Electroanalytical Response Research Articles

Novel TiO2 nanoparticle-based sensor for xanthate quantification in mineral flotation samples

A voltammetric method for xanthate quantification was developed by fabricating a new electrode based on TiO2 nanoparticles (TiO2 NPs). The nanomaterial in the anatase phase was synthesized by a simple sol-gel method followed by a thermal treatment (9 h at 500 °C). The nanoparticles have a spheroidal morphology with an average size of 20.61 ± 6.01 nm. The band gap energy (3.7 eV) was determined by means of UV–visible spectroscopy from the absorption band at 335 nm. The TiO2 based sensor was employed as working electrode (electroactive area: 0.02248 cm2) in a cyclic voltammetry study, and a greater peak current was observed for the electrooxidation of isopropyl xanthate at pH 10 as compared to the unmodified electrode. The electrode optimization showed that the percentage of TiO2 and the amount of mineral oil in the electrode have a significant influence on the electrochemical response, with 18.4 % of TiO2 NPs, 0.74 mL of mineral oil, and 18 h of electrode rest before the first use as optimal conditions. In the polarization studies, the charge transfer reaction occurred through a lower overpotential with respect to the open circuit potential. The exchange current density was three times higher for the modified electrode. Electrochemical impedance spectroscopy indicated the detection of xanthate with lower charge transfer resistance than when the unmodified electrode was used. The electrochemical sensor allows the quantification of xanthate from 5 μmol/L to 10 mmol/L by cyclic voltammetry and the square wave technique. For the cyclic voltammetry calibration, the limits of detection and quantification were 40.6 μmol/L and 135 μmol/L, respectively. The limit of detection by square wave voltammetry was 2.4 μmol/L, and the limit of quantification was 7.9 μmol/L. The repeatability of the method showed a relative dispersion of 3.1 % at 0.51 mmol/L. The electroanalytical response of the sensor was reproducible up to 30 days. The recoveries of xanthate in real flotation samples were 91.9 % and 94.6 % for concentrations of 0.55 and 1.1 mmol/L, respectively. No statistically significant differences were found between the quantification using the sensor and the UV spectrophotometric method. Dicresyl dithiophosphate showed statistically significant interference with the xanthate oxidation signal.

Highly Sensitive and Selective Electrochemical Monitoring of Antibiotic Ciprofloxacin Using Electrochemically Exfoliated@reduced Graphene Oxide/Clay Graphite Electrode

This research work covers the development of a green, sensitive, selective, and simple electrochemical strategy for the detection of ciprofloxacin (Cipro) in biological fluids, wastewater, and drug samples. Herein the carbon paste electrode was modified using reduced graphene oxide and clay nanocomposite based on the electrochemical reduction of GO (ErGO-Clay@CPE). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were used for the electro-characterization of ErGO-Clay@CPE, and the results supported that the ErGO-Clay improved the electrode’s conductivity and surface area. Moreover, the electrochemical performance was inspected by differential pulse voltammetry (DPV) and chronoamperometry in phosphate buffer (PB, pH = 6). The data demonstrated a magnificent sensitivity of ErGO-Clay@CPE regarding Cipro. Under the optimized operating conditions, the electro-analytical response was linearly related to the Cipro concentration in the range of 0.03–2.0–50.0 μM with a lower detection limit (DL = 3 × SDblank/P) and sensitivity of 2.24 nM and 96.28 μA μM−1 cm−2, respectively. Furthermore, the ErGO-Clay@CPE was applied to identify the Cipro in drugs, wastewater, and urine samples, with satisfied recoveries.

Ultra-sensitive detection of methylparathion using palladium nanoparticles embedded reduced graphene oxide redox nanoreactors

The environment-friendly and energy-efficient monodispersed carbon-based nanosystems for environment monitoring are always in colossal demand. The present work has come up with a novel reverse microemulsification route which is inherently safer, energy-efficient and toxicant free approach for synthesis of monodisperse palladium nanoparticles embedded RGO based nanoreactors (Pd@NrGO/GCE). In present system, Pd@NrGO/GCE are acting as nanoreactors by providing large surface areas for electrocatalysis of methylparathion and allowing the study of redox attributes at faster rates. The successful characterization was done using X-ray diffraction studies, Raman spectroscopy, field emission scanning electron microscopy, small angle X-ray scattering and high resolution transmission electron microscopy analysis. The electroanalytical response in the square wave anodic stripping voltammetry has been generated by the adsorption of MP followed by subsequent redox catalysis by Pd@NrGO/GCE. The homogeneous film fabrication was enabled by smooth spherical nanostructures imparting higher surface areas with small particle size. The sensor performance towards oxidation of MP poses wide linearity and a low limit of detection of 1.067 ngml−1 with successful application to real time analysis.

In situ or Ex situ Synthesis for Electrochemical Detection of Hydrogen Peroxide-An Evaluation of Co2SnO4/RGO Nanohybrids.

Nowadays, there is no doubt about the high electrocatalytic efficiency that is obtained when using hybrid materials between carbonaceous nanomaterials and transition metal oxides. However, the method to prepare them may involve differences in the observed analytical responses, making it necessary to evaluate them for each new material. The goal of this work was to obtain for the first time Co2SnO4 (CSO)/RGO nanohybrids via in situ and ex situ methods and to evaluate their performance in the amperometric detection of hydrogen peroxide. The electroanalytical response was evaluated in NaOH pH 12 solution using detection potentials of -0.400 V or 0.300 V for the reduction or oxidation of H2O2. The results show that for CSO there were no differences between the nanohybrids either by oxidation or by reduction, unlike what we previously observed with cobalt titanate hybrids, in which the in situ nanohybrid clearly had the best performance. On the other hand, no influence in the study of interferents and more stable signals were obtained when the reduction mode was used. In conclusion, for detecting hydrogen peroxide, any of the nanohybrids studied, i.e., in situ or ex situ, are suitable to be used, and more efficiency is obtained using the reduction mode.

Adjusting the Connection Length of Additively Manufactured Electrodes Changes the Electrochemical and Electroanalytical Performance.

Changing the connection length of an additively manufactured electrode (AME) has a significant impact on the electrochemical and electroanalytical response of the system. In the literature, many electrochemical platforms have been produced using additive manufacturing with great variations in how the AME itself is described. It is seen that when measuring the near-ideal outer-sphere redox probe hexaamineruthenium (III) chloride (RuHex), decreasing the AME connection length enhances the heterogeneous electrochemical transfer (HET) rate constant (k0) for the system. At slow scan rates, there is a clear change in the peak-to-peak separation (ΔEp) observed in the RuHex voltammograms, with the ΔEp shifting from 118 ± 5 mV to 291 ± 27 mV for the 10 and 100 mm electrodes, respectively. For the electroanalytical determination of dopamine, no significant difference is noticed at low concentrations between 10- and 100-mm connection length AMEs. However, at concentrations of 1 mM dopamine, the peak oxidation is shifted to significantly higher potentials as the AME connection length is increased, with a shift of 150 mV measured. It is recommended that in future work, all AME dimensions, not just the working electrode head size, is reported along with the resistance measured through electrochemical impedance spectroscopy to allow for appropriate comparisons with other reports in the literature. To produce the best additively manufactured electrochemical systems in the future, researchers should endeavor to use the shortest AME connection lengths that are viable for their designs.

A rapid in vitro electrochemical screening of extracellular matrix of Saccharomyces cerevisiae by palladium nanoparticles-modified electrodes

Herein, a rapid electrochemical screening of yeasts (Saccharomyces cerevisiae) in vitro mode depending on their optical density, cultivation time and growth medium used was conducted in 3 min by palladium nanoparticles (Pd-NPs)-modified electrodes. Pd-NPs-modified electrodes operated in cyclic voltammetry mode at low scan rates, i.e. 5–20 mV/s supported a low oxidative process in the yeast extracellular matrix. The electrochemical screening relied on an efficient electrooxidation of secondary metabolites, i.e. organohydrazines formed in the extracellular medium as a result of microbial activity of yeast cells.More importantly, during the study the impact of fundamental parameters, viz. type of the matrix and pH on electroanalytical response of Pd-NPs-based electrodes in real fermentation medium was investigated in detail. The efficiency of the proposed in vitro electrochemical screening of yeast extracellular matrix was not affected by pH of the samples or composition of the multicomponent medium, but more likely exclusively depended on the presence of organohydrazines. The potential of this electroanalytical approach towards profiling of the extracellular matrix of Saccharomyces cerevisiae was compared with results obtained by gas chromatography mass-spectrometry (GC–MS) and genetically encoded biosensor (ro-GFP2) assays.

Molecularly imprinted voltammetric sensor sensibilized by nitrogen-vacancy graphitized carbon nitride and Ag-MWCNTs towards the detection of acetaminophen.

The overdose of acetaminophen (AP) can cause serious acute liver injury even the irreversible liver necrosis. The quantitative detection of AP is of great significance not only for clinical applications but also for the quantity control of its pharmaceutical formulations. In this paper, a sensitive molecularly imprinted voltammetric sensor towards AP was constructed based on synergistic enhancement of nitrogen-vacancy graphitized carbon nitride (NV-g-C3 N4 ) and carboxylated MWCNTs loaded with silver nanoparticles (Ag-MWCNTs). The powder X-Ray diffraction spectrum, field emission scanning and transmission electron microscopes, cyclic voltammetry (CV), and electrochemical impedance spectrum were used to characterize the composites. The results show that NV-g-C3 N4 and Ag-MWCNTs closely embedded each other, forming loose porous hybrid structure by hydrogen bond. The prepared sensor molecular imprinting polymer (MIP)/C3 N4 /Ag-CNTs/GCE shows a strong synergistic enhancement of electroanalytical response by CV and differential pulse voltammetry (DPV) tests when compared with NV-g-C3 N4 /GCE, Ag-CNTs/GCE, and MIP/GCE. Through the optimization of the ratio of monomer and template, electropolymerization cycle, elution cycle, incubation time, and pH, linear ranges of 0.007-5 and 5-100 μM were found with the limit of detection of 2.33 nM by DPV. Moreover, its selectivity towards AP was satisfied when compared with detection towards ascorbic acid, dopamine, and glucose. The recovery range of 96.3%-100.5% was obtained in the spiked human serum and urine samples with the SD below 3.0%. In addition, the prepared sensor shows great detecting robustness with good anti-interference, reproducibility, and stability.

Role of nanocellulose in tailoring electroanalytical performance of hybrid nanocellulose/multiwalled carbon nanotube electrodes

Nanocellulose has emerged as a promising green dispersant for carbon nanotubes (CNTs), and there is an increasing trend in developing nanocellulose/CNT hybrid materials for electrochemical detection of various small molecules. However, there have been very few comprehensive studies investigating the role of nanocellulosic material properties upon the electroanalytical performance of the resultant hybrid electrodes. In this work, we demonstrate the influence of both nanocellulose functionalization and geometry, utilizing sulfated cellulose nanocrystals, sulfated cellulose nanofibers, and TEMPO-oxidized cellulose nanofibers. Transmission electron microscopy tomography enables direct visualization of the effect of nanocellulosic materials on the hybrid architectures. High resolution X-ray absorption spectroscopy verifies that the chemical nature of CNTs in the different hybrids is unmodified. Electroanalytical performances of the different nanocellulose/CNT hybrid electrodes are critically evaluated using physiologically relevant biomolecules with different charge such as, dopamine (cationic), paracetamol (neutral), and uric acid (anionic). The hybrid electrode containing fibrillar nanocellulose geometry with a high degree of sulfate group functionalization provides the highest electroanalytical sensitivity and strongest enrichment towards all studied analytes. These results clearly demonstrate for the first time, the extent of tailorability upon the electroanalytical response of nanocellulose/CNT hybrid electrodes towards different biomolecules, offered simply by the choice of nanocellulosic materials.

Glycerol oxidation at Pd nanocatalysts obtained through spontaneous metal deposition on carbon substrates

Spontaneous deposition of Pd is carried out on five different carbon-based screen-printed electrodes (SPEs) in the absence of solute reductant species in the Pd ions solution. Pd nanoparticles (NPs) with mean sizes ranging between 11.2 and 17.9 nm and homogeneous distribution are obtained on the carbon supports. The NPs mean size and amount of available metal are found to depend on the type of the carbon SPE, i.e. carbon (C110), mesoporous carbon (MC), carbon nanofibers (CNF), single- or multi-walled carbon nanotubes (SWCNT or CNT). Overlapping and agglomerating particles are found only in the SWCNT case whereas for all other electrodes the individual NPs are well isolated. Glycerol oxidation is studied at the five types of Pd nanocatalysts and data for the mass activity are obtained for glycerol and KOH concentrations used in fuel cells applications. The data for the mass activity correlate with the electroactive surface area (EASA) of the metallic particles for three of the electrodes (C110, MC and CNF) whereas Pd NPs supported by multi walled CNTs show a very high mass activity not to be associated with increased EASA alone. In separate experiments the applicability of the Pd-carbon-based SPEs is studied in view of electroanalytical detection of glycerol. A stable electroanalytical response is found for the MC, CNT and CNF SPEs. The concentration dependence of the glycerol oxidation peak current is modeled by a Langmuir type function that allows for detection of glycerol in the 0.2 to 15 mmol/l concentration range. The ease of preparation of the Pd nanocatalysts and the use of disposable SPEs present a good prospect for practical applications.

Voltammetric Electrochemical Behavior of Carbon Paste Electrode Containing Intrinsic Silver for Determination of Cysteine

In this paper, the electrochemical behavior of cysteine is described, using carbon paste electrodes (CPEs) modified with ternary silver-copper sulfide containing intrinsic silver at two pH values (pH 3 and 5). Experiments have revealed that presence of cysteine has a large impact on the electrochemical behavior of modified CPEs. Observed phenomena take place in solution, as well as at the surface of the modified CPEs, and can be applied for electroanalytical purposes. Based on the electrochemical behavior observed in the examined system, differential pulse voltammetry (DPV) was selected as an electroanalytical method for determination of cysteine. The effects of the various parameters on the electroanalytical signal, such as the amount of electroactive material, electroanalytical parameters, pH etc., were investigated using differential pulse voltammograms. The results indicated that electrochemical signal characterized with well-defined cathodic peak at 0.055 V vs. Ag/AgCl (3 M) in acetic buffer solution at pH 5 can be used for indirect electrochemical determination of cysteine. The optimization procedure revealed that the most sensitive and stabile electrode was that containing 5% modifier. The DPV response of the electrode, in the presence of cysteine, showed two different linear concentration ranges of 0.1 to 2.5 μM, and 5.6 to 28 μM. The explanation of the origin of two linear ranges is proposed. The lower concentration range was characterized by remarkable sensitivity of the 11.78 μA μM−1, owing to the chosen indirect method of determination. The calculated limit of detection (LOD), as well as limit of quantification (LOQ) were 0.032 and 0.081 μM, respectively. The influence of interfering agents on the electroanalytical response was examined, and low or no interference on the DPVs was observed. The proposed method was validated and applied for the determination of cysteine in pharmaceutical preparations with satisfactory recoveries in the range of 97 to 101.7%.

Platinum nanoparticles loaded carbon black: reduced graphene oxide hybrid platforms for label-free electrochemical DNA and oxidative DNA damage sensing

• Rapid and effective synthesis of platinum nanoparticles on the carbon black:reduced graphene oxide hybrids were achieved. • Facile and efficient electrode modification was performed with the hybrids. • Characterization of the surfaces proved homogeneous and robust distribution of the structures. • Sensitive fsDNA detection was accomplished with a low detection limit. • DNA damage and protection monitoring were carried out successfully. Carbon black-based hybrid materials have attracted great attention in the design of electrochemical sensors due to their consistent electroanalytical properties. With this in mind, for the first time, we present the preparation of platinum nanoparticles loaded carbon black:reduced graphene oxide (PtNPs/CB:rGO) hybrid platforms for label-free electrochemical DNA and DNA damage sensing. Synthesis of different hybrids was performed via microwave-assisted reduction method for the impregnation of platinum nanoparticles efficiently. These materials were characterized with X-ray diffraction analysis (XRD), Raman spectroscopy, transmission emission spectroscopy (TEM) and subsequently they were used for pencil graphite electrode modification in order to improve the characteristics of the surface. Modified electrodes were firstly applied for fish sperm DNA (fsDNA) analysis. The effect of different ratios (wt.:wt. %) of CB and rGO was investigated and it was shown that the hybrid material with 50:50 ratio had better sensitivity with a low detection limit of 0.14 mg L −1 and a good linearity to fsDNA between 1 and 200 mg L −1 (n = 3) based on guanine (G) oxidation by using differential pulse voltammetry (DPV). In order to expand this comparison, PtNPs/CB and PtNPs/rGO modified electrodes were also incorporated. Furthermore, the electroanalytical response of the hybrid material modified electrode was investigated based on the oxidation of thymine (T). Later on, oxidative DNA damage detection in the presence of Cu(II)/H 2 O 2 reagents and protection studies in the presence of ascorbic acid were performed successfully by using electrochemical impedance spectroscopy (EIS). The study pointed out the remarkable reproducibility and sensitivity of the CB-based modification for nanoparticle decoration.

Voltammetric Determination of Diazepam on Antimony Film Screen- Printed Electrode in Pharmaceutical Formulations

Background: Diazepam belongs to the group of 1,4-benzodiapines. It is used for the treatment of anxiety, convulsions and as muscle relaxants. The presence of a 4,5-azomethine group enables its electrochemical detection. Introduction: A screen-printed electrode modified with antimony film was used for the determination of diazepam in pharmaceutical preparations Methods: Electrode modification was done by ex-situ deposition of antimony on a commercially available screen-printed electrode. Parameters affecting the electroanalytical response of the sensor, such as deposition potential, deposition time, and antimony concentration, were examined and optimized. The modified electrode showed enhanced electroactivity for diazepam reduction compared to the unmodified electrode. Under optimal conditions, linear sweep voltammetry was used for the determination of the analyte. Results: The sensor showed linear dependence in the range from 0.5 to 10 μmol/L, the correlation coefficient was 0.9992. The limit of detection was 0.33 μmol/L, corresponding limit of quantification was 1.08 μmol/L. Modification enabled determination of diazepam in the presence of oxygen. Conclusion: The modified electrode was used for the determination of diazepam in tablets. Results confirmed the applicability of the electrochemical sensor.

A 2D tungsten disulphide/diamond nanoparticles hybrid for an electrochemical sensor development towards the simultaneous determination of sunset yellow and quinoline yellow

We present the development of an electrochemical sensor towards the simultaneous analysis of a mixture of food additives: sunset yellow (SY) and quinoline yellow (QY) dyes. The sensor is based on the synergetic effect observed between diamond nanoparticles (DNPs) and WS2 nanosheets obtained by liquid exfoliation. The prepared TMDs were characterized using Raman spectroscopy, X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The AFM characterization showed isolated WS2 flakes with different lateral dimensions scattered over the flat background. The combination of WS2 and DNPs allows resolution of the oxidation signals of the analytes, which overlap working with the bare glassy carbon (GC) electrode. The best electroanalytical response was obtained with a sensor containing both nanomaterials deposited employing the drop-casting method in a sequential manner, a first layer of WS2 and a second layer of DNPs (GC/WS2/DNPs). Electrochemical impedance spectroscopy experiments showed that for the GC/WS2/DNPs system the charge transfer is clearly improved. Under optimized differential pulse voltammetry conditions, the GC/WS2/DNPs sensor allows the determination of SY at +100 mV and QY at +850 mV with detection limits of 0.086 and 3.4 μM respectively, with relative errors ≤ 8.40 % and a relative standard deviation ≤ 12.6 %. The proposed methodology was applied to the determination of SY and QY in commercial throat lozenge samples with very good recoveries on average: 93 %, for QY and 106 % for SY.

Green and facile solvent-free synthesis of NiTe2 nanocrystalline material applied to voltammetric determination of antioxidant morin

Nanocrystalline nickel ditelluride, NiTe2, has been prepared mechanochemically using ball milling in an inert atmosphere at room temperature, starting from Ni34Te66 powder mixtures. Structural and microstructural characterization of the Ni34Te66 alloy was performed by X-ray powder diffraction analysis and transmission electron microscopy. The formation of a trigonal NiTe2 phase (with P-3 m1 symmetry) occurs along with 3 h, and the pure-phase sample with average crystallite size of about 18 nm is achieved with 6 h of milling. The nanocrystalline samples show a paramagnetic behavior at 2 K, with a magnetic moment decreasing at room temperature. The Ni34Te66 alloy containing 18 nm nanocrystallites of NiTe2 was applied in the construction of carbon paste electrodes to the voltammectric determination of morin, a phenolic and antioxidant compound present in red wines generally considered to act as UV protectant and free-radical scavenger. The electroanalytical response is linear from 0.014–32.0 μmol L−1 with a limit of detection of 0.0133 μmol L‒1 and a recovery range of 101–120 % (n = 3). The proposed sensor NiTe2/CPE was successfully applied to the determination of morin in high, medium and low polyphenols content red wines such as Tannat, Cabernet Sauvignon and Pinot Noir.

A simple adsorptive chronopotentiometric stripping method for determination of vitamin B1 in pharmaceutical products

A new electroanalytical method for vitamin B1 determination, based on adsorptive chronopotentiometric stripping analysis and non-specific adsorption onto mercury film electrode, was developed and validated. Stripping chronopotentiograms showed a single well-defined oxidation wave corresponding to vitamin B1 at about − 0.43 V in citrate buffer pH 6.0. The most important experimental factors affecting the monitored electroanalytical response of vitamin B1 were investigated and optimised. Under the optimal experimental conditions, linear response of vitamin B1 was obtained in the concentration range of 5–50 mg dm−3, with the achieved limit of detection of 1.64 mg dm−3, and the limit of quantitation of 4.97 mg dm−3. A mean recovery of 97.1% and relative standard deviations of 3.75% were achieved. The developed electrochemical procedure was successfully applied for the determination of vitamin B1 in pharmaceutical products. The results of the proposed method were in good agreement with those obtained by parallel HPLC analyses, confirming an accuracy of the developed method.

Peroxide Electrochemical Sensor and Biosensor Based on Nanocomposite of TiO2 Nanoparticle/Multi-Walled Carbon Nanotube Modified Glassy Carbon Electrode.

A hydrogen peroxide (H2O2) sensor and biosensor based on modified multi-walled carbon nanotubes (CNTs) with titanium dioxide (TiO2) nanostructures was designed and evaluated. The construction of the sensor was performed using a glassy carbon (GC) modified electrode with a TiO2–CNT film and Prussian blue (PB) as an electrocalatyzer. The same sensor was also employed as the basis for H2O2 biosensor construction through further modification with horseradish peroxidase (HRP) immobilized at the TiO2–fCNT film. Functionalized CNTs (fCNTs) and modified TiO2–fCNTs were characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-Ray DifFraction (XRD), confirming the presence of anatase over the fCNTs. Depending on the surface charge, a solvent which optimizes the CNT dispersion was selected: dimethyl formamide (DMF) for fCNTs and sodium dodecylsulfate (SDS) for TiO2–fCNTs. Calculated values for the electron transfer rate constant (ks) were 0.027 s−1 at the PB–fCNT/GC modified electrode and 4.7 × 10−4 s−1 at the PB–TiO2/fCNT/GC electrode, suggesting that, at the PB–TiO2/fCNT/GC modified electrode, the electronic transfer was improved. According to these results, the PB–fCNT/GC electrode exhibited better Detection Limit (LD) and Quantification Limit (LQ) than the PB–TiO2/fCNT/GC electrode for H2O2. However, the PB film was very unstable at the potentials used. Therefore, the PB–TiO2/fCNT/GC modified electrode was considered the best for H2O2 detection in terms of operability. Cyclic Voltammetry (CV) behaviors of the HRP–TiO2/fCNT/GC modified electrodes before and after the chronoamperometric test for H2O2, suggest the high stability of the enzymatic electrode. In comparison with other HRP/fCNT-based electrochemical biosensors previously described in the literature, the HRP–fCNTs/GC modified electrode did not show an electroanalytical response toward H2O2.

The Role of Surface Chemistry in Impedimetric Aptasensing

Surface chemistry is a key parameter in the choice of proper materials for electrochemical detection. It has been previously shown that the presence of oxygen containing groups (OCGs) on the surface of graphene oxide (GO) can be both effective and detrimental. This poses a question when GO materials are used as electrochemical platforms for biosensing. In this work, we study how the surface chemistry of graphene oxide nanocolloids (GONCs) affects the impedimetric biosensing of ochratoxin A (OTA), in terms of immobilization of biorecognition element and detection step. OCGs on GONCs were tuned by applying increasing reduction potentials from 0.3 V to 1.2 V, resulting in GONC platforms with decreasing amounts of oxygen functionalities. It was discovered that the sensitivity of biosensing is correlated to the residual amount of OCGs on GO surface. For a more detailed investigation, three representative materials, namely unreduced GONCs, as well as GONCs reduced at potentials of 0.8 V and 1.2 V were chosen. Results were compared in terms of calibration sensitivity, selectivity and reproducibility of the impedimetric response. GONCs reduced at 1.2 V have shown the best electroanalytical response for the impedimetric detection of OTA. These findings are anticipated to contribute to the design of novel biosensors, whereby an optimized platform is employed for the immobilization of the biorecognition element.

Sensitive and cost effective disposable composite electrode based on graphite, nano-smectite and multiwall carbon nanotubes for the simultaneous trace level detection of ascorbic acid and acetylsalicylic acid in pharmaceuticals

In this study, we used nano-smectite (SMT) and multiwall carbon nanotube (MWCNT) as a recognition surface over the disposable pencil graphite electrode for the low-level detection of ascorbic acid (AA) and acetyl salicylic acid (ACA). Firstly, nano-semectit was obtained by the purification of natural bentonite clay. XRD patterns and Scanning electron microscopy (SEM) were employed to ensure the purity of the bentonite samples. Pencil graphite rodes were immersed into suspensions of SMT, MWCNT or the both.The surface morphology of the sensor was investigated by cyclic voltammery (CV), electrochemical impedance spectroscopy (EIS) and SEM techniques. The effect of pH, percentage composition of modifiers, immobilization time, accumulation time and accumulation potential was optimized for reaching the best electroanalytical response for AA and ACA. The sensor developed proved to give good recovery, notable electro-catalytic activity and appropriately distant signals for the simultaneous determination of the analytes. Common contaminates, uric acid, l-cysteine, dopamine, glucose, Na+, Cl- and citric acid were investigated for their interference effects. Uric acid, citric acid and dopamine were found to interfere to some extent. The electrode exhibited wide working ranges and a fairly satisfactory detection limit of 0.096 and 0.241 μM for AA and ACA, respectively. The electrode system proved to be practical for the analysis of pharmaceutical tablets and the recovery results are very satisfactory.

Influence of Electrostatic Interactions Induced via a Nanocomposite Film onto a Glassy Carbon Electrode Used for Highly Selective and Sensitive Ascorbic Acid Detection

A study of the electroanalytical detection of ascorbic acid (AH2) using a glassy carbon electrode (GCE) modified with nanocomposite films constructed with multiwall carbon nanotubes (MWCNT) or functionalized with carboxylic groups (fMWCNT) and gold nanoparticles (AuNP) stabilized with poly(diallyldimethylammonium chloride) (PDDA) or poly(vinylbenzyltrimethylammonium chloride) (pVBA) is presented. A larger loading of AuNP was reached using the fMWCNT instead of the MWCNT, increasing the oxidation current of AH2. However, the modified GCE with the higher electro-analytical response, e.g. GCE/fMWCNT/AuNP@PDDA, also exhibited the adsorption of the analyte onto the electrode, a process that was completely eliminated by attaching a DNA-bioinspired polyanion (P16−) onto the electrode surface. Consequently, the GCE/fMWCNT/AuNP@PDDA/P16− was able to electro-oxidize AH2 thru a diffusion-controlled process, with a sensitivity of (64.6 ± 0.5) nA μM-1 and a detection limit of (75 ± 5) nM at pH 7. The electroanalytical response of the modified GCE was extremely stable over 70 reusing cycles or during several days under certain storage conditions. Additionally, accurate quantification of AH2 was obtained in the presence of interfering compounds or in real complex matrixes. These results indicate the relevance of specific interactions between the electroactive surface and the analyte to obtain better electroanalytical responses.

Bioelectrochemical Systems as Technologies for Studying Drug Interactions Related to Cytochrome P450

The electrocatalytic activity of cytochrome P450 3A4 as the main enzyme of drug metabolism was studied. Cytochrome P450 electrodes allowed to register 10−11–10−12 mol of enzyme/electrode. The study has shown that the developed electrochemical systems based on cytochromes P450 are effective non-invasive models for the analysis of drug–drug interactions at the level of biotransformation of xenobiotics. The effect of clinically significant drug combinations on the activity of cytochrome P450 3A4 was studied. The electroanalytical response of cytochrome P450 3A4 enzyme was interpreted in terms of its impact on drug interference and assessment of heme protein activity. The results can be used for modulation of cytochrome P450 activity in case of comorbid patients with polypharmacy.