title: Displacement of molecules near a metal surface as seen by an SPR-SPFS biosensor.
abstract: Movement of a fluorophore-labeled antibody on the surface of a self-assembled monolayer (SAM) was observed by surface plasmon resonance and surface-plasmon field-enhanced fluorescence spectroscopy (SPFS). At an extremely low surface coverage, the antibody lies close to the biotin-functionalized SAM surface. As additional nonlabeled antibodies were bound, the fluorophore-labeled antibody was displaced away from the SAM surface (and thus the gold surface) due to the constraint imposed by the neighboring nonlabeled antibody. A greater SPFS fluorescence signal was observed due to the weaker fluorescence quenching at large distances from the gold surface. The magnitude of the displacement is proportional to the available biotin binding sites on the sensor surface. The displacement is theoretically explained on the basis of the relationship between the fluorescence intensity and the evanescent field amplitude within the dielectric medium.
authors.affiliation: Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand. sanong@chula.ac.th
authors.forename: Sanong
authors.initials: S
authors.lastname: Ekgasit
authors.forename: Fang
authors.initials: F
authors.lastname: Yu
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Knoll
mesh_terms: D000906:Antibodies / Q000032:analysis* / Q000276:immunology; D001665:Binding Sites; D015374:Biosensing Techniques; D001710:Biotin / Q000737:chemistry; D019921:Biotinylation; D004553:Electric Conductivity; D004563:Electrochemistry; D006046:Gold / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D020349:Surface Plasmon Resonance / Q000379:methods; D013499:Surface Properties
chemical_list: D000906:Antibodies; D008670:Metals; D001710:Biotin; D006046:Gold