New variants of enzyme immunoassay of antibodies to DNA

Citrinin (CIT) determination in rice samples using a micro fluidic electrochemical immunosensor

The development of an electrochemical immunosensor incorporated in a micro fluidic cell for quantification of citrinin (CIT) mycotoxin in rice samples is described for the first time. Both CIT present in rice samples and immobilized on a gold surface electrodeposited on a glassy carbon (GC) electrode modified with a cysteamine self-assembled monolayer were allowed to compete for the monoclonal mouse anti-CIT IgG antibody (mAb-CIT) present in solution. Then, an excess of rabbit anti mouse IgG (H+L) labelled with the horseradish peroxidase (secAb-HRP) was added, which reacts with the mAb-CIT which is in the immuno-complex formed with the immobilized CIT on the electrode surface. The HPR, in the presence of hydrogen peroxide (H(2)O(2)) catalyzes the oxidation of catechol (H(2)Q) whose back electrochemical reduction was detected on a GC electrode at -0.15 V vs Ag/AgCl by amperometric measurements. The current measured is proportional to the enzymatic activity and inversely proportional to the amount of CIT present in the rice samples. This immunosensor for CIT showed a range of work between 0.5 and 50 ng mL(-1). The detection (LOD) and the quantification (LOQ) limits were 0.1 and 0.5 ng mL(-1), respectively. The coefficients of variation intra- and inter-assays were less than 6%. The electrochemical detection could be done within 2 min and the assay total time was 45 min. The immunosensor was provided to undertake at least 80 determinations for different samples with a minimum previous pre-treatment. Our electrochemical immunosensor showed a higher sensitivity and reduced analysis time compared to other analytical methods such as chromatographic methods. This methodology is fast, selective and very sensitive. Thus, the immunosensor showed to be a very useful tool to determine CIT in samples of cereals, mainly rice samples.

Complexing of heavy metals with DNA and new bioaffinity method of their determination based on amperometric DNA-based biosensor

The immobilized single-stranded DNA (ssIDNA) has been found to be a very effective biospecific analytical reagent when used in a newly developed bioaffinity method of the determination of heavy metals based on the amperometric DNA-based biosensor. This has been concluded from the comparative study of the complexing of heavy metals with double-stranded DNA, single-stranded DNA, and ssIDNA, using Fe(III) and Cu(II) as a model (metal/nucleotide ratio and stability constants are maximum for ssIDNA), from the study of adsorption of Fe(III), Cu(II), Pb(II), and Cd(II) on nitrocellulose membranes, containing single-stranded DNA, and from the determination of their binding constants with ssIDNA. According to these data, the chosen heavy metals can be lined up in a series of binding strengths with ssIDNA: Cu(II) > Pb(II) > Fe(III) > Cd(II). The method of the determination of heavy metals is based on biospecific preconcentration of metal ions on the biosensor followed by the destruction of DNA-metal complexes with ethylenediaminetetraacetate and voltammogram recording has been proposed. The lower detection limits are 4.0 x 10(-11), 1.0 x 10(-10), 1.0 x 10(-9), and 5.0 x 10(-9) M for Cu(II), Pb(II), Cd(II), and Fe(III), respectively. The heavy metals have been assayed in multicomponent environmental and biological systems such as natural and drinking water, milk, and blood serum samples.

An amperometric immunosensor for separation-free immunoassay of CA125 based on its covalent immobilization coupled with thionine on carbon nanofiber

A carbon nanomaterial, soluble carbon nanofiber, was used for the first time to construct an immunosensor for a rapid separation-free immunoassay. The acidic oxidation of the carbon nanofiber provided its solubility and wettability for convenient preparation of a porous carbon nanofiber membrane and a larger number of active sites for covalent binding of carcinoma antigen-125 (CA125) and thionine as electron transfer mediator. This matrix was a suitable environment for the immobilized protein. The immobilized HRP-labeled immunoconjugate showed good enzymatic activity for the oxidation of thionine by hydrogen peroxide. With a competitive mechanism, the differential pulse voltammetric peak current of this system decreased linearly with increasing CA125 concentration (from 2 to 75 U/ml) in the incubation solution. The CA125 immunosensor showed good precision, high sensitivity, acceptable stability and reproducibility with a detection limit of 1.8 U/ml. The soluble carbon nanofiber is a novel method for preparation of immunosensors.

Continuous-flow/stopped-flow system using an immunobiosensor for quantification of human serum IgG antibodies to Helicobacter pylori

Conventional methods, such as gastric biopsy, enzyme-linked immunosorbent assay (ELISA), culture, require a long time for the determination of Helicobacter pylori infections. This study reports an amperometric immunoreactor for rapid and sensitive quantification of human serum immunoglobulin G (IgG) antibodies to H. pylori. Antibodies in the serum sample are allowed to react immunologically with the purified H. pylori antigens that are immobilized on a rotating disk. The bound antibodies are quantified by horseradish peroxidase (HRP) enzyme-labeled second antibodies specific to human IgG. HRP in the presence of hydrogen peroxide catalyzes the oxidation of hydroquinone to p-benzoquinone. The electrochemical reduction back to hydroquinone is detected on a glassy carbon electrode surface at -0.15 V. The electrochemical detection can be done within 1 min, and the analysis time does not exceed 30 min. The calculated detection limits for amperometric detection and the ELISA procedure are 0.6 and 1.9 U ml-1, respectively. The amperometric immunoreactors showed higher sensitivity and lower time consumed than did the standard spectrophotometric detection ELISA method. It can also be used for rapid analysis in conventional and field conditions in biological, physiological, and analytical practices.

Amperometric biosensor based on denatured DNA for the study of heavy metals complexing with DNA and their determination in biological, water and food samples

Amperometric biosensor (BS) has been elaborated based on the stationary mercury-film electrode (SMFE) with silver support and cellulose nitrate (CN) membrane containing immobilized single-stranded DNA (ssIDNA). The sorption isotherms and ssDNA-heavy metal binding constants have been obtained with the BS. According to these data, the chosen heavy metals form the following series of binding strength with ssIDNA: Pb(II)>Fe(III)>Cd(II). It has been found that upon the competitive adsorption, there exists practically simultaneous sorption of different ions at ssIDNA containing membrane. The method of the determination of heavy metals based on preconcentration of metal ions on the BS followed by the destruction of DNA-metal complexes with ethylenediamine tetraacetate (EDTA) and voltammogram recording has been proposed. The lower limits of detectable contents are 1.0x10(-10), 1.0x10(-9) and 1.0x10(-7) mol l(-1) for Pb(II), Cd(II) and Fe(III), respectively. Heavy metals have been assayed in natural and drinking water, milk and blood serum samples even under simultaneous presence with a selectivity factor of 1:10. The effect of matrix components has been estimated.

Renewable amperometric immunosensor for Schistosoma japonium antibody assay

A renewable amperometric immunosensor has been proposed for the determination of Schistosoma japonium antibody (SjAb) in rabbit serum. A paraffin-graphite-Schistosoma japonium antigen (SjAg) biocomposite, which needs no additional curing, was directly used to construct the immunosensors. The analytical sample containing the desired SjAb was mixed with SjAb labeled with horseradish peroxidase (HRP) to form the incubation solution for the competitive binding assay. Amperometry was used to determine the amount of HRP fixed on the sensor surface, which was related to the content of desired SjAb. Assay conditions were optimized, including the selection of substrate, the loading of SjAg in the biocomposite, the amount of labeled SjAb in the incubation solution, the incubation time, and the temperature. Using o-aminophenol (o-AP) as a substrate, amperometric detection at -200 mV (vs SCE) resulted in a pseudolinear detection range of about 0.36 to 14 microg/mL, with a detection limit of 0.36 microg/mL. Rabbit serum samples with varying infection degrees were analyzed, and the results demonstrated that the concentration that is detectable in this system meets the demands of clinical analyses. A new surface on the immunosensor for use in another competitive assay can be obtained by removing the original one and polishing the surface.