Not All Fluorescent Nanodiamonds Are Created Equal: A Comparative Study

Abstract

Fluorescent nanodiamonds (FNDs) are vital to many emerging nanotechnological applications, from bioimaging and sensing to quantum nanophotonics. Yet, understanding and engineering the properties of fluorescent defects in nanodiamonds remain challenging. The most comprehensive study to date is presented, of the optical and physical properties of five different nanodiamond samples, in which fluorescent nitrogen‐vacancy (NV) centers are created using different fabrication techniques. The FNDs' fluorescence spectra, lifetime, and spin relaxation time (T1) are investigated via single‐particle confocal fluorescence microscopy and in ensemble measurements in solution (T1 excepted). Particle sizes and shapes are determined using scanning electron microscopy and correlated with the optical results. Statistical tests are used to explore correlations between the properties of individual particles and also analyze average results to directly compare different fabrication techniques. Spectral unmixing is used to quantify the relative NV charge‐state (NV− and NV0) contributions to the overall fluorescence. A strong variation is found and quantified in the properties of individual particles within all analyzed samples and significant differences between the different particle types. This study is an important contribution toward understanding the properties of NV centers in nanodiamonds. It motivates new approaches to the improved engineering of NV‐containing nanodiamonds for future applications.

High-throughput nitrogen-vacancy center imaging for nanodiamond photophysical characterization and pH nanosensing

“…Our technique can be easily implemented to screen different NDs samples to study the proportion of single NV/ND and the charge stability of the NV center since measuring >100 NDs takes only seconds unlike methods already described. 23,24,50,51 Since we used a statistical approach to define the photon count provided by a single NV, it is difficult to confirm that a given ND contains only one NV center based on a single observation if no charge transitions are observed. For this reason, photon-correlation experiments are more suited for determining the number of emitting NV centers per particle.…”

“…As a result, there are numerous efforts to manufacture small, bright, and high-purity NDs that differ by size, nitrogen content and surface chemistry; these ND samples display different NV center emission spectra and intensity levels due to interactions with the surface, or due to a different number of NV centers per particle. 22,23 For these reasons, the photophysical characterization of NDs is crucial to ensure successful applications in bioimaging, especially using single-molecule microscopy. Further, since NDs are increasingly implemented in quantum technologies, the characterization of NV centres in NDs is an important endeavor, as most of our knowledge on the photophysics of the NV centre originated from studies performed in bulk diamond.…”

Fluorescence and Physico-Chemical Properties of Hydrogenated Detonation Nanodiamonds

“…Fluorescence microscopy and spectroscopy experiments were conducted using a custom-built confocal fluorescence setup described in more detail elsewhere [30]. Briefly, a picosecond pulsed white light laser (WhiteLase SC400-8, Fianium/NKT Photonics, UK) operating at 532 nm, 5 MHz repetition rate, and 50 µW total beam power was used for excitation using a 532 nm laser line filter (Semrock, West Henrietta, NY, USA) and a 100× air objective with numerical aperture (NA) 0.9.…”

Brilliant blue, green, yellow, and red fluorescent diamond particles: synthesis, characterization, and multiplex imaging demonstrations

“…Lifetime values were determined from double exponential (FNDs) and single exponential (dyes) fits to the decay traces as previously reported. 23 Due to a low amount of available material, the 'fancy blue' particles were not characterized for lifetime.…”

“…This non-uniformity can arise from the starting material, processing conditions, and particle size and shape, among other factors. 23 Novel irradiation approaches have been demonstrated as a means to improve fluorescence uniformity, 34 and the RTA approach may offer a unique post processing step to facilitate higher particle fluorescence uniformity, or, at the very least, brighter particles, which are also greatly needed.…”