Author(s): Khlebtsov B, Khlebtsov N
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Abstract Plasmon-resonant nanoparticle-labeled immunoassays provide a simple, low-cost and effective way of detecting target molecules in solutions. The optical mechanisms behind their efficiency, however, have not been addressed until now. We present the first theoretical description of nanoparticle-labeled dot immunoassay and its experimental verification with functionalized 15 nm colloidal gold nanospheres and silica/gold nanoshells (GNs). Three types of GNs, with silica core diameters of 100, 140 and 180 nm and a gold shell thickness of about 15 nm, were studied in our experiments. The fabricated markers were characterized by electron and atomic-force microscopy, UV-vis spectroscopy and dynamic light scattering. A normal rabbit serum (the target IgG molecules) and sheep antirabbit antibodies (the probing molecules) were used as a biospecific model. The minimal detection limit for IgG target molecules was about 15 ng in the case of a standard dot-assay protocol based on 15 nm colloidal gold particles conjugated with probing molecules. In contrast to this observation, a simple replacement of 15 nm gold labels by GN conjugates resulted in a drastic increase in detection sensitivity of up to 0.25 ng in the case of 180/15 nm GNs and of up to 0.5-1 ng for 100/15 and 140/15 GNs. By using the theory developed, we explained the dependences of the low detection limit, the maximal-color intensity and the probe-load saturation limit on the particle parameters.
This article was published in Nanotechnology
and referenced in Journal of Nanomedicine & Nanotechnology