The increased availability of diamonds due to industrial production have extended their use beyond jewelry and abrasives. Their properties make possible their potential use as semiconductors suitable for building microchips, and as heat sinks in electronics. When made fluorescent, their applications extend into such realms as high tech sensors, and bit manipulation for quantum computing.
On the micro (1x10-6) and nano (1x10-9) scale, their unique properties make diamonds ideal for biomedical purposes. Diamonds are easily sterilized, are non-toxic, and their surfaces are easily functionalized for attachment of proteins. Their lubricity, which causes the diamond crystals to slide like ice against each other, can provide a durable, bio-compatible, non-wearing surface for artificial joints. And fluorescent nanodiamonds, when emitting in the near infrared region of the spectrum, can provide deep tissue imaging without background interference or photo-bleaching.
Pure diamond contains only carbon-carbon bonds, and is optically transparent between the ultraviolet, through the visible, to the microwave regimes. Non-carbon contaminants, (nitrogen, boron, nickel, etc.) and/or atomic defects (such as vacancies) within the diamond crystal produce visible colors, many of which are also fluorescent. Over 500 fluorescent diamond colors have been compiled and a number of these are of high interest as near-infrared (NIR) reagents for biomedical imaging. However, only a few types of fluorescent diamond have been studied in any great detail.
The best studied fluorescent diamond is the NV-color center, which consists of a nitrogen atom adjacent to a vacancy within the diamond lattice. NV centers are optically excited with a green laser and emit red fluorescence between 650 to 710 nm. The unique optical properties of NV-center diamonds include their intense fluorescence, and extreme photostability even under intense laser excitation (>1GW/cm2). Finally, their unique photophysics makes them exquisite sensors for magnetic fields, electric fields, and thermal changes. The main features of NV-center diamonds are summarized below.