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The structure–electroactivity relationship of graphene has been studied using coronene (Cor), polyaromatic hydrocarbon (PAH), and a subunit of graphene as a model system by chemically modified elec...

Search for simple and economical electrocatalyst for the hydrogen gas evolution reaction (HER), which can resemble to the performance of Pt and other precious metals, is a challenging research interest. In this work, a systematic effect of pre-treatment potential of screen-printed carbon (SPCE) surface on the HER performance in 0.5 M H2SO4 was carried out. A new observation of a low potential HER (onset potential, Eonset = −0.02 V vs. RHE) at a cathodic potential, −0.5 V vs. Ag/AgCl on 1 hr pre-treated screen-printed carbon electrode (SPCE*, * = pre-treated) was observed. Physicochemical and electrochemical characterizations of the SPCE* by field emission scanning electron-microscope, Raman, IR and X-Ray photoelectron spectroscopes reveals specific generation of carboxylic acid functionalized carbon surface and in turn for the enhanced HER on the modified electrode surface. Electrochemical characterization of SPCE* with Fe(CN)63− support the observation. A marked decrement in the peak current and significant increase in the peak-to-peak separation potential response due electrostatic repulsion between the anion sites of Fe(CN)63− and –COO– were noticed. This observation is in parallel with the reduced electrical double layer capacitance value of the SPCE* system. The Eonset and Tafel value (54.7 mV dec−1) obtained here are comparable to those at Pt, MoS2, MoSe2 and superior over the N- and P-doped graphene/carbon electrocatalysts for HER. A prototype HER system was developed and demonstrated for H2 gas production at a rate of 0.0053 μM s−1 (Operating potential = −0.5 V vs Ag/AgCl), which is comparable to that of precious metal and metal compound electrocatalysts based HER performance.

A three-dimensional hierarchical network of bismuth nanoparticles decorated graphene-carbon nanotubes nanocomposite (Bi NPs@Gr-CNTs) was synthesized and employed for electrocatalytic detection of mercury (Hg (II)). The electrocatalyst was characterized via scanning electron microscopy, transmission electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray diffraction, FT-IR, electrochemical impedance spectroscopy, and cyclic voltammetry. The electrocatalytic activity of Bi NPs@Gr-CNTs modified screen-printed carbon electrode (SPCE) toward Hg (II) was studied using cyclic voltammetry, and differential pulse voltammetry. The Bi NPs@Gr-CNTs/SPCE exhibited excellent electrocatalytic ability to Hg (II) in comparison to control electrodes. Under optimized conditions, Bi NPs@Gr-CNTs/SPCE exhibits excellent Hg (II) sensing attributes in the range of 1.0 nM–217.4 µM with 0.2 nM of detection limit. The electrode was specific for Hg (II) in presence of other metal ions ascribe excellent selectivity. Practicality of the method was demonstrated in tap water, fish oil tablet, human serum, and urine samples (spiked method), which presented acceptable recoveries.

pH value of a non-invasive sample is an important biomarker in diagnosing certain clinical disorders of a human body. Herein, we report, a stable, surface-confined and redox active poly(1-naphthylamine) (PNPA) on multiwalled carbon nanotube modified gold and pencile graphite electrodes (Au/MWCNT@PNPA and PGE@PNPA) prepared via electrochemical polymerization of 1-naphthylamine (1-NPA) in pH 7 phosphate buffer solution for sensitive and selective pH monitoring of non-invasive samples (saliva, tears and urine). Control experiment with 2-NPA isomer failed to show such redox feature, indicating the selective electrochemical polymerization of 1-NPA. Physicochemical characterizations of MWCNT@PNPA by SEM, TEM, XPS, Raman, FTIR, UV–vis (an ethanolic extract) and several control electrochemical experiments revealed that 4th (para) position of 1-NPA isomer is involved in the initiation of electro-polymerization on a carbon surface and followed by a stable redox polymer formation. Interestingly, the redox peak responsible for pH sensing showed negligible to permissible level of alteration with several biochemicals. As as a diverse application, selective monitoring of bacterial (E. coli) growth was demonstrated using this new electrochemical pH sensor system with result comparable to that of conventional pH sensor.

Due to their explicit properties, screen-printed electrode (SPE) based technologies are superior to other conventional electro-analytical methods. SPE technology can be extended to a miniaturized system, which requires only a few microlitres of the test sample. The surface of SPEs is feasible for a variety of modifications and it eliminates the possibility of tedious cleaning, which is needed for traditional electrodes. Similarly, carbon nanotubes (CNT), one of the more advanced carbon nanomaterials, have a unique graphitic tubular structure with excellent electronic properties. In this chapter, we will focus on CNTs chemically modified SPEs for biochemical sensing applications. We have sub-divided the articles under the following headings: (i) direct surface modification of CNT on SPE, (ii) functionalized CNTs modified SPE, (iii) electroactive species immobilized CNTs modified SPE, (iv) bulk modified SPE, (v) enzyme-immobilized CNT modified SPE, (vi) flow injection analysis of CNT-modified SPE and (vii) separation technique coupled electroanalysis using CNT based SPEs. Details of the preparation, characterization and electrochemical sensor for biomedical applications are included along with 160 references.

A simple method for molecular wiring of glucose oxidase (GOx) enzyme with a low cost Mn polypyridine complex, Mn(phen)2Cl2, carboxylic acid functionalized multiwalled carbon nanotube (f-MWCNT) and Nafion (Nf), which is useful for glucose oxidation and sensing application in pH 7 phosphate buffer solution, has been demonstrated. In the typical preparation, f-MWCNT, Mn(phen)2Cl2, Nafion and GOx solution/suspension were successfully drop-casted as layer-by-layer on a cleaned glassy carbon electrode and potential cycled using cylic voltametric (CV) technique. In this preparation procedure, the Mn(phen)2Cl2 complex is in-situ converted as a dimer complex, Mn2(phen)2(O)(Cl2). A cooperative interaction based on π-π, covalent, ionic, hydrophilic and hydrophobic are operated in the bioelectrode for molecular wiring and electron-transfer shutting reaction. The modified electrode is designated as GCE/f-MWCNT@Mn2(phen)2(O)(Cl2)-Nf@GOx. CV response of the bioelectrode showed a defined redox peak current signal at an apparent standard electrode potential, E°'=0.55V vs Ag/AgCl. Upon exposure of glucose, the modified electrode showed a current linearity in a range, 0-6mM with a current sensitivity value, 349.4μAmM-1cm-2 by CV and a current linearity in a window, 50-550μM with a current sensitivity, 316.8μAmM-1cm-2 at applied biased potential, 0.65V vs Ag/AgCl by amperometric i-t methods. Obtained glucose oxidation current sensitivity values are relatively higher than Os-complex based transducer systems.

The search for a new and efficient transducer that can electrically connect enzyme active sites, like flavin adenine dinucleotide in glucose oxidase (GOx), with the electrode surface is a cutting-edge research area. Currently, Os(bpy)-complex pendent polyvinylpyridine/polyvinyl imidazole/pyridinium hydrogel based chemically modified electrodes have been widely used for this purpose (bpy = 2,2’-bipyridine). Herein, we report, a [Mn2III(phen)4(O)(Cl)2]2+ complex/Nafion-immobilized carboxylic acid-functionalized multiwalled carbon nanotube modified glassy carbon electrode (GCE/f-MWCNT@Mn2(Phen)4O(Cl)2-Nf, phen = 1,10-phenanthroline), prepared by an in-situ electrochemical method using the precursor, Mn(phen)2Cl2, as an efficient and low cost alternate to the Os-complex transducer, for the glucose oxidase enzyme (GOx) based bio-electro-catalytic system. The existence of the key active site, [Mn2III(phen)4(O)(Cl)2]2+, on the modified electrode was confirmed by physicochemical characterizations using transmissi...

Most of the common redox mediators such as organic dyes and cyanide ligand-associated metal complex systems that have been used for various electrochemical applications are hazardous nature. Sesamol, a vital nutrient that exists in natural products like sesame seeds and oil, shows several therapeutic benefits including anticancer, antidiabetic, cardiovascular protective properties, etc. Herein, we introduce a new electrochemical redox platform based on a sesamol derivative, sesamol-quinone (Ses-Qn; oxidized sesamol), prepared by the in situ electrochemical oxidation method on a carbon nanoblack chemically modified glassy carbon electrode surface (GCE/CB@Ses-Qn) in pH 7 phosphate buffer solution, for nontoxic and sustainable electrochemical, electroanalytical, and bioelectroanalytical applications. The new Ses-Qn-modified electrode showed a well-defined redox peak at Eo = 0.1 V vs Ag/AgCl without any surface-fouling behavior. Following three representative applications were demonstrated with this new redox system: (i) simple and quick estimation of sesamol content in the natural herbal products by electrochemical oxidation on GCE/CB followed by analyzing the oxidation current signal. (ii) Utilization of the GCE/CB@Ses-Qn as a transducer, bioelectrocatalytic reduction, and sensing of H2O2 after absorbing the horseradish peroxidase (HRP)-based enzymatic system on the underlying surface. The biosensor showed a highly selective H2O2 signal with current sensitivity and detection limit values 0.1303 μA μM–1 and 990 nM, respectively, with tolerable interference from the common biochemicals like dissolved oxygen, cysteine, ascorbic acid, glucose, xanthine, hypoxanthine, uric acid, and hydrazine. (iii) Electrochemical immunosensing of white spot syndrome virus by sequentially modifying primary antibody, antigen, secondary antibody (HRP-linked), and bovine serum albumin on the redox electrode, followed by selective bioelectrochemical detection of H2O2.

Chromium(III) species is an essential micronutrient, whereas, its hexavalent form, Cr(VI) is considered to be a carcinogen. For the selective detection of Cr(III) in presence of Cr(VI), separation coupled spectroscopic techniques have been often used. For the first time in this work, we report a flow injection analysis coupled dual electrochemical detector (FIA-DECD) for separation-free detection of Chromium (III) and (VI) species. A gold nanoparticles decorated carbon nanofibres-chitosan modified electrode has been prepared by a quick and in-situ electrochemical deposition of Au3+ ion in pH 7 phosphate buffer solution (PBS) and has been used as a dual electrochemical detector for Cr(VI)-reduction and Cr(III)-oxidation reactions in pH 2 PBS. Under an optimal hydrodynamic FIA-DECD condition, i.e., at applied potentials 0.1 V (for Cr(VI)-reduction) and 1 V vs Ag/AgCl (for Cr(III)-oxidation) and at a flow rate = 0.8 mL min−1, calculated linear range and detection limit values are; 0.1–100 ppm and 0.69 ppb (0.72 ppt for 20 μL sample loop volume) for Cr(III) and 0.1–100 ppm with detection limit, 0.32 ppb (0.33 ppt for 20 μL) for Cr(VI). No marked interference from other cations and anions like Cu2+, Zn2+, Cd2+, Pb2+, Co2+, Ca2+, Fe2+, Mg2+, NO3−, NO2−, SO32− and SO42− were noticed. Selective detection of Cr species (Cr(III) and Cr(VI)) in industrial waste water samples with data comparable to ICP-OES was demonstrated.

A human whole blood-chemically modified electrode prepared using graphitized mesoporous carbon and Nafion, as an in-vitro model system, has been studied for the specific interaction of hydrogen peroxide at biased potentials by cyclic volumetric technique. A blood-chemically modified electrode prepared by modifying a few drops of human whole blood with the carbon nanomaterial and Nafion had showed a well-defined redox peak at an apparent standard electrode potentials, E°′~− 0.38 V vs Ag/AgCl in N2 purged pH 7 phosphate buffer solution, similar to an isolated hemoglobin protein redox feature. When the blood modified electrode is exposed with dilute solution of hydrogen peroxide, selective electrochemical reduction behaviour where the heme site redox potential exists was noticed. The electrochemical reduction reaction is found to follow diffusion controlled mechanism. The H2O2 reduction peak current was linear with the concentration in a range of 100 to 800 μM with a current sensitivity of 0.048 μA μM−1. Qualitative cyclic voltammetric patterns of the blood modified electrode in the entire concentration window of H2O2 are same indicating intact biomolecular arrangement of the heme site. Kinetic parameters of the electron-transfer reaction of H2O2 were estimated using rotating disc technique and Michaelis-Menten reaction approaches. The electron-transfer function of the heme in the RBC is not influenced by any other electroactive biochemicals such as glucose, nitrate, ascorbic acid, uric acid and dopamine, except nitrite. As an independent study, the blood-chemically modified electrode has been used as an electrochemical sensor system for the flow injection analysis of H2O2.

RuO2 is an unparalleled electrode with wider applications. Chloride, bound water, and surface stoichiometry are the inherent residues of RuO2 left upon the high-temperature pyrolysis of a RuCl3⋅xH2O precursor. Although the electrocatalytic properties of RuO2 for specific applications have been studied extensively, there is a paucity of studies linking the intrinsic electron-transfer (ET) activity of RuO2 with the oxide preparation temperature-dependent inherent residual parameters. This paper presents the intrinsic ET activity-oxide residue correlations for RuO2 electrodes. The ET kinetic parameters were estimated using a surface oxide-sensitive Fe3+/Fe2+ redox probe by rotating disc electrode voltammetry. Oxide powder-based electrodes (RuO2 powder-PVC/Pt-modified electrodes), which were fabricated conveniently at room temperature even with high-temperature oxides, were used instead of the traditional thermally prepared electrodes to circumvent the primary problems at the coating|support interface and inefficient chloride removal. RuO2 powders prepared at five temperatures (Tprep), i.e., 300, 400, 500, 600, and 700 °C, were used for electrode fabrication. The results showed that the electron exchange rate was highest for the 400 °C RuO2 electrode, and it was independent of the Tprep in the range 500 to 700 °C. The oxide powders were characterized using a range of techniques. The measured intrinsic ET activity and the associated structural correlation over the Tprep range 300–700 °C suggest that the best activity of the 400 °C electrode can be attributed to the optimal chloride and bound water contents in a completely formed rutile surface layer containing the catalyst sites of a particular nature with the highest electroactivity.

Development of simple and selective detection of poisonous arsenic species [As(III)] in drinking water is the subject of continued research in the multi-disciplinary areas of chemistry and biology. In this paper is reported, a well dispersed gold nanoparticle decorated-carbon nanofiber-chitosan modified carbon screen printed electrode (SPE/CNF-CHIT@Aunano) prepared using an inexpensive and simple electrochemical method for electro-catalytic oxidation and flow injection analysis (FIA) of inorganic As(III) species in a neutral (pH 7) phosphate buffer solution. The modified electrode has about a four times higher current signal for the arsenic oxidation than that of a gold polycrystalline electrode. The SPE/CNF-CHIT@Aunano system is highly stable in vigorously stirred solutions. Rotating disc electrode (RDE) studies performed using a glassy carbon electrode–rotating disc electrode (GCE–RDE) with its surface modified using the CNF-CHIT@Aunano film gave a heterogeneous rate constant, kcat = 1.92 × 104 mol−1 dm3 s−1 for the electrochemical oxidation of As(III). Furthermore, SPE/CNF-CHIT@Aunano was used as an efficient electrochemical detector (ECD) for the FIA of arsenic(III) in a neutral pH solution. The present FIA-ECD shows zero interference with other common cationic and anionic species. As an analytical application, selective detection of As(III) in arsenic polluted industrial effluent and tap water samples were determined satisfactorily with good recovery values. The analysis results from FIA-ECD were comparable with those obtained using the inductively coupled plasma – optical emission spectrometry method.

Studies related to interaction of whole blood with dissolved oxygen with a new analytical method is a continued research interest in the interdisciplinary areas of biomedical, biochemistry and analytical chemistry. There has been significant number of reports for spectroscopic and electrochemical investigation for the interaction of heme/hemoglobin with dissolved oxygen. Indeed, there is no direct study relating to electron-transfer behaviour of whole blood and oxygen reduction reaction. Complex nature of the blood and difficulty in transferring the electron from the buried hemoglobin in the blood cell are the limitations for the observation. Herein, we report, a human whole blood modified electrode system using graphitized mesoporous carbon and Nafion as a matrix for direct-electron-transfer reaction with dissolved oxygen in physiological solution. The blood modified electrode exhibits a specific redox peak at an apparent standard electrode potential, E°′ = − 0.38 V vs Ag/AgCl corresponding to the electron-transfer reaction of hemoglobin-Fe(III)/Fe(II) redox system and shows a mediated oxygen reduction reaction similar to a commercial Hb modified electrode response. Using the new bio-analytical system, interaction between the blood and dissolved oxygen was studied in terms of oxygen reduction reaction (ORR). Cyclic voltammetry, rotating disc electrode and flow injection analysis coupled with a dual electrode system, wherein, blood and MnO 2 modified electrode systems are used for signals corresponding to the oxygen reduction and H 2 O 2 oxidation reactions, kinetics and mechanism. As an extension to practical applicability, quantification of dissolved oxygen using the blood modified electrode was demonstrated with result comparable to that of a commercial dissolved oxygen measurement kit.

The mystery of > 2000 years of Hindu culture holy basil plant-Tulsi (Ocimum tenuiflorum)’s active ingredient for health benefit has been revealed by performing a blind cyclic voltammetric based electrochemical experiment (without pre-targeted chemicals) with a crude solution of the Tulsi-plant-water extract (TE) using a graphitized mesoporous carbon nanomaterial modified glassy carbon electrode (GCE/GMC) in pH 2 solution. The as-prepared chemically modified electrode was characterized using TEM, FTIR, Raman, UV–Vis, HPTLC, UPLC and with several control samples to identify the active molecular species trapped by GMC. It has been revealed that amongst various phytochemicals-ingredients, the rosmarinic acid (RA) in the TE-extract trapped selectively on the graphitic sites and showed an exceptionally efficient redox behavior at an apparent standard electrode potential, Eo’ = 0.550 V vs Ag/AgCl with a peak-to-peak potential difference, ΔEp ∼ 0 V. A specific interaction between the π-electrons of the aromatic compound and sp2 carbon of GMC is found to be an influencing parameter for the selective electrochemical micro-extraction of the RA from the TE (GMC@TE-RA). This electrochemical methodology helps for qualitative and quantitative analysis of the phytochemical, RA in the TE. The GMC@TE-RA is found to involve selective electrocatalytic oxidation of phenylhydrazine-pollutant in pH 2 KCl-HCl medium. Electrochemical impedance spectroscopic analysis of the modified electrode showed a superior electronic activity over the respective unmodified electrode. A scanning electrochemical microscopy (SECM) has been used to image the active site of the electrocatalytic surface. As a sustainable and green electrochemical approach, a highly selective electrocatalytic oxidation and flow injection analysis-based sensing of phenylhydrazine using the GCE/GMC@TE-RA has been demonstrated without any interference from hydrazine and other common electroactive chemicals and biochemicals.

Isoniazid (INZ) is an effective anti-tuberculosis drug that has been widely used for chemotherapy of tuberculosis. Development of new and simple electroanalytical method for routine analysis of INZ is a continued research interest in the field of analytical and pharmaceutical chemistry. Although there have been several electroanalytical reports, flow injection analysis coupled electrochemical detection of INZ, which is an advanced electrochemical technique useful for practical applications, is rarely reported in the literature. Instability problem associated with the underlying electrode by the amino-functional group of the INZ is the prime reason for the limitation. Herein, we report a gold nanoparticles decorated carbon nanofibers-chitosan modified carbon screen printed electrode, designated as Aunano@CNF-CHIT/SPE, prepared by drop-casting of Au3 + ion directly on CNF-CHIT/SPE underlying electrode followed by electrochemical potential cycling, as an elegant electrochemical detector system for high stable FIA of INZ in pH 7 phosphate buffer solution. The modified electrode showed about fifty times higher electrocatalytic current and 700 mV reduction in the over-potential values than that of a polycrystalline gold modified electrode towards INZ. Under an optimal hydrodynamic FIA condition, the present ECD showed a wide linear range from 1 μM to 1 mM with regression coefficient and sensitivity values of 0.9958 and 16.1 nA μM− 1 respectively. The calculated limit of detection and limit of quantification values are 172 nM (i.e., 472 pg/20 μL) and 570 nM (i.e., 1.57 μg/20 μL), respectively. The present FIA-ECD was successfully applied for the real sample analysis by detecting INZ in two pharmaceutical formulations with satisfactory good recovery values.

Lactoferrin (LAF), an iron-binding glycoprotein has several health benefits ranging from anti-cancer, anti-inflammatory and antimicrobial activities against large number of microorganisms and is present abundantly in milk. Enzyme linked immunosorption assay based analytical protocol has been often referred for the selective detection of LAF in real samples. Herein, we report a simple electrochemical methodology for the direct recognition of LAF in raw milk using a methylene blue (MB) immobilized iron impurity (2.1 wt.%) containing multiwalled carbon nanotube/nafion modified glassy carbon electrode system. It is interesting to observe that upon potential cycling of GCE/Nf-MWCNT in MB dissolved milk system, both MB and LAF got co-immobilized on the electrode surface, designated as GCE/Nf-MWCNT@MB-LAF and showed a selective bio-electrocatalytic reduction signal for H2O2 at −0.4 V vs Ag/AgCl in milk or pH 7 PBS system. From control electrochemical experiments such as loading MB in pH 7 phosphate buffer solution and simulated milk sample and effect of carbon material (activated charcoal, graphite nanopowder and functionalized MWCNT) on preparation of the LAF modified electrode, it is revealed that iron impurity in the MWCNT, MB and LAF of the modified electrode involved in the electron-shuttling process to facilitate the H2O2 reduction reaction. By utilizing this novel process, selective bio-electrocatalytic sensing of H2O2 with current sensitivity and detection limit values 0.035 μA μM−1 and 3.2 μM respectively and specific recognition of LAF in raw and water diluted milksamples have been successfully demonstrated.

Owing to facile electron-transfer reaction, metal complex based molecular architecture has attracted much interest in electrochemistry, especially for bioinspired electrocatalytic and electrochemical sensor applications. Indeed, preparation of stable surface-confined molecular system is a challenging task. In general, derivatization methodology, in which, a specific functional groups such as thiol, carboxylic acid, pyrene and amino bearing inorganic complexes synthesized discreetly by chemical approach have been attached suitably on electrode surface via any one of the following techniques; self-assembly, covalent immobilization, electrostatic interaction, ionic exchange and encapsulation. Herein, we report a copper-bipyridyl complex immobilized multiwalled carbon nanotube (MWCNT)-Nafion (Nf) modified glassy carbon electrode (GCE/Nf-MWCNT@bpy-Cu2+) prepared by a new strategy in which sequential modification of bipyridyl (bpy) ligand on MWCNT via π-π interaction followed by in-situ complexation with copper ion for efficient electrochemical reduction of H2O2. The copper species chemically modified electrode showed highly stable and well-defined surface-confined Cu2+/1+ redox peak response, without any Cu1+/0 redox transition, at an equilibrium potential, E1/2 = −135 mV vs Ag/AgCl in a pH 7 phosphate buffer solution. Detailed physico-chemical characterization by SEM, FT-IR, Raman and ESI-MS and electrochemical characterization reveals that [Cu(bpy)2(H2O)2]+ (molecular weight 413.4) like species was immobilized as a major species on the modified electrode. A bioinspired electro-catalytic reduction of H2O2 was studied using cyclic voltammetric and rotating disc electrode techniques. In further, electrochemical sensing of H2O2 by amperometric i-t and flow injection analysis methods with a detection limit values 4.5 and 0.49 μM respectively were demonstrated.

Development of new sensor material suitable for simple, cost effective and quick practical application is a demanding research interest in electroanalytical chemistry. Carbon based inks prepared using different type carbon materials and binders as a gel or suspension have been often used as active sensor materials. Unfortunately, those systems are involved with complicated preparation route and usage of hazardous chemicals. Herein, we report a water based carbon ink composed of low cost carbon black powder, chitosan and acetic acid (prepared within 15 ± 2 min) for electrochemical sensor applications. A new carbon ink modified electrode was fabricated in this work by drop-casting of micro-litre quantity of the CB-Chit ink on a cleaned glassy carbon electrode (GCE) followed by air drying in room temperature for 10 ± 2 min. The CB-Chit ink modified GCE (GCE/CB-Chit) showed enhanced electrical conductivity, surface area and electrochemical activity than that of the unmodified GCE. Investigated simultaneous electrochemical oxidation and sensing of three biologically important molecules such as ascorbic acid, dopamine and uric acid on GCE/CB-Chit displayed excellent peak current signals at well-defined peak potentials with linear concentration ranges of 25–1600, 0.1–1400, and 5–1800 μM and detection limit of 0.1 μM (S/N = 3) for the all analytes. The newly fabricated sensor was validated by applying to the detection of AA, DA, and UA in vitamin C tablets, dopamine hydrochloride injection and human urine real samples. The sensor can be operated without any surface pre-treatment and analyte adsorption, unlike to the carbon nanotube and graphite based electrode systems with serious adsorption complications.

Pencil lead is composed of clay and graphite and it has been widely used as a low-cost electrode system in electrochemistry. There are a few reports on chemical modification of PGE as oxygen functionalized surface that has been prepared via a pre-anodization technique for electro-analytical applications. For the first time in this work, we introduce a new strategy for electrochemical derivatization of PGE as Prussian blue (PB) and Fe(bpy) 3 2 + functionalized PGEs (i.e., PGE-PB and PGE-Fe(bpy) 3 2 + ), utilizing its intrinsic iron (1.31 wt.%), in 0.1 M KCl-HCl medium. Potential cycling of the PGE with Fe(CN) 6 3 − (as solution phase system) and bipyridyl (as surface adsorbed system) resulted in a facile formation of the hybrid complexes on the PGE surface. Physico and electrochemical characterization of PGE-PB and PGE-Fe(bpy) 3 2 + modified electrodes by Raman, FT-IR and UV–Vis spectroscopies, cyclic voltammetry and several control experiments (graphite nano powder, clay, Fe 2 O 3 modified electrodes) evidenced the formation of surface confined complexes on PGE. It was found that the intrinsic iron in clay is responsible for the complexation reactions. Selective electrocatalytic function for the H 2 O 2 reduction reaction was demonstrated as an application of the PGE-PB system.

The detection of thiol-containing amino acids, particularly L-cysteine (L-CySH), without any interference from other biochemicals is a challenging research interest in electroanalytical chemistry. Amongst various electrodes, the nanogold modified electrode has been reported to be effective for low potential electrochemical oxidation (∼0 V vs. Ag/AgCl) and sensing of L-CySH. Herein, we report a conductive carbon black (CB, CL-08) modified glassy carbon electrode (GCE/CL-08) with a high surface area (1000 m2 g−1), prepared by a simple drop-casting technique for efficient electrocatalytic oxidation at the lowest oxidation potential, −0.13 V vs. Ag/AgCl, and sensing of L-CySH in a pH 6.65 phosphate buffer solution. The trace metal impurities such as Ni (0.18 wt%) and Fe (0.42 wt%) in CL-08 are found to be key for such unique and unusual electrocatalytic property observed in this study. Compared with the multiwalled carbon nanotube and graphite powder modified electrodes, the GCE/CL-08 showed about 400 mV reduction in the oxidation potential and twenty times enhancement in the current signal for the CySH. A chronoamperometry detection of L-CySH on the GCE/CL-08 at an applied potential = −0.13 V vs. Ag/AgCl yielded a current linearity from 50 to 700 μM with a LOD = 45.87 nM. There are no interferences by common biochemicals such as ascorbic acid, dopamine, uric acid, xanthine, hypoxanthine and homo-cysteine on the L-CySH oxidation potential. Selective chronoamperometric detection of L-CySH in the blood serum demonstrated ∼100% recovery value as a validation for the present protocol.

Analyzing catabolism of the fish cycle, wherein hypoxanthine (Hx) and xanthine (X) as intermediates and uric acid (UA) as the end product are formed, provides vital information about the freshness of fish. Biosensors based on xanthine oxidase have often been used for this purpose. Herein, we introduce an enzyme-free electrochemical sensor developed using an ultra-low cost 4B grade pencil graphite electrode (PGE) pre-anodized at 2 V vs. Ag/AgCl (4B-PGE*, where * means pre-anodized) as a novel electrode system for separation-free and simultaneous differential pulse voltammetric (DPV) detection of three purine bases, Hx, X and UA, in a pH 7 phosphate buffer solution. Stable and well-defined peaks at 0.95, 0.65 and 0.3 V vs. Ag/AgCl were noticed upon electrochemical oxidation of Hx, X and UA respectively at the 4B-PGE*. The 4B-PGE* is found to show about a twenty five times higher electrochemical response than the 4B-PGE (non-preanodized) for the purine oxidations. Under optimal DPV conditions, the 4B-PGE* showed linear calibration plots with current linearities in the ranges 6–30 μM, 8–36 μM and 3–21 μM with current sensitivities of 0.921 μA μM−1, 1.742 μA μM−1 and 0.499 μA μM−1 for Hx, X and UA respectively. Ten consecutive detections of 10 μM Hx, X and UA showed a relative standard deviation (RSD) of 2.14%, 4.95% and 0.32%, respectively. In order to validate the analytical approach, separation-free and simultaneous electrochemical detection of Hx, X and UA in five freshly dead fish samples, stored at different temperatures and for different storage times, was successfully demonstrated.

Most of the conventional electrochemical cells require a minimum sample volume of 2–5 mL for the analyses. However most of the times, availability of biological sample in this much quantity is challenging and may be the reason for misreading. Besides, a lower volume cell is always preferred for analyzing rare or expensive materials. Thus, development of a miniaturized electrochemical cell setup (MECS) with a lower volume capacity at an affordable cost is a paramount of interest. In this present work, a home-made MECS is developed using a disposable graduated microcentrifuge tube vial as a low-volume (150 μL) holding electrochemical cell and 0.7 mm HB-pencil graphite electrode (PGE), Ag wire and PGE as working, reference and counter electrode respectively. These three electrodes are fused into the disposable graduated microcentrifuge tube vial. In our preliminary investigations, kinetic parameters and electro-catalytic response of uric acid (UA) on working electrode (PGE* = predanodized PGE) was demonstrated as a model system for the application of this newly developed MECS. Furthermore, the developed electroanalytical approach was validated by testing the concentration of UA in non-invasive bio-samples (urine and saliva) with an electrode recovery value of ~ 100%.

Coenzyme Q10 (2,3-dimethoxy-5-methyl-6-decaprenyl-1,4-benzoquinone, Q10) is a fat soluble, hydrophobic, vitamin-like quinone present in the cell membranes, regulates metabolic pathways via redox signalling. There have been considerable reports relating to the structural bio-mimics of Q10, wherein, lipid type molecular matrix stabilized Q10 modified micro-porous electrode systems have been used. Most of the reported procedures showed either nil or very poor redox functional activity of the Q10 in cyclic voltammetry (CV) analysis. Here in, we report, a Q10 stabilized functionalized-multiwalled carbon nanotube modified glassy carbon electrode (GCE/f-MWCNT@Q10) as a functional biomimetic system for Q10. CV response of the GCE/f-MWCNT@Q10 showed a well-defined redox active at E 1/2 = −138 mV vs Ag/AgCl with peak-to-peak separation (Δ E p ) and surface excess ( Γ Q10 ) values of 275 mV (at v = 10 mV s −1 ) and 12.57 n mol cm −2 respectively. Amongst various carbon nanomaterials investigated, f-MWCNT was found to be the best for the Q10 functional activity. From the physicochemical characterizations it was identified that interactions such as pi-pi, hydrogen-bonding and iron metal impurity-oxygen existing in f-MWCNT@Q10 aided to stabilize molecular structure of the Q10 on f-MWCNT surface. Using CV technique, pro-oxidant activity of Q10 with NADH, ascorbic acid, cysteine, glucose and hydrazine were tested and found that observed interactions were similar to one existing with the real biological system. The f-MWCNT@Q10 system showed efficient pH sensing ability with Nernstian type proton-electron transfer mechanism.

Phenol and its derivatives are important aromatic compounds and that have been widely used in pharmaceutical, cosmetic, industrial applications for many years. Selective and direct detection of phenol, especially monophenol, is a challenging research interest in analytical chemistry. Although electrochemical methodology offers simple and straightforward route for phenol oxidation reaction, complications like tarry polymeric products formation and electrode surface fouling problems limit the electrodes for further extension to practical applications. In order to solve the problems, indirect electrochemical and biosensor based protocols have been often employed. Here in, we report an elegantly designed flow-injection analysis coupled dual electrochemical detector (FIA-DECD) made-up off a screen-printed carbon ring (SPCE-R*) and disk (SPCE-D*), which have been pre-anodized at 2 V vs Ag/AgCl at 300 s in pH 7 phosphate buffer solution, for direct and simple detection of monophenols using 0.05 M H2SO4 solution as a carrier solution. In this protocol, phenol got first electro-oxidized on SPCE-D* (disk part) at Eapp = 1.5 V vs Ag/AgCl to quinone like intermediates (1,2-dihydroxy, 1,4-dihydroxy and 1,2,4-trihydroxy benzene) that have been subsequently detected on SPCE-R* at Eapp = 0.1 V vs Ag/AgCl. The SPCE-D* was found to trap fraction of the intermediates (quinone like derivatives) on its surface. Discreet electrochemical and physico-chemical characterizations of the phenol exposed SPCE-D* by cyclic voltammetry, Raman spectroscopy and Gas chromatography coupled mass spectroscopy confirmed the formation of different types of quinone like products on its surface. A complicated phenolic compound, zinc phenolsulfonate (ZPS), which has been widely used as an antimicrobial agent in cosmetics, was taken as a model phenolic system for the FIA-DECD. Selective detection of ZPS in different cosmetic real samples has been demonstrated as a validation for the present protocol.

Phenothiazine (PTZ), a thiazine class heterocyclic compound, is a well-known electron donating system and has been widely used as a starting compound to prepare various phenothiazine dyes and pharmaceutically important compounds. Quinones and its derivatives are constituents of biologically active molecules serve as excellent electron-acceptor systems. Oxidation of PTZ by chemical and electrochemical methods often resulted into monohydroxylation of benzene ring moiety, S-oxidized and polymerized compounds as end products. Electrochemical oxidation of PTZ on a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode in pH 7 phosphate buffers solution (PBS) has been investigated in this work. A highly redox active surface confined PTZ-bi-1,4-quinone derivative (PTZ-biQ) on MWCNT modified glassy carbon electrode, designated as GCE/MWCNT@PTZ-biQ, as a product was unusually observed. The GCE/MWCNT@PTZ-biQ showed well-defined redox peaks at E1/2 = −0.07 and +0.29 V vs Ag/AgCl corresponding to surface confined electron-transfer behavior of the bi-quinone (acceptor) and PTZ-cationic radical species (donor) respectively. No such electrochemical characteristics were noticed when unmodified GCE was subjected to the electrochemical oxidation of PTZ. Existence of PTZ-biQ was confirmed by XRD, Raman spectroscopy, FT-IR and GC-MS (methanolic extract of the active layer) analyses. Position of biQ in PTZ-biQ as 1,4-quinone isomer was confirmed by observation of absence of copper-complexation with 1,4-quinone and H2O2 electrochemical reduction reactions at −0.1 V vs Ag/AgCl unlike to the specific copper-complexation and H2O2 reduction with 1,2-quinone isomer in pH 7. Cysteine (CySH) oxidation was studied as a model system to understand the electron-transfer function of the MWCNT@PTZ-biQ. A highly selective electrocatalytic oxidation and sensing by amperometric i-t and flow injection analysis of CySH at low oxidation potential, 0.3 V vs Ag/AgCl in pH 7 PBS with detection limit values (signal-to-noise ratio = 3) of 11.10 μM and 110 nM respectively, without any interference from other biochemicals like uric acid, dopamine, nitrite, citric acid and H2O2, unlike the conventional chemically modified electrodes with serious interference's, have been demonstrated.

In the present work, we report a simple chemical precipitation method for the preparation of different levels of Cu doped MnO2 nanocrystals. X-ray diffraction, field emission transmission electron microscope and X-ray photoelectron spectroscopy were used to study the material properties. To demonstrate the suitability of the doped products for electrode applications electrochemical properties were evaluated by Cyclic Voltammetry (CV), galvanostatic charge–discharge studies and impedance spectroscopy. The results indicate that the MnO2 electrode modified with 0.1 M of Cu has a better electrode property with a specific capacitance of 583 F/g and an energy density of 80 W h kg−1.

Developments of new decomposition or degradation methods of environmentally hazardous azo dyes from textile industries are very important. Usually, strong acid-based chemical/electrochemical and neutral pH-based bacterial decomposition methods were widely used. Here, we report a mild, simple, and facile electrochemical method for decomposition of azo dye (Sudan yellow; SY) into a highly redox active copolymer of polyanilines via aniline derivatives as intermediates on a MWCNT modified glassy carbon electrode (GCE/MWCNT) surface unusually in a neutral pH using phosphate buffer solution (PBS) (GCE/MWCNT@SY-CoPANIpH7). One of the intermediate products, aniline (Mw = 93 mol g–1, calculated) was identified by an in situ cyclic voltammetry-electrochemical quartz crystal balance experiment. No such SY electrochemical reaction was observed on a naked GCE surface. Physico-chemical characterizations by TEM, Raman, IR, and UV–vis spectroscopic methods supported the formation of polymeric product on MWCNT surface (GC...

Electrochemical oxidation of phenol on carbon electrodes has often been associated with problems such as serious adsorption, formation of electro-inactive tarry polymers and surface fouling. Thus, it is highly challenging to develop a phenol electrochemical sensor without encountering such problems. Alternately, biosensors, which comprise of enzymes such as tyrosinase and polyphenol oxidase, were widely used for the aforesaid purpose. Herein, we introduce an ultra-low cost 6B grade pencil graphite, pre-anodized at 2 V vs. Ag/AgCl, designated as 6B-PGE*, where * = preanodized, as a novel electrochemical sensor for surface fouling-free and efficient differential voltammetric (DPV) detection of phenols (meta-cresol and phenol) in pH 7 phosphate buffer solution (PBS). A well-defined cyclic voltammetric peak at 0.65 ± 0.02 V vs. Ag/AgCl, which is stable under multiple electrochemical cycling, was noticed upon electrochemical-oxidation of meta-cresol and phenol at 6B-PGE*. The 6B-PGE* showed eight times higher DPV current signal and 60 mV lower oxidation potential than non-preanodized electrode (PGE) for the phenol detection. Under optimal DPV conditions, the 6B-PGE* showed a linear calibration plot with current linearity in a range of 40–320 μM with current sensitivity and detection limit (signal-to-noise = 3) values of 1.43 μA μM−1 cm−2 and 120 nM, respectively. Six repeated detections of 80 μM meta-cresol without any interim surface cleaning process showed a relative standard deviation (RSD) value of 0.21%. This electro-analytical approach was validated by testing total phenolic contents in three different insulin formulations with an electrode recovery value of ∼100%.

Organic redox mediator functionalized carbon nanomaterials has been considered the future of advanced nanomaterials owing to their exemplary behaviors. It is highly challenging to prepare stable functional carbon nanomaterials. Herein, we report a simple preparation of highly redox active and stable quinoline quinone (QLO) functionalized multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/MWCNT@QLO) by in-situ electrochemical oxidation of 8-hydroxyquinoline (QL) on a GCE/MWCNT in pH 7 phosphate buffer solution. Unlike the formation of electro-inactive and tarry polymeric products with electrochemical oxidation of QL at glassy carbon electrode, a multi-redox active QLO derivative intermediate was electro-generated as intermediate species and was trapped on a MWCNT modified electrode in this work. Specific pi-pi interaction between QL and MWCNT and its diffusion restrictive electrochemical oxidation process are keys for the selective entrapment of QLO on the underlying electrode. The QLO trapped MWCNT modified electrode (GCE/MWCNT@QLO) was characterized by Transmission electron microscope, X-ray photoelectron spectroscopy, Raman spectroscopy, Infrared spectroscopy, gas liquid chromatography coupled mass spectrometry and in-situ cyclic voltammetry (CV) electrochemical quartz crystal microbalance. CV of the GCE/MWCNT@QLO has displayed three well-defined redox peaks at E1/2 = -0.45 V (A1/C1), -0.1 V (A2/C2) and 0 V vs Ag/AgCl (A3/C3) corresponding to the electron-transfer behaviors of pyridinium ion, 2,3 and 5,8 diquinone functional groups of the MWCNT@QLO. The intermediate trapped modified electrode showed excellent electrocatalytic behavior and amperometric current-time sensing response to an environmental pollutant, hydrazine at 0 V vs Ag/AgCl in pH 7 phosphate buffer solution with a calibration plot linearity and detection limit values of 25-450 μM and 12 μM respectively without any interference from ascorbic acid, uric acid, cysteine and nitrate. In further, flow injection analysis coupled electrochemical of hydrazine at 0 V vs Ag/AgCl with a detection limit value 0.7 μM was also demonstrated.

Prussian blue (PB), an inorganic iron-hexacyanoferrate polymer, is a potential redox system. In general, it can be prepared on any conducting substrate by electrochemical deposition technique in which a working electrode is potential cycled with millimolar quantities of a mixture FeCl 3 and [Fe(CN) 6 ] 3− in an alkaline metal ion containing acid solution (pH 6 ] 3− is subjected to the electrochemical potential cycling technique with a Iron(III) adsorbed multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT–Fe 2 O 3 ), as a template, in pH 2 KCl–HCl. The PB electrode thus designated as GCE/MWCNT–Fe 2 O 3 @PB showed well-defined redox peaks at apparent standard electrode potentials, 190 ± 5 and 850 ± 5 mV vs Ag/AgCl and synergistic effect of PB, MWCNT and Fe 2 O 3 systems. As prepared MWCNT–Fe 2 O 3 @PB was characterized by various physico-chemical techniques such as Scanning electron microscopy, Energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. Presence of trace amount of the precursor, Fe 2 O 3 within the inner core of the hybrid PB system was evident from the characterization results. In further, it was found that one of the metallic impurities, iron in the MWCNT has influenced the PB formation. The new hybrid PB electrode exhibited 17 times higher reduction current value over the conventionally prepared GCE/PB for the H 2 O 2 electrocatalysis. Applicability of the electrode to sensing of H 2 O 2 in real sample such as milk, cream bleach and clinical solution was successfully demonstrated.

Adenine (A) and guanine (G), important bases of nucleic acids, are often analyzed by separation coupled spectroscopic detection methods. Herein, we are demonstrated a new flow-injection analysis (FIA) coupled dual electrochemical detector (DECD), where a chitosan-carbon nanofiber (Chit-CNF) modified glassy carbon electrode prepared by a simple technique and pH 7 phosphate buffer solution as a carrier system, for separation-less quantification of G and A. This method is highly selective and no interference by the presence of the other DNA bases (Thymine and Cytosine). The FIA-DECD was operated at two different operating potentials, E1 = 0.80 V and E2 = 0.95 V vs Ag/AgCl, where G and {G + A} get oxidized, respectively. Amount of A was calculated from the difference between the FIA current signals, measured at E20.95V and E10.80V. The GCE/Chit-CNF was characterized by cyclic voltammetry with potassium ferricyanide system and Raman spectroscopy. The modified electrode showed unique electron-transfer feature with metal like conductivity. Under an optimal condition, FIA-DECD showed linear calibration plots for G and A in a concentration range, 200 nM—50 μM with current sensitivity values 13.83 ± 0.48 and 4.84 ± 0.11 nA μM−1 respectively. Calculated detection limit (signal-to-noise ratio = 3) values were 46.8 nM and 73.8 nM for G and A respectively. Applicability of the present technique was further demonstrated by detecting G and A in beef kidney sample and DNA hybridization process.

Electrochemical immobilization of 4-nitrophenol (4-NP) was conducted on a purified multi-walled carbon nanotube (p-MWCNT) modified glassy carbon electrode (GCE/p-MWCNT) in pH 7 phosphate buffer solution (PBS). The electrochemical reduction of 4-NP to stable in situ electrogenerated hydroxylamine (ONHOH) intermediate species within the p-MWCNT matrix may be the underlying mechanism of immobilization. The ONHOH-stabilized p-MWCNT modified electrode, GCE/ONHOH@p-MWCNT, showed stable and well-defined surface-confined redox peaks at −0.11 V (A1/C1) and 0.080 V (A2/C2) vs. Ag/AgCl over other CNT-modified GCEs. The modified electrode system suggested quasi-reversible and reversible electron transfer mechanisms for the A1/C1 and A2/C2 redox couples. TEM analysis of the ONHOH@p-MWCNT hybrid powder demonstrated the presence of ONHOH species on the surfaces, as well as on the inner walls of the p-MWCNTs. The XRD peaks exhibited shifts in 2θ values for the hybrid material compared with the unmodified materials, which confirmed the stabilization of ONHOH within the p-MWCNT via π–π interactions. Electrochemical characterization of the GCE/ONHOH@p-MWCNT revealed two electron transfer mechanisms with adsorption-controlled and Nernstian behaviours. A highly sensitive electrocatalytic oxidation of dihydronicotinamide adenine dinucleotide (NADH) at 0.02 V vs. Ag/AgCl was achieved with the GCE/ONHOH@p-MWCNT. Furthermore, the hybrid electrode successfully sensed NADH amperometrically with 2.9 nA μM−1 sensitivity, a 0.043 μM limit of detection and a linear detection range from 100 μM to 1 mM for ten successive additions of 100 μM NADH at an applied potential of 0.02 V vs. Ag/AgCl in pH 7 PBS.

Pyrene (PYR) is a rigid, carcinogenic, unreactive, and nonelectrooxidizable compound. A multiwalled carbon nanotube (MWCNT)-modified gold electrode surface-bound electrochemical oxidation of PYR to a highly redox-active surface-confined quinone derivative (PYRO) at an applied potential of 1 V versus Ag/AgCl in pH 7 phosphate buffer solution has been demonstrated in this work. Among various carbon nanomaterials examined, the pristine MWCNT-modified gold electrode showed effective electrochemical oxidation of the PYR. The MWCNT's graphite impurity promotes the electrochemical oxidation reaction. Physicochemical and electrochemical characterizations of MWCNT@PYRO by Raman spectroscopy, FT-IR, X-ray photoelectron spectroscopy, and GC-MS reveal the presence of PYRO as pyrene-tetrone within the modified electrode. The quinone position of PYRO was identified as ortho-directing by an elegantly designed ortho-isomer-selective complexation reaction with copper ion as an MWCNT@PYRO-Cu(2+/1+)-modified electrode. Finally, a cytochrome c enzyme-modified Au/MWCNT@PYRO (i.e., Au/MWCNT@PYRO-Cyt c) was also developed and further demonstrated for the selective biosensing of hydrogen peroxide.

White spot syndrome virus (WSSV) is a major devastating virus in aquaculture industry. A sensitive and selective diagnostic method for WSSV is a pressing need for the early detection and protection of the aquaculture farms. Herein, we first report, a simple electrochemical immunosensor based on methylene blue dye (MB) immobilized graphene oxide modified glassy carbon electrode (GCE/GO@MB) for selective, quick (35 ± 5 mins) and raw sample analysis of WSSV. The immunosensor was prepared by sequential modification of primary antibody, blocking agent (bovine serum album), antigen (as vp28 protein), secondary antibody coupled with horseradish peroxidase (Ab2-HRP) on the GCE/GO@MB. The modified electrode showed a well-defined redox peak at an equilibrium potential (E1/2), −0.4 V vs Ag/AgCl and mediated H2O2 reduction reaction without any false positive result and dissolved oxygen interferences in pH 7 phosphate buffer solution. Under an optimal condition, constructed calibration plot was linear in a range of 1.36 × 10−3 to 1.36 × 107 copies μL−1 of vp28. It is about four orders higher sensitive than that of the values observed with polymerase chain reaction (PCR) and western blot based WSSV detection techniques. Direct electrochemical immunosensing of WSSV in raw tissue samples were successfully demonstrated as a real sample system.

A hemoglobin (Hb) modified glassy carbon electrode consisting of low cost as commercially received impure-multiwalled carbon nanotube (i-MWCNT, 90% purity) and nafion (GCE/i-MWCNT@Hb/Nf) has been demonstrated for improved electric wiring of Hb and efficient direct electron-transfer characteristics. This report is the first attempt for coupling i-MWCNT with Hb for the biosensor purpose. The Hb electrode was assembled by a simple preparation procedure within 38.3 (±2.5) min of time, without any linker, surfactant, promoters, and extensive functionalization of the MWCNT. Impurities within the i-MWCNT such as metal oxides (Fe3O4, Co3O4, and NiO), graphite, and amorphous carbon were quantitatively identified by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The metal oxide impurities were found to assist the binding of Hb onto i-MWCNT, whereas the graphitic impurity facilitated the direct electron-transfer reaction. The measured surface excess value of the Hb on the GCE/CNT@Hb/Nf with respect to...

A graphitized mesoporous carbon modified glassy carbon electrode (GCE/GMC) prepared by drop coating method without any pre-anodization of the underlying GCE or external binder/matrix, has been demonstrated for simultaneous electrochemical oxidation of guanine (G) and adenine (A) at oxidation potentials 0.60 and 0.85 V vs. Ag/AgCl, respectively, in the presence of thymine (T) by differential pulse voltammetric method in pH 7 phosphate buffer solution. Control voltammetric experiments with unmodified GCE, graphite nanopowder and multiwalled carbon nanotube modified electrodes yielded either feeble or with high-background current responses. Interestingly, the GCE/GMC showed highly efficient, stable and well-defined voltammetric signals. Thymine oxidation signal noticed discretely at 1.15 V vs. Ag/AgCl on the GCE/GMC was not influenced for the simultaneous determination of G and A. Constructed DPV calibration graphs were linear in the range of 25–200 and 25–150 μM, respectively, for the G and A. Corresponding detection limit (S/N = 3) values are 0.76 and 0.63 μM. Real sample analyses for the detection of G and A concentrations in calf-thymus DNA (detected [G]/[A] ratio = 0.82), beef brain and beef liver were successfully demonstrated with recovery values ~100 %.

Selective detection of dopamine (DA) in presence of ascorbic (AA) is an important analytical problem, due to its combined existence in the biological system. In the present study, we are reporting an electrochemical detection method for dopamine (DA) in the presence of ascorbic acid (AA) using graphitized nanoporous carbon (NPC) modified glassy carbon electrode (GCE/NPC) in 0.1 M phosphate buffer solution. The modified electrode shows excellent electrocatalytic activities towards the oxidations of DA and AA in neutral pH buffer solution. Compared to unmodified GCE, GCE/NPC shows well separated and enhanced oxidation peak currents. Differential pulse voltammetric technique used as qualitative analytical tool for the detection of DA. The oxidation peak potentials for DA and AA were at -80 and 136 mV vs Ag/AgCl respectively. The modified electrode shows good stability and reproducibility with the relative standard deviation value of 2.6 %. The analytical application of the modified electrode (GCE/NPC) was demonstrated for the individual determination of DA in clinical injection and pharmaceutical tablet by using standard addition method.

Simple preparation of anthraquinone (AQ)–carbon nanotube (CNT) hybrid architecture on a glassy carbon electrode without any AQ-derivatization step, has been described. The method consisting of drop casting of AQ solution on a CNT modified GCE, in contrast to the time consuming conventional preparation methods with several synthetic steps. Amongst various forms of carbon nanotubes examined for the AQ immobilization process including single walled carbon nanotube, multiwalled carbon nanotube (MWCNT) and functionalized MWCNT (f-MWCNT), the f-MWCNT modified electrode has shown the best electrochemical features in our work. The optimal electrode gives stable and well-defined two surface confined redox peaks at E1/2 values of −230 (A1/C1) and −530 mV vs Ag/AgCl (A2/C2) in pH 7 phosphate buffer solution, unlike to a single redox peak response of conventional AQ modified electrodes. The reason for the observation might be due to adsorption of AQ on different energetic sites of the carbon nanotubes. The AQ@f-MWCNT hybrid electrode showed an efficient electrocatalytic response to hydrogen peroxide reduction reaction. Interaction of electrons between pi–pi bonds of AQ and sp2 sites of CNT, was proposed as a plausible mechanism for the AQ stabilization on the carbon nanotube modified electrode.

Hybrid nickel-hexacyanoferrate-functionalized multiwalled carbon nanotube modified glassy carbon electrode (GCE/Ni-NCFe@f-MWCNT) has been prepared using electrodeposited Ni on functionalized MWCNT modified GCE (GCE/Ni@f-MWCNT) as a template and [ Fe ( CN ) 6 ] 3 - as an in-situ chemical precipitant, without any additional linker. Characterization of the GCE/Ni-NCFe@f-MWCNT by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy and cyclic voltammetry (CV) collectively revealed that the functionalized MWCNT is effective to uptake large amount of Ni species and, in turn, substantial quantity of Ni-NCFe units within its internal structure. Cyclic voltammetry of the GCE/Ni-NCFe@f-MWCNT showed non-stoichiometric K+/e− and insertion/exertion behavior (∂Epa/∂log [KCl] = 42.9 and (∂Epc/∂log [KCl] = 117 mV/decade) due to some kinetic limitation to the insertion of K+ ion through the hydrophobic basal planes of the hybrid electrode. A quantitative model has been proposed to estimate the influencing components (underlying support, surface functional groups, basel plane, impurities, and insertion into edge-plane defects) in the formation of the hybrid Ni@f-MWCNT and, in turn, the Ni-NCFe@f-MWCNT. Electrocatalytic hydrazine oxidation on the GCE/Ni-NCFe@f-MWCNT showed 33 times enhancement in the current signal over GCE/f-MWNT in a pH 7 phosphate buffer solution. Amperometric i–t method of hydrazine detection yielded current sensitivity and calibration range of 120.2 μA/μM and 20–200 μM, respectively. The hybrid GCE/Ni-NCFe@f-MWCNT material is tolerable to other co-existing interferences such as oxalic acid, citric acid and nitrite. Finally, three different water real sample analyses were successfully demonstrated with appreciable recovery values.

A screen-printed silver strip with a built-in three-in-one electrode (SPAgE) configuration of Ag-working, Ag-counter and Ag/AgxO (silver oxides) pseudoreference electrodes has been developed for sensitive and selective electrochemical flow injection analysis (FIA) of aluminum chlorohydrate (ACH) present in antiperspirants, through the free Cl � ion liberated from ACH in aqueous medium, as a redox signal at Ag-working electrode in pH 6 phosphate buffer solution (PBS). The solution phase and instrumental parameters were systematically optimized. The calibration graph was linear in the window 1–200 ppm concentration of ACH and the lowest detection limit (S/N = 3) was 295 ppb with a slope of 0.0989 mA/ppm and regression coefficient of 0.998. Calculated relative standard deviation (RSD) values for the detection of 5 and 50 ppm ACH by this method are 2.21 % and 2.16 %, respectively. Four different antiperspirant deodorants real samples with and without ACH content were successfully analyzed and the detected values obtained were found to be in good agreement with the product labeled values.

Electrochemical-assisted encapsulation of a neurotransmitter, catechol (CA), as nanoaggregates on a multiwalled carbon nanotube (>90% of carbon basis MWNT) modified gold electrode (Au/CA@CNT) has been demonstrated without any derivatization or electrode preactivation procedures. Characterization of the CA@CNT by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared attenuated total reflection (FTIR/ATR) spectroscopy, and cyclic voltammetry (CV) collectively revealed stable encapsulation of the CA within strained and misalignment areas of the MWNT capsule. The Au/CA@CNT shows a couple of redox peaks centered at 0 (A1/C1) and 200 mV vs Ag/AgCl (A2/C2) due to the encapsulated (chemisorbed) and physisorbed CA moieties, respectively. The calculated chemisorbed catechol surface excess, Gamma(CA), value was 98.3 x 10(-10) mol x cm(-2). Control solution phase preparations of CA@CNTs yielded poor loading and instability problems, if it is chemically modified on the gold electrode. Electrochemical mediated oxidation of hydrazine on the Au/CA@CNT was demonstrated with an approximately 20 times increase in peak current and 200 mV reduction in the overpotential values in a pH 7 phosphate buffer solution.

Aluminum chlorohydrate (Al2(OH)5Cl · 2H2O, ACH) is an active ingredient in many antiperspirants and deodorants formulation to reduce the body odors (mainly sweat) through interaction with apocrine sweat glands to produce insoluble aluminum hydroxide and free chloride, which then plugs the sweat gland that stops the flow of sweat to the skins surface. We demonstrated here an one drop (50 mL) electrochemical sensing of the ACH using an in-built three screen-printed electrodes assembly containing Ag as working and pseudo reference and carbon as counter electrode system (AgSPE). The free Cl � ion librated from ACH/H2O reaction was detected at AgSPE surface at 0.072 V vs. pseudo Ag reference electrode system in pH 2 phosphate solution by Cyclic voltammetric Technique. Under optimal working condition the AgSPE shows a linear calibration plot in the window of 30 - 2000 ppm of ACH with sensitivity and regression values of 0.104 mA/ppm and 0.998 respectively. Calculated detection limit is 3.03 ppm. RSD values of intra- and interassays were 0.19% and 2.79% respectively. Finally, real sample (antiperspirant deodorant lotions) assays were successfully demonstrated with results comparable to the predicted values.

We successfully demonstrated microliter (mL) volume determination of Mercury (Hg) using an in-built screen-printed three electrodes containing partially crosslinked poly(4-vinlylpyridine) (designated as pcPVP) modified carbonworking, carbon-counter, and Ag þ -quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 mL-droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag þ quasi-reference system shifted the Hg-SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100 – 1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N ¼ 3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin-lightening agents in parallel with ICP-OES measurements.

We report here a highly stable and sensitive chemically modified screen-printed carbon electrode (CMSPE) for sulfide analysis. The CMSPE was prepared by first ion-exchanging ferricyanide into a Tosflex anion-exchange polymer and then sealing with a tetraethyl orthosilicate sol-gel layer. The sol-gel overlayer coating was crucial to stabilize the electron mediator (i.e., Fe(CN)6(3-)) from leaching. The strong interaction between the oxy-hydroxy functional group of sol-gel and the hydrophilic sites of Tosflex makes the composite highly rigid to trap the ferricyanide mediator. An obvious electrocatalytic sulfide oxidation current signal at approximately 0.20 V versus Ag/AgCl in pH 7 phosphate buffer solution was observed at the CMSPE. A linear calibration plot over a wide range of 0.1 microM to 1mM with a slope of 5.6 nA/muM was obtained by flow injection analysis. The detection limit (S/N=3) was 8.9 nM (i.e., 25.6 ppt). Practical utility of the system was applied to the determination of sulfide trapped from cigarette smoke and sulfide content in hot spring water.

Efficient and stable electrocatalytic activity for the reduction of O2 at activated screen-printed carbon electrodes modified with palladium nanoparticles (SPE*-Pd) was demonstrated in this study. X-ray photoelectron spectroscopy confirmed the formation of > C¼O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both > C¼O and chloride functional groups were essential for the excellent stability of the SPE*-Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as-prepared Pd nanoparticles. The SPE*-Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE-Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 mA/ppm and 0.9936, respectively. The variation coefficient of ipc for 7 DO determinations with O2-saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter.

Cuprous iodide (γ-CuI) is an important semiconductor material having a bang gap of 3.1 eV often used for visible light assisted photoelectrochemical and solar energy conservation systems. We report the first and unique preparation of fine and precisely controlled γ-CuI semiconductor nanocrystallites on the surface of a screen-printed carbon electrode using a photoelectrochemical copper nanoparticle deposition method with tris(hydroxymethyl)aminomethane (Tris) buffer solution as a control medium. Tris buffer helps to split CuO and CuIIO oxidation states through specific complexation mechanism and in turn to selective iodination of CuO to the formation of γ-CuI on the electrode. Stable and linear photoelectrochemical response was further demonstrated against variable light intensity up to 400 Klux using the γ-CuI modified system.

We introduce here the application of barrel plating technology for mass production of disposable-type electrodes. Easy for mass production, barrel plating rhodium electrode (Rh-BPE) is for the first time demonstrated for analytical application. Hydrazine was chosen as a model analyte to elucidate the electrocatalytic and analytical ability of the RhBPE system in pH 7 phosphate buffer solution. Flow injection analysis (FIA) of hydrazine showed a linear calibration range of 25 – 1000 ppb with a slope and a regression coefficient of 5 nA/ppb and 0.9946, respectively. Twenty-two replicate injections of 25 ppb hydrazine showed a relative standard deviation of 3.17% indicating a detection limit (S/ N ¼ 3) of 2.5 ppb. The system can be continuously operated for 1 day without any alteration in the FIA signals and is tolerable to the interference of oxalic acid, gelatine, Triton X-100, and albumin for even up to 100 times excess in concentration with respect to 400 ppb hydrazine. Since the fabrication cost of the electrode is cheap, it is thus disposable in nature. Furthermore, barrel plating technique can be extendable to other transition metals for application in many fields of research interest.

Natural iron-intercalated clay (nontronite, SWa-1) was converted into a more efficient catalyst by formation of lead ruthenate pyrochlore (Py, Pb2Ru2−xPbxO7−y) directly inside the matrix. The new material can take advantage of the electrocatalytic properties of both Py and nontronite and can even generate new catalytic active sites due to interaction of Py and nontronite. The combination of these two interesting catalysts results in a more reactive electrode (designated as SWa-1/PyCME) for electroanalytical applications. The preparation and characterization of the SWa-1/PyCME as well as its electrocatalytic behavior toward the oxidation of dopamine are described in this study. Surface saturation kinetics in terms of Michaelis-Menten kinetics suited well the oxidation of dopamine on this modified electrode. Under optimized conditions, the detection limit (S/N= 3) was 0.54 nM by square-wave voltammetry.