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The analysis of plasmonic photoelectrochemical reactions on nanostructured noble metal electrodes is an attractive field, but little is known about the detailed competition between the photochemica...

The economical, efficient and durable oxygen reduction catalysts facilitate the enhancement of electrochemical energy devices competitiveness towards widespread applications. In view of this, we provide an innovative sulfuration inducing method for the synthesis of ZnS and cobalt nanoparticles decorated N, S co-doped CNTs (ZnS/Co-NSCNTs) catalyst. S introduced into the zinc-based zeolitic imidazolate frameworks (ZIF-8) and cobalt-based zeolitic imidazolate frameworks (ZIF-67) precursors via pyrolysis, and induced the generation of ZnS/Co-NSCNTs have been confirmed by XRD, SEM, TEM, and XPS techniques. The key features including activity sites, transfer channels and adsorption energy back up the excellent electrocatalytic activity of the as-prepared ZnS/Co-NSCNTs towards oxygen reduction reactions (ORR). ZnS/Co-NSCNTs additionally exhibited a positive half-wave potential of 0.871 V (vs. RHE) with improved current density towards ORR. In alkaline medium, ZnS/Co-NSCNTs catalyst displayed a high tolerance towards methanol and an excellent long-term cycling stability. The observed onset potential for our prepared ZnS/Co-NSCNTs catalyst is analogous with the commercially available noble metal catalysts. Also, ZnS/Co-NSCNTs catalyst as a cathode in zinc-air battery displayed an enhanced electrochemical performance with a highly specific capacity of 750.1 mAh g−1, outstanding cycling stability, and high rate behavior. This work provides a new approach for the construction of stable low-cost alternative air-cathode catalysts for other energy conversion and storage applications.

Metal–organic frameworks (MOFs) are the more desirable electrode materials in the recent development of electrocatalyts. Still, the electrocatalytic behavior as well as the stability of the prepared MOFs were diminished by its poor conductance. In this work, Cobalt hydroxide (Co (OH)2) functionalized multi-walled carbon nanotubes (MWCNTs) with enhanced electro activity has been prepared using Co-based metal−organic framework (Co MOF, ZIF-67) templates through room temperature electrochemical synthesis. The as synthesized composite has been utilized in the construction of MWCNTs-Co(OH)2 modified glassy carbon electrode (GCE) for the determination of hydrazine (N2H4) and hydrogen peroxide (H2O2). The higher electrochemical performance of MWCNTs-Co(OH)2/GCE compared to individual MWCNTs/GCE and Co(OH)2/GCE was evident from the cyclic voltammetric studies. The characterizations of the composite have been carried out using various techniques. The electrochemical parameters such as linear range, limits of detection and sensitivity of MWCNTs-Co(OH)2/GCE were found to be more comparable with the previous N2H4 and H2O2 amperometric sensors reported in the literatures. The outcomes of practicability inspections were adequate with the recovery results of conventional methods. The high selectivity of MWCNTs-Co(OH)2 modified GCE towards N2H4 and H2O2 has been further demonstrated in the presence of several biologically interfering molecules.

Hydrogen peroxide (H2O2) sensing and oxygen reduction reaction (ORR) has considered to be a highly desirable in the areas of sensing and energy production. In recent years, researchers focus on the replacement of noble metal-based electrocatalyst used for the ORR and H2O2 sensing by low-cost materials. In this current work, we have synthesized carbon black supported LaMnO3 (LMO@C) via dry particle coating method and studied its electrocatalytic activity towards ORR and H2O2 sensing. The characterization of synthesized LMO@C was performed by using field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy techniques. Furthermore, the synergistic effect between LMO and carbon was established through electrochemical measurements. In case of ORR, our prepared LMO@C composite possess longer life-time (89.8%) than 20 wt% Pt/C (77.6%). In another case, this electrocatalyst (LMO@C) owns wide working range, low limits of detection and high sensitivity for the determination of H2O2. The experimental data of LMO@C towards the electrochemical sensing of H2O2 and ORR demonstrates its potential applications in the construction of sensors and energy generation devices.

The synthesis of highly stable metallic organic–inorganic hybrid nanocomposites from the non-toxic and biodegradable organic–inorganic metallic precursors, which are the natural polymer products of organic molecules, carbohydrates, and amino acids, has engrossed the recent researchers. In this work, a simple potentiostatic approach has been designed for the electrochemical preparation of gold nanoparticle-decorated copper cross-linked pectin (CuCP–AuNPs). Here, CuCP act as a scaffold or stabilizing agent for the preparation of uniform AuNPs. The studies for surface morphology and crystal structure of our composite were carried out using field emission scanning electron microscopy (FESEM) and X-ray diffraction spectroscopy (XRD). Energy-dispersive X-ray spectroscopy (EDX) was employed for the elemental analysis of the composite. A remarkable cathodic peak current response was obtained by our modified electrode for the presence of H2O2. CuCP–AuNP-modified glassy carbon electrode (GCE) possesses the values for limits of detection (LOD) and sensitivity of 0.22 μΜ and 6800 μA mM cm−2, respectively, in a linear range from 1 to 2110 μΜ. The detection of H2O2 in presence of other biologically interfering molecules represents the high selectivity of our fabricated electrode. The examination for the sensitive determination of H2O2 conducted in commercially available lens cleaning solutions validates the practical feasibility of the proposed modified electrode.

Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) can provide the fingerprint information at the molecular level during electrochemical processes and the laser used in the EC-SERS process can simultaneously induce the plasmon-mediated chemical reaction (PMCR). In this work, EC-SERS has been used to understand the plasmonic effects on the selective dimerization reduction route of para-halonitrobenzene on the AgNPs@Ag electrode. Para-iodonitrobenzene (pINB) was first chosen as the probe molecule for photoelectrochemical reductions and investigated in acidic and neutral electrolyte solutions. The density functional theory (DFT) calculations confirmed that the electrochemical reduction of pINB produces 2-amino-5-iodophenol in HClO4 and p,p’-diiodoazobenzene (DIAB) in neutral electrolyte. However, when the PMCR is introduced in the electroreduction of pINB, the route of reduction path can be altered to the reduction product DIAB. Thus DIAB was generated firstly both in acidic and neutral conditions by PMCR and then reduced to p-iodoaniline. Finally, all the para chloro- and bromo- nitrobenzene can generate the p,p’-dihalo-azobenzene dimer by the PMCR under acidic conditions. Therefore, the plasmonic photoelectrochemical dimerization and reduction reactions can give us an idea to introduce the light on the selectivity of chemical reactions on plasmonic noble electrodes of nanostructures to alter the reduction pathway. This is practically significant for obtaining highly selective reduction products.

A novel, single step preparation of copper nanoparticles decorated silver nanoleaves (AgNLs–CuNPs) bimetallic composite at glassy carbon electrode (GCE) was done through electrochemical potentiostatic method. Three different morphologies namely, nanoparticles, nanodentrites and nanoparticles decorated nanoleaves were obtained for copper, silver and silver–copper as the result of deposition. Moreover, the obtained AgNLs–CuNPs composite is highly dense compared to their individuals. This was confirmed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The crystal planes and elemental composition of the prepared nanocomposites were examined by X-ray diffraction (XRD) spectroscopy, Energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The highly dense AgNLs–CuNPs composite modified GCE showed a well-defined cathodic peak at −0.195 V towards H 2 O 2 . The cyclic voltammetry and amperometric studies revealed the excellent electrocatalytic ability of AgNLs–CuNPs/GCE towards the reduction of H 2 O 2 compared to only AgNDs and CuNPs. Remarkably, the fabricated AgNLs–CuNPs/GCE displayed a very low detection limit (0.095 μM) with high sensitivity (6190 μA mM −1 cm −2 ). Our demonstrated sensor holds good in a linear range from 0.5 to 1015 μM. Additionally, the selective determination of hydrogen peroxide was achieved using AgNLs–CuNPs/GCE even in the presence of other interfering biomolecules. The real sample analysis was performed in commercial clinical lens cleaning solutions to demonstrate the practicability of our sensor.

Manganese oxide nanoflakes incorporated functionalized multi-walled carbon nanotubes (f-MWCNTs/MnO2 NFs) have been prepared through a simple chemical method. The morphology and structure of the prepared composites were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS). Our present study demonstrated that enzymeless hydrogen peroxide sensor holds good in a wide linear range from 5 to 4530 μM with the calculated limits of detection and sensitivity values to be 0.952 μM and 219.05 μA mM−1, respectively. During hydrogen peroxide detection, f-MWCNT/MnO2 NF-modified glassy carbon electrode reached 95% of the steady-state response current within 4 s. In addition, our finding selectively detects hydrogen peroxide even in the presence of other interfering biomolecules. Ease of preparation, good electrocatalytic ability, and feasible practicality can potentially extend our fabricated electrode towards the applications of such biosensors and energy storage devices in the near future.

We delineate the electrochemical preparation of cobalt hydroxide nanoflakes Co(OH)2 NFs on multi-walled carbon nanotubes (MWCNTs) by potentiostatic methods. The preparation was done on the surface of glassy carbon electrode (GCE). The prepared nanocomposite was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction spectroscopy (XRD) and X-ray photo electron spectroscopy (XPS). The resulting f-MWCNTs/Co(OH)2 NFs modified GCE exhibits a good electrocatalytic activity for the oxidation of hydrazine in terms of decreasing over potential and increasing peak current. The modified electrode holds good in the linear range from 0.5 to 15.5 μM with limit of detection as 87.5 nM. The sensitivity of our modified electrode is calculated to be 5733 μA/mM cm-2. Remarkably, the obtained LOD value of our sensor is very lower compared to the recommended concentration of hydrazine in water by World health organization (WHO) and Environmental protective agency (EPA). The modified electrode detects hydrazine selectively even in the presence of common interferants. Various water samples were chosen to study the practical feasibility of our sensor. The sensor also exhibited an appreciable stability, repeatability and reproducibility.

Several nanomaterials and techniques for the detection of mercuric ions (Hg 2+ ) have been developed in the past decade. However, simple, low-cost and rapid sensor for the detection of heavy metal ions yet remains an important task. Herein, we present a highly sensitive electrochemical sensor for the femtomolar detection of Hg 2+ based on polypyrrole, pectin, and graphene (PPy/Pct/GR) which was prepared by one step electrochemical potentiodyanamic method. The effect of concentration of pectin, polypyrrole and graphene were studied for the detection of Hg 2+ . The influence of experimental parameters including effect of pH, accumulation time and accumulation potential were also studied. Different pulse anodic stripping voltammetry was chosen to detect Hg 2+ at PPy/Pct/GR/GCE modified electrode. The fabricated sensor achieved an excellent performance towards Hg 2+ detection such as higher sensitivity of 28.64 μA μM −1 and very low detection limit (LOD) of 4 fM at the signal to noise ratio of 3. The LOD of our sensor offered nearly 6 orders of magnitude lower than that of recommended concentration of Hg 2+ in drinking water by United States Environmental Protection Agency and World Health Organization. Compared to all previously reported electrochemical sensors towards Hg 2+ detection, our newly fabricated sensor attained a very LOD in the detection of Hg 2+ . The practicality of our proposed sensor for the detection of Hg 2+ was successfully demonstrated in untreated tap water.

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co3O4 NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co3O4 NHs are transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co3O4 NHs on the pre-cleaned glassy carbon electrode (GCE). GR−Co3O4 modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co3O4 NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM−1 cm−2. As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co3O4 NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.

Renal insufficiencies and muscle diseases can be easily identified from the concentration of creatinine in blood and urine. Although various chemical sensors have been developed to detect creatinine, selectivity and robustness of chemical sensors are the main obstacles for many researchers. To overcome these difficulties, finding a suitable chemical biosensor with long-term stability, low cost, high sensitivity and selectivity for the detection of creatinine is immensely desirable. Herein, we have developed a novel enzymeless creatinine biosensor for the trace level detection of creatinine using reduced graphene oxide (RGO)/ silver nanoparticles (AgNPs) which was prepared by simple one step electrochemical potentiodyanamic method. The anodic peak current of AgNPs gradually decreased when the concentration of creatinine was increased. Based on the decrease of anodic peak current, we have introduced a new platform for the detection of creatinine. The adsorption of creatinine on AgNPs was confirmed by various techniques. The newly proposed biosensor exhibited a very low detection limit of 0.743 pM with linear range from 10 pM to 120 pM. The demonstrated sensor can detect creatinine even in the presence of other interfering biomolecules such as glucose, ascorbic acid, uric acid, urea and creatine.

β-cyclodextrin (β-CD) functionalized silver nanoparticles (AgNPs) and reduced graphene oxide (RGO) via one step electrochemical potentiodyanamic method has been prepared. Scanning electron microscopy, Energy-Dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the role of β-CD on preparation of AgNPs and RGO. RGO/β-CD/AgNPs modified GCE showed good electrochemical activity towards electro-oxidation of hydrazine in terms of decreasing the over potential and increasing the peak current. The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) of the modified electrode towards hydrazine were determined to be 0.66 and 0.97×10−6 cm2 s−1, respectively. The LOD of our sensor was many folds lower than that of recommended concentration of hydrazine in drinking water by United States Environmental Protection Agency and World Health Organization. The sensor exhibited a wide linear range from 0.08 to 1110 µM and a very low detection limit (LOD) of 1.4 nM. In addition, the sensor selectively determined hydrazine even in the presence of common interferents.

Copper (I) oxide nanocubes (Cu2O NCs) covered with cobalt oxide nanohexagons (Co3O4 NHs) were prepared through simple chemical method. Here, ascorbic acid is used as reducing and capping agent for the synthesis of nanocubes and nanohexagons. Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD) were employed to confirm the prepared nanocomposite. Cu2O NCs−Co3O4 NHs nanocomposite is drop cast on the glassy carbon electrode (GCE) for the fabrication of glucose sensor. The fabricated Cu2O NCs−Co3O4 NHs/GCE exhibited a better electrocatalytic activity towards the determination of glucose than that of individually fabricated Cu2O NCs and Co3O4 NHs modified GCE. Our finding exhibited a wide linear range from 1 μM to 5330 μM with LOD of 0.63 towards glucose. In addition, the sensor attained appreciable stability, repeatability and reproducibility. Practicality of the sensor was demonstrated in human serum samples. The main advantages of the fabricated sensor are simple, biocompatible, cost effective, fast response and highly stable electrode surface.

Copper nanoparticles (CuNPs) with an average diameter of 70 ± 20 nm were deposited on glassy carbon electrode (GCE) through a simple, facile and template free electrochemical potentiostatic method. The sizes of CuNPs were readily controlled using a biomolecule, histidine that acts as stabilizing agent. The effect of histidine concentration on the formation of CuNPs was studied in the fixed concentration of copper ions. To increase their surface area and the catalytic activity, histidine stabilized CuNPs were deposited on the surface of reduced graphene oxide (RGO) to form RGO/histidine-CuNPs nanocomposite. The as-prepared nanocomposite was confirmed by various techniques. RGO/histidine-CuNPs/GCE was used to develop a highly sensitive and selective sensor for the detection of hydrogen peroxide (H 2 O 2 ). The sensor showed a good linear response to H 2 O 2 in the range of 1 μM to 5 mM with a low detection limit (LOD) of 75 nM. The fabricated modified electrode detected H 2 O 2 selectively even in the presence of other biomolecules such as dopamine, ascorbic acid, uric acid, acetaminophen, glucose and L-cysteine. Practicality of the sensor was demonstrated in human urine samples. The important features of this nanocomposite are simple, low cost, ecofriendly and easy fabrication of sensor for sensitive and selective determination of H 2 O 2 .

Plasmonic metal nanomaterials (PMNMs) have been targeted as noble photocatalysts in various energy related applications because of their strong surface plasmon resonance (SPR). It has been recently revealed that, these PMNMs on photoexcitation can induce the efficient hot carriers (hot electron/hole) transfer to the targeted molecules which is essential for the rate-limited process of photocatalysis. The profound understanding of reaction mechanisms is in need for the development of novel plasmonic catalysts towards chemical transformations of targeted molecules at PMNMs modified electrodes. The two diversely unique properties of electric field and electromagnetic field co-occur with different nanostructures in electrochemical surface enhanced Raman spectroscopy (EC-SERS) systems. Further, the EC-SERS experiments and their applications are deliberated from the construction of PMNMs coated electrodes for studying the SERS mechanisms and characterization of adsorption configuration and photoelectrochemical reaction mechanisms of targeted species. In this review, the recent investigation of the plasmon mediated photoelectrochemical transformation of para-aminothiophenol (PATP) at PMNMs modified electrodes will be discussed using EC-SERS method and theoretical calculations. The influence of applied potential, solution pH, and applied laser light power for binding and transformation of PATP at PMNMs will be discussed in detail. Ultimately, summary and future prospective of this study have been discussed briefly.

Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal–air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe3C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe3C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power − 150 W; frequency − 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe3C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS–GR/Fe3C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS–GR/Fe3C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air–cathode catalysts for the energy conversion and storage application.

We describe a simple and elegant electropolymerization method to prepare highly stable tetraamino functionalized cobalt phthalocyanine (pTACoPc) at electrochemically reduced graphene oxide (RGO). The described method efficiently bridges the excellent physicochemical properties of RGO with the rich redox chemistry of TACoPc. Graphene oxide was electrochemically reduced to RGO at the electrode surface along with concominent electropolymerization of TACoPc. The electrochemical studies showed that RGO on pTACoP/GCE increased effective surface area, reduced charge transfer resistance and enhanced electrochemical signal. The RGO-pTACoPc film modified electrode exhibits excellent electrocatalytic ability to oxidize cysteine and hydrazine. To determine cysteine, the RGO-pTACoPc sensor displayed a linear concentration range of 50 nM to 2.0 μM, detection limit of 18.5 nM and sensitivity of 10.19 nA nM−1 cm−2. Besides, the sensor displayed a linear concentration range of 50 nM to 2.6 μM, detection limit of 10 nM and sensitivity of 1.62 nA nM−1 cm−2 to determine hydrazine. The electrocatalytic ability of RGO-pTACoPc shows better performance over other cobalt phthalocyanine derivatives. Furthermore, the described sensor exhibited long-term storage stability, good repeatability and reproducibility. The practical applicability of the sensor has been assessed in biological and water samples.

Herein, we have demonstrated a preparation of palladium nanoparticles on electroactivated graphite nanosheets modified screen printed carbon electrode (PdNPs-EGNS/SPCE) by a simple electrochemical method. The well-prepared electrocatalyst was potentially applied to the high performance electrocatalytic oxidation of hydrazine in neutral medium. The PdNPs-EGNS novel composite was characterized by scanning electron microscope (SEM) and the average diameter and thickness of PdNPs and EGNS were found to be ∼38 nm and 85 nm, respectively. The high performance electrocatalytic determination of hydrazine was performed by the amperometric i-t method. The fabricated sensor displayed irreversible electrocatalytic oxidation of hydrazine with diffusion-controlled electrode process. The oxidation of hydrazine at PdNPs-EGNS/SPCE showed wider linear range 0.05–1415 µM and high sensitivity 4.382 µA µM−1 cm−2. The as-prepared electrocatalyst achieved quick response towards hydrazine with a lower detection limit 4 nM.

A simple electrodeposition approach has been described for the preparation of copper nanoparticles (CuNPs) using biopolymer pectin as a scaffold and graphene as a support. The formation of graphene/pectin-CuNPs was confirmed by scanning electron microscopy, UV-Visible spectroscopy and X-ray diffraction studies. The graphene/pectin-CuNPs film modified electrode was prepared and its electrocatalytic applications to the oxidation of glucose and reduction of H2O2 have been explored. An amperometric glucose sensor was fabricated which exhibited excellent sensor performance in terms of wide linear range (10 μM–5.5 mM), low detection limit (2.1 μM) and high sensitivity (0.0457 μAμM−1 cm−2). Likewise, an amperometric sensor has been fabricated for the determination of H2O2 which displayed linear range of 1 μM–1 mM, detection limit of 0.35 μM and sensitivity of 0.391 μAμM−1 cm−2. The sensor displayed appreciable repeatability, reproducibity and stability. Furthermore, practical feasibility of the sensor has been demonstrated in human serum and contact lens cleaning solution to determine glucose and H2O2, respectively. The main advantages of sensor include simple and green fabrication approach, roughed and stable electrode matrix, high sensitivity and stability, fast in sensing and highly reproducible.

A simple and elegant electrochemical potentiostatic method has been described for the preparation of highly stable and electrocatalytically active bismuth nanoribbons (BiNRs). The average length and width of the BiNRs were of 100±50 nm and 10±5 µm, respectively. Here, disodium ethylene diamine tetraacetate was employed as a scaffold for the growth of BiNRs. The formation of BiNRs was confirmed by surface morphological, elemental and cyclic voltammetric analyses. The BiNRs exhibited excellent electrocatalytic ability in detecting biologically poisoning heavy metal ions such as lead and cadmium. The described BiNRs based sensor presents good linear dependence on lead and cadmium ions in the concentration range of 1–50 µg/L for both metal ions with a detection limit of 0.104 µg/L for lead and 0.145 µg/L for cadmium.

A simple glucose biosensor has been developed based on direct electrochemistry of glucose oxidase (GOx) immobilized on the reduced graphene oxide (RGO) and β-cyclodextrin (CD) composite. A well-defined redox couple of GOx appears with a formal potential of ∼−0.459 V at RGO/CD composite. A heterogeneous electron transfer rate constant (Ks) has been calculated for GOx at RGO/CD as 3.8 s−1. The fabricated biosensor displays a wide response to glucose in the linear concentrations range from 50 µM to 3.0 mM. The sensitivity and limit of detection of the biosensor is estimated as 59.74 µA mM−1 cm−2 and 12 µM, respectively.

We have described the fabrication of high-performance amperometric sensors derived from graphene oxide–multiwalled carbon nanotube (GO–MWCNT) composite for the sensitive determination of diuron and fenuron. GO–MWCNT composite was prepared by simple solution-based approach, and its formation was confirmed by scanning electron microscopy, transmission electron microscopy and UV-visible spectroscopy methods. GO–MWCNT film-modified glassy carbon electrode exhibited excellent electrocatalytic performance in the oxidation of diuron and fenuron in terms of less overpotential and highly enhanced peak currents. GO–MWCNTs have presented significantly improved electrocatalytic performance than dimethylformamide-dispersed MWCNTs. GO–MWCNT-based amperometric sensor has been fabricated which detects diuron in wide linear range between 9 μM and 0.38 mM with high sensitivity of 0.645 μA μM−1 cm−2. The amperometric sensor also detects fenuron in broad linear range between 0.9 and 47 μM with sensitivity of 1.20 μA μM−1 cm−2. Moreover, the sensor offers appreciable repeatability, reproducibility, and stability results. Practical feasibility of the prepared amperometric sensor has been assessed in various water samples collected from agricultural areas.

Hydrazines are well-known for their diverse biological properties but especially for their toxicity. An amperometric hydrazine sensor was developed at multi-walled carbon nanotubes (MWCNT) and iron tetrasulfonated phthalocyanine (FeTsPc) composite modified electrode for the first time. The TEM and UV-Vis spectroscopy results revealed the successful formation of MWCNT/FeTsPc composite. Compared with the response of MWCNT and FeTsPc modified electrodes, the MWCNT/FeTsPc composite showed enhanced oxidation current response with lower overpotential for hydrazine. Under optimum conditions, the amperometric i–t response of hydrazine was linear in the concentration range from 100 nM L−1 to 3 μM L−1 with the detection limit of 7.6 nM L−1. The response time of hydrazine was found as 6 s with a high sensitivity of 7.615 μA/μM L−1 cm−2.

We prepared graphene (GR)-cobalt phthalocyanine (CoPc) and GR-iron phthalocyanine (FePc) composites by simple and facile chemical reduction method for enzymatic fuel cell (EFC) applications. The successful formation of the composites was confirmed by scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction and electrochemical methods. The as-prepared composites were used for the construction of glucose/O2 EFC. The anode of the EFC was prepared by immobilizing glucose oxidase (GOx) at the GR-CoPc composite modified glassy carbon electrode (GCE). GCE/GR-CoPc/GOx exhibited excellent electrocatalytic ability towards oxidation of glucose. In addition, the modified electrode showed appreciable stability, repeatability and reproducibility. GR-FePc composite exhibited superior electrocatalytic ability towards oxygen reduction reaction (ORR). A membraneless glucose/O2 EFC has been fabricated employing GCE/GR-CoPc/GOx and GCE/GR-FePc as anode and cathode respectively. The fabricated EFC offered a maximum power density of 23 μW cm−2 which is comparable with the previously reported EFCs and it exhibited appreciable stability and repeatability. From this study, we infer that GR based MPcs have great potential for the fabrication of EFCs.

The nickel tetrasulfonated phthalocyanine (NiTsPc) functionalized multiwalled carbon nanotube (MWCNT) nanocomposite was prepared by a simple so- nochemical method. Here, NiTsPc served as a dispersing agent for MWCNT via pp interaction between MWCNT and NiTsPc. The activated glassy carbon elec- trode (AGCE) modified with MWCNT-NiTsPc composite exhibited a good electrocatalytic ability toward dopamine and displayed a good linear dependence in the concentra- tion range of 20 nM-1.384 mM with a sensitivity of 0.17 mA mM � 1 cm � 2 . The detection limit is 1 nM based on the signal-to-noise ratio of 3.

We describe a glassy carbon electrode (GCE) modified with gold nanoparticles that were stabilized with calcium-crosslinked pectin (CCLP) and electrodeposited on multiwalled carbon nanotubes (MWCNTs) by cyclic voltammetry. The resulting electrode was used for the selective determination of L-cysteine (L-Cys). Its characterization showed that the CCLP acts as a scaffold to form highly stable, uniform and electrochemically active AuNPs. Electrochemical studies showed the MWCNT to significantly promote the electrodeposition of the CCLP-AuNPs. The new GCE exhibited excellent electrocatalytic ability towards oxidation of L-Cys in showing a lower overpotential and giving a higher oxidation peak current. The diffusion coefficient for the oxidation of L-Cys was calculated to be 3.0 × 10−6 cm2 s−1. This amperometric sensor displays a wide linear range (from 0.1 to 1,000 μM), high sensitivity (0.46 μA μM−1 cm−2) and a detection limit as low as 19 nM (at a signal-to-noise ratio of 3). The sensor was applied to specifically detect L-Cys even in the presence of 500-fold excess of interferents. It also is stable and possesses good repeatability and reproducibity, and was successfully applied to the determination of L-Cys in spiked samples of human serum.

Herein, we have described a simple electrochemical method for the deposition of the calcium ions cross linked pectin film (CCLP) along with gold nanoparticles (GNPs) on the graphene (GR) modified glassy carbon electrode (GCE) and applied for the determination of hydrazine. The formation of composite film was confirmed by cyclic voltammetry, scanning electron microscopy, Energy-Dispersive X-ray spectroscopy and X-ray diffraction studies. The GR/CCLP-GNPs/GCE film exhibited significantly enhanced electro catalytic ability towards oxidation of hydrazine. The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) for the hydrazine oxidation were determined as 0.46 and 2.91 × 10−6 cm2 s−1, respectively. Two linear ranges were observed in the amperometric determination of hydrazine: (1) 10–600 nM with sensitivity of 47.6 nAnM−1 cm−2 and (2) 0.6–197.4 μM with sensitivity of 1.786 μAμM−1 cm−2. The sensor is able to detect trace level of hydrazine in nanomolar range with very low deletion limit (LOD) of 1.6 nM. This is the lowest LOD achieved compare to all the reported electrochemical amperometric sensors so far. In addition, the sensor is able to detect hydrazine even in the presence of 500 folds excess quantity of interfering ions present in the water and biological liquid. The practicality of the proposed sensor has been demonstrated in water and urine samples. Other advantages of the sensor are repeatability, reproducibility and stability.

A simple electrochemical deposition strategy is proposed for the preparation of gold nanoparticles (Au NPs) at the electrode surface using biopolymer pectin as stabilizing agent. The formation of the nanoparticles was confirmed by scanning electron microscopy (SEM), UV-visible spectroscopy and X-ray diffraction (XRD) studies. A pectin-stabilized, gold nanoparticle film-modified glassy carbon electrode (pectin–Au NP/GCE) was prepared, which exhibited excellent electrocatalytic ability towards oxidation of dopamine (DA). At the pectin–Au NP/GCE, the redox couple corresponding to the redox reaction of DA was observed at the formal potential of 0.20 V with highly enhanced peak currents. A thin layer of nafion coating was applied on the pectin–Au NP composite to improve its selectivity. Two linear ranges of detection were found: (1) 20 nM to 0.9 μM with a limit of detection (LOD) of 6.1 nM, (2) 0.9 μM to 1 mM with a LOD of 0.64 μM. The fabricated sensor selectively detects DA even in the presence of high concentrations of interferents. Moreover, practical feasibility of the sensor was addressed in pharmaceutical samples, which presented appreciable recovery results. The main advantages of the sensor are its very simple and green fabrication approach, roughed and stable structure, and fast and highly reproducible detection of dopamine.

A simple and rapid green synthesis using Bischofia javanica Blume leaves as reducing agent was developed for the preparation of gold nanoparticles (AuNPs). AuNPs decorated graphene oxide (AuNPs/GO) was prepared and employed for the sensitive amperometric determination of chloramphenicol. The green biosynthesis requires less than 40s to reduce gold salts to AuNPs. The formations of AuNPs and AuNPs/GO were evaluated by scanning electron and atomic force microscopies, UV-Visible and energy dispersive X-ray spectroscopies, X-ray diffraction studies, and electrochemical methods. AuNPs/GO composite film modified electrode was fabricated and shown excellent electrocatalytic ability towards chloramphenicol. Under optimal conditions, the amperometric sensing platform has delivered wide linear range of 1.5-2.95μM, low detection limit of 0.25μM and high sensitivity of 3.81μAμM(-1)cm(-2). The developed sensor exhibited good repeatability and reproducibility, anti-interference ability and long-term storage stability. Practical feasibility of the sensor has been demonstrated in food samples (milk, powdered milk and honey) and pharmaceutical sample (eye drops). The green synthesized AuNPs/GO composite has great potential for analysis of food samples in food safety measures.

Amitrole is a biologically toxic nonselective herbicide which contaminates surface and ground waters at unprecedented rates. All reported modified electrodes that detect amitrole within sub-micromolar to nanomolar levels were based on the electro-oxidation of amitrole. Herein, we developed a new conceptual idea to detect picomolar concentrations of amitrole based on calcium cross linked pectin stabilized gold nanoparticle (CCLP-GNP) film modified electrode which was prepared by electrodeposition. When the electrochemical behavior of amitrole was investigated at the CCLP-GNP film, the reduction peak current of the GNPs linearly decreased as the concentration of amitrole increases. We have designed a determination platform based on the amitrole dependent decrease of the GNP cathodic peak. The described concept and high sensitivity of square wave voltammetry together facilitate the great sensing ability; as a result the described approach is able to reach a low detection limit of 36 pM which surpassed the detection limits of existing protocols. The sensor presents a good ability to determine amitrole in two linear concentration ranges: (1) 100 pM–1500 pM with a detection limit of 36 pM; (2) 100 nM–1500 nM with a detection limit of 20 nM. The preparation of CCLP-GNPs is simple, rapid and does not require any reducing agents.

A highly selective amperometric sensor was developed for the trace level determination of hydrazine at bismuth nanoparticles (Bi) decorated graphene nanosheets (GR) composite film modified glassy carbon electrode (GCE). GR–Bi nanocomposite has been successfully prepared via simple and facile chemical reduction approach and its structure was characterized by various techniques. Surface morphological and X-ray diffraction studies revealed the formation and high loading of Bi nanoparticles on graphene sheets. GR–Bi nanocomposite modified GCE exhibited greatly enhanced electrocatalytic performance towards electro-oxidation of hydrazine in terms of decrease in overpotential and increase in oxidation peak current ( I p ). The kinetic parameters such as electron transfer coefficient ( α ) and diffusion coefficient ( D o ) of the hydrazine oxidation were determined to be 0.70 and 2.65×10 −5 cm 2 s −1 , respectively. An amperometric sensor has been fabricated which detects trace level concentration of hydrazine. The sensor exhibited a wide linear range from 20 nM to 0.28 mM and a very low detection limit (LOD) of 5 nM. Remarkably, this is the lowest LOD achieved for the determination of hydrazine in neutral pH among other reported electrochemical hydrazine sensors. In addition, the sensor selectively detects hydrazine even in the presence of 1000 fold excess quantity of common interferrants. The practical feasibility of the sensor has been assessed in water and urine samples with good recoveries. Furthermore, the sensor exhibited appreciable stability, repeatability and reproducibility results.