Abstract
The fluorescent nitrogen-vacancy (NV) defect in diamond has remarkable photophysical properties, including high photostability which allows stable fluorescence emission for hours; as a result, there has been much interest in using nanodiamonds (NDs) for applications in quantum optics and biological imaging. Such applications have been limited by the heterogeneity of NDs and our limited understanding of NV photophysics in NDs, which is partially due to the lack of sensitive and high-throughput methods for photophysical analysis of NDs. Here, we report a systematic analysis of NDs using two-color wide-field epifluorescence imaging coupled to high-throughput single-particle detection of single NVs in NDs with sizes down to 5–10 nm. By using fluorescence intensity ratios, we observe directly the charge conversion of single NV center (NV− or NV0) and measure the lifetimes of different NV charge states in NDs. We also show that we can use changes in pH to control the main NV charge states in a direct and reversible fashion, a discovery that paves the way for performing pH nanosensing with a non-photobleachable probe.
Highlights
Nanodiamonds (NDs) as single-photon sources and bioimaging probes have attracted significant interest in the past two decades.[1,2,3] A major reason for this attention is that, for NDs with a diameter of 35 nm or more, the fluorescent nitrogen-vacancy (NV) centers in the ND emit bright photoluminescence without blinking or photobleaching.[4]
ND applications in bioimaging have been limited by the low brightness of sub 20 nm NDs, since a single NV center is 10-times less bright than a typical organic fluorophore used in single-molecule fluorescence detection
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
Summary
Nanodiamonds (NDs) as single-photon sources and bioimaging probes have attracted significant interest in the past two decades.[1,2,3] A major reason for this attention is that, for NDs with a diameter of 35 nm or more, the fluorescent nitrogen-vacancy (NV) centers in the ND emit bright photoluminescence without blinking or photobleaching.[4]. A facile way for nanosensing is to detect changes in the charge of the NV center as charge transitions (NV− and NV0) are triggered by chemical events or variations of electrical. Despite their promise, ND applications in bioimaging have been limited by the low brightness of sub 20 nm NDs, since a single NV center is 10-times less bright than a typical organic fluorophore used in single-molecule fluorescence detection. Since NDs are increasingly implemented in quantum technologies, the characterization of NV centres
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