  Fluorescent nanodiamonds are attracting major attention in the field of
bio-sensing and biolabeling. In this work we demonstrate a robust approach to
surface functionalize individual nanodiamonds with metal-phenolic networks that
enhance the photoluminescence from single nitrogen vacancy (NV) centers. We
show that single NV centres in the coated nanodiamonds also exhibit shorter
lifetimes, opening another channel for high resolution sensing. We propose that
the nanodiamond encapsulation suppresses the non-radiative decay pathways of
the NV color centers. Our results provide a versatile and assessable way to
enhance photoluminescence from nanodiamond defects that can be used in a
variety of sensing and imaging applications
