Enhanced detection of fluorescent nanospheres using two-channel radially polarized surface plasmon microscopy

We detected single dye-stained latex nanospheres as small as 20 nm using a two-detection channel modified surface plasmon microscope. We found that a radially polarized incident beam leading to excitation of well-focused surface plasmons induces both fluorescence and elastic linear scattering from the spheres. The two complementary emitted signals were detected in parallel by the two separated channels, leading to well-colocalized images. We obtained high spatial resolutions for both channels down to 250 nm in the lateral direction and 300 nm along the longitudinal axis. We believe this multimodal microscope can be useful to track nano objects and to compensate for intermittent fluorescence, thanks to a permanently activated parallel scattering detection channel.