Synthesis and electrochemical characterization of myoglobin-antibody protein immobilized self-assembled gold nanoparticles on ITO-glass plate

We report a protein immobilized self-assembled monolayer (SAM) of gold nanoparticles (GNPs) on indium-tin-oxide (ITO) coated glass plate. The protein-antibody, Mb-Ab, was covalently immobilized over the self-assembly of GNPs through a mixed SAM of 11-mercapto undecanoic acid (MUA) and 3-mercapto propionic acid (MPA) via carbodiimide coupling reaction using N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The whole assembly was constructed on 0.25 cm² area of ITO-glass plate (Mb-Ab/MUA-MPA/GNPs/APTES/ITO-glass) and an impedimetric study was carried out for its application in myoglobin detection. This prototype assembly was characterized by scanning electron microscopy, atomic force microscopy and electrochemical techniques. The modified electrode showed an increased electron-transfer resistance on coupling with protein antigen, Mb-Ag, in the presence of a redox probe [Fe(CN)₆]^3−/4−. Its exhibits an electrochemical impedance response to protein myoglobin-antigen, Mb-Ag, concentration in a linear range from 0.01 μg to 1.65 μg mL⁻¹ with a lowest detection limit of 1.4 ng mL⁻¹.     

Electrochemical detection of prostate-specific antigen based on gold colloids/alumina derived sol-gel film

An electrochemical immunosensor for total prostate-specific antigen (PSA) was fabricated based on anti-PSA antibody-functionalized gold colloids/alumina sol-gel film. The presence of colloidal gold provides a good microenvironment for the immobilization of biomolecules. The fabrication process of the immunosensor was characterized by cyclic voltammetry. A direct electrochemical immunoassay format was employed to detect PSA on the basis of the potential change before and after the antigen-antibody interaction. Under optimal conditions, the potential change was proportional to PSA concentration ranging from 4.0 to 13 ng mL^− 1 with a detection limit of 3.4 ng mL^− 1. In addition, the performance and factors influencing the performance of the immunosensor were investigated and optimized.     

Langmuir-Blodgett films of polyaniline for low density lipoprotein detection

Langmuir-Blodgett (LB) films of polyaniline (PANI) were utilized for the fabrication of impedimetric immunosensor for detection of human plasma low density lipoprotein (LDL) by immobilizing anti-apolipoprotein B (AAB) via EDC-NHS coupling. The modified electrodes were characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. AAB/PANI-SA LB immunoelectrodes studied by EIS spectroscopy revealed detection of LDL in the wide range of 0.018 μM (6 mg/dl) to 0.39 μM (130 mg/dl), covering the physiological range in blood, with a sensitivity of 11.25 kΩ μM^− 1.     

Antibody immobilized cysteamine functionalized-gold nanoparticles for aflatoxin detection

Aflatoxin B₁ antibody (aAFB₁) covalently attached to cysteamine functionalized-gold nanoparticles (C-AuNP) has been immobilized onto 4-mercaptobenzoic acid (MBA) based self assembled monolayer (SAM) on gold electrode (MBA/Au), for the fabrication of BSA/aAFB₁-C-AuNP/MBA/Au immunoelectrode. This immunoelectrode has been characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and electrochemical characterization techniques. The electrochemical response studies reveal that the BSA/aAFB₁-C-AuNP/MBA/Au immunoelectrode can be used to detect AFB₁ in the range of 10-100 ng dL^− 1 and has sensitivity as 0.45 μA ng^− 1 dL, limit of detection as 17.90 ng dL^− 1 and a response time of 60 s.     

Chemiluminescence immunoassay based on dual signal amplification strategy of Au/mesoporous silica and multienzyme functionalized mesoporous silica

A chemiluminescent dual signal amplification strategy for the determination of α-fetoprotein (AFP) was proposed based on a sandwich immunoassay format. Monoclonal antibody of AFP immobilized on the gold nanoparticles doped mesoporous SiO₂ (Au/SiO₂) were prepared and used as a primary antibody. Horseradish peroxidase (HRP) and HRP-labeled secondary antibody (Ab₂) co-immobilized into the mesoporous SiO₂ nanoparticles (HRP-Ab₂/SiO₂) were used as the labeled immunological probe. Due to the high ratio surface areas and pore volumes of the mesoporous SiO₂, not only the amount of AFP monoclonal antibody but also the amount of the modified HRP and Ab₂ in HRP-Ab₂/SiO₂ were largely increased. Thus the chemiluminescent signal was amplified by using the system of luminol and H₂O₂ under the catalysis of HRP. Under the optimal conditions, two linear ranges for AFP were obtained from 0.01 to 0.5 ng mL⁻¹ and 0.5 to 100 ng mL⁻¹ with a detection limit of 0.005 ng mL⁻¹ (3σ). The fabricated signal amplification strategy showed an excellent promise for sensitive detection of AFP and other tumor markers.     

Single-walled carbon nanotubes modified carbon ionic liquid electrode for sensitive electrochemical detection of rutin

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10^− 7 to 8.0 × 10^− 4 mol/L with the detection limit as 7.0 × 10^− 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.     

Sensitive and selective imprinted electrochemical sensor for p-nitrophenol based on ZnO nanoparticles/carbon nanotubes doped chitosan film

A sensitive and selective molecularly imprinted electrochemical sensor for p-nitrophenol detection has been developed based on ZnO nanoparticles/multiwall carbon nanotubes (MWNTs)-chitosan (CTS) nanocomposite. This nanocomposite was dripped onto an indium tin oxide electrode and then imprinted sol-gel solution was electrodeposited onto the modified electrode to construct the proposed sensor. The morphologies and electrochemical behaviors of the imprinted sensor were characterized by scanning electron microscope, X-ray diffraction, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry. The imprinted sensor displayed excellent selectivity towards the target molecule p-nitrophenol. Meanwhile, the introduced nanocomposite increased surface area and active sites for electron transfer, thus remarkably enhancing the sensitivity of the imprinted sensor. Under optimal conditions, the peak current was linear to p-nitrophenol concentration ranging from 1.0 × 10^− 8 to 2.0 × 10^− 4 mol·L^− 1 with a detection limits of 1.0 × 10^− 9 mol·L^− 1 (S/N = 3). This proposed sensor was applied to the detection of p-nitrophenol in various water samples successfully.     

Electrochemical studies of cystine modified self-assembled monolayer for Escherichia coli detection

An electrochemical DNA biosensor based on cystine modified self-assembled monolayer (cys-SAM) onto gold electrode (AuE) has been fabricated for Escherichia coli (E. coli) detection. This biosensing electrode has been characterized using scanning electron microscopy (SEM), FT-IR spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum conditions, this DNA biosensor can be used to detect complementary target DNA concentration in the range of 1 × 10^− 6 M to 1 × 10^− 20 M within 60 s of hybridization time at 25 °C and has been found to be stable for about four months when stored at 4 °C.     

Application of dispersion–solidification liquid–liquid microextraction for the determination of triazole fungicides in environmental water samples by high-performance liquid chromatography

A simple, rapid and environmentally friendly method has been developed for the determination of four triazole fungicides (myclobutanil, tebuconazole, triadimenol, hexaconazole) in water samples by dispersion–solidification liquid–liquid microextraction coupled with high performance liquid chromatography-diode array detection. Several variables that affect the extraction efficiencies, including the type and volume of the extraction solvent and dispersive solvent, extraction time, effect of pH and salt addition, were investigated and optimized. Under the optimum conditions, the proposed method is sensitive and shows a good linearity within a range of 0.5–200 ng mL⁻¹, with the correlation coefficients (r) varying from 0.9992 to 0.9998. High enrichment factors were achieved ranging from 190 to 450. The recoveries of the target analytes from water samples at spiking levels of 1.0, 5.0 and 50.0 ng mL⁻¹ were between 84.8% and 110.2%. The limits of detection (LODs) for the analytes were ranged in 0.06–0.1 ng mL⁻¹, and the relative standard deviations (RSD) varied from 3.9% to 5.7%. The proposed method has been successfully applied for the determination of the triazole fungicides in real water samples.     

Determination of selenium in natural waters by adsorptive differential pulse cathodic stripping voltammetry

In this work bovine albumin was used innovatively as a medium for adsorptive accumulation of Se–I₂ on thin mercury film electrode. Se–I₂ was formed by reaction between Se(IV) and iodide in HCl media. The adsorbed Se–I₂ was stripped in 0.05 M HCl by differential pulse cathodic potential scan. The proposed method was successfully applied to analysis of Se(IV) and Se(VI) in natural waters sampled from some lagoons south of Caspian Sea. The optimum reaction conditions and other analytical parameters and influence of cations and anions were studied. The detection limit was 0.37 ng mL⁻¹. The obtained results were compared with the results of DPCSV after electrochemical preconcentration, HG-AAS and ICP-AES.     

L-Aspartic acid/L-cysteine/gold nanoparticle modified microelectrode for simultaneous detection of copper and lead

This paper presents an electrochemical microsensor for simultaneous detection of copper (II) and lead (II) using an l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode. The microelectrode was fabricated by Micro Electro-Mechanical System technique. The complex of gold nanoparticles (AuNPs) and amino acid with carboxyl group was used as the selective ligand for metal ions. The microelectrode was firstly modified with AuNPs to increase the sensitive area of the working electrode. Subsequently, the AuNPs/gold electrode was modified with l-cysteine and then covalently linked with a monolayer of l-aspartic acid using glutaraldehyde. Electrochemical analysis of metal ions was achieved by using square wave voltammetry without stirring. The microsensor exhibited an excellent linear range from 5 μg L^− 1 to 2000 μg L^− 1 with the limit of detection of 1 μg L^− 1. This metal ion detection method based on l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode is simple, sensitive and it could be used for electrochemical analysis of copper (II) and lead (II).     

Trace-level sensing of creatine in real sample using a zwitterionic molecularly imprinted polymer brush grafted to sol-gel modified graphite electrode

Zwitterionic molecularly imprinted polymeric chains were tethered to the sol-gel modified graphite electrode in brush pattern of high density, for the quantitative estimation of creatine at trace level, without any cross reactivity, in real samples. The modified electrode was activated by preanodization at + 1.4 V (vs. saturated calomel electrode) for the fast ion-exchange recapture of creatine, under mild basic condition (pH 7.1). The detection limit was as low as 1.3 µg mL^− 1 (signal/noise = 3) employing differential pulse, cathodic stripping technique.     

Voltammetric detection of bisphenol a by a chitosan-graphene composite modified carbon ionic liquid electrode

In this paper 1-ethyl-3-methylimidazolium tetrafluoroborate based carbon ionic liquid electrode (CILE) was fabricated and further modified with chitosan (CTS) and graphene (GR) composite film. The fabricated CTS-GR/CILE was further used for the investigation on the electrochemical behavior of bisphenol A (BPA) by cyclic voltammetry and differential pulse voltammetry. A well-defined anodic peak appeared at 0.436 V in 0.1 mol/L pH 8.0 Britton-Robinson buffer solution, which was attributed to the electrooxidation of BPA on the modified electrode. The electrochemical parameters of BPA on the modified electrode were calculated with the results of the charge transfer coefficient (α) as 0.662 and the apparent heterogeneous electron transfer rate constant (k_s) as 1.36 s^− 1. Under the optimal conditions, a linear relationship between the oxidation peak current of BPA and its concentration can be obtained in the range from 0.1 μmol/L to 800.0 μmol/L with the limit of detection as 2.64 × 10^− 8 mol/L (3σ). The CTS-GR/CILE was applied to the detection of BPA content in plastic products with satisfactory results.     

High capacitive performance of nanostructured Mn-Ni-Co oxide composites for supercapacitor

Nanostructured Mn-Ni-Co oxide composites (MNCO) were prepared by thermal decomposition of the precursor obtained by chemical co-precipitation of Mn, Ni and Co salts. The chemical composition and morphology were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The electrochemical capacitance of MNCO electrode was examined by cyclic voltammetry, impedance and galvanostatic charge-discharge measurements. The results showed that MNCO electrode exhibited the good electrochemical characteristics. A maximum capacitance value of 1260 F g⁻¹ could be obtained within the potential range of −0.1 to 0.4 V versus saturated calomel electrode (SCE) in 6 mol L⁻¹ KOH electrolyte.     

Direct electrochemical behavior of cytochrome c on sodium dodecyl sulfate modified electrode and its application to nitric oxide biosensor

Polyacrylamide (PAM), sodium dodecyl sulfate (SDS) and cytochrome c (Cyt c) were immobilized on the surface of a glass carbon electrode (GCE), respectively, to form a Cyt c /SDS/PAM/GCE. The modified electrode was characterized with the electrochemical impedance. The direct electrochemical behaviors of Cyt c on SDS/PAM/GCE were obtained by using cyclic voltammetry. A pair of well-defined and reversible redox peaks could be observed in a 0.10 M pH 7.0 phosphate buffer solution. The anodic and cathodic peak potentials of Cyt c were at 0.051 V and − 0.003 V (vs. Ag/AgCl), respectively. The Cyt c on SDS/PAM/GCE exhibited well electrocatalytic activity to reduction of nitric oxide. The relative electrochemical parameters were obtained. The resulted electrode displayed a rapid amperometric response to the reduction of nitric oxide. The catalytic current is linear to the nitric oxide concentration in the range of 8.0 × 10^− 7 M to 9.5 × 10^− 5 M and the detection limit was 1.0 × 10^− 7 M (Signal/Noise = 3). The proposed biosensor could be used to detect quantitatively nitric oxide.     

Determination of sulfamethoxazole in foods based on CeO2/chitosan nanocomposite-modified electrodes

An electrochemical immunosensor based on nanocomposite-modified glass carbon (GC) electrode has been developed. The biospecific surface was a CeO₂-chitosan (CHIT)-modified nanocomposite to which anti-sulfamethoxazole (SMX) polyclonal antibody (Ab) was immobilized. The assay was based on competition of SMX and horseradish peroxidase (HRP)–SMX to the antibody immobilized. Electrochemical voltammetry and impedance spectroscopy studies revealed that the presence of CeO₂-CHIT nanocomposite significantly enhanced conductivity of the electrode. The large electro-active surface area of nanoCeO₂-CHIT/GC electrode resulted in the high loading of anti-SMX polyclonal antibody. The electrochemical signals of the immunosensor mainly resulted from the HRP catalyzed hydrogen peroxide reduction in the presence of thionine. The immunosensor showed high sensitivity for the detection of SMX. The electrochemical response signals of the immunosensor were found to be linearly proportional to SMX concentration in the range from 5 × 10^? 7 to 5 × 10^? 4 mg mL^? 1 with a regression coefficient of 0.9935 and a detection limit of 3.25 × 10^? 7 mg mL^? 1. No cross-reactivity of antibodies with other antibiotics of sulfonamide family was found. Under optimal conditions, the immunosensor was successfully applied to the electrochemical determination of SMX in milk, honey and egg samples, showing excellent stability and anti-interference ability.     

Synthesis and enhanced electrochemical properties of pod-shaped gold/silica nanoparticles

Pod-shaped gold/silica nanoparticles (PGSNPs) were prepared using perfluorooctanoic acid (PFOA) and cetyltrimethylammonium bromide (CTAB) as cotemplates. The PGSNPs were utilized to explore a novel biosensor through coupling myoglobin (Mb) with chitosan (Chi). Compared with Mb-Chi-PSNPs (pod-shaped silica nanoparticles)/GC modified electrode, Mb-Chi-PGSNPs/GC electrode exhibited a pair of much stronger redox peaks at − 0.28 V (vs. Ag/AgCl). Moreover, facilitated direct electron transfer of the metalloenzymes with smaller peak-to-peak separation (ΔEp) of about 46 mV was acquired on the PGSNPs-based enzyme electrode. The PGSNPs-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with a wide linear range (1-540 µM) and high sensitivity (661 mA cm^− 2 M^− 1). Together, the Mb-Chi-PGSNPs film is one of ideal candidate materials for direct electrochemistry of redox proteins, and may find potential applications in biomedical, food, and environmental analysis and detection.     

Preparation and characterization of poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonate) composite thin films highly loaded with platinum nanoparticles

In this work, we propose a simple and efficient, low-temperature (∼120 °C) process to prepare transparent thin films of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) loaded with high concentration (up to 22.5 wt%) of platinum (Pt) nanoparticles. Firstly, an improved polyol method was modified to synthesize nano-sized (∼5 nm) and mono-dispersed Pt particles. These nanoparticles were incorporated into the matrix of PEDOT:PSS thin films via a spin coating/drying procedure. The electrochemical activities of the PEDOT:PSS thin film modified electrodes with respect to the I⁻/I₃⁻ redox reactions were investigated. It was found that the modified electrode of PEDOT:PSS thin film containing 22.5 wt% Pt exhibited the electrochemical activity comparable to the conventional Pt thin film electrode, suggesting that this electrode has good potential to serve as a counter electrode in dye-sensitized solar cells.     

Preparation and characterization of poly(indole-3-carboxaldehyde) film at the glassy carbon surface

Indole-3-carboxaldehyde (In3C) monomer was oxidized by electrochemical methods at the glassy carbon (GC) electrode in 0.05 M tetrabutylammonium tetrafluoroborate in acetonitrile, with the aim to prepare a modified electrode. Modification was performed using cyclic voltammetry (CV) scanning from 0.0 V to 2.0 V at a scan rate of 50 mV s^− 1 for 10 cycles in 1 mM In3C monomer solution. The modified GC surface (In3C-GC) was characterized by CV response of potassium ferricyanide and ferrocene redox probes as well as by the electrochemical impedance spectroscopy. The modified surface was analyzed by reflection-absorption infrared spectroscopy and compared with the spectrum of the monomeric In3C. Elemental composition of the surface was determined by X-ray photoelectron spectroscopy. Contact angle measurements was also performed to check the changes in hydrophobic character of the bare GC and compared to that of In3C-GC surface. Thickness of the oligomeric/polymeric film was investigated by ellipsometric measurements and a surface confined polymerization mechanism was proposed.     

Amperometric hydrogen peroxide biosensor based on cobalt ferrite-chitosan nanocomposite

A novel H₂O₂ biosensor based on horseradish peroxidase (HRP) immobilized into CoFe₂O₄-chitosan nanocomposite has been developed for the detection of hydrogen peroxide. The nanocomposite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). HRP has been entrapped into CoFe₂O₄-chitosan nanocomposite film and the immobilized enzyme could retain its bioactivity. This biosensor exhibited a fast amperometric response to hydrogen peroxide. The linear range for H₂O₂ determination was from 3 × 10^− 2 to 8 mM, with a detection limit of 2 × 10^− 3 mM based on S/N = 3. The response time of the biosensor was 4 s. The effects of the pH and the temperature of the immobilized HRP electrode were also studied.