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A europium nanoparticle-based lateral flow immunoassay for highly sensitive detection of chloramphenicol residue was developed. The detection result could be either qualitatively resolved with naked eye or quantitatively analyzed with the assistance of a digital camera. In the qualitative mode, the limit of detection (LOD) was found to be 0.25 ng/mL. In the quantitative mode, the half-maximal inhibition concentration (IC50) was determined to be 0.45 ng/mL and the LOD can reach an ultralow level of 0.03 ng/mL, which is ~100 times lower than that of the conventional colloidal gold-based lateral flow immunoassay. Potential application of the established method was demonstrated by analyzing representative cow milk samples.

Development of a microsphere-based competitive fluorescence immunoassay for the determination of hazardous low-molecular-weight compounds in food is described. In this method, antigens are covalently bound to carboxy-modified microspheres to compete monoclonal antibody with low-molecular-weight compounds in food samples; mouse IgG/fluorescein isothiocyanate conjugate is used as the fluorescent molecular probe. Thus, the hazardous low-molecular-weight compounds are quantified using a multiparameter flow cytometer. This method has been evaluated using clenbuterol as a model compound. It has a sensitivity of 0.01 ng/mL with dynamic range of 0.01-100 ng/mL, and the concentration of clenbuterol providing 50% inhibition (IC(50)) is 1.1 ng/mL. The main advantages of this method are its high efficiency, biocompatibility, and selectivity, as well as ultralow trace sample consumption and low cost.

Objective: Based on immunoassay, we developed a method to detect Potato Virus A (PVA) using one-step cytometric bead array (CBA)., Methods: Using fluorescent beads as carriers, we formed the complexes of bead-capture antibody-PVA-fluoresceinisothiocyanate (FITC) labeled detection antibody by immunoreaction of double antibody sandwich on bead surface. We measured the fluorescent signals produced from beads and from FITC with a multiparameter flow cytometer., Results: By optimization test, capture antibody and detection antibody (from PVA detection kit, Agdia, USA) were finally diluted at 1:50 (4 ug/mL) and 1:25 to be used in one step CBA, respectively. A total CBA reaction time of 2 h was needed. No cross reactivity with other plant virus similar to potato virus Y, lettuce mosaic virus and tomato ring spot virus were found. Detection sensitivity for positive control sample in one-step CBA was 4 folds higher than that in normal plate double antibodies sandwich enzyme-linked immunosorbent assay (DAS-ELISA)., Conclusion: A one-step CBA method for rapid and sensitive detection of PVA is developed.

Abstract: The lateral flow immunoassay is used in commercial pregnancy detection, and is an accepted point-of-care testing technique. The most widely used format for lateral flow immunochromatographic strips uses gold nanoparticles for colorimetric detection. However, this method often suffers from poor quantitative discrimination and low analytical sensitivity. To address these limitations, lanthanide chelate-loaded silica nanoparticles have been used as fluorescent labels. The fluorescent nanoparticles can easily bind to antibodies, with dextran as a linker. The strip reader described here was based on a sandwich immunoreaction performed on a strip, using lanthanide-labeled antibodies that served as signal vehicles for the fluorescent readout. The strip reader was used as a quantitative test system. In this work, Pantoea stewartii subsp. stewartii (Pss) was used as a model analyte to demonstrate the use of the strip reader. Under optimal conditions, the detection limit was determined as 103 cfu/mL. The quantification limit was calculated to be 104 cfu/mL. The detection limit for Pss was 100 times lower than those displayed by colloidal gold-labeled strips or ELISAs. No cross-reactions were observed with the other nine strains, indicating the good specificity of the Pss strip. This strip showed good stability in repeated tests. The tests using the fluorescence immunochromatographic strip were easy to perform, rapid, and sensitive. Methods using fluorescence strips and a strip reader have the potential to be a powerful tool for the quantification of bacteria. [Copyright &y& Elsevier]

A bead-based competitive fluorescence immunoassay for the detection of triazophos has been developed. In this method, a conjugate of hapten and ovalbumin covalently bound to carboxylated fluorescent bead was used as a coating antigen and goat anti-mouse IgG/R-phycoerythrin conjugate was used as the fluorescent molecular probe. For standards (in 5% methanol in phosphate-buffered saline), the detection range was 0.02–50 ng/ml and the average coefficient of variation (CV) was 8.9%. This bead-assay was highly specific for triazophos, and none of other the structurally similar compounds (diazinon, malathion, parathion and fenitrothion) were recognised (<0.01% cross-reactivity). Vegetable samples (cabbage, carrot, green pepper, spinach, eggplant) were spiked with triazophos in the range of 1.0–100.0 ng/g and analysed by the bead-based immunoassay. The mean recovery and CV were 90.6 and 11.9%, respectively. The results confirmed that the bead-based fluorescence immunoassay is applicable for analysis and quantification of highly hydrophobic pesticide residues in vegetables. [ABSTRACT FROM PUBLISHER]

A portable immuno-microchip system consisting of low-cost biocompatible-polystyrene chips, a mini-vacuum pump, and a base unit for a LED light source as a miniaturized optical readout was devised. The surfaces of the micro-channels were processed with plasma to be more hydrophilic and were characterized by kinetic coating with a CCD scanning method. To demonstrate the feasibility of this novel system for the determination of a small molecule control assay, a simple, specific, and rapid method was established for drug analysis of morphine and its analogs, 6-monoacetylmorphine and morphine-3-glucuronide. Morphine-3-site antigen and a multi-target polyclonal antibody to morphine and derivatives were prepared and a competitive immunoassay was performed on the chip. The measurement can be carried out automatically and avoids time-consuming incubation steps. A detection sensitivity of below 1.0 ng/mL was achieved, which is comparable with the enzyme-linked immunosorbent assay (ELISA) technique. [ABSTRACT FROM AUTHOR]