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Sol‐gel‐derived silica thin films generated onto electrode surfaces in the form of organic‐inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica‐based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non‐ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol‐gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others. [ABSTRACT FROM AUTHOR]

This review article comprehensively discusses the various electrochemical approaches for measuring and detecting oxidative stress biomarkers and enzymes, particularly reactive oxygen/nitrogen species, highly reactive chemical molecules, which are the byproducts of normal aerobic metabolism and can oxidize cellular components such as DNA, lipids, and proteins. First, we address the latest research on the electrochemical determination of reactive oxygen species generating enzymes, followed by detection of oxidative stress biomarkers, and final determination of total antioxidant activity (endogenous and exogenous). Most electrochemical sensing platforms exploited the unique properties of micro- and nanomaterials such as carbon nanomaterials, metal or metal oxide nanoparticles (NPs), conductive polymers and metal-nano compounds, which have been mainly used for enhancing the electrocatalytic response of sensors/biosensors. The performance of the electroanalytical devices commonly measured by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in terms of detection limit, sensitivity, and linear range of detection is also discussed. This article provides a comprehensive review of electrode fabrication, characterization and evaluation of their performances, which are assisting to design and manufacture an appropriate electrochemical (bio)sensor for medical and clinical applications. The key points such as accessibility, affordability, rapidity, low cost, and high sensitivity of the electrochemical sensing devices are also highlighted for the diagnosis of oxidative stress. Overall, this review brings a timely discussion on past and current approaches for developing electrochemical sensors and biosensors mainly based on micro and nanomaterials for the diagnosis of oxidative stress. [ABSTRACT FROM AUTHOR]

The study of planar energy storage devices, characterized by low-cost, high capacity, and satisfactory flexibility, is becoming a valuable research hotspot. Graphene, monolayer sp2 hybrid carbon atoms with a large surface area, always acts as its active component, yet there is a tension between its high conductivity and ease of implementation. Although the difficult-to-assemble graphene can easily achieve planar assemblies in its highly oxidized form (GO), the undesirable conductivity, even after proper reduction, still restricts its further applications. Here, a facile "Top-down" method has been proposed to prepare the graphene planar electrode via in situ electro-exfoliation of graphite supported on a piece of laser-cutting patterned scotch tape. Detailed characterizations have been performed to study its physiochemical property evolution during electro-exfoliation. The obtained flexible graphene planar electrodes show decent energy storage performance, e.g., 40.8 mF cm−2 at a current density of 0.5 mA cm−2 and an 81% capacity retention at a current density of 8 mA cm−2 for the optimized sample G-240. Their high conductivity also makes it possible to couple them with other redox-active materials through electrodeposition to improve their performance, e.g., ferrocene-functionalized mesoporous silica film (Fc-MS), MnO2, and polyaniline (PANI). The highest capacity was achieved with the PANI functionalized sample, which achieved a 22-fold capacity increase. In a word, the versatility, practicality, and adaptability of the protocol to prepare the planar graphene electrode proposed in this work make it a potential candidate to meet the continuously growing energy storage demands. [ABSTRACT FROM AUTHOR]

Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H2O)6]2+ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)3]2+ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in situ formation of the [Fe(bpy)3]2+ complex is evidenced by its characteristic optical absorption spectrum, and elemental composition analysis using X-ray photoelectron spectroscopy. The measured optical and electrochemical properties of immobilized [Fe(bpy)3]2+ complexes are not altered by confinement in the nanostructured silica thin film. [ABSTRACT FROM AUTHOR]

The electrochemical regeneration of the reduced form of nicotinamide adenine dinucleotide cofactor (NADH) was realized in a hybrid flow reactor coupling fuel cell technology and redox flow device, paying attention to the robust immobilization of all catalysts. The rhodium catalyst Rh(Cp✶)(bpy)Cl+ was covalently immobilized on a multi‐walled carbon nanotube (MWCNT) layer and the association with the gas diffusion electrode was carefully optimized. High stability and activity of the electrochemical system were assessed by cyclic voltammetry and amperometry in the flow reactor. Afterwards, the optimal cofactor regeneration was applied to NADH‐dependent biosynthesis using immobilized lactate dehydrogenase for the conversion of pyruvate to lactate in the flow cell in the presence of cofactor concentration as low as 10 μM. 79 % Faradaic efficiency was achieved and remarkable total turnover number (TTN) were reached: 2500, 18000, and 180000, for NADH, Rh complex and L‐lactate dehydrogenase (LDH), respectively. [ABSTRACT FROM AUTHOR]

Beta‐nicotinamide adenine dinucleotide (NAD+/NADH) is an important enzymatic co‐factor that can be efficiently regenerated using a rhodium‐based catalyst as electron transfer mediator (ie, [Cp*Rh(bpy)Cl]+, where Cp* = pentamethylcyclopentadienyl and bpy = 2,2‐bipyridine). Here, the above mediated regeneration of NADH is implemented in a redox flow bioreactor hybridized with a gas diffusion electrode for hydrogen oxidation. The reactor was initially optimized with respect to rhodium complex and NAD+ concentrations, humidification of the hydrogen gas, flow rates of both H2 gas and electrolytic solution, and solution pH. The integration of an enzymatic reaction consuming the generated NADH was then investigated in a flow process, combining in series the electrochemical reactor to a biochemical cell with immobilized l‐lactic dehydrogenase for the conversion of pyruvate to lactate. A high activity was achieved with a turnover number up to 370 h−1 for NADH regeneration. Coupled electrochemical regeneration to enzymatic reaction led to total turnover number values of 2000 and 6.3 × 106 for NADH electrochemical regeneration and bioconversion, respectively. [ABSTRACT FROM AUTHOR]

The scientific problem aimed to be solved by our research is to improve the charge transport of Ni2+salen polymer semiconductors by isolation of individual chains inside mesoporous silica channels capable of ensuring the suppression of interchain interactions that cause the charge carrier trapping in the continuous polymer films. Elimination of charge trapping is the primary motivation for energy transport improvement in polymer semiconductors serving as interconnections in molecular electronics. With this in mind, we prepared molecular wires based on structurally privileged ortho substituted Ni2+salens, offering the molecular structure facilitating its linear electropolymerization growth inside the confined space of a silica matrix containing vertical channels that are 2 nm in diameter. We noticed that the analogical embedment of ortho unsubstituted poly(Ni2+salen)s was not possible. Thus, we used quantum chemical calculations utilizing density functional theory to explain this phenomenon. Hence, we succeeded in recognizing structure–property relationships of Ni2+salens governing their local electropolymerization ability inside vertical nanochannels. Isolation of polymer chains allowed us to gain insight into the intrinsic properties of Ni2+salen polymers creating a better understanding of their charge transport and polymerization mechanisms. The prepared molecular wires exhibited improved electronic properties evidenced by electrochemical measurements revealing the energetically favored charge transporting polymer forms and the increased ratio between anodic and cathodic charges. Furthermore, we directly evidenced the presence of a Ni2+salen polymer inside silica nanochannels using high-resolution X-ray photoelectron spectroscopy combined with very low-energy argon ion beam sputtering, as well as using atomic force microscopy and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Fine particles of Ayous sawdust (AS) were successfully modified by maleic anhydride to increase their accumulation capability towards carbendazim (Cbz). For a more efficient use of the biosourced material as electrode modifier for electrochemical detection, the functionalized particles were mixed with carbon nanotubes to yield a conductive composite. After electrochemical characterization, the modified GCE was applied to Cbz detection. A sensitivity of (2.61±0.08) μA M−1 and a detection limit of 0.04 μM were obtained under optimized experimental conditions. Moreover, the designed sensor was found efficient for Cbz determination in real samples (spring water and commercial pesticide product). [ABSTRACT FROM AUTHOR]

The regeneration of the NADH cofactor is crucial for bioelectrocatalytic reactors. This can be achieved by using an electrochemical mediator such as the rhodium complex [Cp*Rh(bpy)Cl]+, but the overall reduction process suffers from the interference of molecular oxygen. This interference can be avoided by using a second porous working electrode (acting as a real oxygen filter) positioned near the surface of the first working electrode. To fabricate the oxygen filter, platinum particles were deposited on the surface of a carbon paper. NADH could be produced in the presence of the oxygen filter with a faradaic yield at 63.4 %, very close to the yields obtained without the filter at 61.7 % in a fully N2‐degased medium, and only at 10.6 % in the presence of oxygen. Moreover, the productivity was also increased by nearly a factor of four. Therefore, the proposed concept of the oxygen filter offers a new avenue in the current strategies for NADH regeneration in biocatalytic reactors based on electrochemical methods. [ABSTRACT FROM AUTHOR]

Indium–tin oxide electrodes modified with vertically aligned silica nanochannel membranes have been produced by electrochemically assisted self-assembly of cationic surfactants (cetyl- or octadecyl-trimethylammonium bromide) and concomitant polycondensation of the silica precursors (tetraethoxysilane). They exhibited pore diameters in the 2–3 nm range depending on the surfactant used. After surfactant removal, the bottom of mesopores was derivatized with aminophenyl groups via electrografting (i.e., electrochemical reduction of in situ generated aminophenyl monodiazonium salt). These species covalently bonded to the ITO substrate were then exploited to grow polyaniline nanofilaments by electropolymerization of aniline through the nanochannels. Under potentiostatic conditions, the length of polyaniline wires is controllable by tuning the electropolymerization time. From cyclic voltammetry characterization performed either before or after dissolution of the silica template, it appeared that both the polyaniline/silica composite and the free polyaniline nanowire arrays were electroactive, yet with much larger peak currents in the latter case as a result of larger effective surface area offered to the electrolyte solution. At identical electropolymerization time, the amount of deposited polyaniline was larger when using the silica membrane with larger pore diameter. All polyaniline deposits exhibited electrochromic properties. However, the spectroelectrochemical data indicated more complete interconversion between the coloured oxidized form and colourless reduced polyaniline for the arrays of nanofilaments in comparison to bulky films. In addition, the template-free nanowire arrays (i.e., after silica dissolution) were characterized by faster electrochromic behaviour than the polyaniline/silica hybrid, confirming the potential interest of such polyaniline nano-brushes for practical applications. [ABSTRACT FROM AUTHOR]

A carbon paste electrode (CPE) modified with Nafion, Graphene oxide and zeolite has been prepared and characterized, and the resulting Nafion/Graphene oxide/Zeolite modified carbon paste electrode (N/G/Z/MCPE) has been applied to the electrochemical detection of Moxifloxacin hydrochloride (MOXI). It exhibited a good electrocatalytic activity in phosphate buffer (optimum at pH 7.4), as pointed out by cyclic voltammetry (CV), and N/G/Z/MCPE can be exploited for MOXI detection by chronoamperometry, electrochemical impedance spectroscopy and differential pulse voltammetry. This latter was the most sensitive one and gave rise to a linear calibration curve in the 0.04 to 250 μM concentration range, with limits of detection and qualification estimated at 1.0 nM and 3.3 nM, respectively. Contrary to previous electrochemical sensors for MOXI (e. g., CPE modified with metal nanoparticles), this new sensor can be used for multiple successive analyses without needing to refresh its surface. [ABSTRACT FROM AUTHOR]

In the present work, we report the electron transfers occurring after ionization of the guest molecules of t-stilbene incorporated in graphitized HZSM-5 zeolites and we compare these results with the data obtained previously for graphite-free zeolites. Complementary diffuse reflectance UV-vis and Raman scattering spectroscopies provide evidence for stabilization of long lived charge separated states as observed in non-graphitized ZSM-5. The spectral features indicate that these species are located in the channels of the zeolite structure. However, the pulsed EPR technique shows strong coupling between unpaired electrons and the 13C atoms in the case of graphitized zeolites while this interaction is not observed in normal zeolites. This is assigned to the presence of charge transfer complexes in the close vicinity of graphite areas and to the possible electron transfer to the graphitized domain. Using cyclic voltammetry, an electrochemical response is observed for the first time in such systems demonstrating the role played by graphite in the electron transfers. [ABSTRACT FROM AUTHOR]

Gold electrodes have been covered with vertically aligned mesoporous silica thin films by electro‐assisted self‐assembly. To ensure uniform surface coverage and good adhesion of the membrane to the gold surface, it was necessary to use a (3‐mercaptopropyl)trimethoxysilane (MPTMS) reagent to act as a "molecular glue" thanks to its thiol functionality, which is able to bind to the gold substrate and to its alkoxysilane moieties enabling condensation with the silica material. The MPTMS layer had, however, a significant effect on film permeability to redox species [Ru(NH3)63+ and ferrocenedimethanol (Fc(MeOH)2)]. MPTMS adsorption should be long enough to ensure proper adhesion of the film but not too long so as to avoid surface blocking or film defects; an optimal time window of 60–600 s soaking in 0.1 mM MPTMS in ethanol was evidenced. In addition, Cu underpotential deposition (UPD) experiments revealed that the silica membrane significantly affected the UPD process, suggesting some barrier effect of the porous membrane, but the interface Au/MPTMS/silica is not sharp and allowed metal UPD between the gold substrate and the silica thin film. [ABSTRACT FROM AUTHOR]

Unmodified and ferrocene‐functionalized mesoporous silica layers exhibiting vertical nanochannels have been grown through electrochemically assisted self‐assembly onto indium‐tin oxide (ITO), and the resulting film electrodes have been applied for the electrochemical detection of cysteine. When using the unmodified film electrode and ferrocenedimethanol (Fc(MeOH)2) as a mediator in solution, both cysteine and glutathione can be oxidized by the Fc(MeOH)2+ generated at the electrode surface, but the electron transfer rates were three times faster with cysteine than with glutathione. This can be exploited for the reagent‐free selective detection of cysteine over glutathione by using a ferrocene‐functionalized mesoporous silica film on an ITO electrode, based on a combination of charge transfer kinetic and mass transport limitations through the oriented nanochannels. This has been demonstrated here by using cyclic voltammetry and amperometry in flow‐injection analysis mode. A sensitivity of 1.28 mA M−1 was measured for the cysteine concentration range of 3–20 μM with a repeatability of the signal between 3 and 12 %. The lowest concentration of cysteine experimentally detected was 3 μM. [ABSTRACT FROM AUTHOR]

Mesoporous silica thin films encapsulating a molecular iron‐triazole complex, Fe(Htrz)3 (Htrz=1,2,4,‐1H‐triazole), have been generated by electrochemically assisted self‐assembly (EASA) on indium‐tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well‐defined voltammetric signals corresponding to the FeII/III centers of the Fe(Htrz)3 species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.6×10−4 mol g−1 Fe(Htrz)3 in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)3 species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)3@SiO2) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of −0.4 V versus Ag/AgCl and by flow injection analysis. The organic‐inorganic hybrid film electrode displays good sensitivity for H2O2 sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM. [ABSTRACT FROM AUTHOR]

Single‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM−1 cm−2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination. [ABSTRACT FROM AUTHOR]

Electrogenerated silica thin films exhibiting a regular hexagonal packing of vertically‐aligned mesopore channels are promising for preconcentration electroanalysis. This work demonstrates the critical role of film thickness on their sensing performance using paraquat as a model analyte, based on mesoporous silica films prepared by electrochemically assisted self‐assembly performed for various deposition times. Films prepared with too short synthesis times (<10 s) led to deposits covering partially the electrode surface and suffered from rather poor sensing performance. Then, uniformly deposited films were obtained (between 10 and 15 s), and sensitivity rose up by increasing deposition times, whereas some limitations started to occur with much thicker films (>15 s deposition times) as a result of less electrochemically accessible paraquat accumulated far away from the electrode surface and restricted mass transport through the whole film thickness. These limitations were also confirmed on the basis of multi‐layered mesoporous silica films, suggesting a behavior that might be typical for other types of film‐modified electrodes. [ABSTRACT FROM AUTHOR]

An injectable purely apatitic calcium phosphate cement (CPC) was successfully combined to a water‐soluble radiopaque agent (i.e., Xenetix®), to result in an optimized composition that was found to be as satisfactory as poly(methyl methacrylate) (PMMA) formulations used for vertebroplasty, in terms of radiopacity, texture and injectability. For that purpose, the Xenetix dosage in the cement paste was optimized by injection of the radiopaque CPC in human cadaveric vertebrae under classical PMMA vertebroplasty conditions, performed by interventional radiologists familiar with this surgical procedure. When present in the cement paste up to 70 mg I mL−1, Xenetix did not influence the injectability, cohesion, and setting time of the resulting composite. After hardening of the material, the same observation was made regarding the microstructure, mechanical strength and alpha‐tricalcium phosphate to calcium deficient apatite transformation rate. Upon implantation in bone in a small animal model (rat), the biocompatibility of the Xenetix–containing CPC was evidenced. Moreover, an almost quantitative release of the contrast agent was found to occur rapidly, on the basis of in vitro static and dynamic quantitative studies simulating in vivo implantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2786–2795, 2018. [ABSTRACT FROM AUTHOR]

Abstract: A bioelectrode for electroenzymatic synthesis was prepared, combining a layer for NADH regeneration and a renewable layer for enzymatic substrate reduction. The covalent immobilization of a rhodium complex mediator ([Cp*Rh(bpy)Cl]+) on the surface of a bucky paper electrode was achieved by following an original protocol in two steps. A bipyridine ligand was first grafted on the electrode by electro‐reduction of bipyridyl diazonium cations generated from 4‐amino‐2,2′‐bipyridine, and the complex was then formed by reaction with [RhCp*Cl2]2. A turnover frequency of 1.3 s−1 was estimated for the electrocatalytic regeneration of NADH by this immobilized complex, with a Faraday efficiency of 83 %. The bucky paper electrode was then overcoated by a bio‐doped porous layer made of glassy fibers with immobilized D‐sorbitol dehydrogenase. This assembly allowed for the efficient separation of the enzyme and the rhodium catalyst, which is a prerequisite for effective bioelectrocatalysis with such bioelectrochemical system, while allowing effective mass transport of NAD+/NADH cofactor from one layer to the other. Thereby, it was possible to reuse the same mediator‐functionalized bucky paper with three different enzyme layers. The bioelectrode was applied to the electroenzymatic reduction of D‐fructose to D‐sorbitol. A turnover frequency of 0.19 s−1 for the rhodium complex was observed in the presence of 3 mM D‐fructose and a total turnover number higher than 12000 was estimated. [ABSTRACT FROM AUTHOR]

Abstract: A generic approach has been developed for sequential heterogeneous surface modification of electrodes. The strategy, which is applicable for a wide range of functional groups, involves two main steps. In the first one, azide‐alkene bifunctionalized electrodes are obtained by electrochemical reduction of a mixture of diazonium salts generated in situ from the corresponding 4‐azidoaniline and 4‐vinylaniline. In that way, we provide reactive sites that are available for further selective functionalization in a sequential process based on ‘click reactions’, in which subsequent immobilization of the targeted molecules is achieved by the azide‐alkyne cycloaddition Huisgen reaction and alkene‐thiol coupling. Feasibility of the method has been first demonstrated for the coimmobilization of two distinct redox moieties (cobaltocenium and ferrocene) as evidenced by cyclic voltammetry and X‐ray photoelectron spectroscopy measurements. The versatility of the sequential method has then been exploited for the coimmobilization of a molecular electrocatalyst [Cp*Rh(bpy) Cl]+ and a biological catalyst, a NAD‐dependent dehydrogenase, that were proved to act in cascade in the electroenzymatic reduction of D‐fructose to D‐sorbitol. Such simple combination of diazonium chemistry and robust chemical reactions (‘click chemistry’) is promising for the environmentally friendly heterogeneous modification of electrodes with multiple chemical and biological catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A review on the preparation methods for porous and transparent metal‐oxide electrodes is provided alongside a discussion of existing and possible electrochemical and electroanalytical applications. The elaboration routes include non‐templated particle deposition, template approaches, physical deposition methods, etching and electrospinning. Applications of such materials are mainly found in energy conversion and storage (photovoltaics, water splitting) and electroanalysis. [ABSTRACT FROM AUTHOR]

The past decade has seen an increasing number of extensive studies devoted to the exploitation of ordered mesoporous carbon (OMC) materials in electrochemistry, notably in the fields of energy and sensing. The present review summarizes the recent achievements made in field of electroanalysis using electrodes modified with such nanomaterials. On the basis of comprehensive tables, the interest in OMC for designing electrochemical sensors is illustrated through the various applications developed to date. They include voltammetric detection after preconcentration, electrocatalysis (intrinsically due to OMC or based on suitable catalysts deposited onto OMC), electrochemical biosensors, as well as electrochemiluminescence and potentiometric sensors. [ABSTRACT FROM AUTHOR]

Electrochemically-assisted deposition is now becoming a widespread method for preparing sol–gel films. It is based on the electrochemical generation of OH− ions, which can then catalyze the sol–gel condensation reactions. It has a key advantage of selectively facilitating the film deposition on electrochemically active surfaces while not affecting the stability of the bulk precursor solution. Experimental studies have clearly shown that the thickness of the electrochemically-assisted deposited films is influenced by the deposition parameters such as the potential and time. However, there is still a lack of quantitative description of the kinetics of film growth due to the complexity of the process. In this preliminary study, we derived quantitative analytical expressions for describing the kinetics associated with the growth of sol–gel films generated by electrochemically assisted deposition. Both heterogeneous and homogeneous condensation reactions were considered. The key strategy was to simplify the process by separating the electrochemical step of generating OH− ions with the condensation steps of film formation under approximation. Furthermore, numerical simulation was carried out to examine the validity and any errors in the analytical expressions in the cases when the required approximations were not fulfilled. The analytical expressions could well explain the trends observed in the experimental studies and could also be used for fitting the experimental results from the literature. This study provides a deeper understanding of the mechanism and quantitative guidance for manipulating electrochemically-assisted deposition processes at a large scale in industry. It may also be referred to in regard to other indirect electrodeposition systems in which the deposition is not an electrochemical step but is instead driven by electrochemically-generated catalysts. [ABSTRACT FROM AUTHOR]

Diffusion of anionic species through ordered mesoporous silica films is considerably restricted due to electrostatic repulsion by the negatively charged silica surface and this effect is even worse in low ionic strength media (owing to Donnan exclusion effects). This is at the origin of the poor electrochemical response of anionic redox probes at electrodes modified with such mesoporous thin films. Here, by using indium-tin oxide (ITO) electrodes covered with vertically aligned mesoporous silica films generated by electrochemically assisted self-assembly (EASA), we show that charge transfer for anionic redox probes [i.e. Fe(CN)63−/4−] can be dramatically amplified by using a neutral [ferrocene dimethanol, Fc(MeOH)2] or cationic [(Ru(NH3)63+] redox mediator. This has been observed by cyclic voltammetry, showing current enhancement in the presence of the mediator, which acts as a mobile electron shuttle between the charge-excluded Fe(CN)63−/4− species from the mesoporous silica film and the underlying ITO surface owing to the ability of the mediator species to diffuse freely through the oriented mesopore channels. This behavior was significantly affected by the relative contents of Fe(CN)63−/4− probe to Fc(MeOH)2 mediator, the potential scan rate, and the supporting electrolyte concentration. The most effective improvements were reached at low Fe(CN)63−/4− concentration, high mediator content, low potential scan rate, and low ionic strength. [ABSTRACT FROM AUTHOR]

Getting oriented mesoporous thin films with functionalized pores accessible from the substrate surface remains one key challenge in materials science, and jumping the step forward to multifunctional layers with perpendicular nanochannels has still to be achieved. Here, a general method is introduced combining the electrochemically assisted deposition of ordered and oriented azide- and thiol-functionalized mesoporous silica with a selective sequential azide-alkyne and thiol-ene 'click chemistry' approach to prepare nanostructured and vertically aligned hybrid films bearing tunable amounts of organo-functional groups. High-resolution electron microscopy is used to evidence the high level of mesostructural order and pore orientation, while the effectiveness of the functionalization processes is proven from spectroscopic and electrochemical measurements. Voltammetric data also demonstrate that both the accessibility through the films and the properties of the incorporated functions are maintained upon derivatization. Feasibility of this simple and generic strategy is illustrated here for two couples of model derivatives (ethynylcobaltocenium/vinylferrocene and propargyl alcohol/allyl cyanide) but such stepwise postfunctionalization can be extensively used for the incorporation of a variety of organic functions in mesoporous silica films. [ABSTRACT FROM AUTHOR]

Modified electrodes from functionalized nanoporous xerogel coatings, prepared by using the electrochemically assisted self-assembly (EASA) method, containing ferrocene moieties grafted onto vertically oriented pores perpendicular to an indium tin oxide (ITO) electrode, have been prepared and studied. The electrochemical behavior of these new materials exhibits the fastest charge transfer ever observed in oxide-modified electrodes. The cyclic voltammetry curves allow us, however, to discriminate two types of ferrocene species inside the coatings and to determine the rate constants for the electron exchange between the ITO electrode and the coatings, with the help of simulations and an advanced software package. [ABSTRACT FROM AUTHOR]

This review (239 references) is dealing with the use of mesoporous materials in the field of electrochemical enzymatic biosensors. After a brief discussion on the interest of mesoporous materials for electrochemical biosensing, a presentation of the various types of inorganic and organic-inorganic hybrid mesostructures used to date in the elaboration of enzymatic bioelectrodes is given and the main bioelectrode configurations are described. The various biosensor applications are then summarized on the basis of a comprehensive table and some representative illustrations. The main detection schemes developed in the field are based on amperometry and mediated electrocatalysis, as well as some on spectroelectrochemistry. [ABSTRACT FROM AUTHOR]

This review presents the interest of electrochemistry for the preparation of two families of porous materials (ordered mesoporous silica and layer\ed double hydroxide), generated as thin films on solid electrode surfaces via an electrochemically assisted local pH tuning. The deposition mechanism is dependent on the target material. The driving force to get the ordered mesoporous silica thin films is the combination of electrochemical interfacial surfactant templating to the electro-assisted sol-gel deposition, leading to the growth of vertically aligned mesopore channels of surfactant-templated silica. The mechanism involved in the generation of layered double hydroxide (LDH) thin films is the electrochemically induced precipitation of the material by the electrogenerated hydroxide anions, which can be also applied to the formation of LDH-based composites. After a presentation of the materials that can be synthesized by the electrochemical manipulation of localized pH at electrode/solution interfaces, their characterization and applications are also briefly discussed. [ABSTRACT FROM AUTHOR]

Well-organized octyl- and hexadecyl-functionalized mesoporous silica thin films are generated onto indium-tin oxide electrodes by combining the electrochemically assisted self-assembly technique and the sol-gel co-condensation route. The electrodeposition is carried out under potential control from mixtures containing various molar ratios of tetraethoxysilane and octyltrimethoxysilane (O-TES) or hexadecyltrimethoxysilane (HD-TES), using cetyltrimethylammonium bromide as surfactant template. Films with hexagonally packed functionalized mesochannels oriented perpendicular to the underlying support are obtained up to, respectively, 20 % O-TES and 5 % HD-TES introduced in the starting sol. Electrochemical investigations using various redox probes demonstrate that the films remain porous despite the presence of long carbon chains inside the mesochannels and that, in the presence of such long chain alkyl groups, the physical diffusion through the pores is not sufficient to describe the mass transport issues, which can also imply accumulation effects owing to the hydrophobic character of the medium. [ABSTRACT FROM AUTHOR]

Amperometric sensors dedicated to the determination of pollutants and other compounds of interest face daily a great challenge: the development of sensitive, reproducible and low-cost devices allowing fast analyses. This review deals with the beneficial role and application of organoclays exploited as sensing materials in various fields of electroanalysis, for the past 15 years (period 2000-2014). After a description of different preparation methods leading to clay minerals chemically modified by organic compounds, the common methods used for their characterization are exposed; then, their application as electrode modifiers is described, covering several approaches that were developed to enhance either the sensitivity or the selectivity of the indexed organoclay-based sensors. Finally, a brief description of voltammetric methods frequently used for electroanalytical purposes is given, followed by an update of recent and salient results achieved for the detection of inorganic and organic electroactive compounds or ions. [ABSTRACT FROM AUTHOR]

A mediator-free choline biosensor was developed using the electrochemically assisted sol-gel deposition on gold screen-printed electrodes. The addition of 12 mM of cationic surfactant CTAB in silica sol allowed enhancing the stability of the sensor. The modified electrode demonstrated catalytic activity and stable amperometric response to choline for over 3 weeks of exploitation with the sensitivity of 6 µA mM-1 and LOD of 6 µM. The interference of ascorbic acid was reduced by pretreating the analyzed solution with MnO2 powder. The application of the sensor with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics. [ABSTRACT FROM AUTHOR]

A review (350 references) is given to the interest of mesoporous materials for designing electrochemical sensors. After a brief summary of the implication of template-based ordered mesoporous materials in electrochemical science, the various types of inorganic and organic-inorganic hybrid mesostructures used to date in electroanalysis and the corresponding electrode configurations are described. The various sensor applications are then discussed on the basis of comprehensive tables and some representative illustrations. The main detection schemes developed in the field are (volt)amperometric sensing subsequent to preconcentration and electrocatalytic detection. [ABSTRACT FROM AUTHOR]

The production of thin mesoporous silica films with small (∼2–3 nm) pores oriented perpendicular to a titanium nitride growth surface is demonstrated using two methods. These are the growth from a Stöber silica solution with surfactant ordering at the surface of the electrode, and electrochemically assisted growth from an acidic sol achieved by polarisation of the electrode surface. The thickness, pore order and pore size that can be achieved with these two methods is contrasted. A number of methods to vary the pore size by using different surfactants and swelling agents are explored. The advantage of applying these growth methods on titanium nitride surfaces is that it provides access to a wider electrochemical window for nanowire growth and sensor applications with non-aqueous electrolytes whilst retaining good film growth and adhesion properties. [ABSTRACT FROM AUTHOR]

Interfacial processes controlled by ion transfer voltammetry at the interface between two immiscible electrolyte solutions were studied by in situ Raman spectroscopy. Raman spectra of the interface between a 5 mM NaCl aqueous solution and 10 mM bis(triphenyl-phosphoranydieneammonium) tetrakis(4-chlorophenyl)borate in 1,2-dichloroethane were recorded at open circuit potential and at various interfacial potential differences. At open-circuit potential, Raman peaks assigned to vibrational modes of 1,2-dichloroethane are clearly visible and peaks of weak intensity are measured for the organic electrolyte ions. When a negative interfacial potential difference is applied, the intensity of the peaks of the cation of the organic electrolyte increases, confirming its transfer induced by the interfacial potential difference applied. The electrochemically assisted generation of mesoporous silica deposits was then followed by in situ confocal Raman spectroscopy. The condensation of mesoporous silica was controlled by the transfer of cetyltrimethylammonium (CTA+) ions to an aqueous phase containing hydrolysed silanes. The transfer of CTA+ at the interface was monitored in situ by confocal Raman spectroscopy, and formation of silica was observed. [ABSTRACT FROM AUTHOR]

This work describes the modification of a glassy carbon electrode with poly(Toluidine Blue O) (GC/poly-TBO) and single-walled carbon nanotubes (SWCNT) for the electrocatalytic oxidation of nitrite. GC/poly-TBO was prepared by electropolymerization and used as such or after immobilizing SWCNT on the polymeric film to give a composite GC/poly-TBO-SWCNT electrode. The electrochemical and catalytic behavior of both electrodes was studied comparatively. It was observed that the presence of SWCNT contributed to enhance the electrocatalytic response for nitrite oxidation, as measured by amperometry at +0.92 V vs. Ag/AgCl/KCl and pH 7. The response was linear with respect to the nitrite concentration in the 0.001-4 mM range, with a detection limit of 0.37 μM (based on signal to noise ratio of 3) for GC/poly-TBO-SWCNT. The proposed method was also applied to the determination of nitrite in a wastewater sample and compared to the spectrophotometric method. [ABSTRACT FROM AUTHOR]