Positive zeta potential of nanodiamonds

In this paper, the origin of positive zeta potential exhibited by nanodiamond particles is explained. Positive zeta potentials in nano-structured carbons can be explained by the presence of graphitic planes at the surface, which leave oxygen-free Lewis sites and so promotes the suppression of acidic functional groups. Electron Microscopy and Raman Spectroscopy have been used to show that positive zeta potential of nanodiamond is only exhibited in the presence of sp2 carbon at the surface

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

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

Nanoscale detection and real-time monitoring of free radicals in a single living cell under the stimulation of targeting moieties using a nanodiamond quantum sensor

Intracellular radicals play important roles in cell signaling and regulation of growth factors, cytokines, transcription, apoptosis, and immunomodulation, among others. To gain a more comprehensive understanding of their biological functions in a spatio-temporal perspective, there is a great need for nanoscale sensitive tools that allow real-timeiin detection of these reactive species. Currently, intracellular radical probes are based on chemical reactions that could significantly alter radical levels during detection. Due to the excellent biocompatibility and favorable photophysical properties of nitrogen-vacancy (NV‒) centers in fluorescent nanodiamonds (fNDs), the fNDs can serve as a powerful and chemically inert nanotool for intracellular radical detection. In this study, a positively charged nanogel (NG) coating was prepared to prevent the precipitation of fNDs and promote cellular internalization. After internalization of nanodiamond-nanogels (fND-NGs), different stimulators, namely somatostatin (SST), triphenylphosphonium (TPP), and trans-activator of transcription (TAT) peptide, which are widely used cell- or organelle- targeting ligands in medicine, drug delivery, and diagnostics, were applied to stimulate the cells. In parallel, the intracellular radical changes under stimulation of SST, TPP, and TAT ligands were monitored by fND-NGs in a home-built ODMR microscope. Our method allows for detecting intracellular radicals in-situ and monitoring their real-time changes during incubation with the targeting ligands in a single living cell. We believe that our method will provide insights into the generation of radical stress in cells, which could improve our fundamental understanding of the pharmacology and signaling pathways of widely used cell- and organelle-targeting ligands associated with free radicals

Unraveling Eumelanin Radical Formation by Nanodiamond Optical Relaxometry in a Living Cell

Defect centers in nanodiamond allow the detection of tiny magnetic fields in their direct surrounding, which makes them an emerging tool for nanoscale sensing applications. The abundant pigment eumelanin plays a major role in biology and material science. We present the first time tracking of the comproportionation reaction in eumelanin by detecting and quantifying semiquinone radicals via the nitrogen-vacancy colour centre as single atom detector. A thin layer of eumelanin is polymerized on the surface of NDs and depending on the environmental conditions, such as pH, near infrared and ultraviolet light irradiation, the radicals undergo maintenance, formation, or disappearance in-situ. By combining experiments and theoretical simulations, we were able to quantify the local number and kinetics of free radicals in the eumelanin layer. Next, the nanodiamond sensor was transported into cells in endosomal vesicles and the number of radicals within the eumelanin layer was also determined. The new quantum sensor could provide valuable insights into the chemistry of eumelanin, which could shine light on eumelanin and melanin-related diseases