A method to observe individual fluorescent crystal defects in nanodiamonds is reported and opens new nanosensing avenues (e.g. pH nanosensing).

We report progress in the development of tunable room temperature triggered single photon sources based on single nitrogen-vacancy (NV) centres in nanodiamond coupled to open access optical micro-cavities. The feeding of fluorescence from an NV centre into the cavity mode increases the spectral density of the emission and results in an output stream of triggered single photons with spectral line width of order 1 nm, tunable in the range 640 - 700 nm. We record single photon purities exceeding 96% and estimated device efficiencies up to 3%. We compare performance using plano-concave microcavities with radii of curvature from 25 μm to 4 μm and show that up to 17% of the total emission is fed into the TEM mode. Pulsed Hanbury-Brown Twiss (HBT) interferometry shows that an improvement in single photon purity is facilitated due to the increased spectral density.

Colour centres in nanodiamonds provide robust sources of fluorescence and can be used as triggered sources of single photons at room temperature. However, practical devices require stability over thousands of hours of operation, and the use of strong pulsed optical excitation, placing significant burden on the robustness of the emitters that requires bespoke testing. In this work we report the response of single NV centres in nanodiamonds of 50 nm and 100 nm diameter to accelerated lifetime testing, exciting the defects close to saturation around 1013 times to simulate the minimum operational lifetime of a practical device. For nanodiamonds 50 nm in diameter, observed changes in the fluorescence intensity and lifetime suggest a progressive size reduction as a result of the pulsed laser excitation, combined with the introduction of non-radiative centres on or near the nanodiamond surface which affect the quantum efficiency of the NV centre and ultimately lead to photobleaching of the emission. We find examples of NV centres in 100 nm nanodiamonds for which triggered single photon emission remains stable for over these accelerated lifetime tests, demonstrating their suitability for use in practical devices.

Overall this analysis highlights the capacity of super-resolved single particle trajectories analysis to provide new insights about the dynamics of cellular structures. 859-PlatChromatin Nanoscale Organization Investigated by FLIM-FRET and STED Superresolution Microscopy Chromatin organization plays an essential role in the regulation of gene activity, which involves the packaging of the genome into transcriptionally active and inactive sites. Chromatin remodeling is generated by the recruitment of nuclear enzymes for a variety of nuclear processes. For instance, chromatin architecture is highly reorganized during DDR (DNA damage response) to promote accurate repair of DNA lesions[1]. However, how the higher-order chromatin structures are formed and then behave in various cellular processes in live cells remains unclear.Here, we adopt a double strategy based on a novel FLIM-FRET assay and super-resolution microscopy to study the nanoscale chromatin organization in intact cells nuclei. The FRET assay is based on the staining of the nuclei with two DNA-binding dyes and the frequency-domain detection of FLIM. We show that the FRET level strongly depends on the relative concentration of the two fluorophores. We describe a method to correct the values of FRET efficiency and demonstrate that, with this correction, the FLIM-FRET assay can be used to quantify variations of nanoscale chromatin compaction in live cells. Super-resolution microscopy is used to investigate, in fixed cells, the nanoscale distribution of specific proteins, like poly(ADP-ribose) polymerase 1 (PARP1), implicated in various DNA repair pathways and in the maintenance of genomic stability [2]. In particular, we apply our recently developed method based on the modulation of the STED power [3]. We show that, by using the phasor approach, we obtain a significant improvement of spatial resolution. We use this double strategy for monitoring changes in nanoscale chromatin organization during the DDR.[1] Hauer HM, Gasser SM, Genes Dev (2017); [2] Chaudhuri AR, Nussenzweig A, Nature Reviews (2017); [3] Sarmento MJ et al, Nat. Commun., (2018);

No abstract

No abstract