Bioconjugated gold nanodots and nanoparticles for protein assays based on photoluminescence quenching

This study describes the first instance of the use of two differently sized Au nanoparticles (Au NPs), acting separately as donor and acceptor, in homogeneous photoluminescence quenching assays developed for the analysis of proteins. Introduction of a breast cancer marker protein, platelet-derived growth factor AA (PDGF AA), to a solution of 11-mercaptoundecanoic acid-protected, 2.0-nm photoluminescent Au nanodots (L_AuND) led to the preparation of PDGF AA-L_AuND as the donor. Thiol-derivative PDGF binding aptamers (Apt) and 13-nm spherical Au NPs were used to synthesize the Apt-Q_AuNP acceptor. The photoluminescence of PDGF AA-L_AuND at 520 nm decreased when photoluminescence quenching occurred between Apt-Q_AuNP and PDGF AA-L_AuND. We used the PDGF AA-L _AuND/Apt-Q_AuNP-based molecular light switching system to analyze PDGFs and PDGF α-receptor in separate homogeneous solutions. In the presence of PDGFs, the interaction between Apt-Q_AuNP and PDGF AA-L_AuND decreased as a result of competitive reactions between the PDGFs and Apt-Q_AuNP. Similarly, the interaction between Apt-Q _AuNP and PDGF AA-L_AuND reduced as a result of competitive reactions between PDGF α-receptor and PDGF AA-L_AuND. The limits of detection (LODs) for PDGF AA and PDGF α-receptor were 80 pM and 0.25 nM, respectively, resulting from a low background photoluminescence signal. When using the Apt-Q_AuNP as selectors for (a) the enrichment of PDGF AA and (b) the removal of matrixes possessing intense background fluorescence from cell media and urine samples, the LOD for PDGF AA decreased to 10 pM. Unlike quantum dots, the L_AuND provide the advantages of biocompatibility, ease of bioconjugation, and minimal toxicity.