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22 February 2008 Magnetic luminescent nanoparticles as internal calibration for an immunoassay for ricin
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Fluorescence techniques rely on measurement of relative fluorescence units and require calibration to obtain reliable and comparable quantitative data. Fluorescent immunoassays are a very sensitive and convenient method of choice for rapid detection of biotoxins, such as ricin. Here we present the application of magnetic luminescent nanoparticles (MLNPs) with a magnetic core of Fe3O4 and a fluorescent shell of Eu:Gd2O3 as carriers for a nanobead-immunoassay for the detection of ricin with internal calibration. A sandwich immunoassay for ricin was performed on the surface of the MLNPs. The particles were functionalized with capture polyclonal antibodies. Anti-ricin antibodies labeled with Alexa Fluor dye were used as the detecting antibodies. After magnetic extraction, the amount of ricin bound to the particle surface was quantified and related to the fluorescence signal of the nanoparticles. In this new platform, the MLNPs have three main functions: (1) a probe for the specific extraction of the target analyte from the sample; (2) a carrier in the quantitative immunoassay with magnetic separation; and (3) an internal standard in the fluorescence measurement of the dye reporter. The MLNPs serve as an internal control for the total analysis including extraction and assay performance. This approach eliminates the experimental error inherent in particle extraction and measurement of absolute organic dye fluorescence intensities. All fluorescent measurements were performed in a microplate reader. The standard curve for ricin had a dynamic range from 20 ng/ml to 100 μg/ml with a detection limit of 5 ng/ml. The configuration that has been developed can be easily adapted to a high throughput miniaturized system.
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Dosi Dosev, Mikaela Nichkova, Zhi-Ya Ma, Shirley J. Gee, Bruce D. Hammock, and Ian M. Kennedy "Magnetic luminescent nanoparticles as internal calibration for an immunoassay for ricin", Proc. SPIE 6865, Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications V, 68650H (22 February 2008);

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