The negatively charged nitrogen-vacancy (NV ^-) centre in nanodiamonds (NDs) has been recently studied for applications in cellular imaging due to its better photo-stability and biocompatibility if compared to other fluorophores. Super-resolution imaging achieving 20-nm resolution of NV ^- in NDs has been proved over the years using sub-diffraction limited imaging approaches such as single molecule stochastic localisation microscopy and stimulated emission depletion microscopy. Here we show the first demonstration of ground-state depletion (GSD) nanoscopy of these centres in NDs using three beams, a probe beam, a depletion beam and a reset beam. The depletion beam at 638 nm forces the NV ^- centres to the metastable dark state everywhere but in the local minimum, while a Gaussian beam at 594 nm probes the NV ^- centres and a 488-nm reset beam is used to repopulate the excited state. Super-resolution imaging of a single NV ^- centre with a full width at half maximum of 36 nm is demonstrated, and two adjacent NV ^- centres separated by 72 nm are resolved. GSD microscopy is here applied to NV ^- in NDs with a much lower optical power compared to bulk diamond. This work demonstrates the need to control the NDs nitrogen concentration to tailor their application in super-resolution imaging methods and paves the way for studies of NV ^- in NDs’ nanoscale interactions.

We present a concealing method in which an anti-point spread function (APSF) is generated using binary optics, which produces a large-scale dark area in the focal region that can hide any object located within it. This result is achieved by generating two identical PSFs of opposite signs, one consisting of positive electromagnetic waves from the zero-phase region of the binary optical element and the other consisting of negative electromagnetic waves from the pi-phase region of the binary optical element.