| Summary: | The N-terminal pro-brain natriuretic peptide (NT-proBNP) is considered an important blood biomarker for heart failure. Herein, we report about a fiber optic nanogold-linked immunosorbent assay (FONLISA) method for the rapid, sensitive, and low-cost detection of NT-proBNP. The method is based on a sandwich immunoassay approach that uses two monoclonal NT-proBNP antibodies, a capture antibody (Ab<sup>C</sup>), and a detection antibody (Ab<sup>D</sup>). Ab<sup>D</sup> is conjugated to a free gold nanoparticle (AuNP) to form the free AuNP@Ab<sup>D</sup> conjugate, and Ab<sup>C</sup> is immobilized on an unclad segment of an optical fiber. The detection of analyte (A), in this case NT-proBNP, is based on the signal change due to the formation of an AuNP@Ab<sup>D</sup>–A–Ab<sup>C</sup> complex on the fiber core surface, where a green light transmitted through the optical fiber will decrease in intensity due to light absorption by AuNPs via the localized surface plasmon resonance effect. This method provides a wide linear dynamic range of 0.50~5000 pg·mL<sup>−1</sup> and a limit of detection of 0.058 pg·mL<sup>−1</sup> for NT-proBNP. Finally, the method exhibits good correlation (<i>r</i> = 0.979) with the commercial central laboratory-based electrochemiluminescent immunoassay method that uses a Roche Cobas e411 instrument. Hence, our method is potentially a suitable tool for point-of-care testing.
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