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An enzyme-free sensitive hydrogen peroxide (H2O2) amperometric sensor is developed to detect H2O2 released from living cells using palladium nanoparticles supported on sulfonic acid functionalized mesoporous silica microspheres (Pd@SO3H-MSM). It is synthesized by an easy and facile method and is subsequently used for fabrication of an electrochemical sensing scaffold via drop-casting modification of a glassy carbon electrode (represented as GC/Pd@SO3H-MSM). Comprehensive characterizations including transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis spectrophotometry and electrochemical impedance spectroscopy to confirm the existence and nature of Pd nanoparticles in Pd@SO3H-MSM. GC/Pd@SO3H-MSM electrode demonstrates electrocatalytic activity for H2O2 reduction in phosphate buffer, leading to a sensitive H2O2 amperometric sensor with wide linear range (47.0 nM-1.0 mM), low detection limit (14.0 nM) and high sensitivity (0.36 μA mM−1 cm-2). It exhibits high selectivity, good reproducibility and long-term stability. More importantly, Pd@SO3H-MSM exhibits no toxicity to living cells and based on its remarkable analytical advantages, it is further unswervingly used to execute real-time detection of H2O2 released from living tumor cells and healthy normal cells. Thus Pd@SO3H-MSM acts as promising material for amperometric determination of H2O2 as well as used to accomplish real-time quantitative detection of H2O2 in biological environment.

Low Z element based room temperature ferromagnetic materials are highly sought after for many applications. In this work, we report the development of fluorine functionalized graphene-hBN out-of-plane heterostructures (hBNCF), which possess large room temperature ferromagnetic ordering (magnetization ∼ 0.05 emu/g and coercivity ∼ 420 Oe) and exhibit T2 relaxation enhancement (0.55 s−1 found for D2O was increased to ∼7 s−1 at 1 mg/ml) in water without causing the T1. The ferromagnetic nature of the hBNCF powder devoid of any metallic magnetic impurities was further shown by magnetic force microscopy. Layered structures of hBNCF that have an optical bandgap of ∼3.89 eV were produced using a two step method: Shear exfoliated hBN layers were modified by surface graphitisation to result into layered graphene heterostructures (hBNC), which were then functionalized with fluorine. Apparent ferromagnetic properties arise from these large scale, vertical, non-van der Waals connected, crystalline layer structures. Density functional calculations show the role of out-of-plane covalently connected BN domains and their interaction with fluorine, that causes the formation of new states in the graphitic lattice. These states exhibit a spin splitting, which contributes to the observed large magnetic ordering.

A new redox-free electrochemical approach for driving the deposition of two-dimensional (2D) layered MoS2 nanosheets is described. First, poly(acylic acid) (PAA) functionalized layered MoS2 nanosheets (PAA-MoS2) is prepared to form a stable aqueous PAA-MoS2 dispersion, which is subsequently used for the electrochemical deposition. In contrast to previous electrodeposition methods of MoS2, which involve the redox of molecular precursors of Mo and S, herein we introduce an electrochemical approach for the deposition of 2D layered MoS2 nanosheets directly from their nanometric building blocks, namely from their aqueous dispersion. This “nano to nano” approach is based on altering the ionic strength at the vicinity of the electrode surface by applying a potential. Specifically, the electrogeneration of Cu2+ ions, cause the PAA-MoS2 nanosheets in the dispersion to aggregate and deposit on the copper electrode. Scanning electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy analysis show clearly that the deposited layered MoS2 maintains its original structure. Furthermore, the electrodeposited PAA-MoS2 nanosheets on copper show excellent catalytic activity for the hydrogen evolution reaction with low overpotential. Hence, we believe that these findings could lead to a generic approach for the formation of thin films or patterns of 2D nanomaterials.

In this report, an electrochemical sensing scaffold (ESS) for hydrazine (HZ) and nitrobenzene (NB) have been developed based on gold nanoparticles decorated mesoporous silica microspheres (Au-MSM) modified glassy carbon (GC) electrode (represented as GC/Au-MSM). The presence and formation of gold nanoparticles in Au-MSM composite material is verified by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and by electrochemical methods. The textural and thermal properties are studied by nitrogen adsorption-desorption and thermogravimetric analysis, respectively. The electrocatalytic sensing behavior of GC/Au-MSM towards HZ and NB are investigated in detail employing various electrochemical techniques. Amperometry measurements as a function of HZ concentration exhibit two linear calibration ranges of 5.0 μM to 0.5 mM and 0.5–18.0 mM. Similarly, the differential pulse voltammetry measurements as a function of NB concentration show a linear calibration range of 0.1 μM to 2.5 mM. The limit of detection is evaluated to be 0.11 μM and 15.0 nM for HZ and NB, respectively. The kinetic parameters for HZ oxidation and NB reduction are discussed using chronoamperometry. The proposed GC/Au-MSM ESS shows good selectivity over potent interferences and applied to determine HZ and NB in various water samples.

An electrochemical sensing platform which comprises gold nanoparticles (Au NPs) incorporated zinc based metal-organic framework (MOF-5) is developed for the sensitive determination of nitrite and nitrobenzene. MOF-5 and Au NPs incorporated MOF-5 (Au-MOF-5) are synthesized and characterized by UV-vis absorption, powder X-ray diffraction, FT-IR, scanning electron microscopy with energy dispersive X-ray analysis and elemental mapping, transmission electron microscopy and atomic force microscopy. Oxidation of nitrite is effectively electrocatalyzed at Au-MOF-5 with significant increase in oxidation current (41 and 38% in comparison with bare glassy carbon (GC) and MOF-5 coated GC (GC/MOF-5) electrodes, respectively) and with considerable decrease in the oxidation potential (0. 17 and 0.25 V in comparison with bare GC and GC/MOF-5 electrodes, respectively). The electrocatalytic reduction of nitrobenzene at GC/Au-MOF-5 is confirmed by an appreciable increase in the reduction current (79 and 36% in comparison with bare GC and GC/MOF-5 electrodes, respectively) and a small shift in the reduction potential (20 mV in comparison with GC/MOF-5). The detection limit is calculated as 1.0 μM with a sensitivity of 0.23 μAμM −1 cm −2 for nitrite and 15.3 μM with a sensitivity of 0.43 μAμM −1 cm −2 for nitrobenzene determinations. The Au-MOF-5 based electrochemical sensing platform shows high stability and selectivity even in the presence of several interferences (including phenols, inorganic ions and biologically important molecules) with a broad calibration range. Certain kinetic parameters of nitrite oxidation and nitrobenzene reduction have also been studied by hydrodynamic voltammetry.

The present work introduces partially reduced graphene oxide (pRGO)-silica (SiO2) particles hybrid system (pRGOSHs) for sensitive and cost effective free cholesterol detection. Fabricated out of thin layers of pRGOSHs, these proposed ChOx/pRGOSHs/ITO based biosensors have a detection range of 2.6–15.5 mM with an appreciable detection limit of 1.3 mM and sensitivity of 11.1 μA/mM/cm2. Low Michaelis–Menten constant (Km) (4.9 × 10− 4 mM) and high diffusivity constant (D) (3.2 × 10− 10 cm2/s) values clearly indicate enhanced immobilization of enzyme over the substrate. Additionally, electrochemical impedance studies indicate that the synergistic combination of SiO2 and pRGO also results in much lower impedance values (40% and 18% decrease in comparison to SiO2 and pRGO respectively) for an overall enhanced sensing performance. These results are further corroborated by the density functional theory based theoretical simulations indicating enhanced electron density (theoretically) in case of the proposed hybrid system. Finally, the present work also highlights the importance of Si–OH bonds formation in the proposed pRGOSHs composite system for attaining such enhanced biosensing ability.

A novel electrochemical sensing platform (ESP) for nitrobenzene (NB) has been developed using palladium nanoparticles decorated polymer-silica nanocomposite (represented as Pd-GG-g-PAM-silica). The polymeric part of the nanocomposite is based on a biodegradable copolymer, guar gum grafted polyacrylamide (GG-g-PAM). The nanocomposite is characterized by spectroscopic, microscopic and electrochemical methods. Pd-GG-g-PAM-silica efficiently catalyzes the electro-reduction of NB. The mechanism and kinetic parameters of the electrocatalytic reduction of NB at Pd-GG-g-PAM-silica modified glassy carbon electrodes (GCE) are evaluated in 0.1 M phosphate buffer solution (pH 7.0) using linear sweep voltammetry, differential pulse voltammetry and chronoamperometry. The observed electrochemical responses at Pd-GG-g-PAM-silica modified GCE exhibit excellent analytical performance for NB detection with high stability, reproducibility, and acceptable selectivity. This novel ESP exhibit a detection limit of 0.06 μM with two linear calibration ranges from 1.0 to 1900 μM and from 1900 to 3900 μM for NB. The diffusion coefficient and catalytic rate constant for NB reduction at the Pd-GG-g-PAM-silica modified GCE is calculated to be 3.88 × 10 −6 cm 2 s −1 and 1.82 × 10 4 M −1 s −1 respectively. In addition, the material is successfully used for the determination of NB in real water samples and the recoveries of the spiked NB are quite satisfactory.

Development of an efficient amperometric sensor for nitrites using Fe(phen) 3 2+ (where phen = 1,10-phenanthroline) incorporated a bentonite film as electrochemical sensing platform (ESP) is reported. The ESP showed high electrocatalytic activity for nitrite oxidation by decreasing the nitrite oxidation potential and increasing the peak current. It shows linear increase in current with increase in the concentration of nitrite from 1.0 μM to 100.0 mM and 1.0 μM to 25.0 mM by cyclic voltammetry and amperometry, respectively. Kinetic parameters such as catalytic rate constant, diffusion coefficient, etc . are evaluated using chronoamperometry and chronocoulometry. Magnitude of interference caused by other species has been examined in simulated mixtures containing high concentration of interfering species and the influence of interferences was found to be negligible. The constructed sensor is successfully applied for the determination of nitrite in potable water samples.

A new palladium nanoparticles immobilized organic-inorganic hybrid nanocomposite material is prepared to combine the mechanical strength offered by the inorganic matrix with flexible binding sites provided by the organic polymer. The organic polymer is based on a natural polysaccharide, gaur gum grafted with poly(acrylamide) and the inorganic matrix is based on silica. The nanocomposite is characterized by physico-chemical methods, surface characterization techniques and electrochemical methods. This material is coated on a glassy carbon electrode and utilized for electrocatalytic oxidation of hydrazine (HZ). Electrocatalytically HZ is oxidized at lowest overpotential (-0.15 V vs. SCE) than ever reported. Based on the linear increase in catalytic current, a sensitive HZ amperometric sensor is constructed. The sensor displays two linear calibration ranges from 50.0 μM to 0.6 mM and from 0.6 mM to 180 mM for HZ with high stability and reproducibility. Limit of detection is found to be 4.1 μM with high sensitivity and selectivity. These properties make the nanocomposite film a promising electrochemical sensing platform for the determination of HZ. Chronoamperometry and cyclic voltammetry studies are used to evaluate kinetic parameters.

The construction and characterization of an electrochemical sensing platform based on a cationic polymer modified electrode are described in this work. The cationic polymer is prepared as a thin film on a glassy carbon electrode (GC) surface by in situ cross-linking of branched polyethylenimine (BPEI) with ethylene glycol diglycidyl ether (EGDE). Positively charged amino groups of this polymer (BPEI-EGDE) act as effective anion exchange groups. The ion exchange properties of BPEI-EGDE are investigated by determining the permeability of electroactive anions through the polymer film using cyclic voltammetry. Furthermore, the modified electrodes are used for the electrochemical detection of ascorbic acid (AA), which is feasible with the films alone or when hexacyanoferrate ([Fe(CN)6]4−), is electrostatically confined (by ion exchange) in the cationic BPEI-EGDE film. When compared with bare GC electrodes, a large decrease in AA oxidation overpotential is observed at the [Fe(CN)6]4−-modified electrode surface. Kinetic parameters of electrocatalytic oxidation of AA by electrogenerated [Fe(CN)6]3− are evaluated by cyclic voltammetry and chronoamperometry. Finally, this method is employed for the determination of AA in a pharmaceutical tablet.

This work is aimed to demonstrate the use of ion exchange voltammetry in the electroanalysis of biologically important molecules based on polymer modified electrodes. To produce improved polymer coatings on electrodes, a random copolymer of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and N-hydroxymethyl acrylamide (NHMA) (represented as P(AMPS-co-NHMA)) was prepared. Sulfonic acid groups allow this copolymer, P(AMPS-co-NHMA) to be used as an effective ion exchanger. The electrochemical behaviors of [Ru(NH 3 ) 6 ] 3+ and [Fe(CN) 6 ] 4− are studied at platinum and glassy carbon electrodes modified with the P(AMPS-co-NHMA). The electroactive cations are efficiently preconcentrated by the polymeric coating whereas the anions are not preconcentrated on the electrode surface. Thus the P(AMPS-co-NHMA) has permselective behavior based on either favorable or unfavorable electrostatic interactions with the analytes. The influence of hydrophobicity of the analytes on the electrochemical properties at P(AMPS-co-NHMA) modified electrodes is studied by methylene blue and thionine. The high preconcentration efficiency of P(AMPS-co-NHMA) at low analyte concentration highlights its possible application in the analysis of catecholamines.

Graft copolymers of polyacrylamide (PAM) and dextran (Dx) are synthesized by grafting PAM chains onto a Dx backbone (Dx-g-PAM) with ceric ion induced solution polymerization technique. Partial hydrolysis of Dx-g-PAM is carried out with sodium hydroxide solution to obtain HDx-g-PAM. To synthesize silver nanoparticles dispersed copolymer nano-composite (Ag-HDx-g-PAM), reduction of silver ions with HDx-g-PAM is carried out using microwave heating. The environmentally benign and biodegradable copolymer, HDx-g-PAM acts as both stabilizer and reducing agent. The copolymer nano-composite, Ag-HDx-g-PAM is characterized by FT-IR, transmission electron microscopy, scanning electron microscopy and optical spectroscopy. Further, the catalytic activity of Ag-HDx-g-PAM nano-composite towards the reduction of environmental pollutants like phenosafranine dye and aromatic nitro compounds are studied.