Electroanalytical Properties Research Articles

A functionalized renewable carbon-based surface for sensor development

This paper describes the surface modification of glassy carbon (GC) electrodes with a bamboo-based renewable carbon (RC) before and after an acid functionalization procedure with a sulfonitric solution (1:3 HNO3/H2SO4). The morphology and structural characterization indicate an increase of functional groups in the functionalized renewable carbon (RCF) surface. The enhanced electroanalytical properties of RC and RCF were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in two different setups, in the presence of the redox couple ([Fe(CN)6]3−/4−) and escitalopram (EST). The results revealed an enhancement for the electrochemical responses of both inorganic and organic compounds in the electrolyte. Therefore, the use of new carbon-based materials such as renewable carbon for development of electrochemical sensors brings a fresh approach to low-cost device development.

Мультисенсорные системы типа «электронный язык» для раздельного определения цефотаксима и цефазолина

Electroanalytical properties of unmodified and modified by polyaniline and by CuO nanoparticles solid-contact potentiometric sensors which are based on associates of tetradecylammonium with complex compounds of silver (I) with cephuroxime, cephotaxime and cephazoline Ag(β-lac)2TDA in solutions of corresponding antibiotics were studied. It was revealed that Ag(β-lac)2TDA –based sensors had no specificity to the basic ion but showed sensitivity to other cephalosporins. Taking into account the potentiometric selectivity coefficients and cross-sensitivity parameters of sensors based on different electrode-active components, their use for creating «electronic tongue» multi-sensor systems was shown. Arrays of low-selective potentiometric sensors were created for separate determination of cephazoline and cephotaxime in two-component model mixtures at concentration intervals of 2,5·10-4 – 0,01 М. The method of artificial neural networks was used for processing analytical signals (the relative error of determination not exceeding 13%).

Electrochemical/chemical synthesis of hydroxyapatite on glassy carbon electrode for electroanalytical determination of cysteine

Hydroxyapatite (HAp)-modified glassy carbon (HAp/GC) electrode was prepared through a two-step chemical reaction process: Hydrogenphosphate, firstly formed by electrodeposition at constant potential, was converted into HAp film via an acid-base reaction in the second step. The electrochemical behavior and potential of electroanalytical determination of cysteine using the HAp/GC electrode were studied using cyclic voltammetry and square wave anodic stripping voltammetry. The HAp/GC electrode exhibited great performance in determination of cysteine, owing to the high absorbability of HAp and electroanalytical properties of GC. Properties, such as absorbability of the optimized HAp film, were studied by electrochemical impedance spectroscopy and Fourier transform infrared spectroscopy and scanning electron microscopy with energy-dispersive spectroscopy analysis. Surface investigation confirmed that transport pathway has complex behavior. The presence of HAp film on the GC surface, as well as the presence of a CySH on the HAp film, is also confirmed and EIS results are in the agreement with FTIR results and indicate that CySH was adsorbed onto inner surface of the pores of HAp film, resulting in a change in impedance response. Both optimized procedure and analytical applicability of HAp/GC electrode were demonstrated by direct electrooxidation of cysteine. A linear response between 0.5 and 10 μmol dm−3 with estimated detection limit of 0.03 μmol dm−3 was obtained. A powerful electroanalytical tool was designed by simple modification of the GC electrode with biofunctional material.

Hybrid nanomaterial/catalase-modified electrode for hydrogen peroxide sensing

Conjugation of biomolecules with hybrid nanomaterials offer opportunities in the assembly of (bio)sensors of improved electrochemical performance. This work reports on developing a novel catalase-functionalized hybrid nanomaterial for the detection of hydrogen peroxide (H 2 O 2 ). The rationally assembled (bio)sensor consists of iron nanoparticles coated with graphene's layers supported on multi-walled carbon nanotubes (Fe@G-MWCNTs), deposited at a screen-printed carbon electrode surface and functionalized with catalase. Transmission electron microscopy, X-ray diffraction-, X-ray photoelectron- and thermogravimetric-analysis were used to characterize the physicochemical properties of the hybrid nanomaterial and better understand its electrochemical behavior. The (bio)sensor response was linear from 0.1 to 7 mM, with a sensitivity of 0.059 μA/(μM.cm 2 ), a limit of detection of 28.2 μM, a Michaelis-Menten constant of 17.9 mM, and high reproducibility. The graphene flakes acted as a protective layer that prevented the loss of the Fe nanoparticles activity, thus improving the long-term stability of the (bio)sensor. • A hybrid nanomaterial (Fe@G-MWCNTs) of enhanced electro-analytical properties with respect to the individual components alone. • The hybrid as a suitable nanoenvironment for the catalase´s direct electrochemistry, maintaining its bioactivity and stability. • Cat/Fe@G-MWCNTs/SPCE biosensor with catalytic activity towards H 2 O 2 reduction, with high sensitivity and stability.

Unique Host Matrix to Disperse Pd Nanoparticles for Electrochemical Sensing of Morin: Sustainable Engineering Approach.

Biomass-based carbon nanospheres derived from Mimosa pudica (commonly called "Touch-me-not") smeared on carbon fiber paper have been used as a host matrix for electrochemical deposition of palladium nanoparticles. The physicochemical characterization of modified electrodes was performed by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the electroanalytical properties of the electrodes. The modified electrode demostrated an excellent electrocatalytic activity for the oxidation of a flavonoid, morin, which gave a sensitive anodic peak at -0.30 V (vs SCE). An ultralow-level detection limit of 572 fM with a linear dynamic range of 37.50-130 pM was achieved. The proposed electrochemical sensor was successfully employed for the analysis of morin in mulberry and guava leaves. This is a sustainable engineering approach where a perfect unique host matrix is created using carbon nanospheres from biomass.

Graphene/ β‐ MnO 2 composites—synthesis and its electroanalytical properties study in the Mg storage battery

Graphene/β-MnO2 composites were synthesized via ultrasonication method, followed by calcination at 400°C for 4 hours. The structural properties of synthesized graphene and graphene/β-MnO2 composites were systematically studied using different instruments, such as XRD, FESEM, TEM, EDX, XPS and FT-IR spectroscopy. Furthermore, magnesium storage performance was scientifically studied using various electroanalytical characterizations like galvanostatic charge/discharge, electrochemical impedance spectra and cyclic voltammetry. The GNS/β-MnO2-20% composite displays the discharge capacity of 110 mAh/g within 60 cycles at a current density of 25 mA/g, which is an excellent rate capability, and magnesium storage performance around 100 cycles. There is a significant improvement in electrochemical properties of GNS/β-MnO2-20% composite materials as cathode for magnesium storage system due to the synergetic interaction between a pure β-MnO2 particle and graphene sheet.

Customized In Situ Functionalization of Nanodiamonds with Nanoparticles for Composite Carbon-Paste Electrodes

The incorporation of nanomaterials on (bio)sensors based on composite materials has led to important advances in the analytical chemistry field due to the extraordinary properties that these materials offer. Nanodiamonds (NDs) are a novel type of material that has raised much attention, as they have the possibility of being produced on a large scale by relatively inexpensive synthetic methodologies. Moreover, NDs can present some other interesting features, such as fluorescence, due to surface functionalization and proved biocompatibility, which makes them suitable for biomedical applications. In addition, NDs can be customized with metallic nanoparticles (NPs), such as silver or gold, in order to combine the features of both. Raw NDs were used as modifiers of sensors due to the electrocatalytic effect of the sp2 and oxygenated species present on their surface. The aim of this research work is evaluating the applicability of NDs modified with silver (Ag@NDs) and gold (Au@NDs) nanoparticles for the development of a suitable (bio)sensing platform. A complete morphological and electrochemical characterization as a function of the prepared nanocomposite composition was performed in order to improve the electroanalytical properties of the developed (bio)sensors. In the present work, the optimal composition for Au@NDs present on the nanocomposite matrix is 3.5% and the one for Ag@NDs is 1%. Good results were obtained in the evaluation of the optimal composition towards hydrogen peroxide and glucose as a model analyte using a (bio)sensor based on graphite-epoxy-Ag@NDs (17:82:1).

The influence of lateral flake size in graphene/graphite paste electrodes: an electroanalytical investigation

We report the electroanalytical properties of graphene and graphite paste electrodes comprising varying lateral flake sizes when applied for sensing relevant biomolecules and prominent drugs of abuse.

Modified solid-contact sensors for determination of cefuroxime and cefalexin in medicines and oral fluid

Cefuroxime, cefuroxime axetil and cefalexin are broad-spectrum pluripotential cephalosporin antibiotics. Their determination in various objects suggests using expensive spectroscopic, chromatographic, electrochemical equipment and organic solvents. Potentiometric sensors can provide rapid detection of cephalosporin antibiotics in a small sample volume without a preliminary sample preparation. The study is aimed at the developing of modified solid-contact potentiometric sensors for determination of cefuroxime and cefalexin in aqueous, biological media, and pharmaceuticals. The electroanalytical characteristics of unmodified and modified polyaniline and copper oxide nanoparticle sensors are evaluated. Tetradecylammonium(TDA) with a silver (I) – cefuroxime complex are used as the active membrane components, whereas polyaniline and copper oxide nanoparticles are used as modifiers. The main electroanalytic and operational characteristics of the studied sensors in aqueous solutions of antibiotics and against the background of oral fluid (LRP) are determined. The results of comparative evaluation of the electroanalytical properties of unmodified and modified solid-contact sensors in aqueous media of some â-lactam antibiotics and against the background of oral fluid are presented. The sensors based on Ag (Cefur)2TDA are characterized by a short response time: for modified polyaniline (PAN) and copper oxide nanoparticles within 5 – 10 sec, for unmodified — 10 – 20 sec. The linear range of the electrode functions for unmodified and modified sensors is 1 × 10–4 – 1 × 10–1 M, the detection limit is 7.4 × 10–5 M for unmodified and 6.3 × 10–5 M for modified sensors, respectively. The potential drift is 6 – 12 and 4 – 6 mV/day, service life is 1.5 and 2 months for unmodified and modified sensors, respectively. The modifiers stabilize the electrode potential, perform the function of the electron transfer mediator thus enhancing the electroanalytical characteristics of the sensors. The effect of the redox agents on the sensor properties is revealed: 1 × 10–3 – 1 × 10–4 MK 2Cr2O7 and FeCl3 solutions reduce the linearity intervals of the electrode functions, KI and Mohr’s salt do not affect the characteristics of the sensors in cefuroxime and cephalexin solutions. The coefficients of potentiometric selectivity of cefuroxime-selective sensors (modified with CuO nanoparticles) with respect to cefazolin, cefotaxime, and cefalexin are close to unity; Kijpot with respect to inorganic anions being part of the oral fluid (, Cl Br,I,HCO3 ,H PO 24 ,HPO4 2) are n × 10–2 – n × 10–3. This indicates the possibility of using sensors for detecting individual cephalosporin antibiotics or their total content in the presence of 100 – 1000 fold excesses of inorganic ions in medicinal and biological environments, small sample volumes, which is important when studying the pharmacokinetics of antibiotics and in determination of the maximum therapeutic dose when adjusting the treatment process.

A Fast and Simple Ozone‐mediated Method towards Highly Activated Screen Printed Carbon Electrodes as Versatile Electroanalytical Tools

AbstractA facile and effective electrochemical activation method of screen printed carbon electrodes (SPCEs) has been performed using ozone gas. Activated SPCEs showed relevant improvements in the electrochemical properties such as an impedance reduction and better electroanalytical outcomes. Such improved properties were attributed to the increase of the electroactive surface area and the functionalization of the electrode surface with carbon‐oxygen groups onto the carbonaceous ink surface. The optimized activation method consisted in the performance of a voltammetric cycle between −2 and 2 V at 10 mV s−1 in 0.1 M NaOH solution with constant ozone gas bubbling. This activation procedure takes 12 min, which allows its use routinely prior to the electrode modifications and electroanalytical measurements. The resulting activated SPCEs exhibited superior sensitivities towards hydrogen peroxide, acetaminophen, hydroquinone and dopamine. This methodology might be considered as a strategy to attain SPCEs with improved electroanalytical properties for multiple applications.

Sn-Containing Oxide Coatings: Formation, Composition, Electroanalytical and Catalytic Properties

Sn-containing oxide coatings were prepared via plasma electrolytic oxidation (PEO) of Ti plate in the electrolytes with [SnII-EDTA]2- complex anions or SnO2 particles in the anode and anodic-cathodic modes. The coatings formed in electrolyte with SnO2 particles stabilized by SAS contain SnO2 and Sn0. In the electrolyte with [Sn-EDTA]2- complex anions, the SnO2-containing coatings were formed in the anodic mode while Sn0-containing ones were obtained in the anodic-cathodic mode. SnO2-containing structures formed in the electrolytes with [Sn-EDTA]2- anions are shown to be active in catalytic oxidation of CO into CO2 at temperatures above 350 °C. They can be the basis for the preparation of both carriers of catalytically active compounds and catalysts for redox reactions. Potentiometric tests showed that the Sn-containing PEO layers on titanium exhibit the most characteristic pH function for the metal oxide electrodes in the direct potentiometry and acid-base titration.

Electrical Impedance Spectroscopy and Its Application in the Study of Electrochemical Sensors

Electrochemical methods are widely used in characterisation of catalytic properties and analytical application of the electrode materials. Study of electrical impedance spectra in electrochemistry, electrochemical impedance spectroscopy (EIS), is a technique frequently used as a supplementary method in the study of electrical properties of electrochemical sensors. However, the interpretation of the EIS results requires more complex knowledge about the electrochemical process, for instance the mechanism of the reaction, morphology and characterization of the electrode material [1]. Among various electrochemical sensors, the glucose ones represent majority of the sensors industry and cyclic voltammetry, chronoamperometry and EIS are used for complex studies of their electrochemical properties. Currently, the scientific community makes an effort to overcome the drawbacks of commercial glucose sensors and to develop nonenzymatic kinds based on the direct oxidation of glucose on the electrodes. Various electrode materials were used to achieve specific electroanalytical properties, such as low limit of detection, wide linear concentration range, sensitivity, and reproducibility [2]. Gold and titanium dioxide represent two different types of materials with diverse electrical properties. Gold as an electrode material displays great conductivity and electrocatalytical activity toward the glucose oxidation. As a transition metal, it displays an ability to attain multiple oxidation states and to absorb electroactive species. Possibility to detect glucose in neutral media is the great advantage because it makes predisposition for development of the continuous glucose sensor. Gold also displays wide linear concentration range and good reproducibility. Titanium dioxide is a multifunctional material which due to its semiconductive nature got an application in electronics and electrochemistry. TiO2 nanotubes are widely used in energy generation, accumulation and saving. In case of electrochemical sensors TiO2 nanotubes are suitable as a substrate because of its great surface area [3]. Electrochemical impedance spectroscopy was used to study the electrochemical properties of the gold and titanium dioxide as potential electrode materials for glucose determination. Even if gold and TiO2 display different electrical properties and mechanisms of interaction with glucose, the EIS measurements display similar results. For the gold electrodes the current response increases linearly with the glucose concentration. Process of glucose oxidation begins with an adsorption of the molecule on the gold surface followed by electrochemical oxidation. In the case of titanium dioxide, the current response decreases in the presence of glucose in comparison with cyclic voltammogram of the blank sample. Current response decrease is probably connected with the formation of the covalent bond between glucose and TiO2. In this study EIS enables the usage of different (in principle) interaction mechanisms between the electroactive material surface and glucose for the similar purpose – detection and its quantitative determination. Acknowledgement: This work was supported by the projects VEGA 1/0074/17 of the Slovak Scientific Grant Agency, APVV-16-0029 of the Slovak Research and Development Agency, VVGS-PF-2018-794 and VVGS-PF-2018-795 of Pavol Jozef Šafárik University in Košice, Slovakia.

Microneedle array sensors based on carbon nanoparticle composites: interfacial chemistry and electroanalytical properties

Conductive microneedle patches consisting of carbon nanoparticles embedded in a polystyrene matrix have been prepared using micro-moulding techniques. The interfacial properties of the structures before and after electrochemical etching have been characterised using X-ray photoelectron spectroscopy and contact angle. Anodisation of the needles leads to a significant increase in oxygen functionality and is shown to dramatically improve the electroanalytical capabilities of the microneedle array. The detection of uric acid in horse blood was used as a model system through which to assess the performance of the system. The composite approach is shown to lead to viable carbon-based sensors and can offer a rapid prototype option for the development of tailored microneedle systems.

Extended coverage of screen-printed graphite electrodes by spark discharge produced gold nanoparticles with a 3D positioning device. Assessment of sparking voltage-time characteristics to develop sensors with advanced electrocatalytic properties

Graphite screen-printed electrodes (SPEs) were modified with gold nanoparticles (AuNPs) produced by electric spark discharge between the SPE and a gold-silicon eutectic alloy (eAu/Si) tip electrode, under atmospheric conditions at 1.2 kV DC using a fully automated procedure. The automation was based on a 3D positioning device, which allowed to precisely adjust the sparking distance and to achieve regular spacing of a predetermined number of sparks across the surface of SPEs (d = 3 mm) by controlling the movement of the eAu/Si tip. Moreover, the effect of voltage-time characteristics of the produced discharges on the morphological and electroanalytical properties of the sparked-modified SPEs was investigated by setting the values of capacitors in the high voltage multiplier cascade, and at the power supply output. It is shown that under specific variables the underlying carbon layer is not appreciably damaged by the spark discharges and does not contribute to electrochemical responses of sparked SPEs, i.e., the active electrode surface has been entirely covered by AuNPs. Sparked surfaces were extensively characterized by scanning electron microscopy and various electrochemical techniques, while the electroanalytical utility of eAu/Si-sparked SPE was investigated with ascorbic acid as a pilot analyte. Advanced electrocatalytic activity is documented by an extreme shift of ascorbate oxidation overpotential (Ep = 89 mV at eAu/Si-sparked SPE) with respect to both bare SPE (Ep = 503 mV) and bulk gold electrode (Ep = 358 mV). Simultaneous differential pulse voltammetric sensing of ascorbic and uric acids in human urine is also demonstrated.

Synthesis and characterization of manganese diselenide nanoparticles (MnSeNPs): Determination of capsaicin by using MnSeNP-modified glassy carbon electrode.

A new type of manganese diselenide nanoparticles (MnSeNPs) was synthesized by using a hydrothermal method. Their surface morphology, crystallinity and elemental distribution were characterized by using transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy which scrutinize the formation of the NPs. The NPs were coated on a glassy carbon electrode (GCE), and electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry were applied to study the electroanalytical properties towards the oxidation of the food additive capsaicin. The modified GCE displays lower charge transfer resistance (R ct = 29.52Ω), a larger active surface area (0.089cm2/g, and more efficient electrochemical oxidation of capsaicin compared to a MnS2/GCE and a bare GCE. The oxidation peak potential is 0.43V (vs. Ag/AgCl) which is lower than that of previously reported GCEs. The sensor has a detection limit as low as 0.05μM and an electrochemical sensitivity of 2.41μAμM-1cm-2. The method was applied to the determination of capsaicin in pepper samples. Graphical abstract Electrochemical determination of capsaicin in pepper extract by using MnSeNPs modified electrode.

Electrified Soft Interface as a Selective Sensor for Cocaine Detection in Street Samples.

A straightforward, direct, and selective method is presented for electrochemical cocaine identification in street samples. The sensing mechanism is based on a simple ion transfer reaction across the polarized liquid–liquid interface. The interfacial behavior of a number of cutting agents is also reported. Interfacial miniaturization has led to improved electroanalytical properties of the liquid–liquid interface based sensor as compared with the macroscopic analogue. The reported method holds great potential to replace colorimetric tests with poor selectivity for on-site street sample analysis.

Graphene oxide activation with a constant magnetic field

The effect of constant magnetic field strength on activation of sensors modified with graphene oxide monolayers was investigated. The use of constant magnetic field resulted in improved electroanalytical properties of the sensors. It was proven that level of GO activation is clearly related to constant magnetic field strength. Moreover, it was demonstrated that observed phenomenon is stable in time.

Ultrasensitive Amperometric Biosensing of Polyphenols Using Horseradish Peroxidase Immobilized in a Laponite/Au/DNA-Bioinspired Polycation Nanocomposite

An ultrasensitive electrochemical biosensor for the determination of hydroquinone (HQ) and chlorogenic acid (CGA) has been prepared by horseradish peroxidase (HRP) immobilization onto nanohydrogels made of laponite, gold nanoparticles (AuNP) and a vinylbenzyltriethylammonium polycation copolymerized with vinylbenzylthymine groups. The structure and active site of the enzyme were not modified upon immobilization, as determined by UV-Vis and FTIR spectroscopies. The biosensor showed remarkable electroanalytical properties for detection of HQ and CGA, e.g. linear stationary current up to 120 μM and 4.2 μM, limit of detection (LOD) of 1.6 ± 0.2 nM and 2.7 ± 0.1 nM for CGA, and sensitivities of 218 ± 4 μA.mM−1 and 132 ± 4 μA.mM−1, respectively. The electroanalytical capabilities of the biosensor was successfully tested in the quantification of the total polyphenol content in green coffee and yerba mate beverages, yielding equivalent results than those obtained with the classical Folin-Ciocalteu method. Nonetheless, our biosensor showed remarkable advantages due to its ultra-sensitivity, together with smaller sample volumes and shorter detection times required, improving its analytical application.

Design of titanium nitride- and wolfram carbide-doped RGO/GC electrodes for determination of gallic acid

In the present paper, the electrochemical behavior and the properties of two modified glassy carbon (GC) electrodes used for quantification of gallic acid in sweet wines were compared. A comparative study was conducted between titanium nitride- or wolfram carbide-doped reduced graphene oxide, labeled as TNrGO and WCrGO, respectively, modified GC electrodes, which are promising composite nanomaterials for electroanalytical applications. For the first time, WCrGO was synthesized and its electroanalytical properties compared with those of TNrGO. Results showed that the proposed materials exhibited enhanced characteristics, e.g., low limits of detection (1.1 μM and 3.1 μM for TNrGO and WCrGO, respectively), wide linear ranges (for TNrGO 4.5–76 μM and for WCrGO 10–100 μM), low adsorption, and low background current, which make them promising candidates for electrochemical sensing applications.

Regulation of the Electroanalytical Performance of Ultrathin Titanium Dioxide Nanosheets toward Lead Ions by Non-Metal Doping.

Three non-metallic elements, sulfur, fluorine, and iodine, were used to dope the ultrathin two-dimensional TiO2 nanosheets, which would regulate their electroanalytical properties toward heavy metal ions. Among these doped materials, fluorine-doped TiO2 nanosheets shows the highest electrochemical sensitivity and a superior detection limit toward Pb(II) when the doping concentration is 10%. When compared with the bare TiO2 nanosheets, the sensitivity increased by 102%, and the detection limit decreased by 36.4%. Through combining further electrochemical experiments and density-functional theory calculations, the enhanced electrochemical performance stemming from element doping was then investigated in detail. The theoretical calculation demonstrated that fluorine doping could greatly increase the adsorption energy of Pb(II) on the TiO2 nanosheets and enhance their loading capacity. Both cyclic voltammetric and electrical impedance spectroscopy analysis indicated the enhanced electron transfer rate on the electrode modified by fluorine-doped TiO2 nanosheets. Further measurement on the desorption performance showed the better stripping response of Pb(II) on the electrode with TiO2 nanosheets after fluorine doping, which suggests that fluorine doping is beneficial for Pb(II) diffuse onto the electrode surface for the reduction and stripping reaction. Therefore, the element doping of two-dimensional TiO2 nanosheets provides a facile method to extend the electronic materials toward detection of heavy metal ions in the environment.