The biocompatibility of fluorescent nanodiamonds and their mechanism of cellular uptake

Fluorescent Nanodiamond – A Novel Nanomaterial for In Vivo Applications

Fluorescent nanodiamonds (FNDs) with a size in the range of 10 – 100 nm have been produced by ion irradiation and annealing, and isolated by differential centrifugation. Single particle spectroscopic characterization with confocal fluorescence microscopy and fluorescence correlation spectroscopy indicates that they are photostable and useful as an alternative to far-red fluorescent proteins for bioimaging applications. We demonstrate the application by performing in vivo imaging of bare and bioconjugated FND particles (100 nm in diameter) in C. elegans and zebrafishes and exploring the interactions between this novel nanomaterial and the model organisms. Our results indicate that FNDs can be delivered to the embryos of both organisms by microinjection and eventually into the hatched larvae in the next generation. No deleterious effects have been observed for the carbon-based nanoparticles in vivo. The high fluorescence brightness, excellent photostability, and nontoxic nature of the nanomaterial have allowed long-term imaging and tracking of embryogenesis in the organisms.

DNA damage in embryonic stem cells caused by nanodiamonds

Because of their unique photoluminescence and magnetic properties, nanodiamonds (NDs) are promising for biomedical imaging and therapeutical applications. However, these biomedical applications will hardly be realized unless the potential hazards of NDs to humans and other biological systems are ascertained. Previous studies performed in our group and others have demonstrated the excellent biocompatibility of NDs in a variety of cell lines without noticeable cytotoxicity. In the present paper, we report the first genotoxicity study on NDs. Our results showed that incubation of embryonic stem cells with NDs led to slightly increased expression of DNA repair proteins, such as p53 and MOGG-1. Oxidized nanodiamonds (O-NDs) were demonstrated to cause more DNA damage than the pristine/raw NDs (R-NDs), showing the surface chemistry specific genotoxicity. However, the DNA damages caused by either the O-NDs or the R-NDs are much less severe than those caused by multiwalled carbon nanotubes (MWNTs) observed in our previous study. These findings should have important implications for future applications of NDs in biological applications.

Group IV nanoparticles: synthesis, properties, and biological applications

In this review, the emerging roles of group IV nanoparticles including silicon, diamond, silicon carbide, and germanium are summarized and discussed from the perspective of biologists, engineers, and medical practitioners. The synthesis, properties, and biological applications of these new nanomaterials have attracted great interest in the past few years. They have gradually evolved into promising biomaterials due to their innate biocompatibility; toxic ions are not released when they are used in vitro or in vivo, and their wide fluorescence spectral regions span the near-infrared, visible, and near-ultraviolet ranges. Additionally, they generally have good resistance against photobleaching and have lifetimes on the order of nanoseconds to microseconds, which are suitable for bioimaging. Some of the materials possess unique mechanical, chemical, or physical properties, such as ultrachemical and thermal stability, high hardness, high photostability, and no blinking. Recent data have revealed the superiority of these nanoparticles in biological imaging and drug delivery.

In vivo imaging and toxicity assessments of fluorescent nanodiamonds in Caenorhabditis elegans

Nanoscale carbon materials hold great promise for biotechnological and biomedical applications. Fluorescent nanodiamond (FND) is a recent new addition to members of the nanocarbon family. Here, we report long-term in vivo imaging of FNDs in Caenorhabditis elegans (C. elegans) and explore the nano-biointeractions between this novel nanomaterial and the model organism. FNDs are introduced into wild-type C. elegans by either feeding them with colloidal FND solution or microinjecting FND suspension into the gonads of the worms. On feeding, bare FNDs stay in the intestinal lumen, while FNDs conjugated with biomolecules (such as dextran and bovine serum albumin) are absorbed into the intestinal cells. On microinjection, FNDs are dispersed in the gonad and delivered to the embryos and eventually into the hatched larvae in the next generation. The toxicity assessments, performed by employing longevity and reproductive potential as physiological indicators and measuring stress responses with use of reporter genes, show that FNDs are stable and nontoxic and do not cause any detectable stress to the worms. The high brightness, excellent photostability, and nontoxic nature of the nanomaterial have enabled continuous imaging of the whole digestive system and tracking of the cellular and developmental processes of the living organism for several days.

Two-photon fluorescence correlation spectroscopy of lipid-encapsulated fluorescent nanodiamonds in living cells

Dynamics of fluorescent diamond nanoparticles in HeLa cells has been studied with two-photon fluorescence correlation spectroscopy (FCS). Fluorescent nanodiamond (FND) is an excellent fluorescent probe for bioimaging application, but they are often trapped in endosomes after cellular uptake. The entrapment prohibits FCS from being performed in a time frame of 60 s. Herein, we show that the encapsulation of FNDs within a lipid layer enhances the diffusion of the particles in the cytoplasm by more than one order of magnitude, and particles as small as 40 nm can be probed individually with high image contrast by two-photon excited luminescence. The development of the technique together with single particle tracking through one-photon excitation allows probing of both short-term and long-term dynamics of single FNDs in living cells.