Particles, just tens of nanometers across, made of diamond and covered in silk, can be injected into living cells. Because they glow when illuminated with certain kinds of light, biologists can use them to peer inside cells and untangle the molecular circuitry that governs cellular behavior or study how cells react to a new drug. The silk-coated diamond particles could also be used someday in the clinic, allowing doctors to send infection-fighting antibiotics to a target.
Nanodiamonds have been explored previously for potential medical use, but this is the first time silk has been incorporated with nanodiamonds, says Asma Khalid of the University of Melbourne, Australia, who is the first author of paper published recently in The Optical Society’s journal, Biomedical Optics Express. “Nanodiamond-silk hybrid material is important due to the potential it offers to the fields of bioimaging, biosensing, and drug delivery,” she explains.
Crystals of carbon, diamonds can be made with defects – other atoms inserted in the crystal structure – and these defects allow them to do tricks that flawless diamonds can’t, such as absorbing and re-emitting light of certain wavelengths, a process called fluorescence. Because these fluorescent nanodiamonds are bright, stable, and harmless to living tissue – and can work at room temperature – researchers have been exploring their use in biological imaging and sensing. But, the edges around the particles tend to be rough and may cause the nanodiamonds to become trapped inside cell membranes.
Other researchers have addressed this problem by coating the particles with lipids, molecules found in fats and waxes. According to the new study, however, a better solution is to cover the nanodiamonds in silk, which is transparent, flexible, compatible with biological tissue, and biodegradable, so it won’t leave any harmful byproducts inside the body.
When the researchers tested their new hybrid material, they found that the silk remains transparent, meaning that it does not block the glow of the nanodiamonds. They also discovered that the silk not only preserves the optical properties of the nanodiamonds, but it enhances their brightness by two to four times. Finally, the new material appears to be safe for use in the body. It left no damaging effects even after spending two weeks implanted inside living tissue, suggesting that it is nontoxic and non-inflammatory, the researchers say.
The team envisions a range of nanodiamond-silk structures that could help future researchers improve techniques for fighting infections in targeted areas of the body. A thin film of the new substance, carrying drugs, could be implanted directly into an infected area, minimizing the patient’s exposure to the drugs. Silk can also be designed to degrade at a certain rate, which would allow clinicians to control the release of medications.
In addition to the University of Melbourne, the researchers on this project are affiliated with the University of Sydney and the Silk Lab at Tufts University in Massachusetts.
The Optical Society