A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and magnetic nanoparticles has been developed. The assay is based on the fluorescence quenching of fluorescein isothiocyanate caused by gold nanoparticles coated with monoclonal antibody. To demonstrate its analytical capabilities, the magnetic nanoparticles were coated with anti-alpha-fetoprotein polyclonal antibodies, which specifically bound with alpha-fetoprotein. Gold nanoparticles coated with anti-alpha-fetoprotein monoclonal antibodies could sandwich the alpha-fetoprotein captured by the magnetic nanoparticle probes. The sandwich-type immunocomplex was formed on the surface of magnetic nanoparticles and could be separated by a magnetic field. The supernatant liquid, which contained the unbound gold nanoparticle probes, was used to quench the fluorescence, and the fluorescence intensity of fluorescein isothiocyanate at 516 nm was proportional to the alpha-fetoprotein concentration. The result showed that the limit of detection of alpha-fetoprotein was 0.17 nM. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis.
We report end-to-end assembly for tuning the optical properties of a gold nanorod/sphere based on oligonucleotide hybridization. The rationale behind the selection of the mercaptoalkyloligonucleotide molecule is based on the fact that the thiol group binds to the ends of the nanorods, which further assemble in an end-to-end fashion through hybridization with the target oligonucleotide. A highly selective, colorimetric polynucleotide detection method based on mercaptoalkyloligonucleotide-modified gold nanorod/sphere probes is also reported.
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