Characterization and Electrocatalytic Property of Cobalt Hexacyanoferrate Film on Carbon Nanotubes Modified Gold Electrode

Abstract

Cobalt hexacyanoferrate (CoHCF) film was formed on multiwalled carbon nanotubes (MWNTs) modified gold electrode by electrodeposition from 0.5 M KCl solution containing CoCl₂ and K₃Fe(CN)₆. The electrochemical behavior and the electrocatalytic property of the modified electrode were investigated. Compared with CoHCF/gold electrode, the CoHCF/MWNTs/gold electrode exhibits greatly improved stability and enhanced electrocatalytic activity toward the oxidation of thiosulfate. A linear range from 5.0×10^?5 to 6.5×10^?3 M (r=0.9990) for thiosulfate detection at the CoHCF/MWNTs/gold electrode was obtained, with a detection limit of 2.0×10^?5 M (S/N=3).     

A Sensitive Hydrogen Peroxide Sensor Based on Hemoglobin Immobilized on Gold Nanoparticles and 1,6-hexanedithiol Modified Gold Electrode

Hemoglobin (Hb) was successfully immobilized on a gold electrode modified with gold nanoparticles (AuNPs) via a molecule bridge 1,6-hexanedithiol (HDT). The AFM images suggested that the HDT/gold electrode could adsorb more AuNPs. UV-vis spectra indicated that Hb on AuNPs/HDT film retained its near-native secondary structures. The electrochemical behaviors of the sensor were characterized with cyclic voltammetric techniques. The resultant electrode displayed an excellent electrocatalytical response to the reduction of hydrogen peroxide (H₂O₂). The linear relationship existed between the catalytic current and the H₂O₂ concentration ranging from 5.0 × 10^?8 to 1.0 × 10^?6 mol · L^?1. The detection limit (S/N = 3) was 1.0 × 10^?8 mol · L^?1.     

Detection of DNA immobilized on bare gold electrodes and gold nanoparticle-modified electrodes via electrogenerated chemiluminescence using a ruthenium complex as a tag

Electrogenerated chemiluminescence (ECL) for DNA hybridization detection is demonstrated based on DNA that was self-assembled onto a bare gold electrode and onto a gold nanoparticles modified gold electrode. A ruthenium complex served as an ECL tag. Gold nanoparticles were self-assembled on a gold electrode associated with a 1,6-hexanedithiol monolayer. The surface density of single stranded DNA (ssDNA) on the gold nanoparticle modified gold electrode was 4.8?×?10¹⁴ molecules per square centimeter which was 12-fold higher than that on the bare gold electrode. Hybridization was induced by exposure of the target ssDNA gold electrode to the solution of ECL probe consisting of complementary ssDNA tagged with ruthenium complex. The detection limit of target ssDNA on a gold nanoparticle modified gold electrode (6.7?×?10^?12 mol L^?1) is much lower than that on a bare gold electrode (1.2?×?10^?10 mol L^?1). The method has been applied to the detection of the DNA sequence related to cystic fibrosis. This work demonstrates that employment of gold nanoparticles self-assembled on a gold electrode is a promising strategy for the enhancement of the sensitivity of ECL detection of DNA.     

Simultaneous Determination of Monoamines,Their Precursor Amino Acids,and Related Metabolites in Mice Brain by High‐Performance Liquid Chromatography with a Coulometric Electrode Array System

Abstract

A method based on high performance liquid chromatography with a coulometric electrode array system (HPLC‐coulometric electrode array) using C₁₈ column has been developed for the simultaneous determination of norepinephrine (NE), epinephrine (E), l‐3,4‐dihydroxyphenylalanine (l‐DOPA), p‐tyrosine (p‐TYR), dopamine (DA), m‐tyrosine (m‐TYR), 5‐hydroxytryptamine (5‐HT), homovanillic acid (HVA), and 5‐hydroxyindoleacetic acid (5‐HIAA) in mice brain. The chromatography was performed using a C₁₈ column (250 mm×4.6 mm i.d. and 5 µm) with sodium acetate buffer (pH 5.0, 0.05 M) and methanol as the mobile phase. Elution of analytes was carried out at a flow rate of 1.0 ml/min. The nine compounds were monitored using an ESA electrochemical detector. Potentials of three electrodes in series were set at 200, 500, and 700 mV, respectively. Optimization of the pH of the mobile phase and the proportion of methanol were also considered. The minimal detection limits were 2–8 ng/ml. Linear (r=0.99) detector performances were observed within a range of 10～2000 ng/ml. Recoveries for the nine compounds in spiked samples were over 90% and the relative standard deviations (RSD) were less than 4.0%.     

Preparation of CuO-Nanoparticle-Modified Electrode and Its Application in the Determination of Rutin

Abstract

In this article, highly pure, well-dispersed, 10-nm CuO nanoparticles were obtained by a hydrothermal reduction process, with oxalic acid as precipitator. The CuO nanoparticles were characterized by x-ray powder diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. The CuO nanoparticles were modified onto a gold electrode to study the effect on the redox of the rutin. Cyclic voltammetry results show that the CuO nanoparticles were very active for rutin and that the CuO-nanoparticle-modified electrode can even determine rutin in a certain range of concentration from 5.0 × 10^?7 to 5.0 × 10^?4 mol L^?1 by differential pulse voltammertry, which provides a new application for CuO nanoparticles.     

Amperometric Immunosensor Based on Gold Nanoparticles/Fe3O4-FCNTs-CS Composite Film Functionalized Interface for Carbofuran Detection

In this paper, a novel amperometric immunosensor for the determination of carbofuran based on gold nanoparticles (GNPs), magnetic Fe₃O₄ nanoparticles-functionalized multiwalled carbon nanotubes-chitosan (Fe₃O₄-FCNTs-CS), and bovine serum albumin (BSA) composite film was proposed. First, GNPs were immobilized onto the glassy carbon electrode (GCE) surface, and then the magnetic Fe₃O₄ nanoparticles mixed with chitosan-functionalized multiwall carbon nanotubes (CS-FCNTs) homogeneous composite (CS-FCNTs-Fe₃O₄) was immobilized onto the GNPs layer by electrostatic interactions between amino groups of CS and GNPs. Because chitosan (CS) contains many amino groups, it can absorb more antibodies. FCNTs have high surface area, high electrical conductivity, and it can enhance the electron transfer rate; Magnetite (Fe₃O₄) nanoparticles can provide a favorable microenvironment for biomolecules immobilization due to their good biocompatibility, strong superparamagnetic property, and low toxicity; and GNPs possess high surface-to-volume reaction, stability, and high conductivity. Gold Nanoparticles/Fe₃O₄-FCNTs-CS composite film was constructed onto the GCE surface, which had significant synergistic effects toward immunoreaction signal amplification. The stepwise assembly process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Under the optimal conditions, the current response was proportional to the concentration of carbofuran ranging from 1.0 ng/mL to 100.0 ng/mL and from 100.0 ng/mL to 200 µg/mL with the detection limit 0.032 ng/mL. The proposed immunosensor exhibited good accuracy, high sensitivity, and stability, and it can be used for detection of carbofuran pesticide.     

Highly Sensitive Electrogenerated Chemiluminescence Isoniazid with NiO Nanoparticles‐modified Graphite Electrode

Abstract

NiO nanoparticles (NiO NPs) were prepared with chemical precipitation method and modified on the surface of vaseline‐impregnated graphite electrode with chitosan. It was found that, based on the catalysis of the NiO NPs for the chemiluminescent reaction of the ECL process, the enhancing effect of isoniazid on the weak electrogenerated chemiluminescence (ECL) signal of luminol at a NiO NPs‐chitosan modified electrode was stronger than that at a bare graphite electrode. Under the optimum experimental conditions, the relative ECL intensity was linear with isoniazid concentration over the range 3.0×10^?10～1.0×10^?6 g/ml at the NiO NPs‐chitosan modified electrode with a detection limit of 1.0×10^?10 g/ml.     

Preliminary Recognition of c-Myc Gene Protein Using an Optical Biosensor with Gold Colloid Nanoparticles Based on Localized Surface Plasmon Resonance

Abstract

The gold colloidal nanoparticles with a diameter of 24 ± 0.2 nm were prepared, characterized by ultraviolet–visible (UV-vis), transmission electron microscopy (TEM), and cyclic voltammetry, and assembled on a gold plate substrate for constructing an optical nanobiosensor. The nanosensor exhibited distinct optical properties of localized surface plasmon resonance (LSPR), which could be used for recognition of oncogene biomolecules such as the c-Myc (3C7) antibody protein. The LSPR nanobiosensor has also been successfully applied to determination of a pCMV-Myc mammalian expression vector, one kind of DNA plasmids with a linear response range of 6.2–20.0 ng/µL and a detection limit of 2.4 ng/µL.     

Disposable electrochemical immunosensor for myeloperoxidase based on the indium tin oxide electrode modified with an ionic liquid composite film containing gold nanoparticles, poly(o-phenylenediamine) and carbon nanotubes

A disposable electrochemical myeloperoxidase (MPO) immunosensor was fabricated based on the indium tin oxide electrode modified with a film composed of gold nanoparticles (AuNPs), poly(o-phenylenediamine), multi-walled carbon nanotubes and an ionic liquid. The composite film on the surface of the electrode was prepared by in situ electropolymerization using the ionic liquid as a supporting electrolyte. Negatively charged AuNPs were then adsorbed on the modified electrode via amine-gold affinity and to immobilize MPO antibody. Finally, bovine serum albumin was employed to block possible remaining active sites on the AuNPs. The modification of the electrode was studied by cyclic voltammetry and scanning electron microscopy. The factors affecting the performance of the immunosensor were investigated in detail using the hexacyanoferrate redox system. The sensor exhibited good response to MPO over two linear ranges (from 0.2 to 23.4 and from 23.4 to 300 ng.mL^?1), with a detection limit of 0.05 ng.mL^?1 (at an S/N of 3).

A novel immunosensor for carcinoembryonic antigen based on poly(diallyldimethylammonium chloride) protected prussian blue nanoparticles and double-layer nanometer-sized gold particles

A highly sensitive amperometric immunosensor has been developed for the detection of carcinoembryonic antigen (CEA). It is based on (a) Prussian Blue nanoparticles coated with poly(diallyldimethylammonium chloride) (P-PB) and (b) double-layer gold nanocrystals. The sensor was obtained by first electrodepositing porous gold nanocrystals on the glassy carbon electrode (GCE), and then by modifying the electrode with the coated P-PB. Subsequently, colloidal gold nanoparticles (nano-Au) were adsorbed onto the GCE by electrostatic interactions between the negatively charged nano-Au and the positively charged P-PB to immobilize CEA antibodies. Finally, bovine serum albumin was employed to block possible remaining active sites and to prevent the non-specific adsorption on the nano-Au. This immunosensor was characterized by cyclic voltammetry and scanning electron microscopy. The working range was adjusted to two concentration ranges, viz. from 0.5 to 10 ng.mL^?1, and from 10 to 120 ng.mL^?1 of CEA, with a detection limit of 0.2 ng.mL^?1 at three times the background noise.     

An amperometric uric acid biosensor based on chitosan-carbon nanotubes electrospun nanofiber on silver nanoparticles

A novel amperometric uric acid biosensor was fabricated by immobilizing uricase on an electrospun nanocomposite of chitosan-carbon nanotubes nanofiber (Chi–CNTsNF) covering an electrodeposited layer of silver nanoparticles (AgNPs) on a gold electrode (uricase/Chi–CNTsNF/AgNPs/Au). The uric acid response was determined at an optimum applied potential of ?0.35 V vs Ag/AgCl in a flow-injection system based on the change of the reduction current for dissolved oxygen during oxidation of uric acid by the immobilized uricase. The response was directly proportional to the uric acid concentration. Under the optimum conditions, the fabricated uric acid biosensor had a very wide linear range, 1.0–400 μmol L^?1, with a very low limit of detection of 1.0 μmol L^?1 (s/n?=?3). The operational stability of the uricase/Chi–CNTsNF/AgNPs/Au biosensor (up to 205 injections) was excellent and the storage life was more than six weeks. A low Michaelis–Menten constant of 0.21 mmol L^?1 indicated that the immobilized uricase had high affinity for uric acid. The presence of potential common interfering substances, for example ascorbic acid, glucose, and lactic acid, had negligible effects on the performance of the biosensor. When used for analysis of uric acid in serum samples, the results agreed well with those obtained by use of the standard enzymatic colorimetric method (P?>?0.05).

Electrochemical Behavior and Application of Pirarubicin at Gold Nanoparticles–Modified Indium Tin Oxide Electrode

Abstract

A new type of gold nanoparticles–attached indium tin oxide electrode was made. By SEM and EDS, the as‐prepared gold nanoparticles–modified ITO electrode was characterized. This modified electrode has been used for the determination of pirarubicin (THP) in urine by cyclic voltammetry. Compared to a bare ITO electrode, the modified electrode exhibited a marked enhancement in the current response. Liner calibration curves are obtained in the range 5×10^?9mol/L～1.5×10^?6 mol/L with a detection limit of 1×10^?9 mol/L. The percentage of the recoveries ranged from 99.3% to 106.3%. The practical analytic utility of the method is illustrated by quantitative determination of THP in urine.     

The Influence of Gold Nanoparticles on Simultaneous Determination of Uric Acid and Ascorbic Acid

A three-dimensional L-cysteine (L-cys) monolayer assembled on gold nanoparticles (GNP) providing simultaneous detection of uric acid (UA) and ascorbic acid (AA) was studied in this work. The cyclic voltammetry demonstrated that, at a bare glassy carbon electrode (GCE) or planar gold electrode, the mixture of UA and AA showed one overlapped oxidation peak; whereas when the electrode was modified with GNP, the oxidation peaks for UA and AA were separated. While a GNP modified electrode was further modified with L-cys monolayer (L-cys/GNP/GCE), namely, three-dimensional L-cys monolayer, a better separation for UA and AA response was obtained. Interestingly, the L-cys monolayer-modified planar gold electrode presented a block effect on the oxidation of AA, which was facilitated by the three-dimensional L-cys monolayer attributed to its distinct structure. The pH of solution presented a noticeable effect on the separation of UA and AA at GNP modified electrodes with or without L-cys monolayer. Wide concentration ranges from 2 × 10^?6?1 × 10^?3 M to UA and 2 × 10^?6?8 × 10^?4 M to AA could be obtained at L-cys/GNP/GCE.     

Sandwich-type amperometric immunosensor for human immunoglobulin G using antibody-adsorbed Au/SiO2 nanoparticles

A novel sandwich-type electrochemical immunosensor for human immunoglobulin G (hIgG) was developed using Au/SiO₂ nanoparticles (NPs) with adsorbed horseradish peroxidase-anti-hIgG as the secondary antibody layer. The signal readout is based on the amperometric response to the catalytic reduction of hydrogen peroxide at an AuNPs-polythionine modified glassy carbon electrode. Under optimized conditions, the linear range is from 0.1 to 200 ng·mL^?1, with a detection limit of 0.035 ng·mL^?1 (at an S/N of 3). The immunosensor exhibited a performance that is better than that based on Au/SiO₂NPs-excluded secondary antibody.     

Studies on the Affinity‐based Biosensors for Electrochemical Detection of HER2 Cancer Biomarker

As cancer diseases are the second main cause of death it is necessary to elaborate fast and efficient early diagnosis methods for their detection. One of the possibilities is the analysis of protein biomarkers, which abnormal concentration in physiological fluids might be an indication of cancer disease progression. Herein, we present the studies on the development of affinity‐based biosensors for electrochemical detection of HER2 protein, which is a common biomarker of breast cancer. The main objective was to verify the possibility of fabrication of HER2‐specific hybrid aptamer‐polyclonal antibody and antibody‐based sandwich sensing layer on gold electrode surface. The effectiveness of each electrode modification step was confirmed using voltammetric and impedimetric techniques in the presence of ferri/ferrocyanide redox couple. It was observed that hybrid construct was unlikely to be formed on the gold electrode due to a higher affinity of secondary polyclonal antibody towards target protein, which resulted in the separation of HER2‐antibody complex from the electrode surface. On the contrary, an antibody‐based sandwich receptor layer allowed for protein discrimination in the range from 1 to 100 ng mL^?1 by the application of TMB/H₂O₂ system and chronoamperometry detection technique. Though, the occurrence of interactions between interfering proteins and antibody‐based layer was noted, it led to at least two times smaller current responses than for HER2 protein.     

Immunosensors Based on Layer‐by‐Layer Self‐Assembled Au Colloidal Electrode for the Electrochemical Detection of Antigen

Colloidal Au particles have been deposited on the gold electrode through layer‐by‐layer self‐assembly using cysteamine as cross‐linkers. Self‐assembly of colloidal Au on the gold electrode resulted in an easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)₆]^4?/[Fe(CN)₆]^3? on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37 °C for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based on this immobilization method exhibits a large linear dynamic range, from 5–400 μg/L for detection of Human IgG. The detection limit is about 0.5 μg/L.     

Study on an immunosensor based on gold nanoparticles and a nano-calcium carbonate/Prussian blue modified glassy carbon electrode

An amperometric carcinoembryonic antigen (CEA) immunosensor was fabricated based on Prussian blue (PB), nano-calcium carbonate (nano-CaCO₃) and nano-gold modified glassy carbon electrode. First, PB as a mediator was deposited on glassy carbon electrode to obtain a negatively charged surface. Then, positive nano-CaCO₃ was adsorbed on the PB modified electrode through electrostatic interaction. Subsequently, gold nanoparticles were deposited on the nano-CaCO₃/PB modified electrode. The use of two kinds of nanomaterials (nano-CaCO₃ and nano-gold) with good biocompatibility as immobilization matrixes not only provides a biocompatible surface for protein loading but also avoids the leaking of PB. The size of nano-CaCO₃ was characterized by transmission electron microscopy (TEM). The factors influencing the performance of the immunosensor presented were studied in detail. Under the optimized conditions, cyclic voltammograms (CV) determination of CEA showed a specific response in two concentration ranges from 0.3 to 20 ng mL^?1 and from 20 to 100 ng mL^?1 with a detection limit of 0.1 ng mL^?1 at a signal-to-noise ratio of 3. The immunosensor presented exhibited high selectivity, sensitivity and good stability.     

Electrochemical sandwich immunoassay for the peptide hormone prolactin using an electrode modified with graphene,single walled carbon nanotubes and antibody-coated gold nanoparticles

We describe a new kind of electrochemical immunoassay for the peptide hormone prolactin. A glassy carbon electrode (GCE) was modified with a hybrid material consisting of graphene, single walled carbon nanotubes and gold nanoparticles (AuNPs) in a chitosan (CS) matrix. The graphene and the single wall carbon nanotubes were first placed on the GCE, and the AuNPs were then electrodeposited on the surface by cyclic voltammetry. This structure results in a comparably large surface for immobilization of the capturing antibody (Ab₁). The modified electrode was used in a standard sandwich-type of immunoassay. The secondary antibody (Ab₂) consisted of AuNPs with immobilized Ab₂ and modified with biotinylated DNA as signal tags. Finally, alkaline phosphatase was bound to the biotinylated DNA-AuNPs-Ab₂ conjugate via streptavidin chemistry. The enzyme catalyzes the hydrolysis of the α-naphthyl phosphate to form α-naphthol which is highly electroactive at an operating voltage as low as 180 mV (vs. Ag/AgCl). The resulting immunoassay exhibits high sensitivity, wide linear range (50 to 3200 pg∙mL‾¹), low detection limit (47 pg∙mL‾¹), acceptable selectivity and reproducibility. The assay provides a pragmatic platform for signal amplification and has a great potential for the sensitive determination of antigens other than prolactine.

The immunoassay for prolactin is based on a glassy carbon electrode modified with SWCNTs, graphene and antibody-coated gold nanoparticles, and a secondary antibody conjugated to other gold nanoparticles via a biotinylated DNA linker

     

Subnanomolar Determination of Indium by Adsorptive Stripping Differential Pulse Voltammetry Using Factorial Design for Optimization

Abstract

A highly sensitive method to determine of indium is proposed by adsorption stripping differential pulse cathodic voltammetry (AdSDPCV) method. The complex of indium ions with xylenol orange is analyzed based on the adsorption collection onto a hanging mercury drop electrode (HMDE). After accumulation of the complex at ?0.20 V vs. Ag/AgCl reference electrode, the potential is scanned in a negative direction from ?0.40 to ?0.75 V with the differential pulse method. Then, the reduction peak current of In(III)–XO complex is measured. The influence of chemical and instrumental variables was studied by factorial design analysis. Under optimum conditions and accumulation time of 60 s, linear dynamic range was 0.1–10 ng/ml (8.7 × 10^?10 to 8.7 × 10^?8 M) with a limit of detection of 0.03 ng/ml (2.6 × 10^?10 M); at accumulation time of 5 min, linear dynamic range was 0.04–10 ng/ml (3.4 × 10^?10 to 8.7 × 10^?8 M) with a limit of detection of 0.013 ng/ml (1.1 × 10^?10 M). The applicability of the method to analysis of real samples was assessed by the determination of indium in water, alloy, and jarosite (zinc ore) samples.     

A disposable immunosensor based on gold colloid modified chitosan nanoparticles-entrapped carbon paste electrode

A new strategy is described to construct disposable electrochemical immunosensors for the assay of human immunoglobulin. It is based on a carbon paste electrode constructed from chitosan nanoparticles modified with colloidal gold. The stepwise assembly process of the immunosensor was characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy. Assay conditions that were optimized included the amount of chitosan nanoparticles in the preparation of carbon paste electrode, antibody concentration, and the incubation time of the antibody immobilization. Using hexacyanoferrate as a mediator, the current change increased with the concentration of human immunoglobulin G. A linear relationship in the concentration range 0.3 to 120 ng mL^?1 was achieved, with a detection limit of 0.1 ng mL^?1 (S/N?=?3). The method combines the specificity of the immunological reaction with the sensitivity of the gold colloid amplified electrochemical detection, and it has potential application in clinical immunoassay.