Gold Nanoparticle−Quantum Dot−Polystyrene Microspheres as Fluorescence Resonance Energy Transfer Probes for Bioassays

The paper describes the development of highly sensitive particle-based fluorescence resonance energy transfer (FRET) probes that do not use molecular fluorophores as donors and acceptors. In these probes, CdSe/ZnS luminescent quantum dots (QDs) were capped with multiple histidine-containing peptides to increase their aqueous solubility while maintaining their high emission quantum yield and spectral properties. The peptide-modified QDs (QD-His) were covalently attached to carboxyl-modified polystyrene (PS) microspheres to form highly emitting PS microspheres (QD-PS). Gold nanoparticles (AuNPs) were then covalently attached to the QD-PS surface to form AuNP-QD-PS composite microspheres that were used as FRET probes. Attachment of AuNPs to QD-PS completely quenched the QD emission through FRET interactions. The emission of QD-PS was restored when the AuNPs were removed from the surface by thiol ligand displacement. The new AuNP-QD-PS FRET platform is simple to prepare and highly stable, and it opens many new possibilities for carrying out FRET assays on microparticle-based platforms and in microarrays. The versatility of these assays could be greatly increased by replacing the linkers between the QDs and AuNPs with ones that selectively respond to specific cleaving agents or enzymes.