Early dynamics of the emission of solvated electrons from nanodiamonds in water.

Solvated electrons are among the most reductive species in an aqueous environment. Diamond materials have been proposed as a promising source of solvated electrons, but the underlying emission process in water remains elusive so far. Here, we show spectroscopic evidence for the emission of solvated electrons from detonation nanodiamonds upon excitation with both deep ultraviolet (225 nm) and visible (400 nm) light using ultrafast transient absorption. The crucial role of surface termination in the emission process is evidenced by comparing hydrogenated, hydroxylated and carboxylated nanodiamonds. In particular, a transient response that we attribute to solvated electrons is observed on hydrogenated nanodiamonds upon visible light excitation, while it shows a sub-ps recombination due to trap states when excited with deep ultraviolet light. The essential role of surface reconstructions on the nanodiamonds in these processes is proposed based on density functional theory calculations. These results open new perspectives for solar-driven emission of solvated electrons in an aqueous phase using nanodiamonds.

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.

Delivery of siRNA to Ewing Sarcoma Tumor Xenografted on Mice, Using Hydrogenated Detonation Nanodiamonds: Treatment Efficacy and Tissue Distribution.

Nanodiamonds of detonation origin are promising delivery agents of anti-cancer therapeutic compounds in a whole organism like mouse, owing to their versatile surface chemistry and ultra-small 5 nm average primary size compatible with natural elimination routes. However, to date, little is known about tissue distribution, elimination pathways and efficacy of nanodiamonds-based therapy in mice. In this report, we studied the capacity of cationic hydrogenated detonation nanodiamonds to carry active small interfering RNA (siRNA) in a mice model of Ewing sarcoma, a bone cancer of young adults due in the vast majority to the EWS-FLI1 junction oncogene. Replacing hydrogen gas by its radioactive analog tritium gas led to the formation of labeled nanodiamonds and allowed us to investigate their distribution throughout mouse organs and their excretion in urine and feces. We also demonstrated that siRNA directed against EWS-FLI1 inhibited this oncogene expression in tumor xenografted on mice. This work is a significant step to establish cationic hydrogenated detonation nanodiamond as an effective agent for in vivo delivery of active siRNA.

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.

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.

Impairing the radioresistance of cancer cells by hydrogenated nanodiamonds.

Hydrogenated nanodiamonds (H-NDs) exhibit a negative electron affinity that confers a high reactivity with oxygen species and a positive charge in aqueous solutions. It allows electron emission from H-NDs following irradiation by photons and in consequence may enhance the effects of radiation on cancer cells. By using three human radioresistant cancer cell lines, we showed a potentialization of cytotoxicity after a co-exposure to H-NDs and irradiation; an event occurring through the induction of DNA damage and reactive oxygen species. This occurred together with a decrease in cell impedance, the activation of G1/S, an unlocking of G2 cell cycle check-points and early low cell death rate. At later stage of exposure, persistent increases in heterochromatinization, large γ-H2AX foci and ß-galactosidase activity were detected providing evidence of cells' entrance into senescence. Similar potentialization was observed with neocarzinostatin (NCS), a radiomimetic drug. This original finding underlines a wide clinical potential of H-NDs to intensify radiation effects on radio-resistant cancer cells.

Plasma hydrogenated cationic detonation nanodiamonds efficiently deliver to human cells in culture functional siRNA targeting the Ewing sarcoma junction oncogene.

The expression of a defective gene can lead to major cell dysfunctions among which cell proliferation and tumor formation. One promising therapeutic strategy consists in silencing the defective gene using small interfering RNA (siRNA). In previous publications we showed that diamond nanocrystals (ND) of primary size 35 nm, rendered cationic by polyethyleneimine-coating, can efficiently deliver siRNA into cell, which further block the expression of EWS/FLI-1 oncogene in a Ewing sarcoma disease model. However, a therapeutic application of such nanodiamonds requires their elimination by the organism, particularly in urine, which is impossible for 35 nm particles. Here, we report that hydrogenated cationic nanodiamonds of primary size 7 nm (ND-H) have also a high affinity for siRNA and are capable of delivering them in cells. With siRNA/ND-H complexes, we measured a high inhibition efficacy of EWS/FLI-1 gene expression in Ewing sarcoma cell line. Electron microscopy investigations showed ND-H in endocytosis compartments, and especially in macropinosomes from which they can escape before siRNA degradation occurred. In addition, the association of EWS/FLI-1 silencing by the siRNA/ND-H complex with a vincristine treatment yielded a potentiation of the toxic effect of this chemotherapeutic drug. Therefore ND-H appears as a promising delivery agent in anti-tumoral gene therapy.

Tritium labeling of detonation nanodiamonds.

For the first time, the radioactive labeling of detonation nanodiamonds was efficiently achieved using a tritium microwave plasma. According to our measurements, the total radioactivity reaches 9120 ± 120 µCi mg(-1), with 93% of (3)H atoms tightly bonded to the surface and up to 7% embedded into the diamond core. Such (3)H doping will ensure highly stable radiolabeled nanodiamonds, on which surface functionalization is still allowed. This breakthrough opens the way to biodistribution and pharmacokinetics studies of nanodiamonds, while this approach can be scalable to easily treat bulk quantities of nanodiamonds at low cost.

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.

Surface chemical modifications and surface reactivity of nanodiamonds hydrogenated by CVD plasma.

The present study focuses on the interaction of hydrogen microwave CVD plasma with nanodiamonds (NDs). Hydrogen treated NDs (H-NDs) were characterized using electron spectroscopies (XPS, AES) without air exposure. A surface temperature higher than 700 °C is needed to remove the oxygen present on raw NDs. The kinetics of oxygen removal were investigated. Moreover, UHV annealings of H-NDs after ageing in ambient air clearly underline that 75% of the oxygen is related to physisorbed species. Finally, H-NDs were efficiently grafted using photochemical reaction with alkenes and a spontaneous coupling of aryldiazonium salts. These results confirm similar electronic surface properties between bulk and nano diamond materials.

Photoluminescent diamond nanoparticles for cell labeling: study of the uptake mechanism in mammalian cells.

Diamond nanoparticles (nanodiamonds) have been recently proposed as new labels for cellular imaging. For small nanodiamonds (size <40 nm), resonant laser scattering and Raman scattering cross sections are too small to allow single nanoparticle observation. Nanodiamonds can, however, be rendered photoluminescent with a perfect photostability at room temperature. Such a remarkable property allows easier single-particle tracking over long time scales. In this work, we use photoluminescent nanodiamonds of size <50 nm for intracellular labeling and investigate the mechanism of their uptake by living cells. By blocking selectively different uptake processes, we show that nanodiamonds enter cells mainly by endocytosis, and converging data indicate that it is clathrin-mediated. We also examine nanodiamond intracellular localization in endocytic vesicles using immunofluorescence and transmission electron microscopy. We find a high degree of colocalization between vesicles and the biggest nanoparticles or aggregates, while the smallest particles appear free in the cytosol. Our results pave the way for the use of photoluminescent nanodiamonds in targeted intracellular labeling or biomolecule delivery.

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.