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Herein, a versatile fluorescent bioanalysis platform for sensitive and specific screening of target miRNA (miR-129-2-3p) was innovatively designed by applying target-induced rolling circle amplification (RCA) for efficient signal amplification. Specifically, miR-129-2-3p was used as a ligation template to facilitate its ligation with padlock probes, followed by an RCA reaction in the presence of phi29 DNA polymerase. The dsDNA fragments and products were stained by SYBR Green I and then detected by fluorescence spectrophotometry. As a result, miR-129-2-3p concentrations as low as 50 nM could be detected. Furthermore, the expression of miR-129-2-3p in breast cancer patients was about twice that in healthy people. Therefore, the results indicated that the RCA-based biosensor system could be a valuable platform for miRNA detection in clinical diagnosis and biomedical study. [ABSTRACT FROM AUTHOR]

Methods based on immunoassays have been developed for cancer biomarker alpha-fetoprotein (AFP), but most involve complicated or stripping procedures and are unfavourable for routine use. Herein we report the proof-of-concept of simple and point-of-care (POC) immunoassay for AFP in hepatocellular carcinoma on a portable personal glucometer (PGM) by using antibodyinvertase cross-linkage nanoparticles as the signal-generation tags. Antibody-invertase cross-linkage nano tags were synthesized by using reverse micellar method with glutaraldehyde. The POC immunoassay was carried out on monoclonal anti-AFP capture antibody-coated microplate with a sandwich-type reaction mode. Introduction of invertase nano labels accompanying target AFP could hydrolyse sucrose into glucose and fructose. The produced glucose molecules could be determined on a portable personal glucometer. Relative to unimolecular invertase labelling, improved analytical features were acquired with antibody-invertase nano labelling. With the nano labels, PGM-based immunoassay exhibited good electrochemical responses for the detection of AFP, and allowed detection of AFP at a concentration as low as 5.4 pgmL-1. Moreover, a good repeatability and intermediate precision could be found down to 12.68%. Good well-matched results were obtained for analysis of human serum specimens between POC immunoassay and commercial human AFP ELISA kit. [ABSTRACT FROM AUTHOR]

In this study, a novel and enzyme-free electrochemical immunoassay was developed for the detection of alpha-fetoprotein (AFP; as a model biomarker) by using a novel redox nanocatalyst, patterned gold-iridium oxide nanoparticle assemblies (Au-IrO), on a Prussian blue (PB) functionalized glassy carbon electrode. The as-prepared Au-IrO nanospheres were not only used for the labeling of secondary anti-AFP antibody but also executed for water oxidation. With a sandwich immunoassay format, the electrochemical measurement was carried out in 0.1 M KNO-HCl, pH 3.2, containing 1.0 mM p-aminophenol (AP). Initially, the added AP was oxidized to p-quinone imine (QI) with the help of the immobilized PB on the electrode, and then the generated QI was reduced back to AP by hydrogenation reaction from water oxidation. The self-produced QI reactants were catalytically recycled and thus amplified the signal of electrochemical response. Under optimal conditions, the electrochemical immunosensor displayed a wide working range of 0.005 to 200 ng/mL with a low detection limit of 0.5 pg/mL AFP (at 3s). Intra- and inter-assay coefficients of variation were below 10%. In addition, the methodology was validated with real serum samples, receiving a good agreement with the results obtained from commercially available electrochemiluminescence automated analyzer. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

new sandwich-type electrochemical immunoassay was developed for the detection of human IgG using doubly-encoded and magnetic redox-active nanoparticles as recognition elements on the surface of a glassy carbon electrode modified with anti-IgG on nanogold particles. The recognition elements were synthesized by coating magnetic FeO nanoparticles with Prussian blue nanoparticles and then covered with peroxidase-labeled anti-IgG antibodies (POx- anti-IgG) on Prussian blue nanoparticles. The immunoelectrode displays very good electrochemical properties towards detection of IgG via using double-encoded magnetic redox-active nanoparticles as trace and hydrogen peroxide as enzyme substrate. Its limit of detection (10 pmol·L) is 10-fold better than that of using plain POx- anti-IgG secondary antibodies. The method was applied to the detection of IgG in serum samples, and an excellent correspondence with the reference values was found. [ABSTRACT FROM AUTHOR]

Abstract  [AuCl4]− was initially deposited by electrochemical reduction on a glassy carbon electrode (GCE) to form porous nanogold layer, then prussian blue (PB) was electrodeposited onto the as-prepared nanogold layer, and then secondary nanogold particles were fabricated again on the PB surface by electrochemical reduction for the immobilization of anti-CEA antibodies. The presence of double-layer porous gold nanoparticles enhanced the immobilized amount of biomolecules, and improved the sensitivity of the immunoassay. PB, as a good redox probe, was facile to electrochemical analysis and measurement. Under optimal conditions, the developed immunoassay exhibited dynamic range from 3.0 to 80.0 ng/mL with a detection limit of 0.9 ng/mL CEA (S/N = 3). Moreover, the selectivity, reproducibility and stability of the immunosensor were acceptable. [ABSTRACT FROM AUTHOR]

Gold nanowires with of designed length on a solid substrate have been proven as an efficiently immobilized affinity support for the detection of carcinoma antigen 125 (CA 125) in this study. The presence of gold nanowires provides a well-defined three-dimensional structure, and greatly amplifies the coverage of the anti-CA 125 protein on the probe surface. Moreover, the amount of anti-CA 125 varied with the change of the morphology of the probe, and achieved an optimal quartz crystal microbalance (QCM) response towards anti-CA 125 adsorption at the number of gold nanolayers of 5. The formed immune-probe exhibits good QCM responses for the detection of CA 125, and allows the detection of CA 125 at concentrations as low as 0.5 U ml−1. The QCM immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy and reproducibility. The as-prepared immunosensors were used to analyze CA 125 in human serum specimens. Analytical results suggest that the developed immunoassay method is a promising alternative approach for detecting CA 125 in the clinical diagnosis. Compared with conventional ELISA, the proposed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the route provides an alternative approach to incorporate multiple gold nanolayers onto the solid matrix for biosensing applications. [ABSTRACT FROM AUTHOR]

Abstract  A new protein assay system for the antigen–antibody interaction was developed by immobilization of carcinoembryonic antibody (anti-CEA) onto magnetic-core/gold-shell nanoparticles-functionalized biomimetic interface on multiporous polythionine modified magnetic carbon paste electrodes (MCPE). Differential pulse voltammetric (DPV) technique was employed to investigate the antigen–antibody interaction in pH 6.8 acetate acid buffer solution after incubation with various CEA samples for 50 min at room temperature. The peak currents decreased with increased CEA concentration, and were proportional to the CEA concentration in the range of 1.5–60 ng/ml with a detection limit of 0.3 ng/ml at a signal-to-noise ratio of 3. Moreover, the selectivity, reproducibility and stability of the proposed immunoassay system were acceptable. Compared with the conventional immunoassays, the developed immunoassay system was simple and rapid without multiple labeling and separation steps. Importantly, the proposed methodology would be valuable for diagnosis and monitoring of carcinoma and its metastasis. [ABSTRACT FROM AUTHOR]

A new electrochemical biosensor for determination of hydrogen peroxide (H2O2) has been developed by immobilizing horseradish peroxidase (HRP) on silver colloids (nanosilver) and use of a DNA-functionalized interface. In the presence of the DNA and the nanosilver the immobilized HRP gives a pair of well-defined redox peaks with an electron-transfer rate constant of 3.27 ± 0.91 s−1 in pH 7.0 PBS. The presence of DNA also provides a biocompatible microenvironment for enzyme molecules, greatly amplifies the amount of HRP molecules immobilized on the electrode surface, and improves the sensitivity of the biosensor. Under optimum conditions the biosensor has electrocatalytic activity in the reduction of hydrogen peroxide with linear dependence on H2O2 concentration in the range 1.5 × 10−6 to 2.0 × 10−3 mol L−1; the detection limit is 5.0 × 10−7 mol L−1 at a signal-to-noise ratio of 3. The $$ K^{{{\text{app}}}}_{{\text{m}}} $$ value of HRP in the composite membrane was found to be 1.62 mmol L−1. These results suggest that the properties of the complex film, with its bioelectrochemical catalytic activity, could make it useful for development of bioelectronic devices and for investigation of protein electrochemistry at functional interfaces. [ABSTRACT FROM AUTHOR]

A direct electrochemical immunoassay system based on the immobilization of α-1-fetoprotein antibody (anti-AFP), as a model system, on the surface of core-shell Fe2O3/Au magnetic nanoparticles (MNP) has been demonstrated. To fabricate such an assay system, anti-AFP was initially covalently immobilized on to the surface of core-shell Fe2O3/Au MNP. Anti-AFP-modified MNP (bio-nanoparticles) were then attached to the surface of carbon paste electrode with the aid of a permanent magnet. The performance and factors influencing the performance of the resulting immunosensor were studied. α-1-Fetoprotein antigen was directly determined by the change in current or potential before and after the antigen–antibody reaction versus saturated calomel electrode. The electrochemical immunoassay system reached 95% of steady-state potential within 2 min and had a sensitivity of 25.8 mV. The linear range for AFP determination was from 1 to 80 ng AFP ml−1 with a detection limit of 0.5 ng AFP ml−1. Moreover, the direct electrochemical immunoassay system, based on a functional MNP, can be developed further for DNA sensor and enzyme biosensor. [ABSTRACT FROM AUTHOR]

A novel label-free amperometric immunosensor for the detection of rubella vaccine was developed by immobilizing anti-rubella serum on bilayer nano-Au/polymerizedo-phenylenediamine film with electrodeposited Prussian Blue (PB) as an electrode transfer mediator on the platinum electrode. The redox reactions of PB as a probe on the platinum surface were blocked due to the binding of the antibody to the antigen, which was investigated by cyclic voltammetry. Therefore, the interaction of the antibody with various concentrations of antigen could be detected by measurements of amperometric response in PBS, and the amperometric response on the surface of the modified electrode was inversely proportional to the concentration of rubella vaccine in the sample. The immunosensor showed a specific response to rubella vaccine in the range 8.1×10-8-8.0×10-6 lgCCID50/ml (cell culture infectious dose) and a detection limit of 4.010-8 lgCCID50/ml at a signal-to-noise ratio of 3. To summarize, the present work provides a low-cost, fast response time, highly sensitive and easy-to-prepare method for the determination of antigen in biological products. [ABSTRACT FROM AUTHOR]

A novel method for fabrication of a diphtheria potentiometric immunosensor has been developed by means of self-assembling compound nanoparticles to a thiol-containing sol-gel network. A cleaned gold electrode was first immersed in a 3-mercaptopropyltrimethoxysilane (MPS) sol-gel solution to assemble a silica sol-gel monolayer. The silane entities were then polymerized into a two-dimensional sol-gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by re-immersion in the MPS sol-gel solution overnight. The compound nanoparticles (nanocompounds) containing gold nanoparticles and silver nanoparticles were then chemisorbed on to the thiol groups of the second silane layer. Finally, diphtheria antibody (anti-Diph) was adsorbed on to the surface of the compound nanoparticles. The modified process was characterized by cyclic voltammetry (CV). Detection is based on the change in the potentiometric response before and after the antigen-antibody reaction. A direct potentiometric response to diphtheria antigen (Diph) was obtained from the immobilized diphtheria antibody. The potentiometric response of the resulting immunosensor was rapid and the linear range was from 22 to 800 ng mL-1 with the linear regression equation ?E=-79.5+69.4 log [Diph] and a detection limit of 3.7 ng mL-1 (at 3d). Up to 19 successive assay cycles with retention of sensitivity were achieved for probes regenerated with 0.2 mol L-1 glycine-hydrochloric acid (Gly-HCl) buffer solution. Moreover, analytical results from several serum samples obtained using the developed technique were in satisfactory agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtheria antigen in clinical diagnosis. [ABSTRACT FROM AUTHOR]

A novel sensing platform for monitoring small molecules without the need for sample separation and washing is developed by using a commercialized personal glucose meter based on bioresponsive controlled release of glucose from aptamer-gated mesoporous silica nanocontainers. [ABSTRACT FROM AUTHOR]

A simple and facile impedance immunoassay strategy for sensitive detection of alpha-fetoprotein (AFP), as a model cancer marker, was developed by using target-induced release of nanogold particle-labelled anti-AFP antibodies from polyvinylpyrrolidone-coated magnetic carbon nanotubes. [ABSTRACT FROM AUTHOR]

This research describes the fabrication process of multifunctional magnetic nanogold microspheres as immunosensing probe for the detection of staphylococcal enterotoxin B, as a model, in food. [ABSTRACT FROM AUTHOR]