafting under a controlled potential of −0.50 V lead to the formation of a poorly-packed organic multi-layer on the electrode surface. X-ray Photoelectron Spectroscopy (XPS), together with Fourier-Transform Infrared Spectroscopy (FTIR) analyses, further evidenced the presence of carboxylic groups onto modified FTO electrodes.

Electrochemical Grafting of Chitosan on Polyaniline and its Characterization

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DNA-Mediated Nanoscale Metal-Organic Frameworks for Ultrasensitive Photoelectrochemical Enzyme-Free Immunoassay.

A novel enzyme-free photoelectrochemical (PEC) immunoassay was developed for the ultrasensitive detection of prostate specific antigen (PSA) based on the DNA-mediated nanoscale zirconium-porphyrin MOFs (NMOFs). By virtue of the intrinsic coordination between unsaturated zirconium sites of the NMOFs frameworks and phosphonate groups, the 5'-phosphorylared ss-DNA-tagged antibody (Ab-DNA) conjugate with a consecutive stretch of guanines as a spacer could be loaded on the NMOFs easily, obtaining a novel type of Ab-DNA-functionalized NMOFs complex. Additionally, as a photocathode PEC active nanomaterial, NMOFs exhibited a significant enhanced photocurrent response with the presence of dopamine under oxygen-containing aqueous media at -0.3 V (vs Ag/AgCl). Furthermore, with the aid of the electrochemical grafting of polyamidoamine (PAMAM) dendrimers functionalized interface, the novel type of Ab-DNA-NMOFs further served as a PEC signal nanoprobe for the ultrasensitive PSA immunoassay. Under optimal conditions, the corresponding immunosensor possessed a wide calibration range of 1 pg mL-1 to 10 ng mL-1 and a limit of detection (LOD) of 0.2 pg mL-1. This present work demonstrated the promising application of DNA-mediated NMOFs in developing highly sensitive, environmentally friendly, and cost-effective PEC biosensors.

A New High Performance Lithium-Ion Battery: Development of 3D Architecture

The increasing energy storage demands of portable electronic devices and electric vehicles leads to the development of high performance lithium-ion batteries. Current technologies cannot reach the power and energy density requirements. More attention has been paid to the development of new electrode materials and electrolytes but performance continues to be limited. The strategy is to develop a 3D battery architecture. The planar configuration is locally reproduced within a 3D matrix. The surface area is increased and the distance between electrodes is reduced. Prieto, a start-up based in Colorado, proposed this new architecture in 2013. They have obtained a 3D anode/electrolyte configuration. However, complete integrated 3D battery shows fast cyclability failure due to the cathode configuration. Our strategy is to start by the cathode. A metallic foam is used as the current collector and as the 3D matrix. A new synthesis to produce an optimized Li-ion cathode for this new battery configuration is presented. Either native metal, or the corresponding oxides, can be used as precursors for the synthesis of the lithiated transition metal oxides. The metallic surface is first oxidised and then lithiated. Alternatively, the metal surface can be directly lithiated. In both cases, the current collector, is directly furnished with active material without the need of either binders or conductive additives. Structural characterization was coupled with morphological analysis to understand the influence of oxide morphology on the synthesis and the lithiation mechanism. In addition, electrochemical characterizations will be presented. A polymer electrolyte was then grafted directly to the cathode surface using electrochemical polymerisation. Electrochemical grafting enables the formation of a uniform, thin polymer electrolyte. A better electrode/electrolyte interface is obtained and ionic resistance are minimised. Furthermore, the porosity of the foam is available for anode materials. The effect of polymerization parameters of monomer concentration, solvent, applied potential and scanning rate were studied. The foam porosity was filled with a low melting point metal that is used both as the anode and the current collector. Electrochemical characterization of this new configuration allows the assessment of the performance gain of this new architecture for lithium-ion batteries. Analysis of the battery interfaces (electrode/electrolyte, electrode/current collector) provide further insight into their influence on battery performance.

Self-Assembled Polystyrene Beads for Templated Covalent Functionalization of Graphitic Substrates Using Diazonium Chemistry.

A network of self-assembled polystyrene beads was employed as a lithographic mask during covalent functionalization reactions on graphitic surfaces to create nanocorrals for confined molecular self-assembly studies. The beads were initially assembled into hexagonal arrays at the air-liquid interface and then transferred to the substrate surface. Subsequent electrochemical grafting reactions involving aryl diazonium molecules created covalently bound molecular units that were localized in the void space between the nanospheres. Removal of the bead template exposed hexagonally arranged circular nanocorrals separated by regions of chemisorbed molecules. Small molecule self-assembly was then investigated inside the resultant nanocorrals using scanning tunneling microscopy to highlight localized confinement effects. Overall, this work illustrates the utility of self-assembly principles to transcend length scale gaps in the development of hierarchically patterned molecular materials.