Nanodiamonds, or diamond nanoparticles, are

diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...

s with a size below 100

nanometers 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...

. 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 Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...

, nanodiamonds are widely investigated as a potential material in biological and electronic applications and quantum engineering.

History

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.

Structure and composition

There are three main aspects in the structure of diamond

nanoparticle A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 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 10 ...

s 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. 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. Occasionally, defects such as nitrogen-vacancy centers can be found in the structure of diamond nanoparticles. 15N NMR research confirms presence of such defects. A recent study shows that the frequency of nitrogen-vacancy centers decreases with the size of diamond nanoparticles.

Production methods

Other than explosions, methods of synthesis include hydrothermal synthesis, ion bombardment, laser bombardment, microwave plasma chemical vapor deposition techniques, ultrasound synthesis, and electrochemical synthesis. In addition, the decomposition of graphitic C₃N₄ under high pressure and high temperature yields large quantities of high purity diamond nanoparticles. However, detonation synthesis of 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. 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. 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. 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. Nanodiamonds are also formed by dissociation of ethanol vapour. and via ultrafast laser filamentation in ethanol.

Potential applications

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. Recent advances (up to 2019) in the field of nanodiamonds in quantum sensing applications using NVs have been summarized in the following review. Applying a

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

pulse to such a defect switches the direction of its

electron spin In atomic physics, the electron magnetic moment, or more specifically the electron magnetic dipole moment, is the magnetic moment of an electron resulting from its intrinsic properties of spin and electric charge. The value of the electron magnet ...

. 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. They efficiently extract spectral coefficients while suppressing decoherence, thus improving sensitivity. Signal-processing techniques were used to reconstruct the entire magnetic field. The prototype used a 3 mm-diameter square diamond, but the technique can scale down to tens of nanometers.

Micro-abrasive

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.

Medical

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. The low cytotoxicity of diamond nanoparticles affirms their utilization as biologically compatible materials. In vitro studies exploring the dispersion of diamond nanoparticles in cells have revealed that most diamond nanoparticles exhibit fluorescence and are uniformly distributed. Fluorescent nanodiamond particles can be mass produced through irradiating diamond nanocrystallites with helium ions. Fluorescent nanodiamond is photostable, chemically inert, and has extended fluorescent lifetime, making it a great candidate for many biological applications. Studies have shown that small photoluminescent diamond nanoparticles that remain free in the cytosol are excellent contenders for the transport of biomolecules.

In-vitro diagnostics

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. Combined with

recombinase polymerase amplification Recombinase polymerase amplification (RPA) is a single tube, isothermal alternative to the polymerase chain reaction (PCR). By adding a reverse transcriptase enzyme to an RPA reaction it can detect RNA as well as DNA, without the need for a separa ...

, nanodiamonds enable single-copy detection of HIV-1 RNA on a low-cost

lateral flow test A lateral flow test (LFT), is an assay also known as a lateral flow device (LFD), lateral flow immunochromatographic assay, or rapid test. It is a simple device intended to detect the presence of a target substance in a liquid sample without the ...

format.

Drug delivery

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 Drug delivery refers to approaches, formulations, manufacturing techniques, storage systems, and technologies involved in transporting a pharmaceutical compound to its target site to achieve a desired therapeutic effect. Principles related to dr ...

has been demonstrated, fundamental mechanisms,

thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of th ...

and kinetics of drug adsorption on nanodiamond are poorly understood. Important factors include purity,

surface chemistry Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid– gas interfaces, solid–vacuum interfaces, and liquid– gas interfaces. It includes the fi ...

, 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 Doxorubicin, sold under the brand name Adriamycin among others, is a chemotherapy medication used to treat cancer. This includes breast cancer, bladder cancer, Kaposi's sarcoma, lymphoma, and acute lymphocytic leukemia. It is often used toge ...

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. Larger nanodiamonds, due to their "high uptake efficiency", have the potential to serve as cellular labels. 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. 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.

Catalysis

Decreasing particle size and functionalizing their surfaces may allow such surface-modified diamond nanoparticles to deliver proteins, which can then provide an alternative to traditional catalysts.

Skin care

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.

Surgery

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 Fibroblast growth factors (FGF) are a family of cell signalling proteins produced by macrophages; they are involved in a wide variety of processes, most notably as crucial elements for normal development in animal cells. Any irregularities in their ...

, both of which encourage bone and cartilage to rebuild and can be delivered orally. Nanodiamond has also been successfully incorporated into gutta percha in root canal therapy.

Blood testing

Defected nanodiamonds can measure the orientation of electron spins in external fields and thus measure their strength. They can electrostatically absorb

ferritin Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including archaea, bacteria, algae, higher plants, and animals. It is the primary ' ...

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.

Electronics and sensors

Sensor

Naturally occurring defects in nanodiamonds called nitrogen-vacancy (N-V) centers, have been used to measure changes over time in weak

magnetic fields A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

, 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.

Nanomechanical sensor and nanoelectromechanical system (NEMS)

Recent studies have shown that nanoscale diamonds can be bent to a local maximum tensile elastic strain in excess of 9%, with the corresponding maximum tensile stress reached ~100 gigapascals, making them ideal for high-performance nanomechanical sensor and NEMS applications.

Optical computing

Nanodiamonds offer an alternative to

photonic metamaterials A photonic metamaterial (PM), also known as an optical metamaterial, is a type of electromagnetic metamaterial, that interacts with light, covering terahertz ( THz), infrared (IR) or visible wavelengths. The materials employ a periodic, cellul ...

for

optical computing Optical computing or photonic computing uses light waves produced by lasers or incoherent sources for data processing, data storage or data communication for computing. For decades, photons have shown promise to enable a higher bandwidth than the ...

. The same single-defect nanodiamonds that can be used to sense magnetic fields can also use combinations of green and

infrared light Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

to enable/disrupt light transmission, allowing the construction of

transistors upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

and other logic elements.

Quantum computing

Nanodiamonds with NV centers may serve as a solid-state alternative to trapped ions for room-temperature quantum computing.

Imaging

Fluorescent nanodiamonds offer a stable reference for the quality control purposes in fluorescence and multiharmonic imaging systems.

Prizes and awards

* 2012 Ig Nobel Peace Prize: The SKN Company, for converting old Russian ammunition into new diamonds * In 2015

Amanda Barnard Amanda Susan Barnard (born 31 December 1971) is an Australian theoretical physicist working in predicting the real world behavior of nanoparticles using analytical models and supercomputer simulations and applied machine learning. Barnard is a ...

, Science Leader of Australia's Office of the Chief Executive (OCE), The

Commonwealth Scientific and Industrial Research Organisation The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...

(CSIRO), received the Theory Prize at the

Foresight Institute The Foresight Institute (Foresight) is a San Francisco-based research non-profit that promotes the development of nanotechnology and other emerging technologies, such as safe AGI, biotech and longevity. Foresight runs four cross-disciplinary pr ...

s' Feynman Awards for nanotechnology. Using theoretical and computational methods, Amanda Barnard increased understanding of the structure and stability of carbon nanostructures and the role that shape plays in establishing properties and interactions under different conditions. The Prize announced focused on her work on diamond nanoparticles (nanodiamonds).

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