New Insights into the Reactivity of Detonation Nanodiamonds during the First Stages of Graphitization

The present study aims to compare the early stages of graphitization of the same DND source for two annealing atmospheres (primary vacuum, argon at atmospheric pressure) in an identical set-up. DND samples are finely characterized by a combination of complementary techniques (FTIR, Raman, XPS, HR-TEM) to highlight the induced modifications for temperature up to 1100 °C. The annealing atmosphere has a significant impact on the graphitization kinetics with a higher fraction of sp²-C formed under vacuum compared to argon for the same temperature. Whatever the annealing atmosphere, carbon hydrogen bonds are created at the DND surface during annealing according to FTIR. A “nano effect”, specific to the <10 nm size of DND, exalts the extreme surface chemistry in XPS analysis. According to HR-TEM images, the graphitization is limited to the first outer shell even for DND annealed at 1100 °C under vacuum.

Using hydrogen isotope incorporation as a tool to unravel the surfaces of hydrogen-treated nanodiamonds

We report here on a robust and easy-to-implement method for the labelling of detonation nanodiamonds (DND) with hydrogen isotopes (deuterium and tritium), using thermal annealing performed in a closed system. With this method, we have synthesized and fully characterized (FTIR, Raman, DLS, 3H/2H/1H and 13C MAS NMR) deuterium-treated and tritium-treated DND and demonstrated the usefulness of isotope incorporation in investigating the surface chemistry of such nanomaterials. For instance, surface treatment with deuterium coupled to FTIR spectroscopy allowed us to discriminate the origin of C-H terminations at the DND surface after the hydrogenation process. As a complementary, tritium appeared very useful for quantification purposes, while 1,2,3H NMR confirmed the nature of the C-1,2,3H bonds created. This isotopic study provides new insights into the characteristics of hydrogen-treated DND.

Hydroxyl radical production induced by plasma hydrogenated nanodiamonds under X-ray irradiation

For the first time, overproduction of hydroxyl radicals (HO˙) induced by plasma hydrogenated detonation nanodiamonds (H-NDs) under X-ray irradiation is reported. Using coumarin (COU) as a fluorescent probe, we reveal a significant increase of 40% of the HO˙ production in the presence of H-NDs (6-100 μg ml^-1) compared with water alone. This effect is related to the negative electron affinity of the hydrogenated nanodiamonds and illustrates the ability of H-NDs to produce reactive oxygen species probably via electron emission in water under X-ray irradiation.

Carboxylated nanodiamonds can be used as negative reference in in vitro nanogenotoxicity studies

Nanodiamonds (NDs) are promising nanomaterials for biomedical applications. However, a few studies highlighted an in vitro genotoxic activity for detonation NDs, which was not evidenced in one of our previous work quantifying γ-H2Ax after 20 and 100 nm high-pressure high-temperature ND exposures of several cell lines. To confirm these results, in the present work, we investigated the genotoxicity of the same 20 and 100 nm NDs and added intermediate-sized NDs of 50 nm. Conventional in vitro genotoxicity tests were used, i.e., the in vitro micronucleus and comet assays that are recommended by the French National Agency for Medicines and Health Products Safety for the toxicological evaluation of nanomedicines. In vitro micronucleus and in vitro comet assays (standard and hOGG1-modified) were therefore performed in two human cell lines, the bronchial epithelial 16HBE14o- cells and the colon carcinoma T84 cells. Our results did not show any genotoxic activity, whatever the test, the cell line or the size of carboxylated NDs. Even though these in vitro results should be confirmed in vivo, they reinforce the potential interest of carboxylated NDs for biomedical applications or even as a negative reference nanoparticle in nanotoxicology. Copyright © 2017 John Wiley & Sons, Ltd.

Surface-sensitive diamond photonic crystals for high-performance gas detection

Diamond slotted photonic crystal (PhC) cavities were fabricated and used for gas detection. They exhibit wavelength sensitivity reaching a 350 nm per unit change of the refractive index of the gaseous environment of the PhC. With a simple oxidized surface termination, diamond PhCs display an ultrahigh sensitivity to the surface adsorption of polar molecules. Gaseous concentrations as low as 80 parts per million (ppm) of hexanol vapor in nitrogen are probed, and a detection limit in the ppm range is inferred, demonstrating a high interest of such devices for trace sensing.

Surface Area of Carbon Nanoparticles: A Dose Metric for a More Realistic Ecotoxicological Assessment

Engineered nanoparticles such as graphenes, nanodiamonds, and carbon nanotubes correspond to different allotropes of carbon and are among the best candidates for applications in fast-growing nanotechnology. It is thus likely that they may get into the environment at each step of their life cycle: production, use, and disposal. The aquatic compartment concentrates pollutants and is expected to be especially impacted. The toxicity of a compound is conventionally evaluated using mass concentration as a quantitative measure of exposure. However, several studies have highlighted that such a metric is not the best descriptor at the nanoscale. Here we compare the inhibition of Xenopus laevis larvae growth after in vivo exposure to different carbon nanoparticles for 12 days using different dose metrics and clearly show that surface area is the most relevant descriptor of toxicity for different types of carbon allotropes.

Nanoparticle Adhesion and Mobility in Thin Layers: Nanodiamonds As a Model

Small size and enhanced properties of nanoparticles (NP) are great advantages toward device miniaturization. However, adhesion is essential for the reliability of such NP layer-based devices. In this work, we present some quick tests to investigate the adhesion behavior of the whole NP layer by mimicking several applicative environments: biological buffers and cells, corrosion, and microfabrication processes. This statistic approach evaluates both adhesion and mobility respectively through particle density and layer homogeneity. We chose nanodiamonds (ND) as reference particles because they are spherical and inert and exhibit either positive or negative zeta potential for the same diameter while surfactant-free. Several deposition methods were used to prepare a wide range of ND layers with various densities and size distribution. We found some unexpected results confirming that the deposition method has to be carefully selected according to the targeted application. A selection of the suitable method(s) to prepare ND layers which are resilient in their applicative environment can be done based on these results. However, ND adhesion still remains critical in some conditions and thus requires further improvement. Most important, this study points out that NP adhesion behavior is more complex than simple particle detachment-or not-from the surface. The particles could also reorganize themselves in clusters. We evidenced, in particular, a surprising mobility driven by air/water interfaces during evaporation of water microdroplets. Further comparison with other materials would indicate if the highlighted phenomena could be extended to any nanoparticles layer.

Boron doped diamond biotechnology: from sensors to neurointerfaces

Boron doped nanocrystalline diamond is known as a remarkable material for the fabrication of sensors, taking advantage of its biocompatibility, electrochemical properties, and stability. Sensors can be fabricated to directly probe physiological species from biofluids (e.g. blood or urine), as will be presented. In collaboration with electrophysiologists and biologists, the technology was adapted to enable structured diamond devices such as microelectrode arrays (MEAs), i.e. common electrophysiology tools, to probe neuronal activity distributed over large populations of neurons or embryonic organs. Specific MEAs can also be used to build neural prostheses or implants to compensate function losses due to lesions or degeneration of parts of the central nervous system, such as retinal implants, which exhibit real promise as biocompatible neuroprostheses for in vivo neuronal stimulations. New electrode geometries enable high performance electrodes to surpass more conventional materials for such applications.

Tritium labeling of detonation nanodiamonds

The radioactive labeling of detonation nanodiamonds was efficiently achieved using a tritium microwave plasma.

Carboxylated nanodiamonds are neither cytotoxic nor genotoxic on liver, kidney, intestine and lung human cell lines

Although nanodiamonds (NDs) appear as one of the most promising nanocarbon materials available so far for biomedical applications, their risk for human health remains unknown. Our work was aimed at defining the cytotoxicity and genotoxicity of two sets of commercial carboxylated NDs with diameters below 20 and 100 nm, on six human cell lines chosen as representative of potential target organs: HepG2 and Hep3B (liver), Caki-1 and Hek-293 (kidney), HT29 (intestine) and A549 (lung). Cytotoxicity of NDs was assessed by measuring cell impedance (xCELLigence® system) and cell survival/death by flow cytometry while genotoxicity was assessed by γ-H2Ax foci detection, which is considered the most sensitive technique for studying DNA double-strand breaks. To validate and check the sensitivity of the techniques, aminated polystyrene nanobeads were used as positive control in all assays. Cell incorporation of NDs was also studied by flow cytometry and luminescent N-V center photoluminescence (confirmed by Raman microscopy), to ensure that nanoparticles entered the cells. Overall, we show that NDs effectively entered the cells but NDs do not induce any significant cytotoxic or genotoxic effects on the six cell lines up to an exposure dose of 250 µg/mL. Taken together these results strongly support the huge potential of NDs for human nanomedicine but also their potential as negative control in nanotoxicology studies.

Surface transfer doping can mediate both colloidal stability and self-assembly of nanodiamonds

Although undoped diamond is insulating, hydrogenated bulk diamond surfaces exhibit surface conductivity under air and are electrochemically active in aqueous solutions. Due to their large surface/volume ratio, similar surface effects may exhibit a dramatic impact on the properties of nanodiamonds. Here we show that plasma-hydrogenated detonation nanodiamonds (NDs-H) display a positive zeta potential in water due to charge transfer with a redox couple involving oxygen in water. The transfer doping of NDs-H in water can be modulated by pH. Surprisingly, after acid addition, strong Coulomb coupling between NDs-H and adsorbed counterions induces the self-assembly of NDs-H into organized macro-structures reaching millimeter scale.

Nanoparticles assume electrical potential according to substrate, size, and surface termination

Electrical potential of nanoparticles under relevant environment is substantial for their applications in electronics as well as sensors and biology. Here, we use Kelvin force microscopy to characterize electrical properties of semiconducting diamond nanoparticles (DNPs) of 5-10 nm nominal size and metallic gold nanoparticles (20 and 40 nm) on Si and Au substrates under ambient conditions. The DNPs are deposited on Si and Au substrates from dispersions with well-defined zeta-potential. We show that the nanoparticle potential depends on its size and that the only reliable potential characteristic is a linear fit of this dependence within a 5-50 nm range. Systematically different potentials of hydrogenated, oxidized, and graphitized DNPs are resolved using this methodology. The differences are within 50 mV, that is much lower than on monocrystalline diamond. Furthermore, all of the nanoparticles assume their potential within -60 mV according to the Au and Si substrate, thus gaining up to 0.4 V difference. This effect is attributed to DNP charging by charge transfer and/or polarization. This is confirmed by secondary electron emission. Such effects are general with broad implications for nanoparticles applications.

Oxygen hole doping of nanodiamond

Surface-graphitized nanodiamonds (NDs) are promising hybrid nanomaterials which appear to combine core properties of diamond with surface properties of graphene-based materials. Here we demonstrate that NDs covered by graphene islands, so-called Fullerene-Like Reconstructions (FLRs), are sensitive to hole doping by molecular oxygen in water. NDs covered by FLRs (NDs-FLRs) are prepared by annealing under vacuum of detonation NDs at 750 °C. We propose that oxygen hole doping is promoted on FLRs due to a unique electronic interaction between the diamond core and the outer graphene layer. As a consequence, NDs-FLRs exhibit positive zeta potential in water, unlike NDs surrounded by several graphitic layers. Surface hole-doped NDs may be promising nanomaterials for new electronic and biomedical applications.

Electrostatic grafting of diamond nanoparticles: a versatile route to nanocrystalline diamond thin films

Nanodiamond (ND) seeding is a well-established route toward the CVD (chemical vapor deposition) synthesis of diamond ultrathin films. This method is based on the deposition onto a substrate of diamond nanoparticles which act as pre-existing sp(3) seeds. Here, we report on a straightforward method to disperse diamond nanoparticles on a substrate by taking advantage of the electrostatic interactions between the nanodiamonds and the substrate surface coated with a cationic polymer. This layer-by-layer deposition technique leads to reproducible and homogeneous large-scale nanoparticle deposits independent of the substrate's nature and shape. No specific functionalization of the nanoparticles is required, and low concentrated solutions can be used. The density of NDs on the substrate can be controlled, as shown by in situ ATR-FTIR (attenuated total reflection Fourier transform infrared) analysis and QCM (quartz crystal microbalance) measurements. Highly dense and compact ND deposits can be obtained, allowing CVD growth of nanocrystalline diamond ultrathin films (70 nm) on various substrates. The synthesis of 3D structured and patterned diamond thin films has also been demonstrated with this method.