Biling Su

Nanoparticle-based sandwich electrochemical immunoassay for carbohydrate antigen 125 with signal enhancement using enzyme-coated nanometer-sized enzyme-doped silica beads.

A novel nanoparticle-based electrochemical immunoassay of carbohydrate antigen 125 (CA125) as a model was designed to couple with a microfluidic strategy using anti-CA125-functionalized magnetic beads as immunosensing probes. To construct the immunoassay, thionine-horseradish peroxidase conjugation (TH-HRP) was initially doped into nanosilica particles using the reverse micelle method, and then HRP-labeled anti-CA125 antibodies (HRP-anti-CA125) were bound onto the surface of the synthesized nanoparticles, which were used as recognition elements. Different from conventional nanoparticle-based electrochemical immunoassays, the recognition elements of the immunoassay simultaneously contained electron mediator and enzyme labels and simplified the electrochemical measurement process. The sandwich-type immunoassay format was used for the online formation of the immunocomplex in an incubation cell and captured in the detection cell with an external magnet. The electrochemical signals derived from the carried HRP toward the reduction of H(2)O(2) using the doped thionine as electron mediator. Under optimal conditions, the electrochemical immunoassay exhibited a wide working range from 0.1 to 450 U/mL with a detection limit of 0.1 U/mL CA125. The precision, reproducibility, and stability of the immunoassay were acceptable. The assay was evaluated for clinical serum samples, receiving in excellent accordance with results obtained from the standard enzyme-linked immunosorbent assay (ELISA) method. Concluding, the nanoparticle-based assay format provides a promising approach in clinical application and thus represents a versatile detection method.

Conductive carbon nanoparticles-based electrochemical immunosensor with enhanced sensitivity for α-fetoprotein using irregular-shaped gold nanoparticles-labeled enzyme-linked antibodies as signal improvement

A new electrochemical immunoassay protocol for sensitive detection of alpha-fetoprotein (AFP, as a model) is designed using carbon nanoparticles (CNPs)-functionalized biomimetic interface as immunosensing probe and irregular-shaped gold nanoparticles (ISNGs)-labeled horseradish peroxidase-anti-AFP conjugates (HRP-anti-AFP-ISNG) as trace label. The low-toxic and high-conductive CNPs provided a high capacity nanoparticulate immobilization surface and a facile pathway for electron transfer. In comparison with conventional label methods, i.e. spherical gold nanoparticles-labeled HRP-anti-AFP and HRP-labeled anti-AFP, the electrochemical immunosensor using HRP-anti-AFP-ISNGs as trace labels exhibited high bioelectrocatalytic response toward enzyme substrate and a wide dynamic range from 0.02 to 4.0 ng/mL with a low detection limit of 10 pg/mL toward AFP (at 3sigma). The developed immunoassay method showed good selectivity and acceptable reproducibility. Clinical serum samples with various AFP concentrations were evaluated by using the electrochemical immunosensor and the referenced enzyme-linked immunosorbent assay (ELISA), respectively, and received in good accordance with results obtained from these two methods.

Enzyme-free electrochemical immunoassay with catalytic reduction of p-nitrophenol and recycling of p-aminophenol using gold nanoparticles-coated carbon nanotubes as nanocatalysts

A novel enzyme-free sandwich electrochemical immunoassay with an ultrahigh sensitivity was developed for detection of alpha-fetoprotein (AFP, as a model analyte) using carbon nanotube-enriched gold nanoparticles (CNT-AuNPs) as nanolabels/nanocatalysts on anti-AFP/glutaraldehyde/thionine-modified glassy carbon electrodes (GCEs). The assays were carried out in a pH 8.0 acetic acid-buffered solution containing 6 mM p-nitrophenol (NP) and 6mM NaBH(4) after the formation of the sandwich-type immunocomplex. Initially, the NP molecules were reduced to p-aminophenol (AP) by the catalysis of the immobilized gold-nanoparticle labels on the CNT-AuNPs with the aid of NaBH(4), then the generated AP molecules were electrochemically oxidized to p-quinone imine (QI) by an electron mediator of thionine, and then the oxidized QI molecules were reduced back to APs by NaBH(4). The redox cycling of AP and QI continuously increased the signaling, leading to a high sensitivity. Compared with individual gold-nanoparticle labels, the immunosensor using CNT-AuNPs as labels displayed a wider linear range of 8.0×10(-7)-2.0×10(2) ng/mL with a lower detection limit (LOD) of 0.8 fg/mL AFP at a signal-to-noise ratio of 3, which was lower 6 orders than that of commercially available ELISA. Intra-and inter-assay coefficients of variation were below 10%. In addition, the assay was evaluated with clinical serum samples, and no significant differences at the 5% confidence level were encountered in the analysis of real samples between the proposed immunoassay and commercially available Roche 2010 Electrochemiluminescent Automatic Analyzer for determination of AFP.

Ultrasensitive Aptamer-Based Multiplexed Electrochemical Detection by Coupling Distinguishable Signal Tags with Catalytic Recycling of DNase I

This work reports an aptamer-based, disposable, and multiplexed sensing platform for simultaneous electrochemical determination of small molecules, employing adenosine triphosphate (ATP) and cocaine as the model target analytes. The multiplexed sensing strategy is based on target-induced release of distinguishable redox tag-conjugated aptamers from a magnetic graphene platform. The electronic signal of the aptasensors could be further amplified by coupling DNase I with catalytic recycling of self-produced reactants. The assay was based on the change in the current at the various peak potentials in the presence of the corresponding signal tags. Experimental results revealed that the multiplexed electrochemical aptasensor enabled the simultaneous monitoring of ATP and cocaine in a single run with wide working ranges and low detection limits (LODs: 0.1 pM for ATP and 1.5 pM for cocaine). This concept offers promise for rapid, simple, and cost-effective analysis of biological samples.

Gold-silver-graphene hybrid nanosheets-based sensors for sensitive amperometric immunoassay of alpha-fetoprotein using nanogold-enclosed titania nanoparticles as labels.

A new sandwich-type electrochemical immunosensor with enhanced sensitivity was developed for detection of alpha-fetoprotein (AFP, as a model analyte) in biological fluids by using nanogold-enclosed titania nanoparticle (AuTi)-labeled secondary antibody on a gold-silver-graphene hybrid nanosheet (AuAgGP)-functionalized glassy carbon electrode (GCE). The presence of the AuAgGP nanosheets not only enhanced the immobilized amount of biomolecules, but also improved the electrochemical properties of the immunosensor. With the aid of AuTi nanolabels, the electrochemical signal was greatly amplified in comparison with pure nanogold or titania-based labels. Under optimal conditions, the sensitivity and dynamic range of the immunosensor were evaluated by using the labeled horseradish peroxidase on the AuTi as trace and H(2)O(2) as enzyme substrate, and exhibited a wide dynamic range of 0.001-200 ng mL(-1) with a low detection limit (LOD) of 0.5 pg mL(-1) AFP (at 3σ). Both the intra- and inter-assay coefficients of variation were less than 10%. The current of the immunosensor at 13th day was as much as 90% of the initial current. In addition, the methodology was evaluated for 8 positive serum specimens obtained from hepatocarcinoma patients and 19 negative sera, and validated with the commercially available Roche 2010 Electrochemiluminescent (ECL) Automatic Analyzer. No significant differences at the 95% confidence level were encountered between two methods.

Ultrasensitive electrochemical immunoassay of staphylococcal enterotoxin B in food using enzyme-nanosilica-doped carbon nanotubes for signal amplification.

A new sandwich-type electrochemical immunoassay for ultrasensitive detection of staphylococcal enterotoxin B (SEB) in food was developed using horseradish peroxidase-nanosilica-doped multiwalled carbon nanotubes (HRPSiCNTs) for signal amplification. Rabbit polyclonal anti-SEB antibodies immobilized on the screen-printed carbon electrode (SPCE) and covalently bound to the HRPSiCNTs were used as capture antibodies and detection antibodies, respectively. In the presence of SEB analyte, the sandwich-type immunocomplex could be formed between the immobilized anti-SEB on the SPCE and anti-SEB-labeled HRPSiCNTs, and the carried HRP could catalyze the electrochemical reduction of H2O2 with the help of thionine. The high content of HRP in the HRPSiCNTs could greatly amplify the electrochemical signal. Under optimal conditions, the reduction current increased with the increase of SEB in the sample, and exhibited a dynamic range of 0.05-15 ng/mL with a low detection limit (LOD) of 10 pg/mL SEB (at 3σ). Intra- and interassay coefficients of variation were below 10%. In addition, the assay was evaluated with SEB spiked samples including watermelon juice, soymilk, apple juice, and pork food, receiving excellent correlation with results from commercially available enzyme-linked immunosorbent assay (ELISA).

Gold nanoparticles-decorated amine-terminated poly(amidoamine) dendrimer for sensitive electrochemical immunoassay of brevetoxins in food samples

A sensitive electrochemical immunosensor for the fast screening of brevetoxin B (BTX-2) in food samples was developed by means of immobilizing BTX-2-bovine serum albumin conjugate (BTX-2-BSA) on the gold nanoparticles-decorated amine-terminated poly(amidoamine) dendrimers (AuNP-PAADs). The presence of gold nanoparticles greatly improved the conductivity of the PAADs, and three-dimensional PAADs increased the surface coverage of the biomolecules on the electrode. Under optimal conditions, three types of immunosensor, i.e. with AuNPs, PAADs, or AuNP-PAADs, were used for the determination of BTX-2 in a competitive-type immunoassay format using horseradish peroxidase-labeled anti-BTX antibodies (HRP-anti-BTX-2) as trace in the H(2)O(2)-o-phenylenediamine (o-PD) system. A low detection limit (LOD) of 0.01 ng/mL and a wide dynamic working linear range of 0.03-8 ng/mL BTX-2 using AuNP-PAADs as matrices were obtained in comparison with those of only using AuNP or PAADs. Intra-batch assay precision was substantially improved by resorting to the AuNP-PAADs manifold. The proposed method features unbiased identification of negative (blank) and positive samples. No significant differences were encountered in the analysis of the spiking real samples between the electrochemical immunosensor and liquid chromatography for the determination of BTX-2. Importantly, this method provided a biocompatible immobilization and a promising immunosensing platform for analytes with small molecules in the analysis and detection of food safety.

Carbon nanotube-based symbiotic coaxial nanocables with nanosilica and nanogold particles as labels for electrochemical immunoassay of carcinoembryonic antigen in biological fluids.

A feasible and practicable amperometric immunoassay strategy for sensitive screening of carcinoembryonic antigen (CEA) in human serum was developed using carbon nanotube (CNT)-based symbiotic coaxial nanocables as labels. To construct such a nanocable, a thin layer of silica nanoparticles was coated on the CNT surface by sonication and sol-gel methods, and then colloidal gold nanoparticles were assembled on the amino-functionalized SiO(2)/CNTs, which were used for the label of horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA-Au/SiO(2)/CNT). In the presence of analyte CEA, the sandwich-type immunocomplex was formed on an anti-CEA/Au/thionine/Nafion-modified glassy carbon electrode by using HRP-anti-CEA-Au/SiO(2)/CNTs as detection antibodies. To embody the advantages of the protocol, the analytical properties of variously modified electrodes were compared in detail on the basis of different nanolabels. Under optimal conditions, the cathodic peak currents of the electrochemical immunosensor were proportional to the logarithm of CEA concentration over the range from 0.01 to 12 ng mL(-1) in pH 5.5 HAc-NaAc containing 5mM H(2)O(2). At a signal-to-noise ratio of 3, the detection limit (LOD) is 5 pg mL(-1) CEA. Intra- and inter-assay coefficients of variation were below 9.5%. Meanwhile, the selectivity and stability of the immunosensor were acceptable. In addition, the technique was evaluated by spiking CEA standards in pH 7.4 PBS and with 35 clinical serum specimens, receiving excellent accordance with results from commercially available electrochemiluminescent enzyme-linked immunoassay.

Sensitive electrochemical immunoassay of carcinoembryonic antigen with signal dual-amplification using glucose oxidase and an artificial catalase.

A new dual-amplification strategy of electrochemical signal based on the catalytic recycling of the product was developed for the antigen-antibody interaction by glucose oxidase (GOD)- conjugated gold-silver hollow microspheres (AuAgHSs) coupled with an artificial catalase, Prussian blue nanoparticles (PB), on a graphene-based immunosensing platform. The first signal amplification introduced in this study was based on the labeled GOD on the AuAgHSs toward the catalytic oxidation of glucose. The generated H(2)O(2) was catalytically reduced by the immobilized PB on the graphene nanosheets with the second amplification. With a sandwich-type immunoassay format, carcinoembryonic antigen (CEA) was monitored as a model analyte by using the synthesized AuAgHSs as labels in pH 6.0 phosphate buffer containing 10mM glucose. Under optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range of 0.005-50 ng mL(-1) with a low detection limit (LOD) of 1.0 pg mL(-1) CEA (at 3σ). Both the intra- and inter-assay coefficients of variation (CVs) were lower than 10%. The specificity and stability of the immunosensor were acceptable. In addition, the assay was evaluated for clinical serum specimens, and received a good correlation with those obtained by the referenced electrochemiluminescent (ECL).

Magneto-controlled electrochemical immunosensor for direct detection of squamous cell carcinoma antigen by using serum as supporting electrolyte

A new magneto-controlled microfluidic device for direct electrochemical determination of squamous cell carcinoma antigen (SCC-Ag) in serum was designed by using anti-SCC antibody (SCC-Ab)-functionalized magnetic mesoporous nanogold/thionine/NiCo(2)O(4) hybrid nanostructures as immunosensing probes (P(1)-Ab) and horseradish peroxidase-SCC-Ab conjugates-labeled nanogold/graphene nanosheets as signal tags (P(2)-Ab). In the presence of the analyte SCC-Ag, the sandwich immunocomplex was formed between the immunosensing probes and the signal tags. With the aid of an external magnet, the formed immunocomplex was attached to the microfluidic device. The assay was implemented in newborn calf serum (NBCS) containing 2.5 mM H(2)O(2) based on the labeled peroxidase on the P(2)-Ab toward the catalytic reduction of H(2)O(2). Under optimal conditions, the increase in the current was proportional to the concentration of SCC-Ag from 2.5 pg/mL to 15 ng/mL. The detection limit (LOD) was 1.0 pg/mL SCC-Ag at 3s(B). The electrochemical immunoassay displayed an acceptable precision, selectivity and stability. Clinical serum specimens were assayed with the method, and the results were in acceptable agreement with those obtained from the referenced electrochemiluminescent method. Importantly, the method can be suitable for on-line use in the mass production of miniaturized lab-on-a-chip devices and open a new opportunity for protein diagnostics and biosecurity.