Alteration of surface pressure of macromolecular monolayer at the air-water interface and electrochemical impedance characteristics

Proteins are very important biological macromolecules, specific in their functions essential for many biological activities. Proteins are among the most vital components of all living matters with thousands of different types, and they are very specific in their nature which makes them important for usage in many biotechnological, biomedical, and food processing applications. Langmuir monolayer studies provide the characteristics of monolayer at the air-liquid interface. Langmuir monolayer of protein is affected by the molecular weight, macromolecular structure, denaturation and its purity. The interaction of the protein with other molecules greatly affects the behaviour of monolayer. Coconut oil layer at the air-water interface was prepared with different sub-phases including casein protein and whey protein. Wilhelmy plate measurement technique has been used to measure the surface pressure of the monolayer at the air-liquid interface. Experiments were carried out to study the stability using electrochemical impedance measurements. The electrostatic forces dominated the coconut oil - protein interaction, and the interface of macromolecules were controlled by expansion and compression. The macromolecules were adsorbed with a preferential orientation at the interface, and the stability of colloidal dispersions was governed by the intermolecular interactions. The stability using electrochemical impedance spectroscopy on the selected protein macromolecules along with other analysis were performed by varying various parameters.

Colorimetric and electrochemical arsenate assays by exploiting the peroxidase-like activity of FeOOH nanorods

The authors describe an electrochemical and an optical method for the determination of As(V) by using iron oxyhydroxide (FeOOH) nanorods that display peroxidase-mimicking activity. The nanorods catalyze the oxidation of substrate ABTS by H₂O₂ to form a green product with an absorption maximum at 418 nm. If, however, As(V) is electrostatically adsorbed on the nanorods, the oxidation is gradually inhibited. A colorimetric assay was worked out based on these findings. Response is linear in the 0 to 8 ppb and 8 to 200 ppb As(V) concentration range, and the detection limit is 0.1 ppb. Even higher sensitivity is achieved in an electrochemical method which is based on the excellent electrical conductivity of FeOOH nanorods. Electrochemical analysis of As(V) was achieved by first adsorbing As(V) on the nanorods. This inhibits the ABTS reduction current signal, best measured at a potential of 150 mV (vs. Ag/AgCl). The linear range extends from 0.04 to 200 ppb, and the detection limit is as low as 12 ppt. Graphical abstract Schematic representation of FeOOH nanorod-based colorimetric and electrochemical assays for arsenate (As(V)). As(V) adsorbed on FeOOH nanorods inhibits the peroxidase-mimicking activity of nanorods, and a colorimetric and electrochemical dual-signal assay was constructed to achieve sensitive determination of As(V).

A taurine-functionalized 3D graphene-based foam for electrochemical determination of hydrogen peroxide

We present a synthesis approach of taurine-functionalized graphene foam (a-NSGF) using hydrothermal reduction, freeze-drying and high temperature annealing. The higher temperature in annealing allowed the N/S atoms of taurine enter into the graphene lattice, which improves its electrocatalytic activity greatly. The a-NSGF consisting of taurine that modified into 3D layers of graphene and endow is of the rapid sensitive to hydrogen peroxide (H₂O₂). The electrode using a-NSGF modification reveals highly sensitive and stable towards the concentration change of H₂O₂ due to the stable 3D structure and good electrical conductivity of a-NSGF. A linear correlation between H₂O₂ concentration and the electrochemical signal is found to be in a range from 1.5 to 300 μM and the correlation coefficient is R² = 0.999. The modified electrode has been applied in the determination of H₂O₂ in rain samples and the results have been compared with the China National Standard Method. The recoveries range from 94.6% to 106.7%. These results show that the proposed sensor is promising for the development of novel electrochemical sensing for H₂O₂ determination.

Corrosion threshold data of metallic materials in various operating environment of offshore wind turbine parts (tower, foundation, and nacelle/gearbox)

This paper outlines corrosion thresholds for different environmental conditions of metallic materials commonly used in the tower, foundation, and nacelle/gearbox of an offshore wind turbine. These threshold values were derived from laboratory corrosion testing employing electrochemical analysis techniques, using the media/solvents that are representative to the operating environment of those wind turbine parts, such as seawater, grease, oils/lubricants, or their combination, at room temperature and at 328K. These values can provide an indication when general/local corrosion or protective film/surface damages have occurred. They can thus be utilised for detecting and monitoring corrosion at certain locations in the wind turbine structure. The presented data have been verified and validated to ensure their repeatability and reliability by means of numerous laboratory tests in accordance to the relevant engineering test standards and an extensive literature/published data review.

Electrochemical detection of paracetamol and dopamine molecules using nano-particles of cobalt ferrite and manganese ferrite modified with graphite

Some electrodes for efficient detection of paracetamol and dopamine were developed from nano sized material of cobalt ferrite (np-CoFe₂O₄) and manganese ferrite (np-MnFe₂O₄). These oxides were synthesized by combustion method using cobalt nitrate, manganese acetate and ferric nitrate as precursors in the presence of sugar and ethanolamine. The crystallite size, shape and morphology of nano material were characterized by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The crystallite sizes of synthesized nano-particles (nps) were in the range from 10 to 12 nm (calculated using Debye-Scherrer equation) with cubic crystal system. These particles were utilized as electrode modified with graphite for simultaneous detection of paracetamol and dopamine through cyclic voltammetry and Differential pulse voltammetry techniques and was found to be superior to reported literatures. The minimum detection limit of paracetamol and dopamine at CoFe₂O₄/GP electrode were 250 nM and 350 nM while at MnFe₂O₄/GP electrode it was 300 nM and 400 nM, respectively. Both the electrodes exhibited the linearity range from3 μM to 200 μM & 3 μM-160 μM for paracetamol and 3 μM-180 μM & 5 μM to 200 for dopamine, respectively. Two oxidation peaks of paracetamol and dopamine were well separated in phosphate buffer (pH = 6) in mixture with 100 mVs^-1 and 50 mVs^-1 scan rate for cyclic voltammetry and Differential pulse voltammetry, respectively. Both the electrodes demonstrated satisfactory results in real samples of paracetamol and dopamine.

Femtomolar electroanalysis of a breast cancer biomarker HER-2/neu protein in human serum by the cellulase-linked sandwich assay on magnetic beads

In cancer diagnostics, specific analysis of blood-circulating proteins biomarkers of cancer is often complicated both by their inherently low concentrations and by strong interference from serum/blood proteins. Here, we report a simple and robust electrochemical cellulase-linked sandwich assay on magnetic beads (MBs) for fM-sensitive analysis of the Human Epidermal growth factor Receptor-2 HER-2/neu protein that is over-expressed in most aggressive breast cancers. In the assay, a sandwich is assembled by capturing HER-2/neu on either antibody (Ab) or aptamer-modified MBs accompanied by reaction with the second Ab or aptamer labelled with cellulase. On application of the sandwiches assembled on MBs onto a cost-effective graphite electrode modified with an insulating nitrocellulose film, the cellulase label digests the film. This results in the pronounced changes in the electrical properties of the modified electrodes. The chronocoulometrically-measured extent of the produced changes was proportional to the 10^-15-10^-10 M HER-2/neu in the analyzed samples, and down to 1 fM of HER-2/neu could be detected in human serum samples in an overall less than 3 h assay. The developed simple and electrochemically label-free methodology is general and can be easily adapted for testing of any other protein.

Reduced graphene oxide nanosheets modified with plasmonic gold-based hybrid nanostructures and with magnetite (Fe3O4) nanoparticles for cyclic voltammetric determination of arsenic(III)

The authors have fabricated reduced graphene oxide nanosheets (rGO) supported with Fe₃O₄ nanoparticles and Ag/Au hollow nanoshells. The material was placed on a glassy carbon electrode which is shown to enable highly sensitive determination of As(III) which is first preconcentrated from solution at a potential of -0.35 V (versus Ag/AgCl) for 100 s. The electrode, typically operated at a working potential as low as 0.06 V, has a linear response in the 0.1 to 20 ppb As(III) concentration range and a 0.01 ppb detection limit. The electrochemical sensitivity is 52 μA ppb^-1. The high sensitivity is assumed to be the result of various synergistic effects. The method was applied to ultratrace (0.1 ppt) determination of As(III) in real water samples. Graphical abstract The hybrid displays a wide linear response in the 0.1 to 20 ppb As(III) concentration range and a 0.01 ppb detection limit. The high sensitivity is attributed to various synergistic effects. The method was applied to ultratrace determination of As(III) in real water samples.

Electrochemical preparation of two nanostructured poly(sulfosalicylic acid) films with different morphologies and properties for selective sensing of dopamine: Comparative study

Two nanostructured poly(sulfosalicylic acid) (PSA) films were synthesized from room temperature ionic liquid (RTIL) or aqueous solution on a glassy carbon electrode (GCE) via potentiodynamic electropolymerization. The morphology and properties of the PSA films were characterized with scanning electron microscopy (SEM), scanning probe microscopy (SPM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It was found that solvent had a major influence on the morphology and electrochemical properties of the resultant PSA films. The PSA(Ι) film, which was prepared from RTIL, consists of granular particles with cracks, whereas the PSA(II) film prepared from aqueous solution consists of nano-triangles with a more compact surface. The blocking effect of the PSA(Ι) film for the [Fe(CN)₆]^3-/4- electrochemical probe is much stronger, and a remarkably enhanced voltammetric response of the [Ru(NH₃)₆]³⁺ electrochemical probe can be observed for the PSA(II) film. When it is used to detect dopamine in the presence of a high concentration of ascorbic acid, PSA(II)/GCE has three linear parts with better discrimination and a detection limit of 0.03μM. For PSA(Ι)/GCE, there are two linear parts with a detection limit of 0.05μM. However, the reproducibility and storage stability of PSA(Ι)/GCE are better than those of PSA(ΙI)/GCE.

Tyramine detection using PEDOT:PSS/AuNPs/1-methyl-4-mercaptopyridine modified screen-printed carbon electrode with molecularly imprinted polymer solid phase extraction

Tyramine (4-hydroxyphenethylamine), which is a monoamine metabolized by monoamine oxidase (MAO), exists widely in plants, animals, fermented foods, and salted foods. The incidence of hypertension, or "cheese effect", which is associated with a large dietary intake of tyramine while taking MAO inhibitors has been reported; therefore, the measurement of tyramine is an urgent concern. Herein, an efficient approach that integrates a molecular imprinting polymer for solid phase extraction (MISPE) technique with a sensitive electrochemical sensing platform (SPCE/PEDOT: PSS/AuNP/1-m-4-MP) for the quantification of tyramine is presented. Enhanced electrode conductivity was achieved sequentially by constructing a conductive polymer (PEDOT: PSS) on a screen-printed carbon electrode (SPCE), followed by electrodeposition with gold nanoparticles (AuNPs) and, finally, by modification with positively charged 1-methyl-4-mercaptopyridine (1-m-4-MP) using an Au-S bond. Tyramine was isolated selectively and pre-concentrated by the MISPE technique; electroanalysis that used differential pulse voltammetry (DPV) in NaOH (0.1M, pH 13) was conducted successively. Experimental parameters (such as modes of electrode modification, ratio of PEDOT: PSS, pH of electrolyte, time required for AuNP deposition, and 1-m-4-MP concentrations) that were associated with optimal detection conditions were evaluated also. We obtained a linear concentration range (5-100nM, R²=0.9939) with LOD and sensitivity at 2.31nM, and 3.11μAnM^-1cm^-2, respectively. The applicability of our technique was demonstrated by analyzing tyramine in spiked serum and milk. The feature of our newly developed analytical methods that coupled sample pre-treatment (sample clean-up and pre-concentration) with sensitive detection makes it a promising tool for quantifying of tyramine.

Nanopore-based analysis of biochemical species

Biological nanochannels or nanopores play a crucial role in basic biochemical processes in cells. Artificial nanopores possessing dimensions comparable to the size of biological molecules and mimicking the function of biological ion channels are of particular interest with respect to the design of biosensors with a sensitivity that can go down to the fM level and even to single molecule detection. Nanopore-based analysis (NPA) is currently a new research field with fascinating prospects. This review (with 118 refs.) summarizes the progress made in this field in the recent 10 years. Following an introduction into the fundamentals of NPA, we demonstrate its potential by describing selected methods for sensing (a) proteins such as streptavidin, certain antibodies, or thrombin via aptamers; (b) oligomers, larger nucleic acids, or micro-RNA; (c) small molecules, (d) ions such as K(I) which is vital to the maintenance of life, or Hg(II) which is dangerous to health. We summarize the results and discuss the merits and limitations of the various methods at last. Graphical abstractSchematic of a signal-off system and a signal-on system in nanopore analysis. The effective diameter of nanopores decreases when targets undergo certain interactions with receptors attached on the inner surface of the nanopore. Correspondingly, the current will drop on appearance of the analyte. This is referred to as a "signal-off" system. Conversely, it is called a "signal-on" system.

Vibrational and electronic spectra of N-aryl ring substituted (Z)-N-(4-amino-5-(4-chlorophenyl)-3-phenylthiazol-2(3H)-ylidene)benzamide compounds

In the present paper the vibrational, electronic and nonlinear optical properties of three N-aryl ring substituted (Z)-N-(4-amino-5-(4-chlorophenyl)-3-phenylthiazol-2(3H)-ylidene)benzamide compounds have been investigated by UV-vis, FT-IR and FT-Raman spectroscopic measurements. The electrochemical properties of the compounds were measured by cyclic voltammetry. Density functional theory calculations with B3LYP/6-31+G(d,p) basis set was used to determine the ground state molecular geometries (bond lengths and bond angles), harmonic vibrational frequencies, infrared intensities and Raman activities of title compounds. Potential energy distributions (PEDs) and normal modes, for the spectral data computed at B3LYP/6-31+G(d,p) level, have also been obtained from force-field calculations. A comparison of the theoretical spectra and experimental FT-IR and FT-Raman spectra of the title molecule has been made and full vibrational assignments of the observed spectra have been proposed. The substituent effect on the electronic properties of the title compounds were investigated by time-dependent density functional theory calculations.

Synergistic Effect of Functionalized Nickel Nanoparticles and Quercetin on Inhibition of the SMMC-7721 Cells Proliferation

The effect of functionalized nickel (Ni) nanoparticles capped with positively charged tetraheptylammonium on cellular uptake of drug quercetin into hepatocellular carcinoma cells (SMMC-7721) has been explored in this study via microscopy and electrochemical characterization as well as MTT assay. Meanwhile, the influence of Ni nanoparticles and/or quercetin on cell proliferation has been further evaluated by the real-time cell electronic sensing (RT-CES) study. Our observations indicate that Ni nanoparticles could efficiently improve the permeability of cancer cell membrane, and remarkably enhance the accumulation of quercetin in SMMC-7721 cells, suggesting that Ni nanoparticles and quercetin would facilitate the synergistic effect on inhibiting proliferation of cancer cells.