  Single molecule microscopy has proven to be an effective tool to characterize
the fluorophore-plasmonic structure interaction. However, as specific
information is hidden in the emission, sophisticated evaluation is required.
Here we investigated the emission polarization of rotationally mobile
fluorophores near plasmonic Au/Ag alloy nanospheres both theoretically and
experimentally. Our work surpasses the results of the previous studies in that
it considers the rotational mobility of the fluorophores attached to metallic
nanoparticles. Through theoretical modeling and elaborate numerical
calculations we determined the expected measurable fluorescence polarization,
and via DNA-PAINT single molecule measurements we validated the theoretical
predictions. Our findings suggest that through measuring the polarization state
of a sequence of single-molecule events, it is possible to infer the
interaction strength of the dye-nanosphere system. A precise description
requires elaborate calculations, however, a simplified model is able to predict
the tendency of the polarization state with the change of experimental
parameters.
