Nanodiamonds, or diamond nanoparticles, are diamonds with a size below 100 nanometers. [2] They can be produced by impact events such as an explosion or meteoritic impacts. Because of their inexpensive, large-scale synthesis, potential for surface functionalization, and high biocompatibility, nanodiamonds are widely investigated as a potential material in biological and electronic applications and quantum engineering. [3] [4]
In 1963, Soviet scientists at the All-Union Research Institute of Technical Physics noticed that nanodiamonds were created by nuclear explosions that used carbon-based trigger explosives. [3] [5]
There are three main aspects in the structure of diamond nanoparticles to be considered: the overall shape, the core, and the surface. Through multiple diffraction experiments, it has been determined that the overall shape of diamond nanoparticles is either spherical or elliptical. At the core of diamond nanoparticles lies a diamond cage, which is composed mainly of carbons. [6] While the core closely resemble the structure of a diamond, the surface of diamond nanoparticles actually resemble the structure of graphite. A recent study shows that the surface consists mainly of carbons, with high amounts of phenols, pyrones, and sulfonic acid, as well as carboxylic acid groups, hydroxyl groups, and epoxide groups, though in lesser amounts. [7] Occasionally, defects such as nitrogen-vacancy centers can be found in the structure of diamond nanoparticles. 15N NMR research confirms presence of such defects. [8] A recent study shows that the frequency of nitrogen-vacancy centers decreases with the size of diamond nanoparticles. [9]
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Detonation synthesis of non or weakly fluorescent nanodiamonds has become the industry standard in the commercial production of nanodiamonds: the most commonly utilized explosives being mixtures of trinitrotoluene and hexogen or octogen. Detonation is often performed in a sealed, oxygen-free, stainless steel chamber and yields a mixture of nanodiamonds averaging 5 nm and other graphitic compounds. [10] In detonation synthesis, nanodiamonds form under pressures greater than 15 GPa and temperatures greater than 3000K in the absence of oxygen to prevent the oxidation of diamond nanoparticles. [10] The rapid cooling of the system increases nanodiamond yields as diamond remains the most stable phase under such conditions. Detonation synthesis utilizes gas-based and liquid-based coolants such as argon and water, water-based foams, and ice. [10] Because detonation synthesis results in a mix of nanodiamond particles and other graphitic carbon forms, extensive cleaning methods must be employed to rid the mixture of impurities. In general, gaseous ozone treatment or solution-phase nitric acid oxidation is utilized to remove sp2 carbons and metal impurities. [10]
Other than explosions, methods of production include hydrothermal synthesis, ion bombardment, laser heating, microwave plasma chemical vapor deposition techniques, ultrasound synthesis, [11] and electrochemical synthesis. [12] In addition, high-yield synthesis of fluorescent nanodiamonds can be achieved by grinding electron-irradiated cubic crystalline diamond obtained from nitrogen-containing or nitrogen-free carbon precursors. [13] Another method is the decomposition of graphitic C3N4 under high pressure and high temperature which yields large quantities of high purity diamond nanoparticles. [14] Nanodiamonds are also formed by dissociation of ethanol vapour. [15] and via ultrafast laser filamentation in ethanol. [16]
The N-V center defect consists of a nitrogen atom in place of a carbon atom next to a vacancy (empty space instead of an atom) within the diamond’s lattice structure. [17] Recent advances (up to 2019) in the field of nanodiamonds in quantum sensing applications using NVs have been summarized in the following review. [18]
Applying a microwave pulse to such a defect switches the direction of its electron spin. Applying a series of such pulses (Walsh decoupling sequences) causes them to act as filters. Varying the number of pulses in a series switched the spin direction a different number of times. [17] They efficiently extract spectral coefficients while suppressing decoherence, thus improving sensitivity. [19] Signal-processing techniques were used to reconstruct the entire magnetic field. [17]
The prototype used a 3 mm-diameter square diamond, but the technique can scale down to tens of nanometers. [17]
Nanodiamonds share the hardness and chemical stability of visible-scale diamonds, making them candidates for applications such as polishes and engine oil additives for improved lubrication. [3]
Diamond nanoparticles have the potential to be used in myriad biological applications and due to their unique properties such as inertness and hardness, nanodiamonds may prove to be a better alternative to the traditional nanomaterials currently utilized to carry drugs, coat implantable materials, and synthesize biosensors and biomedical robots. [20] The low cytotoxicity of diamond nanoparticles affirms their utilization as biologically compatible materials. [20]
In vitro studies exploring the dispersion of diamond nanoparticles in cells have revealed that most diamond nanoparticles exhibit fluorescence and are uniformly distributed. [21] Fluorescent nanodiamond particles can be mass produced through irradiating diamond nanocrystallites with helium ions. [22] Fluorescent nanodiamond is photostable, chemically inert, and has extended fluorescent lifetime, making it a great candidate for many biological applications. [23] Studies have shown that small photoluminescent diamond nanoparticles that remain free in the cytosol are excellent contenders for the transport of biomolecules. [24]
Nanodiamonds containing nitrogen-vacancy defects have been used as an ultrasensitive label for in vitro diagnostics, using a microwave field to modulate emission intensity and frequency-domain analysis to separate the signal from background autofluorescence. [25] Combined with recombinase polymerase amplification, nanodiamonds enable single-copy detection of HIV-1 RNA on a low-cost lateral flow test format.
Diamond nanoparticles of ~5 nm in size offer a large accessible surface and tailorable surface chemistry. They have unique optical, mechanical and thermal properties and are non-toxic. The potential of nanodiamond in drug delivery has been demonstrated, fundamental mechanisms, thermodynamics and kinetics of drug adsorption on nanodiamond are poorly understood. Important factors include purity, surface chemistry, dispersion quality, temperature and ionic composition.
Nanodiamonds (with attached molecules) are able to penetrate the blood–brain barrier that isolates the brain from most insults. In 2013 doxorubicin molecules (a popular cancer-killing drug) were bonded to nanodiamond surfaces, creating the drug ND-DOX. Tests showed that tumors were unable to eject the compound, increasing the drug's ability to impact the tumor and reducing side-effects. [3]
Larger nanodiamonds, due to their "high uptake efficiency", have the potential to serve as cellular labels. [24] Studies have concluded that diamond nanoparticles are similar to carbon nanotubes and upon being treated with surfactants, the stability and biocompatibility of both carbon nanotubes and the nanodiamonds in solution greatly increase. [21] In addition, the ability to surface functionalize nanodiamonds of small diameters provides various possibilities for diamond nanoparticles to be utilized as biolabels with potentially low cytotoxicity. [21]
Decreasing particle size and functionalizing their surfaces [21] may allow such surface-modified diamond nanoparticles to deliver proteins, which can then provide an alternative to traditional catalysts. [26]
Nanodiamonds are well-absorbed by human skin. They also absorb more of the ingredients in skin care products than skin itself. Thus they cause more of the ingredients to penetrate the deeper layers of the skin. Nanodiamonds also form strong bonds with water, helping to hydrate the skin. [3]
During jaw and tooth repair operations, doctors normally use invasive surgery to stick a sponge containing bone-growth-stimulating proteins near the affected area. However, nanodiamonds bind to both bone morphogenetic protein and fibroblast growth factor, both of which encourage bone and cartilage to rebuild and can be delivered orally. [3] Nanodiamond has also been successfully incorporated into gutta percha in root canal therapy. [27]
Defected nanodiamonds can measure the orientation of electron spins in external fields and thus measure their strength. They can electrostatically absorb ferritin proteins on the diamond surface where their numbers can be measured directly as well as the number of iron atoms (as many as 4,500) that make up the protein. [3]
Naturally occurring defects in nanodiamonds called nitrogen-vacancy (N-V) centers, have been used to measure changes over time in weak magnetic fields, much like a compass does with Earth's magnetic field. The sensors can be used at room temperature, and since they consist entirely of carbon, they could be injected into living cells without causing them any harm, Paola Cappellaro says. [17] Moreover, nanodiamond can be exploited as sensor for some specific analytes. Boron-doped diamond (BDD) produced by energy-assisted (plasma or hot filament, HF) Chemical Vapor Deposition (CVD) processes is a good candidatein Dopamine detection, however it is not selective towards some interferents. This issue, can be overcome via further post-synthesis treatments for BDD surface modifications including anodization, hydrogen plasma, etching into porous forms, carbon-based nanomaterials, polymer films and nanoparticles. Recent studies, [28] propose a new approach for the realization of Titanium doped diamond-based electrodes with a native selectivity towards dopamine, through substrate pre-treatments (lapping, electropolishing and chemical etching) instead of post-process treatments. Moreover, Nanodiamond has been proven to modify some electronic properties of polymer-based matrix. [29] Those modifications, which can be summarised as an increase in the ionic conductivity of the system, thus of a decrease in the impedance, are likely due to the presence of functional groups on the nanodiamond particle surface. Those groups can interact with polymer chains, thus facilitating ionic exchanges.
Recent studies have shown that nanoscale diamonds can be bent to a local maximum tensile elastic strain in excess of 9%, [30] with the corresponding maximum tensile stress reached ~100 gigapascals, making them ideal for high-performance nanomechanical sensor and NEMS applications.
Nanodiamonds offer an alternative to photonic metamaterials for optical computing. The same single-defect nanodiamonds that can be used to sense magnetic fields can also use combinations of green and infrared light to enable/disrupt light transmission, allowing the construction of transistors and other logic elements. [3]
Nanodiamonds with NV centers may serve as a solid-state alternative to trapped ions for room-temperature quantum computing. [3]
Fluorescent nanodiamonds offer a stable reference for the quality control purposes in fluorescence and multiharmonic imaging systems. [31]
A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). They are one of the allotropes of carbon. Two broad classes of carbon nanotubes are recognized:
Nanomaterials describe, in principle, chemical substances or materials of which a single unit is sized between 1 and 100 nm.
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At the lowest range, metal particles smaller than 1 nm are usually called atom clusters instead.
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. It is a crystal that is transparent to opaque and which is generally isotropic. Diamond is the hardest naturally occurring material known. Yet, due to important structural brittleness, bulk diamond's toughness is only fair to good. The precise tensile strength of bulk diamond is little known; however, compressive strength up to 60 GPa has been observed, and it could be as high as 90–100 GPa in the form of micro/nanometer-sized wires or needles, with a corresponding maximum tensile elastic strain in excess of 9%. The anisotropy of diamond hardness is carefully considered during diamond cutting. Diamond has a high refractive index (2.417) and moderate dispersion (0.044) properties that give cut diamonds their brilliance. Scientists classify diamonds into four main types according to the nature of crystallographic defects present. Trace impurities substitutionally replacing carbon atoms in a diamond's crystal structure, and in some cases structural defects, are responsible for the wide range of colors seen in diamond. Most diamonds are electrical insulators and extremely efficient thermal conductors. Unlike many other minerals, the specific gravity of diamond crystals (3.52) has rather small variation from diamond to diamond.
Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a non-stoichiometric oxide.
Detonation nanodiamond (DND), also known as ultradispersed diamond (UDD), is diamond that originates from a detonation. When an oxygen-deficient explosive mixture of TNT/RDX is detonated in a closed chamber, diamond particles with a diameter of c. 5 nm are formed at the front of the detonation wave in the span of several microseconds.
Nanochemistry is an emerging sub-discipline of the chemical and material sciences that deals with the development of new methods for creating nanoscale materials. The term "nanochemistry" was first used by Ozin in 1992 as 'the uses of chemical synthesis to reproducibly afford nanomaterials from the atom "up", contrary to the nanoengineering and nanophysics approach that operates from the bulk "down"'. Nanochemistry focuses on solid-state chemistry that emphasizes synthesis of building blocks that are dependent on size, surface, shape, and defect properties, rather than the actual production of matter. Atomic and molecular properties mainly deal with the degrees of freedom of atoms in the periodic table. However, nanochemistry introduced other degrees of freedom that controls material's behaviors by transformation into solutions. Nanoscale objects exhibit novel material properties, largely as a consequence of their finite small size. Several chemical modifications on nanometer-scaled structures approve size dependent effects.
As the world's energy demand continues to grow, the development of more efficient and sustainable technologies for generating and storing energy is becoming increasingly important. According to Dr. Wade Adams from Rice University, energy will be the most pressing problem facing humanity in the next 50 years and nanotechnology has potential to solve this issue. Nanotechnology, a relatively new field of science and engineering, has shown promise to have a significant impact on the energy industry. Nanotechnology is defined as any technology that contains particles with one dimension under 100 nanometers in length. For scale, a single virus particle is about 100 nanometers wide.
The nitrogen-vacancy center is one of numerous photoluminescent point defects in diamond. Its most explored and useful properties include its spin-dependent photoluminescence, and its relatively long (millisecond) spin coherence at room temperature. The NV center energy levels are modified by magnetic fields, electric fields, temperature, and strain, which allow it to serve as a sensor of a variety of physical phenomena. Its atomic size and spin properties can form the basis for useful quantum sensors. It has also been explored for applications in quantum computing, quantum simulation, and spintronics.
Magnetic nanoparticles (MNPs) are a class of nanoparticle that can be manipulated using magnetic fields. Such particles commonly consist of two components, a magnetic material, often iron, nickel and cobalt, and a chemical component that has functionality. While nanoparticles are smaller than 1 micrometer in diameter, the larger microbeads are 0.5–500 micrometer in diameter. Magnetic nanoparticle clusters that are composed of a number of individual magnetic nanoparticles are known as magnetic nanobeads with a diameter of 50–200 nanometers. Magnetic nanoparticle clusters are a basis for their further magnetic assembly into magnetic nanochains. The magnetic nanoparticles have been the focus of much research recently because they possess attractive properties which could see potential use in catalysis including nanomaterial-based catalysts, biomedicine and tissue specific targeting, magnetically tunable colloidal photonic crystals, microfluidics, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation, nanofluids, optical filters, defect sensor, magnetic cooling and cation sensors.
An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.
A localized surface plasmon (LSP) is the result of the confinement of a surface plasmon in a nanoparticle of size comparable to or smaller than the wavelength of light used to excite the plasmon. When a small spherical metallic nanoparticle is irradiated by light, the oscillating electric field causes the conduction electrons to oscillate coherently. When the electron cloud is displaced relative to its original position, a restoring force arises from Coulombic attraction between electrons and nuclei. This force causes the electron cloud to oscillate. The oscillation frequency is determined by the density of electrons, the effective electron mass, and the size and shape of the charge distribution. The LSP has two important effects: electric fields near the particle's surface are greatly enhanced and the particle's optical absorption has a maximum at the plasmon resonant frequency. Surface plasmon resonance can also be tuned based on the shape of the nanoparticle. The plasmon frequency can be related to the metal dielectric constant. The enhancement falls off quickly with distance from the surface and, for noble metal nanoparticles, the resonance occurs at visible wavelengths. Localized surface plasmon resonance creates brilliant colors in metal colloidal solutions.
Nanoparticles are classified as having at least one of its dimensions in the range of 1-100 nanometers (nm). The small size of nanoparticles allows them to have unique characteristics which may not be possible on the macro-scale. Self-assembly is the spontaneous organization of smaller subunits to form larger, well-organized patterns. For nanoparticles, this spontaneous assembly is a consequence of interactions between the particles aimed at achieving a thermodynamic equilibrium and reducing the system’s free energy. The thermodynamics definition of self-assembly was introduced by Professor Nicholas A. Kotov. He describes self-assembly as a process where components of the system acquire non-random spatial distribution with respect to each other and the boundaries of the system. This definition allows one to account for mass and energy fluxes taking place in the self-assembly processes.
A carbon nanothread is a sp3-bonded, one-dimensional carbon crystalline nanomaterial. The tetrahedral sp3-bonding of its carbon is similar to that of diamond. Nanothreads are only a few atoms across, more than 300,000 times thinner than a human hair. They consist of a stiff, strong carbon core surrounded by hydrogen atoms. Carbon nanotubes, although also one-dimensional nanomaterials, in contrast have sp2-carbon bonding as is found in graphite. The smallest carbon nanothread has a diameter of only 0.2 nanometers, much smaller than the diameter of a single-wall carbon nanotube.
Nanoclusters are atomically precise, crystalline materials most often existing on the 0-2 nanometer scale. They are often considered kinetically stable intermediates that form during the synthesis of comparatively larger materials such as semiconductor and metallic nanocrystals. The majority of research conducted to study nanoclusters has focused on characterizing their crystal structures and understanding their role in the nucleation and growth mechanisms of larger materials.
Graphene quantum dots (GQDs) are graphene nanoparticles with a size less than 100 nm. Due to their exceptional properties such as low toxicity, stable photoluminescence, chemical stability and pronounced quantum confinement effect, GQDs are considered as a novel material for biological, opto-electronics, energy and environmental applications.
Carbon quantum dots also commonly called carbon nano dots or simply carbon dots are carbon nanoparticles which are less than 10 nm in size and have some form of surface passivation.
Techniques have been developed to produce carbon nanotubes (CNTs) in sizable quantities, including arc discharge, laser ablation, high-pressure carbon monoxide disproportionation, and chemical vapor deposition (CVD). Most of these processes take place in a vacuum or with process gases. CVD growth of CNTs can occur in a vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth are making CNTs more commercially viable.
Although diamonds on Earth are rare, extraterrestrial diamonds are very common. Diamonds so small that they contain only about 2000 carbon atoms are abundant in meteorites, and some of them formed in stars before the Solar System existed. High pressure experiments suggest large amounts of diamonds are formed from methane on the ice giant planets Uranus and Neptune, while some planets in other planetary systems may be almost pure diamond. Diamonds are also found in stars and may have been the first mineral ever to have formed.
Silicon quantum dots are metal-free biologically compatible quantum dots with photoluminescence emission maxima that are tunable through the visible to near-infrared spectral regions. These quantum dots have unique properties arising from their indirect band gap, including long-lived luminescent excited-states and large Stokes shifts. A variety of disproportionation, pyrolysis, and solution protocols have been used to prepare silicon quantum dots, however it is important to note that some solution-based protocols for preparing luminescent silicon quantum dots actually yield carbon quantum dots instead of the reported silicon. The unique properties of silicon quantum dots lend themselves to an array of potential applications: biological imaging, luminescent solar concentrators, light emitting diodes, sensors, and lithium-ion battery anodes.
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