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Metal and heteroatom-free electro-active carbon soot nanoparticles of average size 50 ± 10 nm have been prepared by simple atmospheric combustion of abundant naphthalene compound. Physicochemical characterizations by Transmission electron-microscope, Infrared, Raman spectroscopy, X-Ray diffraction, and CHN analysis techniques revealed that the soot has a graphitic core with highly defective oxygen structure composed of carbonyl, hydroxyl, ether, furan, pyran, pyrone and carboxylic acid along with aliphatic carbons on the surface. Electrochemical characterization with a bench mark redox system, Fe(CN)63− reveals the efficient conductive behaviour of the new soot material even after mixing with the anionic-Nafion membrane (Nf). The GCE/Soof-Nf showed a well-defined oxygen reduction reaction (ORR) current signal at cathodic peak potential, −0.39 V vs Ag/AgCl similar to that of the heme, hemoglobin and quinone based electrochemical systems for oxygen reduction reaction (ORR) in neutral media. Obtained ORR peak current signal is found to be 2–5 times higher than that of the current signals noticed with activated charcoal, graphite nanopowder, functionalized MWCNT and bulk gold electrodes. Rotating disc electrode and bio-potentiostat coupled flow-injection analysis techniques have been adopted to find out the kinetics and mechanism of the ORR. Utilizing the new carbon soot material, sensitive detection of dissolved oxygen with detection limit 8.6 ppb was demonstrated in neutral buffer solution.

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.

Indole and its derivatives are important core constituents of several natural, biological and pharmaceutical relevant compounds. In general, electrochemical oxidation of indole on solid electrodes in acid and non-aqueous conditions results in the formation of polyindole like compounds as an end product. Selective and controlled electrochemical oxidation of indole and its derivatives to redox active intermediate compound/s without over-oxidation to the polymeric product is a challenging research task. Herein, we report an electrochemical oxidation of electro-inactive indole to a multi-redox active Indole Tetraone (1H-Indole-2,3,4,7-Tetraone)-a new organic redox species (Ind-Tetraone) and entrapment as a surface-confined redox active species on multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT@Ind-Tetraone) in physiological pH solution. GCE/MWCNT@Ind-Tetraone showed a well-defined surface-confined redox peaks at E1/2, −0.270 V (A1/C1) and +0.270 V (A2/C2) vs Ag/AgCl. From the physicochemical characterizations by Raman and IR spectroscopy, XPS, LC-MS (an ethanolic extract) and control electrochemical experiments with various substituted indole derivatives, it is confirmed the formation of Ind-Tetraone species without any polyindole formation upon the electrochemical oxidation of indole on MWCNT surface. Electrochemical oxidation of nitrogen atom as a radical species and subsequent electron-transfer/water addition reaction is proposed as a possible mechanism for the Ind-Tetraone product formation. A simultaneous electrocatalytic oxidation of hydrazine and reduction reaction of hydrogen peroxide at two discreet potentials has been demonstrated as a bifunctional application of the GCE/MWCNT@Ind-Tetraone system. In further, the GCE/MWCNT@Ind-Tetraone as a electrochemical detector, simultaneous flow injection analysis of hydrazine and hydrogen peroxide was also demonstrated as a proof of concept for the bifunctional application.

Understanding the electron-transfer (ET) functionality of enzymes in relation to their molecular orientation and dynamics is a cutting-edge research interest in the interdisciplinary areas of chemistry and biology. In this work, we demonstrate how the molecular structure and orientation of a redox polymer influence the ET behavior and specific catalytic functionality to target substance, ascorbic acid (AA) or cysteine (CySH) in a physiological condition. In the literature, Fe(CN)63−, a well-known benchmarking redox system, based chemically modified electrodes (CME) prepared by the ion-exchange method, has been widely used as an electrocatalyst for ascorbic acid oxidation reaction without the interference of CySH. In this work, a Fe(CN)63− bearing copoly(ionic liquid)-ethanol solution modified glassy carbon electrode, designated as GCE@{Fe(CN)63−}-coPIL, prepared as a homogenous solution followed by CME formation, has shown a unique and selective CySH oxidation reaction, rather than expected AA mediation, similar to the Thiol Oxidase enzyme-based biomimetic functionality. Andrieux and Saveant and Michaelis-Menten kinetic models were adopted to explain the reaction mechanism. The polymer network orientation and dynamics are found to influence strongly on the electrocatalytic functionality of the new CME. It has been revealed that underlying surface, functional groups, and solvent nature impact the molecular architectures of the {Fe(CN)63−}-caped polymer back-bone (insulating) network as a fully (H2O and CHCl3) or partially (C2H5-OH and CH3CN) shielded structures and decide its electron-transfer and selective mediated oxidation reaction functionalities. This observation is similar to the protein folding of enzymes at various external stimuli conditions and its unfolded structures for direct electron transfer and selective mediated oxidation/reduction reaction. As a proof of concept, electroanalytical application of thiol functional group (CySH) oxidation to disulfide bond (CyS-SyC) catalyzed by the GCE@{Fe(CN)63−}-coPIL in neutral pH solution has been demonstrated.

A unique gold(111) oriented nanoparticles trapped carbon nanofiber-chitosan modified electrocatalyst coated glassy carbon electrode(GCE/CNF-CHIT@Aunano) was prepared by an in-situ electrochemical procedure for efficient bifunctional electrocatalytic oxidation and reduction of formaldehyde and hydrogen peroxide in neutral pH solution. In the typical preparation, a microliter quantity of Au3+ solution was drop-casted on GCE/CNF-CHIT surface and potential cycled in pH 7 PBS. The GCE/CNF-CHIT@Aunano showed well-defined electrochemical response of gold nanoparticles of calculated electrochemically active surface area, 0.1347 cm2, which is about 3–3000 times higher than that of the surface area of the respective unmodified electrodes such as polycrystalline Au (0.0407 cm2), GCE/CNF@Aunano (0.0034 cm2) and GCE@Aunano (0.0005 cm2). Physicochemical characterizations such as FESEM, EDAX, TEM, XRD, Raman, FTIR and XPS spectroscopic techniques revealed stabilization of 10 ± 5 nm sized Au(111) phase oriented nanoparticles by the amino functional group of chitosan in the composite matrix. The detailed electrochemical characterization by cyclic voltammetry(CV), rotating disk electrode (RDE) and in-situ CV-electrochemical quartz crystal microbalance (EQCM; Mw = 44 ± 1 g mol−1 species was identified) techniques showed direct oxidation of formaldehyde to formate as an intermediate (45 g mol−1) without any CO poisoning, unlike the conventional Pt and Au based electrodes. Using a bipotentiostat, selective and simultaneous flow injection analyses of formaldehyde and hydrogen peroxide in a mixture at discreet applied potentials (Eapp = 0.5 V/0.15 V and −0.15 V vs Ag/AgCl) were demonstrated. The applicability of the GCE/CNF-CHIT@Aunano was tested by detecting formaldehyde and hydrogen peroxide in a commercial hair dye formulation with about 100% 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.

The electron-transport chain that involves a proton-coupled electron-transfer (ET) reaction between hydroquinone (H2Q) and Cytochrome c (Cyt c) in the acid pool is one of the key processes of the respiratory complex 1 in cytoplasmic membrane of the bacterium and mitochondrial complexes, complex III (cytochrome bc1 or ubiquinol:cytochrome c oxidoreductase) of photosynthesis systems. In the literature, several spectroscopic techniques in association with electron-transfer inhibitors have been reported for this purpose. Till now, there is no straight forward voltammetric proof to reveal the mechanistic feature of the direct ET process. In the electrochemistry point of view, it is a challenging task to prepare a chemically modified bio-electrode composed of H2Q and Cytc redox systems with proper ET channels between them and to probe the mixed-potential reaction by direct voltammetric technique. Herein, we report a carboxylic acid functionalized hydroquinone (2,5-dihydroxy benzoic acid; H2Q-COOH) immobilized multiwalled carbon nanotube modified glassy carbon electrode (GCE/MWCNT@H2Q-COOH), prepared by in-situ electrochemical oxidation of 2-hydroxy benzoic acid (Ph-COOH), as a molecular wiring system for unfolded Cytc protein and further to study the direct voltammetric ET reaction using H2O2 as a specific probe in pH 2 KCl-HCl medium. The formation of surface-confined H2Q-COOH was confirmed by physicochemical and spectroscopic characterization techniques including IR, Raman, UV-Vis, Thin-layer chromatography, NMR and GC-MS. The GCE/MWCNT@H2Q-COOH showed well-defined redox peaks corresponding to consecutive one-electron-transfer reactions of H2Q-COOH/•QH-COOH (Eo'= 0.410 V vs Ag/AgCl, A1/C1) and •QH-COOH/Q (Eo'= 0.750 V vs Ag/AgCl, A2/C2), similar to one occurs with a membrane-bound ubiquinone and plastoquinone systems in the biological systems. The unfolded Cytc modified electrode, GCE/MWCNT@H2Q-COOH@Cytc prepared by chemical modification technique, has exhibited a specific and selective bioelectrocatalytic reduction current signal in between the redox potentials of QH2/•QH and Cytc in pH 2 KCl-HCl biomimicking the biological electron-transport chain reaction. In further amperometric techniques have been used to successfully demonstrate the ET reaction.

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.

Bay-region containing polyaromatic hydrocarbons (PAHs) like Benzo(a)pyrene (BaP), which comprise several strained benzenoid rings, are representative organic compounds for the carcinogenic and mutagenic activities in physiological system. In general, cytochrome c, peroxidase and certain soil-bacteria oxidize these compounds to respective hydroxylated metabolites like BaP-7,8-diol (BaP–2OH), that can interact with DNA, RNA and protein, and in turn makes the cellular system dysfunctional. The structure - activity relationship of these compounds is still unclear and therefore, it is necessary for a new analytical approach to delineate the intricate mechanism behind the oxidation of the PAHs. Herein, we report, a simple electrochemical approach of surface-confined oxidation of BaP on multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/MWCNT) in physiological condition (pH 7 phosphate buffer solution). It has been found that MWCNT-surface adsorbed BaP (electro-inactive compound) gets electro-oxidized to highly redox active BaP–2OH compound at high positive potential, 1.2 V vs Ag/AgCl, in which, the water molecule was oxidized to molecular oxygen via hydroxyl radical intermediate. From the collective electrochemical and physicochemical studies using Raman, FTIR, GC-MS and 1,2-dihydroxy redox active probe, cysteine (CySH), it has been observed that the hydroxyl radical species produced on the surface has assisted the BaP oxidation to BaP-7,8-diol product, which is similar to the biocatalyzed oxidation of BaP observed in the physiological system. The BaP-7,8-diol surface confined MWCNT modified GCE showed a well-defined and stable redox peak at an apparent standard electrode potential, Eo’ = 0 V vs Ag/AgCl. The redox process is found to be proton-coupled electron-transfer in nature. As an independent study, selective electrocatalytic oxidation of CySH has been demonstrated as an application.

Owing to the high demand of conducting molecular systems for various electronics and technological applications, development of new polyaniline (PANI)/carbon nanomaterial is a continued research interest in cross-disciplinary area of material chemistry. In the literature, for the preparation of PANI/carbon nanomaterial composite electrode systems ex-situ preparation method, in which, chemical oxidation of aniline in presence of carbon nanomaterial, followed by modification on solid substrate has been widely adopted. In this work, a systematic study has been carried out for in-situ electrochemical polymerization of 4-chloroaniline and other substituted aniline monomers to respective PANI on graphitized mesoporous carbon (GMC), that show porous structure and enormous sp2 sites to aniline and PANI for π-π interaction, unusually in neutral pH condition. The new GMC@PANI modified electrode showed a highly redox active peak at Eo’ = 0.12 V vs Ag/AgCl in pH 7 phosphate buffer solution. No such behaviour was noticed when an unmodified glassy carbon was used as working electrode for the polymerization in the above mentioned condition. The redox peak is found to be stable, surface-confined and Nernstian type of proton-coupled electron-transfer in nature. Based on the physicochemical characterization techniques using Raman, IR, X-Ray photoelectron-spectroscopy, scanning electron-microscope and scanning electrochemical microscope (SECM) instruments and electrochemical studies with several ortho, para and meta substituted aniline monomers, mechanism for the in-situ polymerization has been revealed that 4-chloroaniline monomer has undergone a surface-confined electrochemical oxidation reaction with involvement of aniline(4-Cl)-cation radical species, anti-orientation of the monomer (that exist in solution phase), head-to-tail collision (C-N bonding), ejection of the para-substituents as Cl- and Cl•, partial chlorination and PANI(4-Cl) formation mechanism. Such a PANI(4-Cl) film showed a wave-like 2D molecular film structure with enhanced redox and electrical property over the conventional PANI system.

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.

Hydrazine is one of the hazardous chemicals present in tobacco and known to be human carcinogen. It is highly challenging to detect hydrazine present in the tobacco selectively. Since, hydrazine molecule didn’t have any chromophore, indirect methods like separation coupled derivatization technique have been reported for the detection. Herein, we report a direct and separation-less flow injection analysis (FIA) coupled electrochemical detection technique (ECD) for hydrazine in tobacco. Quercetin (Qn, a plant-derived flavonoid found in fruits, vegetables, leaves and grains) tethered pristine-multiwalled carbon nanotube modified glassy carbon electrode (GCE/pristine-MWCNT@Qn) has been developed as a selective electrochemical detector for FIA and characterized by electro-chemical and physico-chemical techniques. At an optimal condition the new FIA-ECD showed a hydrazine calibration plot in a range 5–3000 μM with a detection limit value 136 nM/20 μL. This electrochemical detector is found to be tolerable to several electro-active chemical entities such as ascorbic acid, uric acid, dopamine, cysteine, nitrite, benzene, ammonium chloride, nitrate, citric acid, oxalic acid (negligible interferences), aromatic amine and sulfide. The applicability of this technique is further tested by analyzing the hydrazine content in different brand of cigarettes with appreciable recovery values.

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.

Riboflavin (vitamin B2) immobilized multiwalled carbon nanotubes modified electrode (GCE/MWCNT@RB) has been prepared and demonstrated as a selective and sensitive electrocatalytic flow injection analysis electrochemical sensor for iodate detection. The GCE/MWCNT@RB modified electrode showed a highly stable and well defined surface confined redox peak at an E 1/2 = 155 ± 20 mV vs. Ag/AgCl with a surface excess value of 4.72 nmol cm −2 . Physicochemical and electrochemical characterizations reveal the presence of surface confined riboflavin sites on GCE/MWCNT system. At an applied potential = −0.1 V vs Ag/AgCl, hydrodynamic flow rate = 800 μL min −1 and phosphate buffer (pH 2) as a carrier solution condition, the analytical characteristics such as stability, repeatability, linear range and detection limit were described. The relative standard deviation of successive 29 injections of 25 μM of iodate was 3.61%. Iodate calibration plot was linear in a range of 25–750 μM with regression coefficient, sensitivity and limit of detection (S/N = 3) of 0.9998, 0.77 μA mM −1 and 2.7 μmol L −1 (9.4 ng/20 μL) respectively. The new system showed absence of interference with iodide, chloride, nitrate, bromate and perchlorate. Quantitative detection of iodate in iodized table salts was further demonstrated.

This is the first report on studies of the underpotential deposition of Pb (upd-Pb) on a disposable screen-printed silver electrode (AgSPE, non-single crystalline surface). The dependence of upd-Pb and bulk Pb deposition (bulk-Pb) on potential scan rate (ν) was demonstrated for the AgSPE in pH 3 KNO3/HNO3 solutions. At ν=20 mV s−1, the extent of formation of reversible upd-Pb was ∼15 times less than that of irreversible bulk-Pb. However, for ν>100 mV s−1, only the upd-Pb was observed. Scanning electron microscopic (SEM) analysis speculated 3D-nucleation (hcp) of bulk-Pb on the AgSPE at low scan rate (ν=1 mV s−1). On the other hand, at a faster scan rate (ν=300 mV s−1), no marked crystallites were obtained. By interpretation with the CV results, the later case was proved to be formation and complete stripping of the upd-Pb on the AgSPE and this property was further utilized for analytical application. The nearly reversible behavior of the upd-Pb process at the disposable AgSPE is a judicious choice for the effective stripping analysis of Pb by square-wave voltammetry.