Showing papers in "Electroanalysis in 2007"

Label-Free Impedance Biosensors: Opportunities and Challenges.

Abstract: Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.

Ion-Selective Electrode Potentiometry in Environmental Analysis

Abstract: This review will illustrate how it is possible to develop ion-selective electrode (ISE) methodologies that meet the stringent requirements (i.e., high selectivities and very low detection limits) for the analysis of important analytes in the environment, and will present a variety of examples on the application of ISEs in environmental analysis. Despite the experimental biases that have limited the analytical performance of ISEs through apparently high detection limits and modest selectivities, there has been a plethora of research in the application of ISEs in the monitoring of environmentally important trace metals and anions in natural waters and soils. Most popular has been the analysis of free metals in natural waters, as this parameter is known to be a master variable in the uptake and toxicology of trace metals on aquatic biota reflecting the bioavailability of trace metals in the environment. Furthermore, as copper is a major trace metal in coastal waters due to its extensive use in antifouling paints on sea vessels and structures, there are many reports in the literature on the use of the copper ISE in assays of either free copper or the copper complexing capacity of natural waters and soil peats. Moreover, there have been a variety of studies showing a strong correlation between free copper levels and the toxicity of copper on a variety of marine and fresh water organisms. Nevertheless, there are numerous reports in the literature that have used ISEs to monitor important anions such as fluoride, phosphate, sulfate, nitrate, nitrite, chloride, cyanide, etc., as well as other important cations such as ammonium and chromium(VI) in waste and natural waters. In conclusion, this review will present new and interesting perspectives on the application of ISEs in environmental analysis using approaches such as real-time remote monitoring of water quality, shipboard monitoring of environmentally important analytes using flow analysis instrumentation, the use of robust all-solid-state ISEs in submersible instruments for long-term deployment in the field, and innovative analytical approaches such as backside calibration and switchtrodes that avoid standard addition analysis and the concomitant perturbation in analyte speciation in natural samples.

Electrochemical Sensing of Explosives

Abstract: This article reviews recent advances in electrochemical sensing and detection of explosive substances. Escalating threats of terrorist activities and growing environmental concerns have generated major demands for innovative field-deployable tools for detecting explosives in a fast, sensitive, reliable and simple manner. Field detection of explosive substances requires that a powerful analytical performance be coupled to miniaturized low-cost instrumentation. Electrochemical devices offer attractive opportunities for addressing the growing explosive sensing needs. The advantages of electrochemical systems include high sensitivity and selectivity, speed, a wide linear range, compatibility with modern microfabrication techniques, minimal space and power requirements, and low-cost instrumentation. The inherent electroactivity of nitroaromatic, nitramine and nitroester compounds makes them ideal candidates for electrochemical detection. Recent activity in various laboratories has led to the development of disposable sensor strips, novel electrode materials, submersible remote sensors, and electrochemical detectors for microchip (‘Lab-on-Chip’) devices for on-site electrochemical detection of explosive substances. The attractive behavior of these electrochemical monitoring systems makes them very promising for addressing major security and environmental problems.

Micro- and Nano- Magnetic Particles for Applications in Biosensing

Abstract: This article reviews the development of electrochemical biosensors, incorporating magnetic particles, for detecting biomolecules (nucleic acids and proteins) and cells. Magnetic particles (MPs) of micro- and nanoscale, mimicking the size of molecules in nature, possess interesting characteristics that facilitate the purification and detection of biomolecules in a wide range of samples. In particular, the high surface area and the paramagnetic or superparamagnetic properties of these tiny particles provide an attractive technology platform for the design of electrochemical biosensors. Examples of electrochemistry-based approaches to achieve the separation and detection of bioentities utilizing MPs are described. Emphasis is placed on the strategies to incorporate the electrochemical labels to the MPs and the methods to achieve the dual function of electrochemical detection and magnetic separation. The protocols to make MPs as labels in biological sensors are also discussed.

Tailoring Zinc Oxide Nanowires for High Performance Amperometric Glucose Sensor

Abstract: ZnO nanowire was tailored both physically and chemically to immobilize the enzyme glucose oxidase (GOD) for construction of a glucose sensor with high performance, which was ascribed to its high specific surface area and high isoelectric point value for efficient immobilization of high concentration of acidic enzymes and the mediating effect by the redox reaction of ZnO nanowires. The apparent Michaelis constants Jmax, and KM were adjusted in a large scope by tailoring the thickness of the GOD/ZnO nanowire layer and the enzyme load in the nanowired network. Thus, a variety of linear region, sensitivities and reaction rates of the sensor could be easily achieved. Moreover, the glucose sensor showed long term stability with the incorporation of the inorganic zinc oxide nanowire.

Electrochemical Sensing of DNA Using Gold Nanoparticles

Abstract: The electrochemical properties of gold nanoparticles (AuNPs) have led to their widespread use as DNA labels. This fact has improved the design strategies for the electrochemical detection of DNA through hybridization event monitoring. The reported DNA hybridization detection modes are based on either AuNP detection after dissolving or the direct detection of the AuNP/DNA conjugates anchored onto the genosensor surface. Various enhancement strategies have been reported so as to improve the detection limit. Most are based on catalytic deposition of silver onto AuNP. Other strategies based on the use of AuNPs as carrier/amplifier of other labels will be also revised. The developed techniques are characterized by sensitivities and specificities that enable further applications of the developed DNA sensors in several fields.

Single Polypyrrole Nanowire Ammonia Gas Sensor

Abstract: We report the synthesis, electrical characterization and ammonia gas sensing with single nanowire of conducting polypyrrole. Three hundred nanometer in diameter and 50 to 60 mm long polypyrrole nanowires were synthesized by chemical polymerization inside SiO2 coated alumina membranes. Temperature dependent electrical resistance studies established that the chemically synthesized nanowires were more ordered compared to electrochemically synthesized nanowires. We further demonstrated that gas sensors based on single polypyrrole nanowire exhibited good sensitivity towards ammonia, and provided a reliable detection at concentration as low as approximately 40 ppm.

Nontraditional Electrode Materials in Environmental Analysis of Biologically Active Organic Compounds

Abstract: This review describes recent results regarding voltammetric and amperometric determination of submicromolar concentrations of various environmentally important biologically active organic substances using nontraditional types of electrodes either in batch analysis or in flow liquid systems (especially HPLC or FIA with electrochemical detection). Attention is paid to solid amalgam electrodes (environmentally friendly alternatives to mercury electrodes), to carbon paste electrodes with easily renewable surface, to boron doped diamond film electrodes with very low noise and broad potential window, and to inexpensive solid composite electrodes with high signal-to-noise ratio, compatibility with organic solvents and easy mechanical or electrochemical pretreatment. The review concentrates on our own results in the context of the general development in the filed.

Direct Electrochemical Sensing and Detection of Natural Antioxidants and Antioxidant Capacity in Vitro Systems

Abstract: This review highlights the role of electrochemical approaches in the sensing of antioxidants and their antioxidant capacity with especial attention to the analytical possibilities of electrochemistry in the direct evaluation of antioxidant capacity exhibited by food and biological samples due to the termed dietary, natural or biological antioxidants (mainly polyphenols, and vitamins C and E). The analytical potency of the electrochemistry is comprehensively stated and the selected results found in the literature are summarized and discussed critically. The main electrochemical approaches used have been cyclic voltammetry (CV) and flow injection analysis with amperometric detection (FIA-ED). In addition, miniaturization is going to break new frontiers in the evaluation of antioxidant activity.

Nanoparticle‐Based Electrochemical Bioassays of Proteins

Abstract: This article reviews a variety of new nanoparticle/biomolecule assemblies for advanced electrical detection of proteins. Effective methods for the reliable and trace measurements of proteins are highly desired for facilitating the diagnosis of disease states and improving drug discovery. Ultrasensitive monitoring of biomolecular interactions of proteins is particularly challenging owing to the absence of PCR-like amplification protocols and their greater nonspecific binding to solid supports compared to oligonucleotides. Recent activity has led to innovative and powerful nanoparticle-based immunoassays and aptamer bioassays of proteins based on a variety of electrochemical detection schemes. The enormous signal enhancement associated with the use of nanoparticle amplifying labels and with the formation of nanoparticle-protein assemblies provides the basis for ultrasensitive electrochemical detection of proteins. Such protocols rely on the use of colloidal gold tags, semiconductor (quantum dot) tracers, ‘carrier’ (amplification) nanomaterials, or magnetic (separation) beads, in connection to electrochemical stripping measurement of the metal tag. Remarkable ‘PCR-like’ sensitivity has been achieved by coupling particle-based amplification units and various amplification processes. The use of nanocrystal tracers for designing electrochemical coding protocols for detecting multiple proteins will also be documented.

Evaluation of Thin Film Titanium Nitride Electrodes for Electroanalytical Applications

Abstract: Titanium nitride is a hard and inert conducting material that has yet not been widely used as electrode material for electroanalytical applications although there are highly developed protocols available to produce well adherent micro and nanostructured electrodes. In this paper the possibilities of using titanium nitride thin films for electroanalytical applications is investigated. Scanning electrochemical microscope (SECM)was used for analysis of the redox kinetics of a selected fast redox couple at thin films of titanium nitride (TiN)in different thicknesses. The investigation was carried out by approaching an amperometric ultramicroelectrode (UME)to the TiN film while the soluble redox couple (ferrocenemethanol/ferrociniummethanol)served as mediator in a SECM configuration. The substrate was biased at a potential so that it rereduces the species being produced at the UME, thus controlling the feedback effect. Normalized current – distance curves were fitted to the theoretical model in order to find the apparent heterogeneous standard rate constant (k8)at the sample. The data are further supported by structural investigation of the TiN films using scanning force microscopy and X-ray photoelectron spectroscopy. It was found that the kinetics are little influenced by prolonged storage in air. The heterogeneous standard rate constants in 2 mM ferrocenemethanol were (0.73 � 0.05) � 10 � 3 cm s � 1 for 20 nm TiN thin layer, (1.5 � 0.2) � 10 � 3 cm s � 1 for 100 nm TiN thin layer and (1.3 � 0.2) � 10 � 3 cm s � 1 for 300 nm TiN thin layer after prolonged storage in air. Oxidative surface treatment (in order to remove organic adsorbates)decreased the kinetics in agreement with a thicker oxide layer on the material. The results suggest that their direct use for amperometric detection of reversible redox systems in particular at miniaturized configurations may be advantageous.

Electrochemical Biosensors for Pollutants in the Environment

Abstract: This article reviews recent advances in electrochemical biosensing and detection of environmental pollutants. Electrochemical biosensors offer precision, sensitivity, rapidity, and ease of operation for on-site environmental analysis. An electrochemical biosensor is an analytical device in which a specific biological recognition element (bioreceptor) is integrated within or intimately associated with an electrode (transducer) that converts the recognition event to a measurable electrical signal for the purpose of detecting a target compound (analyte) in solution. This approach not only provides the means for on-site analysis but also removes the time delay and sample alteration that can occur during transport to a centralized laboratory. We first address the basic principles of merging of electrochemistry and biology into a biosensing system, and then we discuss various environmental monitoring strategies involving this technology.

New Fully Portable Instrument for the Versatile Determination of Cations and Anions by Capillary Electrophoresis with Contactless Conductivity Detection

Abstract: A new portable capillary electrophoresis instrument with capacitively coupled contactless conductivity detection was developed and optimized for the sensitive field measurements of ionic compounds in environmental samples. It is powered by batteries and the high voltage modules are capable of delivering up to 15 kV at either polarity for more than one working day. Inorganic cations and anions, including ions of heavy metals and arsenate, could be determined with detection limits in the range from about 0.2 to 1 mM. The instrument was field tested in a remote region of Tasmania and nitrite and ammonium could be determined on-site at concentrations as low as 10 ppb in presence of other common inorganic ions at concentrations which were 2 to 3 orders of magnitude higher.

Electroactivity of Nonconjugated Proteins and Peptides. Towards Electroanalysis of All Proteins

Abstract: Present proteomics and biomedicine require sensitive analytical methods for all proteins. Recent progress in electrochemical analysis of peptides and proteins based on their intrinsic electroactivity is reviewed. Tyrosine and/or tryptophan-containing proteins are oxidizable at carbon electrodes. At mercury electrodes all peptides and proteins (about 13 peptides and >25 proteins were tested) produce chronopotentiometric peak H at nanomolar concentrations. This peak is sensitive to changes in protein structure. Microliter sample volumes are sufficient for the analysis. Electrochemical methods can be used in studies of nucleic acid-protein interactions and can be applied in biomedicine. Examples of such applications in neurogenerative diseases and cancer are presented.

Electroanalysis Utilizing Amperometric Microdisk Electrode Arrays

Abstract: This article reviews the literature dealing with electroanalytical applications of ultramicroelectrode arrays over the past twenty years. A brief theoretical description of the mass transport mode governing their behavior is given, after which the main fabrication methods are described. The applications described in the later sections of this review range from conventional electroanalysis, namely trace metal stripping methods, using mercury modified arrays to more recent advances in the field of biosensors (enzymatic, immunosensors and nucleic acid based ones).

Anodic Stripping Voltammetry of Heavy Metals at Nanocrystalline Boron-Doped Diamond Electrode

Abstract: Boron-doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen Diluted electrolyte (001 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media For � 17 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time Understanding different metal-metal interactions shows the limits to the simultaneous determination of heavy metals at BDD Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks The performance of the BDD was compared with that of another C-based solid electrode: the glassy carbon electrode (without mercury plating) A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD

A Novel Functionalized Single‐Wall Carbon Nanotube Modified Electrode and Its Application in Determination of Dopamine and Uric Acid in the Presence of High Concentrations of Ascorbic Acid

Abstract: Multilayer films of negatively charged single-wall carbon nanotubes (SWCNTs) and positively charged cetylpyridinium bromide (CPB) have been deposited on a glassy carbon electrode (GCE) using layer-by-layer (LBL) technique. The assembled multilayer films have been investigated by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and quartz crystal microbalance (QCM) measurements. The voltammetric signal of dopamine (DA), uric acid (UA), and ascorbic acid (AA) could be observed well-separated with the assembled SWCNTs/CPB multilayer films in pH 7.0 PBS. The oxidation peak potentials of DA, UA, and AA are centered at about 169 mV, 292 mV and −10 mV on differential pulse voltammograms (DPVs), respectively. The peak-to-peak potential separation was 123 mV, 179 mV, and 302 mV for DA-UA, DA-AA, and UA-AA in DPVs, respectively. This permits the simultaneous detection of DA and UA in the presence of AA.

3D-Ensembles of Gold Nanowires: Preparation, Characterization and Electroanalytical Peculiarities

Abstract: Nanoelectrode ensembles (NEEs) of gold nanodisks, prepared by electroless template deposition of gold within the pores of track-etched polycarbonate membranes, are treated with oxygen plasma or with solvent mixtures in order to achieve controlled etching of part of the polycarbonate of the template. This causes the structure of the final ensemble to change from a 2-D flat structure into a 3-D one. The cyclic voltammetric (CV) behavior of redox probes at the 3DNEEs is examined and compared with the behavior observed at 2D-NEEs. Finally, 3D-NEEs are examined in order to test possible applications for the development of mediated sensors.

Carbon Nanotubes Paste Electrodes. A New Alternative for the Development of Electrochemical Sensors

Abstract: Fil: Rivas, Gustavo Adolfo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones en Fisico-quimica de Cordoba. Universidad Nacional de Cordoba. Facultad de Ciencias Quimicas. Instituto de Investigaciones en Fisico-quimica de Cordoba; Argentina

Direct Bioelectrocatalysis of PQQ‐Dependent Glucose Dehydrogenase

Abstract: The direct bioelectrocatalysis was demonstrated for pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-dependent GDH) covalently attached to single-walled carbon nanotubes (SWNTs). The homogeneous ink-like SWNT suspension was used for both creating the SWNT network on the microelectrode carbon surface and for enzyme immobilization. Functionalization of the SWNT surface by forming active ester groups was found to considerably enhance SWNT solubility in water with a range from 0.1 to 1.0 mg/mL. The PQQ-dependent GDH immobilized on the surface of the SWNTs exhibited fast heterogeneous electron transfer with a rate constant of 3.6 s � 1 . Moreover, the immobilized PQQ-dependent GDH retained its enzymatic activity for glucose oxidation. A fusion of PQQ-dependent GDH with SWNTs has a great potential for the development of low-cost and reagentless glucose sensors and biofuel cells.

Electrochemical Characteristics of Glucose Oxidase Adsorbed at Carbon Nanotubes Modified Electrode with Ionic Liquid as Binder

Abstract: Multiwall carbon nanotubes (CNTs)-modified electrode has been prepared by using ionic liquid (IL) as the binder. The as-prepared CNTs-IL composite modified electrode has good biocompatibility and is a suitable matrix to immobilize biomolecules. Glucose oxidase (GOx), containing flavin adenine dinucleotide as active site, stably adsorbed on modified electrode surface has resulted in the direct electron transfer. The electron transfer rate of 9.08 s(-1) obtained is much higher than that of GOx adsorbed on the CNTs papers (1.7 s(-1)), and the process is more reversible with small redox peak separation of 23 mV This may be due to the synergetic promotion of CNTs and IL to electron transfer of the protein, especially the IL as the binder, showing better electrochemical properties than that of chitosan and Nafion. Furthermore, GOx adsorbed at the modified electrode exhibits good stability and keeps good electrocatalytic activity to glucose with broad linear range up to 20 mM. Besides, the simple preparation procedure and easy renewability make the system a basis to investigate the electron transfer kinetics and biocatalytic performance of GOx and provide a promising platform for the development of biosensors.

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

Abstract: The electrochemical behavior of L-cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L-cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, kh were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L-cysteine showed a linear dependent on the L-cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10−5 M–2.2×10−3 M and 1.5×10−5 M–3.2×10−3 M of L-cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10−5 M and 1.4×10−6 M by CV and DPV methods.

Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

Abstract: A novel amperometric glucose biosensor based on layer-by-layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) on multiwalled carbon nanotubes (CNTs) was described Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt-DENs layer and an anionic GOx layer Transmission electron microscopy images and ζ-potentials proved the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage The excellent electrocatalytic activity of CNTs and Pt-DENs toward H2O2 and special three-dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 25 μM, a wide linear range of 5 μM–065 mM, a short response time (within 5 s), and high sensitivity (3064 μA mM−1 cm−2) and stability (80% remains after 30 days)

Investigation of Graphite Electrodes Modified with Cellobiose Dehydrogenase from the Ascomycete Myriococcum thermophilum

Abstract: The catalytic properties of cellobiose dehydrogenase (CDH) from the ascomycete fungus Myriococcum thermophilum adsorbed on a graphite electrode were investigated for a large variety of carbohydrate substrates. The effects of applied potential, pH and buffer composition were tested and optimized, and the most suitable conditions were used to evaluate the detection limit, linear range, and sensitivity of the sensor for different carbohydrates in the flow injection mode. Subsequently, the long term stability of the modified electrodes was determined. Additionally, the direct and mediated electron transfer between the active site of the enzyme and the electrode has been investigated by amperometric flow injection measurements in the absence and presence of the mediator 1,4-benzoquinone in the presence of cellobiose or lactose.

Guidelines for Improving the Lower Detection Limit of Ion‐Selective Electrodes: A Systematic Approach

Abstract: Zero-current membrane fluxes are the principal source of bias that has prohibited researchers from obtaining true, thermodynamic selectivity coefficients for membrane-based ion selective electrodes (ISEs). They are also responsible for the mediocre detection limits historically seen with these types of potentiometric sensors. By choosing an experimental protocol that suppresses these fluxes, it becomes possible to obtain unbiased thermodynamic selectivity coefficients that are needed to produce ISEs with greatly improved detection limits. In this work, a Cs+-selective electrode based on calix[6]arene-hexaacetic acid hexaethyl ester (Cs I) is used to systematically demonstrate how unbiased selectivity coefficients can be obtained, and how they can be used to optimize inner filling solutions for low detection limit measurements. A comparison of biased selectivity methods (e.g., classical separate solution method (SSM), fixed interference method (FIM), matched potential method (MPM)) with the unbiased modified separate solution method (MSSM) found that selectivity coefficients were underestimated in several cases by more than 4 orders of magnitude. The importance of key experimental parameters, including diffusion coefficients and diffusion layer thicknesses in the aqueous and organic phases, on the minimization of ion fluxes and the improvement of lower detection limits is also described. A dramatic reduction of membrane fluxes by themore » covalent attachment of a Ca2+-selective ionophore to a methyl methacrylate-decyl methacrylate copolymer matrix is also demonstrated. The ionophore-immobilized ISE exhibited no super-Nernstian response and yielded a detection limit of 40 ppt with an inner filling solution of 1 x 10-3 M KCl. Finally, a set of guidelines for experimental protocols leading to obtaining unbiased selectivity coefficients and producing ISEs for trace level analyses is given.« less

Electrochemical Determination of Ascorbic Acid in Room Temperature Ionic Liquid BPPF6 Modified Carbon Paste Electrode

Abstract: A room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPF6) was used as a binder to make an ionic liquid modified carbon paste electrode (IL-CPE), which showed good characteristics such as simple preparation procedure, fast electrochemical response and good conductivity. The electrochemical oxidation of ascorbic acid (AA) on the new IL-CPE was carefully studied. The oxidation peak potential of AA on the IL-CPE appeared at 109 mV (vs. SCE), which was about 338 mV decrease of the overpotential compared to that obtained on the traditional carbon paste electrode (CPE) and the oxidation peak current was increased for about four times. The electrochemical parameters of AA on the IL-CPE were calculated with the charge transfer coefficient (α) and the electrode reaction rate constant (ks) as 0.87 and 0.800 s−1, respectively. Based on the relationship of the oxidation peak current and the concentration of AA a sensitive analytical method was established with cyclic voltammetry. The linear range for AA determination was in the range from 1.0×10−5 to 3.0×10−3 mol/L with the linear regression equation as Ip (μA)=−2.52–0.064C (μmol/L) (n=13, γ=0.9942) and the detection limit was calculated as 8.0×10−6 mol/L (3σ). The proposed method was free of the interferences of coexisting substances such as dopamine (DA) and amino acids etc., and successfully applied to the vitamin C tablets determination.

Determination of Caffeine at a Nafion‐Covered Glassy Carbon Electrode

Abstract: A simple differential pulse voltammetric method based on a Nafion-covered glassy carbon electrode was developed for the quantitative determination of caffeine in cola beverages. The modified electrode exhibits a clear improvement of the current response compared to that observed at a bare glassy carbon electrode. The method allows quantifying the analyte in the 9.95×10−7–1.06×10−5 M range, with a detection limit of 7.98×10−7 M in 0.1 M sulfuric acid solutions. The developed procedure was tested by recovery studies. The results are described and discussed in the light of the existing literature.

Carbon Paste Electrode Modified with Functionalized Nanoporous Silica Gel as a New Sensor for Determination of Silver Ion

Abstract: A new dipyridyl-functionalized silica gel (DPSG) was synthesized. The potentiometric response of silver ion was investigated at a carbon paste electrode chemically modified with functionalized nanoporous silica gel. The electrodes with a DPSG proportions of 10.1% (w/w), showed very stable potential. Calibration plots with Nernstian slopes for Ag+ were observed, 58.7 (±0.9) mV decade−1, over a wide linear range of concentration (5.0×10−7 to 1.0×10−1 M). The electrode has a detection limit of 1.0×10−7 M. The selectivity coefficients measured by the match potential method in acetate buffer, pH 5.5, were investigated. The electrode has fast response time, high performance, high sensitivity in wide cation activity ranges, and good long term stability (more than 6 months). The method was satisfactory and used to determine the concentration of silver ion in waste waters contaminated by this metal.

Simultaneous Determination of Ranitidine and Metronidazole at Glassy Carbon Electrode Modified with Single Wall Carbon Nanotubes

Abstract: Single-walled carbon nanotubes(SWCNTs) were dispersed into DMSO, and a SWCNTs-film coated glassy carbon electrode was achieved via evaporating the solvent. The results indicated that CNT modified glassy carbon electrode exhibited efficiently electrocatalytic reduction for ranitidine and metronidazole with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the potential for reduction of selected analytes is lowered by approximately 150 mV and current is enhanced significantly (7 times) in comparison to the bare glassy carbon electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for these analytes determinations by hydrodynamic amperometry. Under optimized condition in amperometric method the concentration calibration range, detection limit and sensitivity were about, 0.1–200 μM, detection limit (S/N=3) 6.3×10−8 mol L−1 and sensitivity 40 nA/μM for metronidazole and 0.3–270 μM 7.73×10−8 mol L−1 and 25 nA/μM for ranitidine. In addition, the ability of the modified electrode for simultaneous determination of ranitidine and metronidazole was evaluated. The proposed method was successfully applied to ranitidine and metronidazole determination in tablets. The analytical performance of this sensor has been evaluated for detection of these analytes in serum as a real sample.

Ultrathin Carbon Nanoparticle Composite Film Electrodes: Distinguishing Dopamine and Ascorbate

Abstract: Ultrathin carbon nanoparticle – poly(diallyldimethylammonium chloride) films (CNP-PDDAC films) are formed on tin-doped indium oxide (ITO) electrodes in a layer-by-layer electrostatic deposition process employing 9 – 18 nm diameter carbon particles. Transparent and strongly adhering films of high electrical conductivity are formed and characterized in terms of their electrochemical reactivity. When immersed in aqueous 0.1 M phosphate buffer pH 7, each layer of CNP-PDDAC (of ca. 5 – 6 nm average thickness) is adding an interfacial capacitance of ca. 10 m Fc m � 2 . Absorption into the CNP – PDDAC nanocomposite film is dominated by the sites in the PDDAC cationomer and therefore anionic molecules such as indigo carmine are strongly bound and retained within the film (cationic binding sites per layer ca. 150 pmol cm � 2 ). In contrast, cationic redox systems such as ferrocenylmethyltrimethyl-ammonium þ fail to bind. For solution phase redox systems such as hydroquinone, the rate of electron transfer is dramatically affected by the CNP-PDDAC film and switched from completely irreversible to highly reversible even with a single layer of carbon nanoparticles. For the mixed redox system ascorbate – dopamine in 0.1 M phosphate buffer pH 7 cyclic voltammograms suggest a rapid and selective temporary poisoning process which causes the ascorbate oxidation to be suppressed in the second potential cycle. This effect is exploited for the detection of micromolar concentrations of dopamine in the presence of millimolar ascorbate.