Glassy Carbon Surface Research Articles

Hierarchical CuS doped with vanadium nanosheets with micro skein overall morphology as a high performance amperometric glucose sensor

In this paper, an easy one-step hydrothermal method was reported to preparation of unique hierarchical porous CuS doped with vanadium (V-CuS) nanosheets with micro skein overall morphology. The fabricated V-CuS micro skein was casted on the surface of glassy carbon (GC) electrode and was used as an efficient electrocatalyst for glucose in alkaline solutions. As a amperometric glucose sensor, this proposed sensor offers a high sensitivity of 1800 μA mM−1 cm−2, with a wide linear range from of 2 μM to 5 mM, and a low detection limit of 0.4 µM (S/N = 3). The non-enzymatic V-CuS/GC electrode-based sensor showed acceptable selectivity and satisfactory stability. Moreover, the designed sensor showed accurate results for the determination of glucose in blood serum samples.

Electrografting of 4-Carboxybenzenediazonium on Glassy Carbon Electrode: The Effect of Concentration on the Formation of Mono and Multilayers.

Grafting of electrodes with diazonium salts using cyclic voltammetry (CV) is a well-established procedure for surface modification. However, little is known about the effect of the concentration of the diazonium salt on the number of layers grafted on the electrode surface. In this work, the impact of concentration on the grafting of 4-carboxybenzenediazonium (4-CBD) onto a glassy carbon electrode (GCE) is elucidated. The number of layers grafted on the GCE was linearly dependent on the concentration of 4-CBD and varied between 0.9 and 4.3 when the concentration was varied between 0.050 and 0.30 mmol/L at 0.10 V.s−1. Characterization of modified glassy carbon surface with X-ray photoelectron spectroscopy (XPS) confirmed the grafting of carboxyphenyl layer on the surface. Grafting with 0.15 mmol/L 4-CBD (1 CV cycle) did not form a detectable amount of carboxyphenyl (CP) moieties at the surface, while a single scan with higher concentration (2.5 mmol/L) or multiple scans (22 cycles) gave detectable signals, indicating formation of multilayers. We also demonstrate the possibility of removing the thin layer grafted on a glassy carbon electrode by applying high oxidation potential +1.40 V.

Gold-doped nano-perovskite-decorated carbon nanotubes for electrochemical sensing of hazardous hydrazine with application in wastewater sample

We report one pot preparation of an Au-doped Sr-Pd-perovskite (Sr2Pd0.7Au0.3O3) carbon nanotubes (CNTs) composite. A thin layer of the composite is formed by drop-cast over a glassy carbon (GC) surface and applies for electrochemical sensing of hydrazine hydrate (HH). For the proposed sensor, current-signal responses for HH oxidation mount 24 and 11 times compared to GC and GC/CNT electrodes, respectively. The HH conversion process is thermodynamically more favored over the sensor surface with oxidation potential value of +95 mV versus a value of +460 mV over GC/CNT electrode. Doping the Sr-Pd perovskite with gold is crucial to the remarkable performance of the sensor. Conductive Au3+ ions inclusion within the crystal lattice create more oxygen-vacancies that stabilize the perovskite structure and enhance both its electronic and ionic conductivities. The practical performance of the sensor is evaluated by amperometry quantification of HH in wastewater sample for a wide concentration range of (0.007–90 μM) and a low detection limit of 0.261 nM in the low concentration range (0.007–1 μM). The GC/(CNT-Sr2PdAuO3) sensor response is stable for one month with excellent anti-interference ability towards common interfering species.

Amperometric assay of hydrazine utilizing electro-deposited cobalt hexacyanoferrate nanocrystals on graphene oxide sheets

In-situ electrochemical deposition of cobalt hexacyanoferrate (CoHCF) on graphene oxide (GO) and its application for the electrocatalytic hydrazine determination in real samples are described in this research study. Co2+ is immobilized on GO and the resulting material, GO-Co2+ is coated on the surface of glassy carbon (GC) electrode. The fabricated electrode (GC/GO-Co2+) is subjected to a continuous potential cycling in the range of 0.0–1.0 V which results in the formation of a thin CoHCF film on the surface of GO coated on the GC electrode (abbreviated as GC/GO-CoHCF). The synthesized GO-CoHCF composite material is characterized by Fourier transform infrared and scanning electron microscopy. GC/GO-CoHCF electrode electrocatalytically oxidizes hydrazine at low overpotential (0.63 V) and this phenomenon is subsequently utilized for the sensitive determination of hydrazine in aqueous solutions. It exhibits a wide linear calibration range (0.1–400 µM), high sensitivity (0.93 µA µM−1 cm−2) and low limit of detection (17.5 nM) for the determination of hydrazine. Further, this electrode is employed for hydrazine determination in real samples.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Electroless deposition of gold nanoparticles on a glassy carbon surface to attain methylene blue degradation via oxygen reduction reactions

A glassy carbon electrode (GCE) surface was modified with gold nanoparticles (Au NPs) via electroless deposition method. It was observed that a pristine GCE surface does not deposit Au NPs through an electroless process. However, while a GCE surface is electrochemically pretreated then sites having negative charges are generated which enables Au (III) particles to be deposited on its surface. The X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the electrode surface. It was found that Au NPs are deposited on the GCE surface (Au-GCE) having flower like shapes. The resultant surface was employed to execute electrocatalytic oxygen reduction reactions (ORR). By analyzing hydrodynamic voltammograms, it was confirmed that ORR undergoes a 2e−transfer pathway and H2O2 is generated on the Au-GCE surface having a standard rate constant (ko) of 5.48 × 10−9 cm s−1 at +0.05 V vs. Ag/AgCl (sat. KCl) in 0.1 M H2SO4. The in-situ generated H2O2 can degrade methylene blue (MB) via Electro-Fenton process. The MB degradation was found to match well with the 1st order kinetic model with a homogeneous rate constant of 4.36 ×10−3 min-1.

Tuning the O–O bond formation pathways of molecular water oxidation catalysts on electrode surfaces via second coordination sphere engineering

A molecular [Ru(bda)]-type (bda = 2,2’-bipyridine-6,6’-dicarboxylate) water oxidation catalyst with 4-vinylpyridine as the axial ligand (Complex 1) was immobilized or co-immobilized with 1-(trifluoromethyl)-4-vinylbenzene (3F) or styrene (St) blocking units on the surface of glassy carbon (GC) electrodes by electrochemical polymerization, in order to prepare the corresponding poly-1@GC, poly-1+P3F@GC, and poly-1+PSt@GC functional electrodes. Kinetic measurements of the electrode surface reaction revealed that [Ru(bda)] triggers the O–O bond formation via (1) the radical coupling interaction between the two metallo-oxyl radicals (I2M) in the homo-coupling polymer (poly-1), and (2) the water nucleophilic attack (WNA) pathway in poly-1+P3F and poly-1+PSt copolymers. The comparison of the three electrodes revealed that the second coordination sphere of the water oxidation catalysts plays vital roles in stabilizing their reaction intermediates, tuning the O–O bond formation pathways and improving the water oxidation reaction kinetics without changing the first coordination structures.

Evaluation of oxidative stress: Nanoparticle-based electrochemical sensors for hydrogen peroxide determination in human semen samples

We have developed electrochemical sensors for the determination of H2O2 in a complex matrix such as human semen as a method to evaluate oxidative stress related to male infertility. Our sensors are based on the modification of conventional electrode surfaces with nanoparticles. We used diamond nanoparticles (DNp) either on glassy carbon or gold surfaces (GC/DNp and Au/DNp sensors, respectively), and copper nanoparticles electrochemically generated directly on glassy carbon surfaces (GC/CuNp). The morphology of the modified electrode surfaces was characterized by Atomic Force Microscopy (AFM), and the H2O2 determination performance evaluated by chronoamperometric measurements at different applied potentials. The best results are obtained for GC/DNp at +1.0 V, Au/DNp at −0.6 V and GC/CuNp at +0.2 V with detection limits (LD) of 1.1 μM, 2.4 μM and 2.6 μM, respectively. The analysis of H2O2 in doped synthetic semen using the GC/CuNp sensor shows the best recoveries, reaching a mean value of 103%. The GC/CuNp sensor was successfully applied to H2O2 analysis in real human semen. In this case, a H2O2 concentration of 1.42 ± 0.05 mM is found and recoveries of 102% on average are obtained.

Multi-walled carbon nanotube functionalization and the dispersing agents study applied for the glassy carbon electrode modification and voltammetric reduction of nitrofurazone

Multi-walled carbon nanotubes (MWCNTs) have structures characterized by remarkable mechanical and electronic properties. However, their applications can be hindered because of their hydrophobic nature, lack of homogeneity due to impurities, and their variable sizes. Thus, MWCNT was treated by acidic oxidation (H2SO4 3:1 HNO3), seeking out to evaluate the influence of this functionalization on the electrochemical reduction behavior of nitrofurazone applying cyclic voltammetry, the glassy carbon surface having been modified as working electrode. The MWCNT functionalization was characterized by using scanning electron microscopy, infrared and Raman spectroscopies, thermogravimetric analysis, and potentiometric titration. Differences between non-functionalized and functionalized MWCNT were observed, suggesting that carboxylic groups were introduced in the carbon nanotube walls. Moreover, the glassy carbon surface modification was also studied concerning the dispersing agents for functionalized MWCNT. Several solvents of different natures, hydrophilic and lipophilic, were evaluated. The best dispersion associated with electrochemical response of nitrofurazone was obtained with 1,3-dioxolane as dispersing agent, which presented higher affinity with MWCNT than the other solvents. The electrochemical response of the glassy carbon electrode modified with MWCNT was evaluated by nitrofurazone voltammetric behavior with emphasis on the $$ \mathrm{R}-\mathrm{N}{\mathrm{O}}_2/\mathrm{R}-\mathrm{N}{\mathrm{O}}_2^{\cdotp -} $$ couple generation and its kinetic stability.

CdTe quantum dots in a glassy carbon electrochemical platform modified by N-substituted polypyrrole: Increasing the functional active surface for conjugation

We developed a biosensing platform by electropolymerizing 2-(1H-Pyrrol-1-yl)ethanamine on glassy carbon (GC) surfaces, followed by the immobilization of carboxyl-coated CdTe QDs onto the films. The immobilization of QDs was studied by applying two procedures: adsorption (electrostatic interactions) and covalent (using crosslinking agents). At a later stage, the covalent immobilization of IgG antibodies was also tested in platforms prepared with and without QDs. The formation of the polymeric film was confirmed by scanning electron microscopy. Furthermore, all surface modifications were monitored using cyclic voltammetry and electrochemical impedance spectroscopy, and K3[Fe(CN)6]/K4[Fe(CN)6] as the redox probe. The covalent crosslinking showed reproducibility and effective QD immobilization. Our study also showed that the QD coating by carboxylic groups leads to a decrease in the charge transfer process. The nanometric size of QDs and their active surfaces highly increased the functional platform area, enabling a high number of available sites for IgG antibodies. Indeed, in the absence of QDs, the platform was not able to detect the anti-IgG molecules. These results were supported by saturation curves constructed from differential pulse voltammetry. Thus, the use of carboxyl-coated CdTe QDs combined with 2-(1H-Pyrrol-1-yl)ethanamine polymer favored the development of a promising and sensitive biosensing electrochemical platform.

Immobilization of Multi-Carbonyl Molecules on High Surface Area Carbon for Energy Storage Applications

The synthesis of diamino-aryl-1,4,5,8-naphtalenetetra-carboxylic diimide molecule (NTCDA-(aryl-NH2)2) was reported. This molecule was characterized by elemental analysis, SEM, IR and TGA. A organic Li-ion electrode with NTCDA-(aryl-NH2)2 as active material was tested and a reversible behavior was observed with a multiple electrons process delivering about 100 mAh.g-1 at an average potential of 2.45 V vs. Li/Li+. In parallel, the diazotization study of this molecule was investigated with a three-electrode assembly. Then, the electrochemical reduction of freshly formed NTCDA-(aryl-N2 +)2 ions was followed by cyclic voltammetry experiments. An irreversible cathodic wave at around 0.0 V vs. Ag/AgNO3 that is associated to the reduction of the in-situ generated NTCDA-(aryl-N2 +)2 ions was observed. The blocking effect of the grafted layer deposited on the glassy carbon surface was verified with ferrocene as a redox probe. Finally, the immobilization of this molecule on Ketjen black carbon powder by spontaneous reduction of freshly formed NTCDA-(aryl-N2 +)2 ions was realized in a one-pot reaction. The redox-active carbon with a loading of grafted groups estimated between 26.4 and 36.7 wt. %, depending of the method of modification, cycled at high rate for thousands of cycles.

Electrochemical Properties of pH-Dependent Flavocytochrome C 3 from Shewanella Putrefaciens Adsorbed Onto Catechol-Modified Carbon Electrode

A century after the demonstration that electrons from microbial metabolism can be harvested with electrodes, electron transfer processes in biofilms of microorganisms performing respiration on extracellular solids are now being studied in order to increase the performance of microbial electrochemical technologies such as microbial fuel cells. Extracellular electron transfer occurring at the microorganism/electrode interface stimulated a wide range of fundamental and applied studies because of important implications in biotechnology, bioenergetics and bioremediation. Most studies focus on two Gram-negative mesophilic bacteria able to transfer electrons from their respiratory metabolism to extracellular solids, namely Shewanella oneidensis MR-1 and Geobacter sulfurreducens. In these model electroactive microorganisms, multiheme c-type cytochromes transfer electrons from cytoplasmic and inner-membrane oxidizing enzymes towards cell surface redox proteins that are responsible for the reduction of solid phase electron acceptors. It is also known that electron transfer is usually coupled to proton transfer which causes acidification in the anodic biofilms and in the anolyte with deleterious consequences for the biofilm metabolism and stability. The fundamental understanding of these processes that involve large proteins (>70 kDa) often with complex redox properties (with ≥10 heme centers in some multihemes cytochromes) is still in its infancy and precludes the optimization of microbial electrochemical technologies. In Gram-negative electroactive bacteria such as Shewanella, several redox proteins have pH-dependent potentials, such as flavocytochrome c 3 (M r = 63.8 kDa) which is one of the most abundant proteins in the periplasm and the only functional fumarate reductase in this microorganism.This work focuses on the design and the development of an efficient and versatile electrochemical platform able to probe charge (electron/proton) transfer properties of proteins from Gram-negative electroactive bacteria on modified carbon electrodes.[1] The electrodes are first modified with pH-responsive electrophores such as quinone units and then proteins are immobilized for electrochemical studies. If relevant, the protein electroactivity can be probed directly at the modified electrode while proton transport, if any, performed by the protein can be detected thanks to the grafted pH sensor.The electrochemical detection of a pH-dependent redox protein from electroactive bacteria at an electrode modified to act additionally as an efficient pH sensor based on a redox readout is demonstrated. The pH sensing electrode was previously designed and showed to allow the immobilization and study of pH-independent and redox active cytochrome c.[1] Here we extend this work to flavocytochrome c 3, a tetraheme FAD-containing periplasmic flavoenzyme isolated from the bacterium Shewanella putrefaciens, taken as a model pH-dependent redox protein from electroactive bacteria [2]. The modification of the electrode surface with the pH sensing modifier (catechol) stems from our previous experience in the tailoring of bio-interfaces of carbon electrodes with covalent electrografting. Flavocytochrome c 3 adsorption onto the modified electrode surface is successfully achieved by cyclic voltammetry in a flavocytochrome c 3 solution containing polymyxin as co-adsorbate. The electrochemical activity of the immobilized flavocytochrome c 3 is detected without alteration of its native structure and by keeping intact its electrochemical properties and its catalytic fumarate reductase activity.[2] The redox activity of the protein arises from its FAD and four hemes cofactors. The experiments evidence that the hemes’ redox potentials of flavocytochrome c 3 from Shewanella putrefaciens, for which no crystal structure is yet available, depend on pH which is at variance with data from the other strains Shewanella frigidimarina or Shewanella oneidensis.[1] Lebègue, E.; Louro, R. O.; Barrière, F. Electrochemical Detection of pH-Responsive Grafted Catechol and Immobilized Cytochrome c onto Lipid Deposit-Modified Glassy Carbon Surface. ACS Omega 2018, 3 (8), 9035–9042. https://doi.org/10.1021/acsomega.8b01425.[2] Lebègue, E.; Costa, N. L.; Fonseca, B. M.; Louro, R. O.; Barrière, F. Electrochemical Properties of pH-Dependent Flavocytochrome C3 from Shewanella Putrefaciens Adsorbed onto Unmodified and Catechol-Modified Edge Plane Pyrolytic Graphite Electrode. Journal of Electroanalytical Chemistry 2019, 847, 113232. https://doi.org/10.1016/j.jelechem.2019.113232. Figure 1

Electrodes modified with clickable thiosemicarbazone ligands for sensitive voltammetric detection of Hg(II) ions

The synthesis of a series of thiosemicarbazone ligands bearing azido groups, which were further immobilized on the surface of phenylethynyl-functionalized glassy carbon (GC) electrodes through a Cu(I)-catalyzed "click" reaction is reported. The modified electrodes presented a remarkable selectivity towards Hg(II) among other metal ions. Under optimized conditions and using the accumulation at open circuit-anodic stripping technique, detection limits below nanomolar level were obtained for Hg(II). Further, we demonstrated that GC electrodes "clicked" with thiosemicarbazone ligands can be used successfully for the analysis of Hg(II) ions from water samples. Moreover, the modified electrodes showed a very good reproducibility, stability over time and reusability, and can therefore be employed as sensitive and selective sensors for Hg(II) ion analysis in environmental samples.

Non-enzymatic Electroanalytical Sensing of Glucose Based on Nano Nickel-Coordination Polymers-Modified Glassy Carbon Electrode

Herein, we introduce a simple set of experiments to construct non-enzymatic glucose sensors. The modification procedure was initiated by electrodeposition of nickel-coordination polymers (denoted henceforth as Ni-CPs) at the surface of glassy carbon (GC) electrode decorated with carbonnanotubes (CNTs). The electrochemical sensing of glucose occurred through the electrocatalytic oxidation of glucose by the Ni-CP using the CNTs as a high-area catalyst support. During potential cycling, the continuous chemical regeneration of the Ni(II) in the reaction between Ni(III) and glucose expresses itself as a dramatic enhancement of the anodic current pertaining to the Ni(III)/Ni(II) redox couple. Effects of various factors such as scan rate and solution pH were evaluated. For the optimized sensor the detection limit was as low as 2.1 μM glucose and with a linear response extending up to 400 μM. The modified electrode showed good reproducibility, excellent anti-interference performance, and high stability during the electrochemical experiments. Moreover, the analytical function of the non-enzymatic sensors for quantitative detection of glucose was assessed in real samples with satisfying results.

Nanomolar detection of lead using electrochemical methods based on a novel phthalocyanine

4-4-[(Bromo-phenylimino)-methyl]-2-methoxy-phenoxy-phthalocyanine (CoTBrIMPPc) complex was synthesized and characterized by different spectroscopic as well as analytical techniques for the first time. The iminephthalocyanine derivative displayed redox peaks ascribed to cobalt (Co+2/Co+1) metal and phthalocyanine ligand (Pc−2/Pc−3). The (CoTBrIMPPc) complex was immobilized by drop coating method on the glassy carbon surface and the modified electrode was utilised for detecting lead (Pb) at nanomolar concentration level by voltammetry and amperometric methods. The cyclic voltammetric method showed linearity in the 100–1000 nmol L−1 range with the limit of detection (LOD) 37 nmol L−1. The addition of lead species did not show the considerable amperometric current response under normal amperometric conditions and hence experiments were performed by the modified methodology. Amperometry technique showed linearity in the 500 to 3000 nmol L−1 range, LOD value of 180 nmol L−1. The current response vs. Lead (Pb) concentration in graph by amperometric method exhibited correlation coefficient of 0.9991 and sensitivity of 0.0035 µA nM−1. The fabricated iminephthalocyanine based sensor is stable, reproducible and free of interference from other metal ion impurities in the electrolyte. The designed sensor has been employed for practical application.

Experimental and theoretical studies of electrochemical oxidation of nicotinamide adenine dinucleotide at the modified SWCNT and graphene oxide.

In recent years, nicotinamide adenine dinucleotide (NADH) and its oxidized form (NAD+) have withdrawn a substantial attention since they possess a significant place in both biosensor and biofuel cell studies. However, the transformation of NADH to NAD+ brings about the surface passivation and fouling at the most of corresponding conductive materials; consequently, significant decrease takes place in the current. In order to overcome these drawbacks, we have performed the surface functionalization of single-walled carbon nanotube (SWCNT) and graphene oxide (GO) immobilized onto glassy carbon surface with dihydroxybenzene (di-HB) using solid-phase synthesis methodology. The di-HB-modified SWCNT and GO were found to exhibit great catalytic activity as they reduce required overpotential of electrochemical oxidation of NADH and lead to enhancement in the peak current, compared with unmodified carbon electrodes. Molecular docking simulation technique was also carried out to enlighten attained experimental findings in detail, and we have found that increase in the binding affinity of NAD+ to functionalized carbon surfaces with di-HB is related to formation of hydrogen bonding interactions Furthermore, our experimental and theoretical outputs were also found to be quite consistent in terms of reactivity of modified surfaces to NADH oxidation.

Surface functionalization of carbon-based sensors with biocompatible polymer to enable electrochemical measurement in protein-rich environment

Electrochemical biosensors have been widely applied to elucidate various information on pharmaceutically important neurotransmitters such as dopamine (DA). However, the biofouling of electrodes has been a critical issue for electrochemical measurements performed in physiological environments. In this study, highly biocompatible polymer brush made of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was employed to modify carbon-based sensors to prevent biofouling. The PMPC brushes with thicknesses ranging from 15 to 30 nm on top of glassy carbon surfaces successfully suppressed protein adsorption in serum environments, and the polymer modification remained stable for at least 8 h in such conditions. The PMPC-modified glassy carbon electrode (GCE) achieved a limit of detection (LOD) as low as 1.8 μM for DA, as determined from cyclic voltammetry (CV), which exhibited better performance than the bovine serum albumin (BSA)-coated GCE with a LOD of 3.9 μM. The results from this study open new avenues for drug discovery and pharmacokinetics by enabling carbon-based biosensors to accurately and sensitively detect pharmaceuticals in protein-rich environments for an extensive period of time.

Effect of Electrolyte Ions on the Formation, Electroactivity, and Rectification Properties of Films Obtained by Electrografting

AbstractThe oxidation of 4‐(4‐nitrophenyl)butyrate ions in acetonitrile was used to modify glassy carbon surfaces with films bearing 3‐(4‐nitrophenyl)propyl groups. The main features of the voltammetric reduction of the grafted nitrophenyl groups were studied in two different supporting electrolytes; n‐Bu4NPF6 and Me4NPF6. The best response was obtained with the less bulky electrolyte, which was explained by the major capability of these ions to diffuse inside the channels of the grafted film, as well as the better stabilization of the radical anions generated during the reduction process. It was also shown that the films electrografted in presence of the bulky n‐Bu4NPF6 are thicker but less compact than those prepared in Me4NPF6. The amount of nitrophenyl groups in the grafted film that can be reduced depends on the size of the electrolyte ions. The permeation of the electrolyte ions inside the film channels determines also the voltammetric behavior of ferrocene as redox probe. A current rectification phenomenon was observed in acetonitrile solutions of bulky and hydrophobic electrolytes like n‐Bu4NPF6 and n‐Hx4NPF6, whose marginal inclusion inside the film channels promotes both the entrance of ferrocene and the expelling of ferrocenium ions from these ones. This phenomenon was emulated through a CEC mechanism in solution, where the diffusion inside the channels was described as single chemical equilibria.

Electrodeposition of Sn and Sn Composites with Carbon Materials Using Choline Chloride-Based Ionic Liquids

Nano carbons, such as graphene and carbon nanotubes, show very interesting electrochemical properties and are becoming a focus of interest in many areas, including electrodeposition of carbon–metal composites for battery application. The aim of this study was to incorporate carbon materials (namely oxidized multi-walled carbon nanotubes (ox-MWCNT), pristine multi-walled carbon nanotubes (P-MWCNT), and reduced graphene oxide (rGO)) into a metallic tin matrix. Formation of the carbon–tin composite materials was achieved by electrodeposition from a choline chloride-based ionic solvent. The different structures and treatments of the carbon materials will create metallic composites with different characteristics. The electrochemical characterization of Sn and Sn composites was performed using chronoamperometry, potentiometry, electrochemical impedance, and cyclic voltammetry. The initial growth stages of Sn and Sn composites were characterized by a glassy-carbon (GC) electrode surface. Nucleation studies were carried out, and the effect of the carbon materials was characterized using the Scharifker and Hills (SH) and Scharifker and Mostany (SM) models. Through a non-linear fitting method, it was shown that the nucleation of Sn and Sn composites on a GC surface occurred through a 3D instantaneous process with growth controlled by diffusion. According to Raman and XRD analysis, carbon materials were successfully incorporated at the Sn matrix. AFM and SEM images showed that the carbon incorporation influences the coverage of the surface as well as the size and shape of the agglomerate. From the analysis of the corrosion tests, it is possible to say that Sn-composite films exhibit a comparable or slightly better corrosion performance as compared to pure Sn films.

Aldehyde-Mediated Protein-to-Surface Tethering via Controlled Diazonium Electrode Functionalization Using Protected Hydroxylamines.

We report a diazonium electro-grafting method for the covalent modification of conducting surfaces with aldehyde-reactive hydroxylamine functionalities that facilitate the wiring of redox-active (bio)molecules to electrode surfaces. Hydroxylamine near-monolayer formation is achieved via a phthalimide-protection and hydrazine-deprotection strategy that overcomes the multilayer formation that typically complicates diazonium surface modification. This surface modification strategy is characterized using electrochemistry (electrochemical impedance spectroscopy and cyclic voltammetry), X-ray photoelectron spectroscopy, and quartz crystal microbalance with dissipation monitoring. Thus-modified glassy carbon, boron-doped diamond, and gold surfaces are all shown to ligate to small molecule aldehydes, yielding surface coverages of 150-170, 40, and 100 pmol cm-2, respectively. Bioconjugation is demonstrated via the coupling of a dilute (50 μM) solution of periodate-oxidized horseradish peroxidase enzyme to a functionalized gold surface under biocompatible conditions (H2O solvent, pH 4.5, 25 °C).