A solid-phase dot assay using silica/gold nanoshells

Boris Khlebtsov,Nikolai Khlebtsov,Vladimir Bogatyrev,Lev Dykman,Vladimir Zharov

doi:10.1007/s11671-006-9021-9

Abstract

We report on the first application of silica-gold nanoshells to a solid-phase dot immunoassay. The assay principle is based on staining of a drop (1 µl) analyte on a nitrocellulose membrane strip by using silica/gold nanoshells conjugated with biospecific probing molecules. Experimental example is human IgG (hIgG, target molecules) and protein A (probing molecules). For usual 15-nm colloidal gold conjugates, the minimal detectable amount of hIgG is about 4 ng. By contrast, for nanoshell conjugates (silica core diameter of 70 nm and gold outer diameter of 100 nm) we have found significant increase in detection sensitivity and the minimal detectable amount of hIgG is about 0.5 ng. This finding is explained by the difference in the monolayer particle extinction.

Highlights

The solid-phase immunoassays are based on adsorption of antigens onto a solid substrate followed by binding of adsorbed target molecules with biospecific labels
We report on the first, to the best of our knowledge, application of silica/gold nanoshells to a solid-phase dot assay in which the nanoshells are used as color markers for biospecific staining of a drop analyte placed on a nitrocellulose membrane strip
Let us suppose that the detection sensitivity at lowest analyte concentrations is determined by the single-particle extinction properties provided that there is some kind of proportionality between the available sites and number of adsorbed markers

Summary

Introduction

The solid-phase immunoassays are based on adsorption of antigens onto a solid substrate followed by binding of adsorbed target molecules with biospecific labels. The application of colloidal gold conjugates is based on visual detection of biospecific binding between adsorbed antigens and functionalized particles due to intense red color of markers [10]. We report on the first, to the best of our knowledge, application of silica/gold nanoshells to a solid-phase dot assay in which the nanoshells are used as color markers for biospecific staining of a drop analyte placed on a nitrocellulose membrane strip. The surface protein A functionalization of silica/gold nanoshells was verified by the minor spectral salt-induced changes of stabilized particles, by the positive interaction with complementary analyte (hIgG) molecules in solid-phase dot-immunoassay, and by the absence of interaction with a negative control (BSA).

Findings

Discussion

Conclusion