Sonogel-Carbon Electrode Research Articles

Comparative study of the electrocatalytic activity of different types of gold nanoparticles using Sonogel-Carbon material as supporting electrode

Abstract The main objective of this study consists of comparing the electrocatalytic activity of different types of gold nanoparticles (AuNPs) obtained from two different synthetic routes (thermal and ultrasonic methods) deposited on the surface of a Sonogel-Carbon (SNGC) matrix and the application of the sensing devices built with them to the determination of ascorbic acid (AA). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to investigate electrocatalytic behaviour of AuNPs-modified SNGC electrodes. The best detection and quantification limits, obtained for gold sononanoparticles (AuSNPs)-modified SNGC electrode, were 3.71 × 10 −6 and 1.24 × 10 −6 M respectively, with a reproducibility value of 1.68% for a linear concentration range from 1.5 μM to 4.0 mM. The electrochemical devices were tested for the determination of AA in commercial apple juice for babies. These results were compared with those obtained by applying high performance liquid chromatography (HPLC) as a reference method. Recovery errors below 5% were obtained in all cases, with standard deviations lower than 5% for the AuSNPs-modified SNGC electrodes. Unmodified and AuNPs-modified SNGC electrodes were structurally characterized with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). AuNPs were characterized by UV–vis spectroscopy and X-ray diffraction (XRD), and information about their size distribution and shape was obtained by applying transmission electron microscopy (TEM) technique. The advantages of employing AuSNPs in SNGC supporting material are also described. This research suggests that the modified electrode can be a very promising voltammetric sensor for the determination of AA.

Characterization and Electrochemical Response of Sonogel Carbon Electrode Modified with Nanostructured TiO2 and ZrO2 Film to Detect Common Neurotransmitters

not Available.

Use of a Sonogel-Carbon electrode modified with bentonite for the determination of diazepam and chlordiazepoxide hydrochloride in tablets and their metabolite oxazepam in urine

Sonogel-Carbon electrode (SngCE) modified with bentonite (BENT) shows an interesting alternative electrode to be used in the determination of 1,4-benzodiazepines by square wave adsorptive cathodic stripping voltammetry (SWAdCSV). Diazepam (DZ) and chlordiazepoxide hydrochloride (CPZ), were determined using SngCE modified by 5% BENT. An electrochemical study of different parameters (such as pH, buffer type, ionic strength, accumulation potential, scan rate, and accumulation time) which affect the determination of DZ and CPZ is reported. Linear concentration ranges of 0.028–0.256μgmL−1 DZ (r=0.9997) and 0.034–0.302μgmL−1 CPZ (r=0.9997) are successfully obtained after an accumulation time of 60s. The quantification and detection limits were calculated to be 14.0 and 4.0ngmL−1 for DZ, and 16.0 and 5.0ngmL−1 for CPZ, respectively.The surface of the proposed electrode was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX).The developed method was applied to the analysis of commercially available tablets and human urine real samples. Analysis was performed with better precision, very low detection limits, and faster than previously reported voltammetric techniques.

Synthesis, characterization and electrochemical properties of mesoporous zirconia nanomaterials prepared by self-assembling sol–gel method with Tween 20 as a template

Zirconium dioxide nanomaterials, including nanoparticles and their derived films, were synthesized using a new surfactant self-assembling sol–gel route, which involves complexation of zirconium alkoxide precursor with acetylacetone as a chelating agent and Tween 20 as a structural directing agent. The properties of the synthesized material were studied using XRD, SEM, SAXS, HRTEM and N 2 adsorption and desorption analysis. It was found that Tween 20 can greatly increase the BET surface area and pore volume, inhibit crack formation in the derived film and retard particle growth at some extent. There exists tetragonal crystalline network with narrow pore size distribution in the ZrO 2 nano-materials prepared with Tween 20 in the sol. Furthermore, a mechanism on the formation of mesopore ZrO 2 structure via the Tween 20 self-assembling sol–gel process is presented. With the selection of the sono-gel carbon electrode modified by the mesoporous ZrO 2 film (M-ZrO 2 film) prepared with 1.10 g Tween 20/ml zirconia sol, enhanced electrochemical responses (i.e., enhanced peak currents) to catechol and ascorbic acid were confirmed using cyclic voltammetry (CV). Moreover, the modified electrode demonstrated additional improved electrochemical properties, such as good reversibility ( i pc/ i pa ≈ 1) and high selectivity (exceptionally resolved oxidation peaks between catechol and ascorbic acid), good stability and repeatability.

1-Furoylthiourea-Sonogel-Carbon electrodes: Structural and electrochemical characterization

A new type of sensor based on Sonogel-Carbon materials modified with 1-(2-furoyl)-3-(1-naphthyl)thiourea is presented to be used as an amperometric sensor for metals. Different percentages of modifier were tested in order to optimise the structural and mechanical properties, as well as the electrochemical behaviour. Scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Fourier transform-infrared spectroscopy (FTIR), single crystal X-ray diffraction (XRD) and powder XRD were used for the structural characterization of these electrodes. The 1-(2-furoyl)-3-(1-naphthyl)thiourea did not modify significantly the structural and mechanical properties of the Sonogel-Carbon electrodes, being similar to other modifications carried out previously in these materials. For the study of the electrochemical response, anodic stripping differential pulse voltammetry (ASDPV) was employed, optimising other parameters of measurement such as pH of the buffer, potential and accumulation time and pulse amplitude. The electrochemical response of the modified electrodes improved significantly with respect to the non-modified electrode, giving good signals and acceptable detection limit.

Sonogel–carbon electrode based on hemin for detection of superoxide

The Sonogel electrode was immersed in hemin solution to obtain the hemin-Sonogel-modified electrode by cyclic voltammetry (CV). It was applied to detect superoxide radicals produced by xanthine oxidase catalyzed hypoxanthine oxidation. The characterization of hemin-Sonogel was modified by impedance and CV.

Electrochemical behaviour of epinephrine and uric acid at a Sonogel–Carbon l-Cysteine modified electrode

The Sonogel–Carbon electrode is a special class of sol–gel electrode that exhibits favourable mechanic and electric properties to be used as electrochemical sensor. In this study, Sonogel–Carbon modified with l-Cysteine was used to prepare a novel electrochemical sensor. The objective of this novel electrode modification was to seek new electrochemical performances for detection of epinephrine in the presence of uric acid. The response of catalytic current with epinephrine concentration shows a linear relation in the range from 1 × 10 −7 to 5 × 10 −4 M with a correlation coefficient of 0.998, and a detection limit of 8.7 × 10 −8 M. The modified electrode had also been applied to the determination of epinephrine and uric acid in biological samples with satisfactory results. A surface characterisation of this modified electrode was carried out helped by scanning electron microscopy (SEM) and X-Ray energy dispersive spectroscopy (EDS).

Characterization and electrochemical response of sonogel carbon electrode modified with nanostructured zirconium dioxide film

A new modified carbon electrode was developed by coating sol–gel derived zirconium dioxide film on the top of graphite carbon electrode, which showed good electrochemical activity and reversibility in the redox process of catechol in acidic aqueous solution (0.1 M H 2SO 4), even in the presence of ascorbic acid (a common interferent). Good electrochemical behavior, including relatively small oxidation and reduction peak separation (Δ E p = 71 mV), improved sensitivity, and good operation stability and reproducibility, can be explained by specific physicochemical properties of sol–gel derived ZrO 2 film. Such properties include robust and interconnected crystal network structure with high ZrO 2 purity, relatively high BET surface area/pore volume, larger interfacial contact area and good adhesion between ZrO 2 film and sonogel graphite carbon material. This study proved that zirconium dioxide film prepared by such a sol–gel route is a promising electrode material for the development of novel conducting electrodes based on sonogel graphite carbon for the detection of neurotransmitters.

Alumina sol–gel/sonogel-carbon electrode based on acetylcholinesterase for detection of organophosphorus pesticides

Two new amperometric biosensors based on immobilization of acetylcholinesterase on a sonogel-carbon electrode for detection of organophosphorous compounds are proposed. The electrodes were prepared applying high-energy ultrasounds directly to the precursors. The first biosensor was obtained by simple entrapping acetylcholinesterase in Al 2O 3 sol–gel matrix on the sonogel-carbon. The second biosensor was produced in a sandwich configuration. Its preparation involved adsorption of the enzyme and modification via a polymeric membrane such as polyethylene glycol and the ion-exchanger Nafion. The optimal enzyme loading was found to be 0.7 mIU. Both biosensors showed optimal activity in 0.2 M phosphate buffer, pH 7.0, at an operating potential of 210 mV. The detection limit achieved for chlorpyriphos-ethyl-oxon was 2.5 × 10 −10 M at a 10-min incubation time.

A third-generation hydrogen peroxide biosensor based on Horseradish Peroxidase (HRP) enzyme immobilized in a Nafion–Sonogel–Carbon composite

A third-generation biosensor based on HRP and a Sonogel–Carbon electrode has been fabricated with the aim of monitoring hydrogen peroxide in aqueous media via a direct electron transfer process. The redox activity of native HRP, typical of thin-layer electrochemistry, was observed. The charge coefficient transfer, α, and the heterogeneous electron transfer rate constant, k s, were calculated to be 0.51 ± 0.04 and 1.29 ± 0.04 s −1, respectively. Topographic study by atomic force microscopy (AFM) shows that the enzyme may have been introduced inside the ionic cluster of the Nafion. The immobilized HRP exhibited excellent electrocatalytical response to the reduction of H 2O 2 and preserved its native state after the immobilization stage. Several important experimental variables were optimized. The resulting biosensor showed a linear response to H 2O 2 over a concentration range from 4 to 100 μM, with a sensitivity of 12.8 nA/μM cm −2 and a detection limit of 1.6 μM, calculated as (3 S.D./sensitivity). The apparent Michaelis–Menten constant K m app was calculated to be 0.295 ± 0.020 mM. The biosensor showed high sensitivity as well as good stability and reproducibility. The performance of the biosensor was evaluated with respect to four possible interferences.

A comparison of three amperometric phenoloxidase–Sonogel–Carbon based biosensors for determination of polyphenols in beers

Three phenoloxidases based biosensors were successfully developed using as electrochemical transducer a new type of electrode recently developed by our group: the “Sonogel–Carbon electrode”. The employed enzymes were Trametes versicolor laccase (Lac), Mushroom tyrosinase (Tyr), and Horseradish peroxidase (HRP). Immobilization step was accomplished by doping the electrode surface with a mixture of the individual enzyme and Nafion ion exchanger as additive-protective. The biosensor responses, optimized in beer real samples, were evaluated for five individual polyphenols. It was found that the developed biosensors were sensitive to nanomolar concentrations of the tested polyphenols. As example, the limit of detection, sensitivity, and response linear range for caffeic acid for Nafion-Lac/Sonogel–Carbon biosensor were 0.06μmolL−1, 99.6nAμmol−1L, and 0.04–2μmolL−1, respectively. The stability and reproducibility of the biosensors were evaluated by applying them directly to beer real samples. It has been demonstrated that the Nafion-Lac/Sonogel–Carbon system is the more stable with a relative standard deviation of 3.3% (n=10), maintaining 84% of its stable response for at least three weeks. Estimation of polyphenol index in eight lager beers and a comparison of the results with those obtained by a classical method was carried out.

Investigation of biosensor signal bioamplification: Comparison of direct electrochemistry phenomena of individual Laccase, and dual Laccase-Tyrosinase copper enzymes, at a Sonogel-Carbon electrode

Direct electrochemistry of Trametes versicolor Laccase (LAC) was found at a Sonogel-Carbon electrode. The bioamplification, performed by dual immobilization of this enzyme and Mushroom Tyrosinase (TYR), of the bio-electrocatalytic reduction of O 2 was investigated. The calculated α transfer coefficients were 0.64 and 0.67, and the heterogeneous electron-transfer rate constants were 6.19 and 8.52 s −1, respectively, for the individual LAC and dual LAC-TYR-based Nafion/Sonogel-Carbon bio-electrodes. The responses of the dual enzymes electrode to polyphenols were stronger than those of the individual LAC or TYR biosensors. Hypotheses are offered about the mechanism of bioamplification. The surfaces of the biosensors were also characterized by AFM.

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.

Multicomponent analysis in the wavelet domain of highly overlapped electrochemical signals: Resolution of quaternary mixtures of chlorophenols using a peg-modified Sonogel–Carbon electrode

Chemometric methods have been applied to resolve mixture of phenols; phenolic compounds are amongst the most interesting chemical species from an environmental viewpoint. However, the number of papers that apply multivariate calibration methods to resolve electroanalytical signals of mixture of phenols is low. In this paper, we propose a new chemometric methodology to resolve, in the wavelet domain, quaternary mixtures of chlorophenols: 4-chloro-3-methylphenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol, in a concentration range from 0.05 to 0.25 mg·L − 1 , using differential pulse adsorptive stripping voltammetry (DPAdSV) as the electrochemical technique, and a new polyethylenglycol-modified Sonogel–Carbon electrode. The results obtained after applying a Fast Wavelet Transform (FWT)-based feature selection algorithm, coupled with different multivariate calibration methods (multilinear regression-MLR and partial least squares regression-PLS) are compared with those obtained from a direct PLS. Besides, an Orthogonal Signal Correction (OSC)-based Calibration Transfer procedure (OSC-CT) is also applied, as a pre-processing tool, in order to improve the results obtained with the previous techniques.

Voltammetric determination of catechol using a sonogel carbon electrode modified with nanostructured titanium dioxide

In this study, we investigate highly efficient sonogel carbon electrode (SGC/TiO 2) modified with nanostructured titanium dioxide synthesized via sol–gel method employing surfactant template for tailor-designing the structural properties of TiO 2. The stable SGC/TiO 2 electrode detects catechol, a neurotransmitter, in the presence of ascorbic acid, a common interferent, using cyclic voltammetry. A possible rationale for the stable catechol detection of SGC/TiO 2 electrode is attributed to most likely the adsorption of catechol onto highly porous TiO 2 (surface area of 147 m 2 g −1 and porosity of 46.2%), and the formation of C 6H 4(OTi) 2 bond between catechol and TiO 2. The catechol absorbed onto TiO 2 rapidly reaches the SGC surface, then is oxidized, involving two electrons (e −) and two protons (H +). As a result, the surface of TiO 2 acts as an electron-transfer accelerator between the SGC electrode and catechol. In addition to the quantitative and qualitative detection of catechol, the SGC/TiO 2 electrode developed here meets the profitable features of electrode including mechanical stability, physical rigidity, and enhanced catalytic properties.

The Sonogel–Carbon materials as basis for development of enzyme biosensors for phenols and polyphenols monitoring: A detailed comparative study of three immobilization matrixes

Three amperometric biosensors based on immobilization of tyrosinase on a new Sonogel–Carbon electrode for detection of phenols and polyphenols are described. The electrode was prepared using high energy ultrasounds (HEU) directly applied to the precursors. The first biosensor was obtained by simple adsorption of the enzyme on the Sonogel–Carbon electrode. The second and the third ones, presenting sandwich configurations, were initially prepared by adsorption of the enzyme and then modification by mean of polymeric membrane such as polyethylene glycol for the second one, and the ion-exchanger Nafion in the case of the third biosensor. The optimal enzyme loading and polymer concentration, in the second layer, were found to be 285U and 0.5%, respectively. All biosensors showed optimal activity at the following conditions: pH 7, −200mV, and 0.02moll−1 phosphate buffer.The response of the biosensors toward five simple phenols derivatives and two polyphenols were investigated. It was found that the three developed tyrosinase Sonogel–Carbon based biosensors are in satisfactory competitiveness for phenolic compounds determination with other tyrosinase based biosensors reported in the literature. The detection limit, sensitivity, and the apparent Michaelis–Menten constant Kmapp for the Nafion modified biosensor were, respectively, 0.064, 0.096, and 0.03μmol, 82.5, 63.4, and 194nAμmol−1l−1, and 67.1, 54.6, and 12.1μmoll−1 for catechol, phenol, and 4-chloro-3-methylphenol. Hill coefficient values (around 1 for all cases), demonstrated that the immobilization method does not affect the nature of the enzyme and confirms the biocompatibility of the Sonogel–Carbon with the bioprobe. An exploratory application to real samples such as beers, river waters and tannery wastewaters showed the ability of the developed Nafion/tyrosinase/Sonogel–Carbon biosensor to retain its stable and reproducible response.

Voltammetric Determination of Catechol in the Presence of an Interferent Ascorbic Acid at a Sonogel-Carbon Electrode Modified with Titanium Oxide (TiO2)

: A newly developed sonogel-carbon electrode was prepared by coating it with a TiO2 sol-gel and heated at 500 ºC. The electrochemical response of the newly developed sonogel-carbon electrode modified with TiO2 was compared to that of an unmodified sonogel- carbon electrode. The modified electrode showed marked enhanced detection of catechol in the prescence of ascorbic acid. Also the sonogel-carbon electrode modified with TiO2 stability was compared to an electrochemically prepared conducting poly(3-methylthiophene) electrode in the detection of catechol over 25 scans. The sonogel-carbon electrode modified with TiO2 was more stable over repetitive scans. This new modified titanium oxide electrode surface could be used in several chemical sensor applications of environmental and biological interest.

Study of the influence of the graphite powder particle size on the structure of the Sonogel-Carbon materials

In this paper, the influence of carbon particles size on structure and on electrochemical and physical properties of the Sonogel-Carbon electrodes, with respect to Sonogel materials without graphite, have been studied. The materials have been characterized electrochemical and structurally; several Sonogel-Carbon materials were synthesized using different types of graphite powder as massive modifiers, adding in some cases other modifiers, such as octadecyl (C18) and polyethyleneglycol (PEG). Differential pulse voltammetry and cyclic voltammetry were the voltammetric techniques employed to evaluate the electrochemical behaviour; Scanning Electron Microscopy, Energy Dispersive Spectroscopy and Infrared Spectroscopy were the techniques employed to realize the superficial/structural characterization of the materials. The results obtained in both studies were very useful to explain the structure of the Sonogel-Carbon materials. Furthermore, they allowed to conclude that electrodes based on RW-B and UF graphites show very similar electrochemical behaviours and internal structures.

Voltammetric determination of trace mercury at a sonogel–carbon electrode modified with poly-3-methylthiophene

The sonogel–carbon electrode is a new class of sol–gel electrode that exhibit favourable mechanics and electrics properties to be used as electrochemical sensor. In this paper, a modified sonogel–carbon electrode is proposed to determine mercury at trace levels. The modified electrode is obtained by electropolymerization of 3-methylthiophene on the surface of a bare sonogel–carbon electrode. This electrode shows high selectivity and sensitivity and linear response towards Hg(II), with a detection limit of 1.4 × 10 −3 mg l −1. The electrode is reusable by a simple chemical cleaning procedure. No deterioration was observed in the electrode response during at least 1 week of successive measurements.

Study of the Responses of a Sonogel-Carbon Electrode Towards Phenolic Compounds

The electrochemical behavior of a sonogel-carbon electrode towards nine phenolic compounds (chloro-, nitro- and alkyl-phenols) was studied; one of them (4-chloro-3-methylphenol) was used to evaluate characteristics of the electrode, such as accumulation and cleaning procedure of the electrode surface, reproducibility of the measurements, and influence of time from fabrication on electrochemical response. A polyethyleneglycol-modified sonogel-carbon electrode was found to improve the electrochemical response towards the analyte. A linear relationship between peak height and concentration in the range 0.005–0.5 mg L−1 was obtained, with a detection limit of 2.8 μg L−1. The studies of electrochemical parameters, as well as interferences, are also included.