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In this paper, we describe the development of a multicomponent lateral-flow assay based on an antibody–antigen reaction for the rapid and simultaneous detection of trace contaminants in water, including a heavy metal, algal toxin, antibiotic, hormone, and pesticide. The representative analytes chosen for the study were lead (Pb(II), microcystin–leucine–arginine (MC–LR), chloramphenicol (CAP), testosterone (T), and chlorothalonil (CTN). Five different antigens were immobilized separately in five test lines on a nitrocellulose membrane. The monoclonal antibodies specifically recognized the corresponding antigens, and there was no cross-reactivity between the antibodies in the detection assay. Samples or standards containing the five analytes were preincubated with the freeze-dried colloidal-gold-labeled monoclonal antibody conjugates to improve the sensitivity of the assay. The results were obtained within 20 min with a paper-based sensor. The cut-off values for the strip test were 4 ng/mL for Pb(II), 1 ng/mL for MC–LR, 0.1 ng/mL for CAP, 5 ng/mL for T, and 5 ng/mL for CTN. The assay was evaluated using spiked water samples, and the accuracy and reproducibility of the results were good. In summary, this lateral-flow device provides an effective and rapid method for the onsite detection of multiple contaminants in water samples, with no treatment or devices required. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we report on the application of versatile gold nanorods (GNRs) in optical sensors for the detection of antibiotics. The target analyte, Gentamicin (GM) and ovalbumin (OVA) – antigen-modified GNRs together competed with antibody-modified GNRs, then influenced the formation of side-by-side aggregates of the GNRs by antibody–antigen interactions. Accordingly, the UV–vis absorption intensity of the side-by-side aggregates was changed in the presence of the target analyte. This assay allowed the selective determination of GM in the range of 0.1–20ng/mL, and the limit of detection (LOD) of GM was 0.05ng/mL. Furthermore, compared with the traditional plate-based immunoassay, the developed method was easy to perform without washing cycles and the results could be read as soon as the nanoprobe-analyte incubation was complete. Therefore, the developed method could be a promising tool for the detection of antibiotic residues. [Copyright &y& Elsevier]

Abstract: An aptamer-based chromatographic strip assay method for rapid toxin detection was developed. The aptamer-based strip assay was based on the competition for the aptamer between ochratoxin A and DNA probes. The sensing results indicated that the sensitivity of the aptamer-based strip was better than that of conventional antibody-based strips. The visual limit of detection of the strip for qualitative detection was 1ng/mL while the LOD for semi-quantitative detection could down to 0.18ng/mL by using scanning reader. The recoveries of test samples were from 96% to 110%. All detections could be achieved in less than 10min, indicating that the aptamer-based strip could be a potential useful tool for rapid on-site detections. [ABSTRACT FROM AUTHOR]

Abstract: Melamine toxicity causing the renal failure and death of animals and humans has recently attracted worldwide attention. Developing an easy, fast, and sensitive method for the routine melamine detection is of great importance. Herein, we report the colorimetric sensing of melamine, based on the 18-crown-6 ether functionalized gold nanoparticles (GNPs) through the formation of cavity complexes with amines. Based on high extinction coefficients and spectral sensitivity of the surface plasmon resonance band of the GNPs, the rapid and sensitive melamine detection was achieved both visually and spectroscopically. Under the optimal conditions, melamine could be selectively detected in a concentration range from 10 to 500ppb with a limit of detection as 6ppb (3σ), which is much lower than the strictest melamine safety requirement of 1ppm. To demonstrate the selectivity and practicality of the method, melamine detection was realized in the real complex samples (dairy) with excellent analyte concentration recovery, indicating its applicability for real-time monitoring of toxins in common products. Crown ether assembly of GNP also opens a new route for the formation of three-dimensional pseudorotaxane-like assemblies of nanoparticles that can be applicable to a variety of amine-bearing ligands. [ABSTRACT FROM AUTHOR]

Abstract: An ultrasensitive and rapid electrochemical platform for the specific detection of ochratoxin A (OTA) was developed. In this method, three single-stranded DNA molecules, including the aptamer, were immobilized on the surface of an electrode. Binding of the OTA target analyte to the aptamer changed the redox current of methylene blue (MB), which was used as the electrochemical probe, in a manner that was dependent on OTA concentration. With signal enhancement from gold nanoparticle-functionalized DNA, the sensitivity of this method for OTA was as low as 30pg/mL, and the effective sensing range was from 0.1 to 20ng/mL. To investigate the sensing process, the conformational switch of the aptamer was studied by circular dichroism (CD), which confirmed the recognition of the aptamer by the target OTA. Given its sensitivity and rapid detection, we believe this approach has the potential to be a main technology for the detection of toxins in the field of food safety, and in other areas. [ABSTRACT FROM AUTHOR]

Abstract: Biotinylated denatured bovine serum albumin (Bt-dBSA)-coated cadmium telluride (CdTe) quantum dot (QD) conjugates were prepared and used to develop the multiplexed fluoroimmunoassay for the simultaneous determination of five chemical residues. An immune complex was formed using avidin as the bridge to link the Bt-dBSA-QDs with the antibodies. Primarily, individual quantitative determinations of five representative chemical residues were carried out based on the different emission properties of the QDs. Five antibodies were then conjugated with the corresponding QDs to establish the indirect competition fluorescent-linked immunosorbent assay (ic-FLISA) for the simultaneous detection of five chemicals in one well of a microplate. The linear range for dexamethason (DEX) was from 0.33μg/kg to 10μg/kg, 0.28μg/kg to 10μg/kg for gentamicin (GM), 0.16μg/kg to 25μg/kg for clonazepam (CZP), 0.17μg/kg to 10μg/kg for medroxyprogesterone acetate (MPA) and 0.32μg/kg to 25μg/kg for ceftiofur (CEF), respectively. The limit of detection (LOD) for the simultaneous determination of DEX, GM, CZP, MPA and CEF were as low as 0.13μg/kg, 0.16μg/kg, 0.07μg/kg, 0.06μg/kg and 0.14μg/kg, respectively. This detection method was used to analyze samples of pork muscle and the recoveries ranged from 61.3% to 80.3% for DEX and from 74.0% to 87.2% for MPA. Further more, good correlation between the novel ic-FLISA and traditional ELISA was demonstrated during the determination of DEX and MPA residues in real samples. The QD-based protocol described here is less time consuming than the classical method and it may be sufficiently flexible to be used in other systems for the simultaneous multicolor detection of the drugs. [Copyright &y& Elsevier]

Abstract: An ultrasensitive and rapid sequential injection analysis (SIA) based on real-time PCR (SIA-rt-PCR) assay was developed by using different nanoparticles for the detection of small molecule chemicals residues. Gold (Au) nanoparticle, conjugated with goat anti-rabbit IgG and duplex strand DNA (dsDNA), was used as a substitute for chemiluminescent probes in an SIA system. By indirect competitive immunoreactions in the SIA system, the gold nanoparticles were attached to antigens which were immobilized by superparamagnetic nanoparticles (SMNPs). The dsDNA on the gold nanoparticles was dehybridized and then the single-stranded DNA (ssDNA) was collected and quantified with rt-PCR, which showed a rather low linearity range from 2.5attomolL−1 (aM) to 250 femtomolL−1 (fM) and the LOD was 1.4aM. This method, which is rapid, automated and capable of high-throughput, was used to detect methyl-3-quinoxaline-2-carboxylic acid (MQCA) residues in real samples. The analytical results had a coefficient of variation of less than 15% and the recovery was 89–108%. [Copyright &y& Elsevier]