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Herein, we report in-situ electrochemical derivatization of the intrinsic iron species in a pristine-multiwalled carbon nanotube (MWCNT) as Prussian blue (PB) modified MWCNT hybrid (MWCNT@PB) using a dilute solution of ferricyanide as a derivatization agent in pH 2 HCl-KCl solution. The PB hybrid system showed a defined redox peak at an apparent standard electrode potential, Eo’ = 0.18 V vs Ag/AgCl with an excess surface value, 1.71 × 10−10 mol cm−2. A discreet EQCM study on the electrochemical preparation of MWCNT@PB using MWCNT and ferricyanide precursors reveal the specific stripping of iron species and uptake of iron species, potassium and ferricyanide ions upon the electrochemical preparation condition. In-situ imaging of MWCNT@PB was carried out using SECM with ferricyanide as a redox mediator under a feedback-current mode. It has been identified that a mixed-potential based electrochemical reaction involving oxidative stripping of iron to iron ion species (step-1) coupled with reduction of ferricyanide to ferrocyanide (step-2) followed by a chemical interaction between the iron ion and ferricyanide (step-3) have occurred for the overall formation of MWCNT@PB hybrid. Electrocatalytic and electroanalytical performance of the MWCNT@PB hybrid towards H2O2 reduction and sensing were demonstrated by performing cyclic voltammetric, amperometric i-t and batch injection analysis.

We report an easy electrochemical route for preparing a catechol derivative (di-ferulyl sesamol derivative, designated as CA-Fer) functionalized low-cost carbon black (CB) modified electrode in a neutral pH buffer solution. As synthesized precursor organic compound, CA-Fer has been electrochemically oxidized over the CB by potential cycling treatment in pH 7 PBS that leads to a high redox active CA-Fer-catechol derivative (CB@CA-Fer-Redox), which exhibited a well-defined and stable surface-confined redox response at Eo’ = 0.150 V vs Ag/AgCl with a surface excess value = 50.46 nmol cm−2. Unlike the conventional redox active mediators, GCE/CB@CA-Fer-Redox modified electrode has failed to show any mediated oxidation/reduction response to various electro-active biochemicals and chemicals, viz., ascorbic acid, glucose, cysteine, caffeic acid, hydrazine, hydrogen peroxide, uric acid, dopamine, creatinine, urea, nitrite, sulfide and sulfate ions, depicting a clear advantage of using it as a voltammetric pH sensor for real-time applications. The modified electrode showed a linear voltammetric potential signal against pH in a window, 3–11, with a slope value of (∂Ep/∂pH) = −59 ± 3 mV pH−1. As an independent study, a CA-Fer-Redox modified three-in-one screen printed electrode was developed, and a sensitive voltammetric pH analysis of some chemical biochemical real sample systems were demonstrated.

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...

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 [Mn

Turning the π-structure and electronic properties of carbon nanotubes (CNTs) is a cutting-edge research topic in interdisciplinary areas of material chemistry. In general, chemical functionalization of CNT has been adopted for this purpose, which has resulted in a few monolayer thickness increment of CNT diameter size. Herein, we report an interesting observation of10-fold increment in the apparent diameter of multiwalled carbon nanotubes (MWCNTs) brought about by a process of self-assembly of the BZ moiety on MWCNT, which is formed by electrochemical oxidation of a surface-adsorbed benzene-water cluster, {BZ

Carbazole-1,4-quinone is a key structural unit of naturally occurring carbazole-quinone alkaloids, for instance, 3-methyl carbazole-1,4-quinone (Murrayaquinone), that are widely used in pharmaceuti...

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.

An ex-situ pharmacokinetic of Triamterene (Trim) drug has been investigated by electrochemical technique using multiwalled carbon nanotube modified glassy carbon electrode, GCE/MWCNT (GCE/MWCNT@Trimads) as a biomimicking carbon network system. Trim is a phenyl ring containing electro-inactive drug that has been widely used for the treatment of diuretic and antihypertensive related diseases. Upon cyclic volumetric measurement of Trim-drug adsorbed GCE/MWCNT at an optimal potential window, −1 to 0.9 V vs Ag/AgCl showed formation of a well-defined surface-confined redox peak at Eo' = 0.1 V vs Ag/AgCl in pH 7 phosphate buffer solution. Calculated surface-excess value is 0.85 × 10−9 mol cm−2 and it is proton-coupled electron-transfer in nature. Collective characterization results of the modified electrode by physicochemical techniques (Raman, IR and Mass spectrophotometer) and electrochemical methods (effect of potential window) reveal hydroxylation of the phenyl ring of the Trim-drug to phenolic derivative (intermediate) in association with involvement of H2O2 intermediate species that have been generated by oxygen reduction reaction at negative potential and subsequent oxidation to trihydroxy benzene-Trim drug (Trim-3HQ). The GCE/MWCNT@Trim-3HQ showed selective mediated oxidation current signals for cysteine in relation with importance of the free thiol molecules and its conversion to disulfide (CyS-SCy) at pathogenic condition in the biological system like human serum albumin. As an independent study, amperometric i-t and flow injection analysis of CySH have been demonstrated with a detection limit value 695 nM.

Herein we report a simple and selective open-circuit potential-time (OCPT) based preparation of nickel hexacyanoferrate (NiHCF) on nickel and iron impurity containing carbon nanotube (CNT*, * = intrinsic metal impurity) modified glassy carbon electrode (GCE/CNT*NiHCF) using pH 2 ferricyanide solution. Unlike potentiodyanamic cycling, OCPT allowed the selective preparation of NiHCF with a distinct redox features at an equilibrium potential = 0.38 V in pH 7 phosphate buffer solution (PBS). Kinetic parameters such as transfer coefficient and rate constant of GCE/CNT*NiHCF were calculated from cyclic voltammetry (CV) studies of the redox peak. Characterization of CNT* and CNT*NiHCF by XRD, TEM, FTIR and Raman spectroscopy techniques revealed the presence of iron and nickel impurities in CNT* and confirmed the formation of CNT*NiHCF and CNT*Fe-NiHCF (Fe-NiHCF = FeHCF + NiHCF) by OCPT and potentiodynamic cycling, respectively. Furthermore, electrocatalytic activity of CNT*NiHCF modified electrode was explored with a model analyte, hydrazine (Hz) in pH 7 PBS. Likewise, electron number involved during the rate determining step, complete electrocatalytic reaction and its heterogeneous rate constant values were calculated using CV technique. At optimal amperometric i-t conditions, GCE/CNT*NiHCF showed a linear calibration plot with a current linearity on a range of 20–200 μM with current sensitivity and detection limit (signal-to-noise = 3) values of 1217.39 nA μM−1 cm−2 and 0.8 μM respectively. It also displayed zero interference from oxalic acid, uric acid, ascorbic acid, sulphate, nitrite, nitrite, magnesium and sodium displaying feasibility to Hz detection in polluted water bodies.

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.

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.

Biomass waste, a good candidate for advanced carbon materials for sustainable electrodes, is receiving more and more attention for high value-added materials because of its promising contribution to economic growth and sustainable development. We proposed a green co-hydrothermal approach to prepare lotus seedpods biochar (BC) decorated molybdenum disulfide (MoS

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.

Development of a new pH sensor system, which is simple to prepare, sensitive, selective and workable with low volume, is demanding research in biomedical and environmental studies. In the literature, organic molecules like methylene blue, toluidine blue, hydroquinone, catechol, anthraquinone and polyaniline-based redox probes have been widely used for this purpose. In general, these redox probes have easily interfered with common biochemicals such as dopamine, ascorbic acid, NADH, H2O2, cysteine, hydrazine, and some transition metal ions, etc., and in turn to marked potential and current drifts (pH-false positive response). In this work, a highly redox-active, stable and interference-free redox polymer based on poly(4-chloroaniline) (PANI(4-Cl)) modified graphitized mesoporous carbon (GMC), designated as GMC@PANI(4-Cl), has been prepared using 4-chloroaniline as a monomer in pH 7 phosphate buffer solution. The new redox polymer system showed a distinct redox peak at Eo’= 0.15 V vs Ag/AgCl with a stable voltammetric response. Transmission electron microscope analysis of the redox polymer composite had shown adhesion of black polymeric solid due to polyaniline like the molecular system as a surface layer on the GMC material. The constructed calibration plot was linear in the pH window 2-11 with a slope and regression values − 58 mV pH−1 and 0.9997, respectively. The GMC@PANI(4-Cl) modified electrode showed a sensitive and selective pH monitoring without any interference from the common biochemicals as listed above. As a practical application, pH sensing of commercial pH solutions, undiluted urine and saliva samples were demonstrated. Also, a three-in-one screen-printed carbon modified GMC@PANI(4-Cl) was explored for pH monitoring of a bacterial (E.coli) growth, which showed a comparable response with the conventional pH electrode.

As an alternate for the conventional glass-based pH sensor which is associated with problems like fragile nature, alkaline error, and potential drift, the development of a new redox-sensitive pH probe-modified electrode that could show potential, current-drift and surface-fouling free voltammetric pH sensing is a demanding research interest, recently. Herein, we report a substituted carbazole-quinone (Car-HQ) based new redox-active pH-sensitive probe that contains benzyl and bromo-substituents, immobilized multiwalled carbon nanotube modified glassy carbon (GCE/MWCNT@Car-HQ) and screen-printed three-in-one (SPE/MWCNT@Car-HQ) electrodes for selective, surface-fouling free pH sensor application. This new system showed a well-defined surface-confined redox peak at an apparent standard electrode potential, Eo′ = − 0.160 V versus Ag/AgCl with surface-excess value, Γ = 47 n mol cm−2 in pH 7 phosphate buffer solution. When tested with various electroactive chemicals and biochemicals such as cysteine, hydrazine, NADH, uric acid, and ascorbic acid, MWCNT@Car-HQ showed an unaltered redox-peak potential and current values without mediated oxidation/reduction behavior unlike the conventional hydroquinone, anthraquinone and other redox mediators based voltammetry sensors with serious electrocatalytic effects and in turn potential and current drifts. A strong π–π interaction, nitrogen-atom assisted surface orientation and C–C bond formation on the graphitic structure of MWCNT are the plausible reasons for stable and selective voltammetric pH sensing application of MWCNT@Car-HQ system. Using a programed/in-built three-in-one screen printed compatible potentiostat system, voltammetric pH sensing of 3 μL sample of urine, saliva, and orange juice samples with pH values comparable to that of milliliter volume-based pH-glass electrode measurements has been demonstrated.

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 naturally occurring water-soluble cobalt-complex cyanocobalamin (Vitamin B12) has been identified as a new and efficient electrocatalyst for the CO2 -to-CO reduction reaction in aqueous solution. Heterogeneous B12-electrocatalysts prepared by a simple electrochemical immobilization technique on graphene-oxide (GO)-modified glassy carbon and carbon paper (CP) electrodes, without any non-degradable polymer-binders, showed a highly stable and well-defined surface-confined redox peak at E'=-0.138 V vs. RHE with a surface-excess value, ΓB12 =4.28 nmol cm-2 . This new electrocatalyst exhibits 93 % Faradaic efficiency for CO2 -to-CO conversion at an electrolysis potential, -0.882 V vs. RHE (an optimal condition) with a high current density, 29.4 mA cm-2 and turn-over-frequency value, 5.2 s-1 , without any surface-fouling problem, in 0.5 m KHCO3 . In further, it follows an eco-friendly, sustainable and water-based approach with the involvement of biodegradable and non-toxic chemicals/materials like B12, GO and CP.

The measurement of time evolution of electrochemical impedance enables enzymatic kinetic studies in real-time, and obviates the need of using additional reagents as in many popular spectroscopic methods. This can eventually lead to the development of enzyme biosensors. We have used the urea–urease system as a model for this study. The usage of a free enzyme (without any immobilization steps) in this work makes the technique very simple and unique for electrochemical measurement on urease. The impedance vs. time measurement of urease exhibits Michaelis–Menten (MM) behaviour with the MM constant ( $$K_{\mathrm {{m}}}$$ ) of 0.8 mM and maximum velocity ( $$V_{\mathrm {{max}}}$$ ) of $$5000\hbox { ohms min}^{{{-1}}}$$ . This $$K_{\mathrm {{m}}}$$ value closely matched the one, which is obtained from the conventional colorimetric method (values). The enzyme kinetics was performed in a standard three-electrode system and reproduced in a fabricated mini electrochemical cell in an Eppendorf tube, which could pave the way for the development of impedimetric biosensors for a variety of enzyme systems, especially the ones for which spectrometric techniques cannot be readily applied.

A simple method for molecular wiring of glucose oxidase (GOx) enzyme with a low cost Mn polypyridine complex, Mn(phen)

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...

DPPH (2,2-diphenyl-1-picrylhydrazil), a free radical-containing organic compound, is used widely to evaluate the antioxidant properties of plant constituents. Here, we report an efficient electroactive DPPH molecular system with excellent electrocatalytic sensor properties, which is clearly distinct from the traditional free radical-based quenching mechanism. This unusual molecular status was achieved by the electrochemical immobilization of graphene oxide (GO)-stabilized DPPH on a glassy carbon electrode (GCE). Potential cycling of the DPPH adsorbed-GCE/GO between − 1 and 1 V (Ag/AgCl) in a pH 7 solution revealed a stable and well-defined pair of redox peaks with a standard electrode potential, E0′ = 0 ± 0.01 V (Ag/AgCl). Several electrochemical characterization studies as well as surface analysis of the GCE/GO@DPPH-modified electrode by transmission electron microscopy, Raman, and infrared spectroscopy collectively identified the imine/amine groups as the redox centers of the electroactive DPPH on GO. The use of different carbon-supports showed that only oxygen-functionalized GO and MWCNTs could provide major electroactivity for DPPH. This highlights the importance of a strong hydrogen-bonded network structure assisted by the concomitant π-π interactions between the organic moiety and oxygen function groups of carbon for the high electroactivity and stability of the GCE/GO@DPPH-NH/NH2-modified electrode. The developed electrode exhibited remarkable performance towards the electrocatalytic oxidation of NADH at 0 V (Ag/AgCl). The amperometric i-t sensing of NADH showed high sensitivity (488 nA μM−1 cm−2) and an extended linear range (50 to 450 μM) with complete freedom from several common biochemical/chemical interferents, such as ascorbic acid, hydrazine, glucose, cysteine, citric acid, nitrate, and uric acid.

Triazophos, O,O-diethyl O-(1-phenyl-1H-1,2,4-triazol-3-yl)phosphorothioate (TPZ), an organophosphorus pesticide, has been widely used in agriculture to control pests, insects, and some nematodes (roundworms). Unfortunately, it has been found that a significant trace of the pesticide residue enters into the agricultural products and creates a major health threat to human. In order to selectively detect the TZP pesticide in real samples, several indirect and time-consuming analytical assays based on acetylcholinesterase enzymes, affinity-based antibody systems, and molecularly imprinted polymers, apart from the separation-coupled mass spectrophotometer, have been demonstrated. For the first time in the literature, we report a direct electrochemical method for the selective and quick detection of TZP based on electrocatalytic oxidation by a Coomassie brilliant-blue dye surface-confined carbon-black-nanoparticle-modified glassy carbon electrode (GCE/CBnano@CoomBB) in a pH 7 phosphate buffer solution. GCE/CBna...