Nanodiamond

A nanodiamond is a carbon nanoparticle with truncated octahedral architecture—the same structure as ordinary diamonds; however, nanodiamonds are significantly smaller, measuring about two to eight nanometers (nm) in diameter. Nanoparticles have many applications in fields such as transportation, energy, food safety, information technology, and medicine. Nanodiamonds have qualities that make them good candidates for treating infectious diseases and for delivering drugs.

Some commercial applications of nanodiamonds include use in lubricants, polishing materials, and polymer coatings, which benefit from ultraviolet resistance. Nanodiamonds are also used in antibacterial and antifungal coatings and as oil and fuel additives. While nanodiamonds have the hardness of diamonds, they also have flexible bonds. This allows the nanodiamonds to both stretch and pucker—one side may stretch and be relatively smooth, while the other side develops folds and ridges, typical of cut diamonds, as the surface is pinched.

Background

Nanotechnology is engineering, science, and technology that takes place at the nanoscale. One nanometer is one billionth of a meter (one inch is about 25.4 million nanometers). The nanoscale is between 1 and about 100 nanometers.

Humans have been manipulating nanoparticles—often unknowingly—for centuries. Craftspeople frequently used high heat to produce glassware, metalwork, and pottery with unique qualities that emerged because of nanoparticles. For example, nanoparticles of gold chloride and other metal oxides in stained-glass produced from the sixth through the fifteenth centuries give cathedral windows brilliant colors, while carbon nanotubes produced by heating and hammering the metal provided strength and sharp edges to Damascus saber blades made from the thirteenth through the eighteenth centuries.

The roots of modern nanotechnology reach to 1959 on the campus of the California Institute of Technology (CalTech). Physicist Richard Feynman gave a talk at the American Physical Society meeting: “There’s Plenty of Room at the Bottom.” He theorized that in the future, scientists would be able to control individual atoms and molecules. Professor Norio Taniguchi coined the term nanotechnology in 1974 in his paper “On the Basic Concept of ‘Nanotechnology,’” which he presented at a meeting of the Japan Society of Precision Engineering.

In 1996, Mike Roco set up a think tank, the National Nanotechnology Initiative, in the United States. It comprised academics, industrialists, and scientists from laboratories around the country tasked with developing a national strategy for nanotechnology. He pitched his ideas to President Bill Clinton in 1999 and received federal funding.

Nanotechnology has been studied for its potential benefits, but researchers have acknowledged a number of concerns that needed to be addressed. These include fears that self-replicating nanomachines could get out of control and the potential dangers of accidental ingestion or inhalation of nanoparticles.

Nanodiamond synthesis, or production, was first discovered in 1963 in the Soviet Union. Researchers outside the Soviet Union discovered nanodiamonds over the course of several decades, all while studying diamond synthesis by shock compression of nondiamond carbon modifications in blast chambers.

Overview

Nanodiamonds can be synthesized a number of ways. These include ion and laser bombarding, ultrasonic, electrochemical, and detonation methods. The method used is chosen based on the form of nanodiamond needed. Just like diamonds on a larger scale, nanodiamonds are extremely hard and chemically stable, and at high magnification are radiant as well. Nanodiamonds have the highest thermal conductivity and the greatest optical transparency.

The first method of synthesizing nanodiamonds, the detonation method, helped lead to their discovery. The detonation method produces nanodiamonds with commercially desirable diameters of from 4 to 6 nm. The method involves detonating explosives that contain carbon in an environment that does not include oxygen. This prevents carbon oxidation from occurring. The explosion lasts for only a fraction of a second. This is not long enough to produce large nanodiamonds, but the nanodiamonds produced will collide and fuse to one another during synthesis. These detonation nanodiamonds form tight aggregates of primary particles that may measure from 200 to 300 nm. Separating the primary particles within the detonation nanodiamonds is difficult, and a successful method was not found until 2005. With that discovery, the availability of nanodiamond particles smaller than 10 nm opened up a range of applications.

Nanodiamonds have many properties that make them well-suited to a variety of uses. They are non-toxic, so they are good candidates for biomedical applications. They have high surface areas as well. Some uses include bioimaging, tissue engineering, and drug delivery. Some nanoparticles are not appropriate for drug delivery due to potential toxicity, although the reason for this is not yet well understood. Carbon-based nanoparticles, such as nanodiamonds, are not toxic and therefore better suited to use for drug delivery. Nanodiamonds smaller than 10nm, so-called single digit particles, have been found to be able to cross the blood brain barrier, which makes them ideal for medical use. For example, a number of chemotherapy drugs have been tried against brain cancer, but have been unable to cross the blood brain barrier. Drugs such as loperamide and doxorubicin have been bound successfully to nanodiamonds, which enables them to cross the intact barrier to reach brain tumors in sufficient quantities to have a beneficial effect. A further benefit of using carbon-based nanoparticles is that they are less targeted by the immune system for elimination, and can continue to function for longer than other types of nanoparticles.

The nanodiamonds’ small size and nearly spherical shape make them useful in lubrication applications, called nanolubricants. Detonation nanodiamonds are chemically and mechanically stable. Their surface chemistry is electron negative and has catalytic properties, which means they can increase the rate of chemical reactions. Their crystallographic lattice structure contains strong bonds between carbon atoms and the highest known atomic density. Because they have high chemical stability, they can withstand harsh conditions, making them useful in applications such as diamond films applied using chemical vapor processes. This process involves high temperature heating of substrates, the surfaces on which the film is to be applied. Then they are exposed to precursor materials, such as nanodiamonds, in a gaseous state. The precursors cling to the substrate and coat it.

Because nanodiamonds have the potential to pass through the blood-brain barrier, they may eventually be used for various medical treatments. This includes the neurological imaging and the treatment of glioblastomas.

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