Systematic Computational Study of the Effect of Silver Nanoparticle Dimers on the Coupled Emission from Nearby Fluorophores.
ABSTRACT We use the finite-difference time-domain method to predict how fluorescence is modified if the fluorophore is located between two silver nanoparticles of a dimer system. The fluorophore is modeled as a radiating point dipole with orientation defined by its polarization. When a fluorophore is oriented perpendicular to the metal surface, there is a large increase in total power radiated through a closed surface containing the dimer system, in comparison to the isolated fluorophore and the case of a fluorophore near a single nanoparticle. The increase in radiated power indicates increases in the relative radiative decay rates of the emission near the nanoparticles. The angle-resolved far-field distributions of the emission in a single plane are also computed. This is informative as many experimental conditions involve collection optics and detectors that collect the emission along a single plane. For fluorophores oriented perpendicular to the metal surfaces, the dimer systems lead to significant enhancements in the fluorescence emission intensity in the plane. In contrast, significant emission quenching occurs if the fluorophores are oriented parallel to the metal surfaces. We also examine the effect of the fluorophore on the near-field around the nanoparticles and correlate our results with surface plasmon excitations.
Article: Fluorescent excitation transfer immunoassay. A general method for determination of antigens.[show abstract] [hide abstract]
ABSTRACT: A general immunochemical method for the assay of haptens and proteins has been devised and applied to morphine, a morphine-albumin conjugate, and human immunoglobulin G. A fluorescein-labeled antigen and a quencher-labeled antibody are employed. By use of fluorescein and rhodamine as the fluorescer and quencher, respectively, dipole-dipole-coupled excitation energy transfer can occur within the antigen-antibody complex. The resulting quenching of fluorescence can be inhibited by competitive binding with unlabeled antigen, Alternatively, separate antibody samples can be labeled with fluorescein and rhodamine, respectively. Unlabeled antigen causes aggregation of the separately labeled components with resultant quenching. Using the latter method, experiments suggest that up to about 20 anti-morphine antibody binding sites will associate with morphine-albumin conjugates. When an excess of the conjugate is present the antibodies appear to assemble in clumps on the protein surface. Mathematical analysis of the quenching of fluorescein-labeled morphine by rhodamine-labeled anti-morphine gives an approximate fit to the quenching data, but the calculations are very dependent on the assumptions used.Journal of Biological Chemistry 08/1976; 251(14):4172-8. · 4.77 Impact Factor