  Nitrogen-vacancy (NV) centers in diamonds are interesting due to their
remarkable characteristics that are well suited to applications in
quantum-information processing and magnetic field sensing, as well as
representing stable fluorescent sources. Multiple NV centers in nanodiamonds
(NDs) are especially useful as biological fluorophores due to their chemical
neutrality, brightness and room-temperature photostability. Furthermore, NDs
containing multiple NV centers also have potential in high-precision magnetic
field and temperature sensing. Coupling NV centers to propagating surface
plasmon polariton (SPP) modes gives a base for lab-on-a-chip sensing devices,
allows enhanced fluorescence emission and collection which can further enhance
the precision of NV-based sensors. Here, we investigate coupling of multiple NV
centers in individual NDs to the SPP modes supported by silver surfaces
protected by thin dielectric layers and by gold V-grooves (VGs) produced via
the self-terminated silicon etching. In the first case, we concentrate on
monitoring differences in fluorescence spectra obtained from a source ND, which
is illuminated by a pump laser, and from a scattering ND illuminated only by
the fluorescence-excited SPP radiation. In the second case, we observe changes
in the average NV lifetime when the same ND is characterized outside and inside
a VG. Fluorescence emission from the VG terminations is also observed, which
confirms the NV coupling to the VG-supported SPP modes.
