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).

Label-free sandwich type of immunosensor for hepatitis C virus core antigen based on the use of gold nanoparticles on a nanostructured metal oxide surface

We report on the construction of a label-free electrochemical immunosensor for detecting the core antigen of the hepatitis C virus (HCV core antigen). A glassy carbon electrode (GCE) was modified with a nanocomposite made from gold nanoparticles, zirconia nanoparticles and chitosan, and prepared by in situ reduction. The zirconia nanoparticles were first dispersed in chitosan solution, and then AuNPs were prepared in situ on the ZrO₂-chitosan composite. In parallel, a nanocomposite was synthesized from AuNPs, silica nanoparticles and chitosan, and conjugated to a secondary antibody. The properties of the resulting nanocomposites were investigated by UV-visible photometry and transmission electron microscopy, and the stepwise assembly process was characterized by means of cyclic voltammetry and electrochemical impedance spectroscopy. An sandwich type of immunosensor was developed which displays high sensitivity to the HCV core antigen in the concentration range between 2 and 512?ng?mL^?1, with a detection limit of 0.17?ng?mL^?1 (at S/N?=?3). This immunosensor provides an alternative approach towards the diagnosis of HCV.

A glassy carbon electrode modified with graphene, gold nanoparticles and chitosan for ultrasensitive determination of lead(II)

We have modified a glassy carbon electrode by single-step electrodeposition of graphene (GR), gold nanoparticles (AgNPs), and chitosan (CS) directly from a solution containing graphene oxide, tetrachloroauric acid, and chitosan. The surface and electrochemical properties of the film-modified electrode were investigated by SEM and TEM images. The AuNPs have a diameter of about 20 nm and are uniformly dispersed in the matrix. Combining the advantages of GR (i.e., high surface area and conductivity), of AuNPs (excellent electrical conductivity) and CS (excellent film-forming ability and good water permeability), the hybrid film effectively enhances electron-transfer and promotes the response to lead(II) ion. Under the optimum conditions, a linear relationship exists between electrical current and the concentration of lead (II) ion in the range between 0.5 to 100 μg?L-1, with a detection limit of 1 ng?L-1 (at an SNR of 3). The electrode was successfully applied to the detection of lead(II) in spiked samples of river water.

Label-free electrochemical immunosensor for the carcinoembryonic antigen using a glassy carbon electrode modified with electrodeposited Prussian Blue, a graphene and carbon nanotube assembly and an antibody immobilized on gold nanoparticles

We described a sensitive, label-free electrochemical immunosensor for the detection of carcinoembryonic antigen. It is based on the use of a glassy carbon electrode (GCE) modified with a multi-layer films made from Prussian Blue (PB), graphene and carbon nanotubes by electrodeposition and assembling techniques. Gold nanoparticles were electrostatically absorbed on the surface of the film and used for the immobilization of antibody, while PB acts as signaling molecule. The stepwise assembly process was investigated by differential pulse voltammetry and scanning electron microscopy. It is found that the formation of antibody-antigen complexes partially inhibits the electron transfer of PB and decreased its peak current. Under the optimal conditions, the decrease of intensity of the peak current of PB is linearly related to the concentration of carcinoembryonic antigen in two ranges (0.2–1.0, and 1.0–40.0 ng·mL^?1), with a detection limit of 60 pg·mL^?1 (S/N?=?3). The immunosensor was applied to analyze five clinical samples, and the results obtained were in agreement with clinical data. In addition, the immunosensor exhibited good precision, acceptable stability and reproducibility.

Accurate determination of the length of carbon nanotubes using multi-angle light scattering

We have prepared a kind of molecularly imprinted nano-porous sensing film for the adsorption of melamine. It consists of a graphite electrode impregnated with paraffin and modified with melamine, chitosan, silver nanoparticles and polyquercetin by employing an electrochemical method. The film displays excellent and highly selective sorption of melamine in the 3-dimensional porous nanomaterial, and this was applied to the determination of melamine in dairy products. The electrode responds linearly to melamine in the concentration range of 1?×?10^?8 to 9?×?10^?7?M, with a detection limit of 1.3?×?10^?9?M (at 3??) in real samples, and with recoveries in the range of 99 to 102%. The surface structure and composition of the sensor was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and electrochemical techniques. The interaction between the porous film and melamine was also studied by using hexacyanoferrate (III) as an electrochemical indicator.

Electrochemical sensing of catechol using a glassy carbon electrode modified with a composite made from silver nanoparticles, polydopamine, and graphene

We report on the modification of a glassy carbon electrode with a composite consisting of silver nanoparticles (AgNPs), polydopamine, and graphene to give an electrochemical sensor for catechol. The composite was characterized by transmission electron microscopy, and the electrochemical behavior of catechol at the modified electrode was studied by cyclic voltammetry. The electrochemical response is greatly enhanced and thought to result from a combination of beneficial effects including the good conductivity and large surface area of the AgNPs, the high conductivity of graphene, the synergistic effects of the composite, and the increased quantity of catechol that is adsorbed on the surface of the electrode. Differential pulse voltammetric responses are proportional to the concentration of catechol between 0.5 and 240?μM levels of catechol, and the detection limit is 0.1?μM (S/N?=?3). The performance of the sensor was evaluated with catechol-spiked water samples, and recoveries range from 96.5 % to 103.1 %. The results indicated that the composite presented here is a promising substrate for use in electrochemical sensing.

Electrochemical immunoassay for subgroup J of avian leukosis viruses using a glassy carbon electrode modified with a film of poly (3-thiophene boronic acid), gold nanoparticles, graphene and immobilized antibody

We have modified a glassy carbon electrode (GCE) with a film of poly(3-thiophene boronic acid), gold nanoparticles and graphene, and an antibody (Ab) was immobilized on its surface through the covalent bond formed between the boronic acid group and the glycosyl groups of the Ab. Subgroup J of avian leukosis viruses (ALV-J) were electrochemically determined with the help of this electrode. There is a linear relationship between the electron transfer resistance (R _et) and the concentration of ALV-J in the range from 527 to 3,162 TCID₅₀?mL^?1 (where TCID₅₀ is the 50?% tissue culture infective dose). The detection limit is 210 TCID₅₀?mL^?1 (at an S/N of 3), and the correlation coefficient (R) is 0.9964. The electrochemical immunoassay showed good selectivity, stability and reproducibility.

Tin disulfide nanoflakes decorated with gold nanoparticles for direct electrochemistry of glucose oxidase and glucose biosensing

Previously, we have prepared nanoflake-like tin disulfide (SnS2) and used for the immobilization of proteins and biosensing. We have now modified an electrode with a composite consisting of nanoflake-like SnS2 decorated with gold nanoparticles (Au-NPs) and have immobilized glucose oxidase (GOx) on its surface in order to study its direct electrochemistry. Scanning electron microscopy, electrochemical impedance spectroscopy, Fourier transform IR spectroscopy and cyclic voltammetry were used to examine the interaction between GOx and the AuNP-SnS2 film. It is shown that the composite film has a larger surface area and offers a microenvironment that facilitates the direct electron transfer between enzyme and electrode surface. The immobilized enzyme retains its bioactivity and undergoes a surface-controlled, reversible 2-proton and 2-electron transfer reaction, with an apparent electron transfer rate constant of 3.87 s ^-1. Compared to the nanoflake-like SnS2-based glucose sensor, the GOx-based biosensor exhibits a lower detection limit (1.0 :M), a better sensitivity (21.8 mA?M ^-1 ?cm ^-2), and a wider linear range (from 0.02 to 1.3 mM). The sensor displays excellent selectivity, good reproducibility, and acceptable stability. It was successfully applied to reagentless sensing of glucose at ?0.43 V.

Biocompatible and label-free amperometric immunosensor for hepatitis B surface antigen using a sensing film composed of poly(allylamine)-branched ferrocene and gold nanoparticles

An amperometric immunosensor has been developed for sensitive determination of hepatitis B surface antigen as a model protein. A glassy carbon electrode was modified with an assembly of positively charged poly(allylamine)-branched ferrocene (PAA-Fc) and negatively charged gold nanoparticles (Au NPs). The formation of PAA-Fc effectively avoids the leakage of Fc, retains its electrochemical activity, and enhances the conductivity of the composite. The adsorption of Au NPs onto the PAA-Fc matrix provides sites for the immobilization of the antigen and a favorable micro-environment to maintain its activity. The morphologies and electrochemistry of the sensing film were investigated via scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Factors influencing the performance of the immunosensor were studied in detail. The concentration of the antigen can be quantitated (by measuring the decrease of the amperometric response resulting from the specific binding between antigen and antibody) in the range between 0.1 and 150?ng?mL^?C1, with a detection limit of 40?pg?mL^?C1 (S/N = 3). The method is economical, efficient, and potentially attractive for clinical immunoassays.

Electrochemical sensors based on graphene materials

Single?Clayered graphene, emerging as a true two?Cdimensional nanomaterial, has tremendous potential for electrochemical catalysis and biosensing as a novel electrode material. Considering the excellent properties of graphene, such as large surface?Cto?Cvolume ratio, high conductivity and electron mobility at room temperature, low energy dynamics of electrons with atomic thickness, robust mechanical and flexibility, we give a general view of recent advances in electrochemical sensors based on graphene. We are highlighting here important applications of graphene and graphene nanocomposites, and the assay strategies in electrochemical sensors for DNA, proteins, neurotransmitters, phytohormones, pollutants, metal ions, gases, hydrogen peroxide, and in medical, enzymatic and immunosensors.

Determination of microcystin-LR with a glassy carbon impedimetric immunoelectrode modified with an ionic liquid and multiwalled carbon nanotubes

We report on a sensitive, simple, label-free impedance-based immunoelectrode for the determination of microcystin-LR (MCLR). The surface of the electrode was modified with a composite made from multiwalled carbon nanotubes and an ionic liquid, and with immobilized polyclonal antibody against MCLR. Cyclic voltammetry and impedance spectroscopy were applied to characterize the modified electrode. It is found that the multi-walled carbon nanotubes act as excellent mediators for the electron transfer between the electrode and dissolved hexacyanoferrate redox pair, while the ionic liquid renders it biocompatible. The method exhibits a wide linear range (0.005 μg?L-1 to 1.0 μg?L-1), a low detection limit (1.7 ng?L-1) and a long-term stability of around 60 days. The ionic liquid 1-amyl-2,3-dimethylimidazolium hexafluorophosphate gave the best impedimetric response. The new immunoelectrode is sensitive, stable, and easily prepared. It has been successfully applied to the determination of MCLR in water samples.

Electrochemistry and voltammetric determination of L-tryptophan and L-tyrosine using a glassy carbon electrode modified with a Nafion/TiO2-graphene composite film

We describe a glassy carbon electrode (GCE) modified with a film composed of Nafion and TiO₂-graphene (TiO₂-GR) nanocomposite, and its voltammetric response to the amino acids L-tryptophane (Trp) and L-tyrosine (Tyr). The incorporation of TiO₂ nanoparticles with graphene significantly improves the electrocatalytic activity and voltammetric response compared to electrodes modified with Nafion/graphene only. The Nafion/TiO₂-GR modified electrode was used to determine Trp and Tyr with detection limits of 0.7 and 2.3 μM, and a sensitivity of 75.9 and 22.8 μA mM^?1 for Trp and Tyr, respectively.

Ultra-sensitive electrochemical DNA biosensor based on signal amplification using gold nanoparticles modified with molybdenum disulfide,graphene and horseradish peroxidase

We have developed an ultra-sensitive electrochemical DNA biosensor by assembling probe ssDNA on a glassy carbon electrode modified with a composite made from molybdenum disulfide, graphene, chitosan and gold nanoparticles. A thiol-tagged DNA strand coupled to horseradish peroxidase conjugated to AuNP served as a tracer. The nanocomposite on the surface acts as relatively good electrical conductor for accelerating the electron transfer, while the enzyme tagged gold nanoparticles provide signal amplification. Hybridization with the target DNA was studied by measuring the electrochemical signal response of horseradish peroxidase using differential pulse voltammetry. The calibration plot is linear in the 5.0?×?10^?14 and 5.0?×?10^?9 M concentration range, and the limit of detection is 2.2?×?10^?15 M. The biosensor displays high selectivity and can differentiate between single-base mismatched and three-base mismatched sequences of DNA. The approach is deemed to provide a sensitive and reliable tool for highly specific detection of DNA.

Label-free immunosensing of microcystin-LR using a gold electrode modified with gold nanoparticles

The hepatotoxic microcystins, especially microcystin?CLR (MC?CLR), are causing serious problems to public health and fisheries. We describe here a label-free amperometric immunosensor for rapid determination of MC?CLR in water sample. The sensor was prepared by immobilizing antibody on a gold electrode coated with L-cysteine-modified gold nanoparticles. The stepwise self-assembly of the immunosensor was monitored and characterized by means of electrochemical impedance spectroscopy and differential pulse voltammetry. A 0.60?mmol L^?1 solution of hydroquinone was used as the electron mediator. The immunosensor was incubated with MC?CLR at 25?°C for 20?min, upon which the differential pulse voltammetric current changed linearly over the concentration range from 0.05 to 15.00???g L^?1, with a detection limit of 20?ng L^?1. The developed biosensor was used to determine MC?CLR in spiked crude algae samples. The recovery was in the range from 95.6 to 105%. This method is simple, economical and efficient, this making it potentially suitable for field analysis of MC-LR in crude algae and water samples.

A sensitive sensor for determination of l-tryptophan based on gold nanoparticles/poly(alizarin red S)-modified glassy carbon electrode

This work described a novel sensor for detection of l -tryptophan (Trp) by electrodeposition of gold nanoparticles (AuNPs) onto the poly(alizarin red S) film pre-cast on a glassy carbon electrode (GCE). Alizarin red S (ARS) was deposited on the surface of the GCE by electropolymerization, and gold nanoparticles (AuNPs) were attached onto the poly(ARS) film by electrodeposition, forming an AuNPs–PARS nanocomposite film-modified GCE (AuNPs–PARS/GCE). Then electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were used to characterize modified electrodes. The Nyquist diagrams of EIS indicated that the PARS film and AuNPs were successfully immobilized on the surface of GCE, and the electron transfer resistance value of electrode changed efficiently. The SEM image showed that the immobilized AuNPs were spherical in shape. The AuNPs–PARS/GEC displayed excellent amperometric response for Trp. The amperometric responses have two linear ranges from 0.02 to 0.5 μM and 0.5 to 20.0 μM, with sensitivities of 1.63(±0.08) and 0.21(±0.01)?μAμM^?1, respectively. Its detection limit was 6.7 nM at a signal-to-noise ratio of 3. The proposed method was applied to determine Trp.

Highly sensitive deoxynivalenol immunosensor based on a glassy carbon electrode modified with a fullerene/ferrocene/ionic liquid composite

We describe a sensitive electrochemical immunosensor for the detection of deoxynivalenol (DON). It is based on a glassy carbon electrode modified with a composite made from fullerene (C₆₀), ferrocene and the ionic liquid. The components were immobilized on the surface of the electrode using chitosan cross-linked with epichlorohydrin. Then, the antibody to DON was covalently conjugated to the surface which then was blocked with serum albumin. The performance of the immunosensor was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. It offers good repeatability (RSD?=?1.2%), selectivity, a stability of more than 180?days, an impedimetric response to DON in the range of 1?pgmL^?1 to 0.3?ng?mL^?1, and a detection limit (at S/N?=?3) of 0.3?pgmL^?1. The limit of detection is better than that of GC, HPLC, GC-MS, HPLC-MS and LC-MS-MS. The effects of omitting C₆₀ or the ionic liquid were also examined. The results indicate that the sensitivity of the biosensor is 2-fold better if C₆₀ and ionic liquids are used. This demonstrates that C₆₀ facilitates electron transfer on the surface of the modified electrode due to its unique electrochemical properties, while the ionic liquid provides a biocompatible microenvironment for the antibody. This results in increased sensitivity and stability. The method was satisfactorily applied to the determination of DON in food samples.

Facile one-step electrochemical fabrication of a non-enzymatic glucose-selective glassy carbon electrode modified with copper nanoparticles and graphene

We have developed a non-enzymatic glucose sensor by using a composite prepared from copper nanoparticles (CuNPs) and graphene which can be prepared by simple 1-step electrochemical reduction using graphene oxide (GO) and copper ion as the starting materials. The GO is electrochemically reduced to graphene at a voltage of ?1.5 V, and this is accompanied by the simultaneous formation of CuNPs on the surface of the graphene. This novel nanocomposite combines the advantages of graphene and of CuNPs and displays good electrocatalytic activity toward glucose in alkaline media. The performance of the respective glucose electrode was evaluated by amperometric experiments and revealed a fast response (<2 s), a low detection limit (200 nM), and high sensitivity (607 μA mM^?1). The sensor also exhibits good reproducibility and very good specificity for glucose over ascorbic acid, dopamine, uric acid, fructose, lactose and sucrose.

Determination of thiourea using a carbon paste electrode decorated with copper oxide nanoparticles

We report on a novel sensor for the electrochemical determination of thiourea (TU). It is based on an active carbon paste electrode modified with copper oxide nanoparticles. The modified electrode and the electrochemical properties of thiourea on its surface were investigated using cyclic voltammetry and differential pulse voltammetry. Under optimized conditions, the detection limit is 20 μg?L^?1 of TU. The method was applied to the determination of thiourea in fruit juice, orange peel and industrial waste water.

Multilayer structured immunosensor based on a glassy carbon electrode modified with multi-wall carbon nanotubes, polythionine, and gold nanoparticles

An immunosensor for determination of salbutamol was developed. It based on glass carbon electrode (GCE) modified with a conductive multilayer film comprised of multi-wall carbon nanotubes, polythionine and gold nanoparticles. Salbutamol antibody was immobilized on the surface of the modified GCE which then was blocked with bovine serum albumin (BSA). The stepwise self-assembly process of the immunosensor was studied by cyclic voltammetry. The detection scheme is based on competitive binding of salbutamol to the sensor surface whose differential pulse voltammetric signal decreases after competitive binding of the salbutamol-BSA conjugate and free salbutamol to the salbutamol antibody. The sensor responds to salbutamol in 5 to 150 nM concentration range, with a detection limit of 1 nM. This method was applied to the precise and sensitive determination of salbutamol in spiked feed samples.

Electrochemical oxidation behavior of guanosine-5��-monophosphate on a glassy carbon electrode modified with a composite film of graphene and multi-walled carbon nanotubes, and its amperometric determination

The electrochemical oxidation of guanosine-5??-monophosphate (GMP) was studied with a glassy carbon electrode modified with a composite made from graphene and multi-walled carbon nanotubes. GMP undergoes an irreversible oxidation process at an oxidation peak potential of 987?mV in phosphate buffer solution. Compared to other electrodes, the oxidation peak current of GMP with this electrode was significantly increased, and the corresponding oxidation peak potential negatively shifted, thereby indicating that the modified material exhibited electrochemical catalytic activity towards GMP. Chronocoulometry demonstrates that the material also effectively increases the surface area of the electrode and increases the amount of GMP adsorbed. Under the optimum conditions, the oxidation current is proportional to the GMP concentration in the range from 0.1 to 59.7???M with a correlation coefficient of 0.9991. The detection limit is 0.025???M (at S/N?=?3).