Nanodiamonds are diamond particles measuring less than 100 nanometers. They are composed of a diamond core with the same sp3 carbon lattice structure as natural diamonds, and an outer surface of sp2 carbon atoms. This small scale imparts unique physical, optical, and chemical properties that distinguish them from larger diamonds. Their high surface area, chemical stability, and hardness make them a subject of extensive research.
Creation of Nanodiamonds
The most common method for producing nanodiamonds is detonation synthesis. This process involves exploding carbon-rich materials, such as a mixture of TNT and RDX, inside a sealed, oxygen-free chamber. The blast’s immense pressure and high temperatures mimic the natural conditions for diamond formation deep within the Earth. This environment forces carbon atoms from the explosives to rapidly arrange into a diamond’s crystalline structure, resulting in particles 4 to 6 nanometers in size.
The resulting mixture, known as detonation soot, contains nanodiamonds along with other carbon forms and metal impurities. This soot undergoes a rigorous purification process, often using strong acids, to remove non-diamond carbon and other contaminants. The nanodiamonds are then isolated for further processing. This method is favored for its efficiency and ability to produce large quantities of nanodiamonds inexpensively.
While detonation is the primary industrial method, other techniques exist. High-Pressure/High-Temperature (HPHT) synthesis, also used for larger synthetic diamonds, can be adapted to make nanodiamonds by subjecting graphite to extreme conditions. Another method is chemical vapor deposition (CVD), where hydrocarbon gases are broken down in a vacuum, allowing carbon atoms to deposit onto a substrate as a thin diamond film. These alternatives offer greater control over size and purity but are more complex and costly than detonation.
Applications in Medicine and Biology
The properties of nanodiamonds make them suitable for biomedical applications, largely due to their biocompatibility. Their non-toxic and chemically inert surfaces allow them to exist within biological systems, such as living cells, without causing adverse reactions. Researchers have found that nanodiamonds around 5 nm in size can be introduced into cells without disrupting normal functions.
One of the most explored medical uses is in targeted drug delivery. The large, functionalizable surface of a nanodiamond allows therapeutic molecules to be attached, creating a transport vehicle for drugs. This vehicle can carry drugs directly to specific targets, such as cancerous tumors. This approach concentrates the therapeutic effect, potentially reducing side effects from widespread drug distribution.
Nanodiamonds also function as tools in bioimaging. Introducing specific defects into their crystal lattice, such as a nitrogen-vacancy (NV) center, can make them fluoresce brightly when illuminated by a laser. These fluorescent nanodiamonds are stable and do not fade like traditional dyes, allowing for long-term tracking of biological processes within living cells in real-time.
Their hardness and biocompatibility make them useful for enhancing medical implants. Incorporating nanodiamonds into materials for joint replacements or dental implants can improve the durability and wear resistance of these devices. Coatings with nanodiamonds create smoother, stronger surfaces that are less likely to degrade, leading to longer-lasting medical devices.
Uses in Technology and Industry
Nanodiamonds also have properties valuable in technology and industry. Their use in quantum technologies is based on the same nitrogen-vacancy (NV) centers used for bioimaging. The quantum state of an NV center is highly sensitive to its environment, particularly magnetic fields. This allows nanodiamonds to be used as nanoscale sensors capable of detecting minute magnetic signals for applications in data storage and medical diagnostics.
The hardness and low coefficient of friction of nanodiamonds are exploited in industrial lubricants and polishing agents. When added to engine oils and other lubricants, nanodiamonds act like microscopic ball bearings, reducing friction between moving parts. This reduction in friction leads to less wear, improved energy efficiency, and a longer operational life for machinery.
Manufacturing electronics and high-precision optics requires an ultra-smooth surface. Nanodiamonds are used in polishing slurries and films for this purpose. Their hardness allows them to abrade surfaces at the nanoscale, removing microscopic imperfections without causing significant scratches. This results in the flawless finishes required for silicon wafers, hard drives, and advanced optical components.