title: Single domain antibody-quantum dot conjugates for ricin detection by both fluoroimmunoassay and surface plasmon resonance.
abstract: The combination of stable biorecognition elements and robust quantum dots (QDs) has the potential to yield highly effective reporters for bioanalyses. Llama-derived single domain antibodies (sdAb) provide small thermostable recognition elements that can be easily manipulated using standard DNA methods. The sdAb was self-assembled on dihydrolipoic acid (DHLA) ligand-capped CdSe-ZnS core-shell QDs made in our laboratory through the polyhistidine tail of the protein, which coordinated to zinc ions on the QD surface. The sdAb-QD bioconjugates were then applied in both fluorometric and surface plasmon resonance (SPR) immunoassays for the detection of ricin, a potential biothreat agent. The sdAb-QD conjugates functioned in fluoroimmunoassays for the detection of ricin, providing equivalent limits of detection when compared to the same anti-ricin sdAb labeled with a conventional fluorophore. In addition, the DHLA-QD-sdAb conjugates were very effective reporter elements in SPR sandwich assays, providing more sensitive detection with a signal enhancement of ~10-fold over sdAb reporters and 2-4 fold over full sized antibody reporters. Commercially prepared streptavidin-modified polymer-coated QDs also amplified the SPR signal for the detection of ricin when applied to locations where biotinylated anti-ricin sdAb was bound to target; however, we observed a 4-fold greater amplification when using the DHLA-QD-sdAb conjugates in this format.
authors.affiliation: Center for Bio/Molecular Science and Engineering, U S Naval Research Laboratory, Washington, DC 20375, USA.
authors.forename: George P
authors.initials: GP
authors.lastname: Anderson
authors.forename: Richard H
authors.initials: RH
authors.lastname: Glaven
authors.forename: W Russ
authors.initials: WR
authors.lastname: Algar
authors.forename: Kimihiro
authors.initials: K
authors.lastname: Susumu
authors.forename: Michael H
authors.initials: MH
authors.lastname: Stewart
authors.forename: Igor L
authors.initials: IL
authors.lastname: Medintz
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Goldman
mesh_terms: D015200:Fluoroimmunoassay / Q000379:methods / Q000592:standards; D011485:Protein Binding / Q000276:immunology; D045663:Quantum Dots; D012276:Ricin / Q000032:analysis* / Q000276:immunology* / Q000378:metabolism; D061905:Single-Domain Antibodies / Q000737:chemistry*; D020349:Surface Plasmon Resonance / Q000379:methods* / Q000592:standards
chemical_list: D061905:Single-Domain Antibodies; D012276:Ricin