Biomedical Applications of Nanodiamonds: Imaging and Therapy
Biomedical Applications of Nanodiamonds: Imaging and Therapy
NDs have been developed in many cases for bioimaging, as an alternative to fluorescent dyes and quantum dots using NDs' characteristic optical-spectroscopic properties, namely photoluminescence (PL; or fluorescence) and Raman signal. It has been well established that the main origins of the NDs' fluorescence are defects and admixtures in the particles core, formed by a diamond lattice. Different fluorescence peaks can predominate, which largely depends upon different methods of production and sizes of NDs. Different wavelengths can excite different defects. Most importantly, ND fluorescence is stable and does not photobleach, which allows for the development of ND-based fluorescence markers. In order to be able to utilize these advantages, methods have been developed to enhance ND fluorescence. Well-studied nitrogen defect color centers (namely, negatively charged nitrogen-vacancy [N-V] centers) can be created in high concentrations with proton beams followed by thermal annealing. Following this treatment, ND fluorescence can be significantly increased. Such a ND is usually defined as fluorescent ND (FND), in contrast with ND (with weak fluorescence, but is still observable and applicable). For detonation NDs, high nitrogen defects content also has been obtained and demonstrated. In addition to (N-V) centers, some other admixtures and lattice defects are used for improving NDs' fluorescence. For example, incorporation of silicon vacancy centers gives bright, narrowband single-photon emission with zero phonon line at 738 nm (lying within the near-infrared window of biological tissue), for 70–80-nm-sized NDs that were produced by bead-assisted sonic disintegration of a polycrystalline chemical vapor deposition film.
It has been reported that ND fluorescence is predominantly emitted from the diamond core and not from the surface. Nevertheless, surface also plays an important role in the fluorescence properties, as well as ND size, surface moieties of the ND host and bandgap structure of the dielectric environment. Mona et al. reported surface modification of 100-nm carboxylated NDs by gas treatments (hydrogen/argon) and significant enhancement of PL intensity and transformation of the shape of the luminescence band was also observed. Effects of NDs' surface passivation with protein molecules were observed on PL spectra owing to the energy transfer between ND cores (color defect centers), surface graphite-like nanoclusters and adsorbed macromolecules. Together with energy transfer, some surface defects and impurities, recombination of donor–acceptor pairs can determine the surface role/input in ND fluorescence.
Recently, ND fluorescence imaging has been demonstrated in a number of studies. Figure 3 shows fluorescence imaging applied in a cellular study, indicating that ND was colocalized with lysosomes after entering a macrophage cell. Imaging has been successfully applied in cellular models and, in a few cases, animal models.
(Enlarge Image)
Figure 3.
Confocal fluorescence imaging of nanodiamonds in cells. (A) The confocal fluorescence image of the mouse macrophage RAW264.7 cell after incubation with 100-nm carboxylated nanodiamonds (25 µg/ml in DMEM medium) for 6 h. The nuclei dyed with 4',6-diamidino-2-phenylindole was excited with a 405-nm wavelength and emission collected in the 415–485-nm region (blue); cytoplasm is dyed with phalloidin–Alexa Fluor® 647 (Invitrogen, CA, USA) excited at 633 nm, with signal collected in the range of 646–725 nm (cyan). (B) LysoTracker® (Sigma, MO, USA) staining lysosomes was excited at 543 nm, signal was detected in the range of 560–625 nm (red). (C) Natural fluorescence of 100-nm nanodiamonds was excited with a 488-nm wavelength and emission detected in the 500–540-nm region (green).
Reproduced with permission from [68].
Diamond has a sharp and isolated characteristic Raman peak (phonon mode of sp-bonded carbon) at 1332 cm, which can be used for spectroscopic detection of NDs in cells or in interactions with other biosystems. Therefore, NDs can also be used as a type of Raman label, which can be detected in the cells using Raman mapping techniques by mapping the distribution of the intensity of the ND Raman signal relative to the distribution of characteristic Raman peaks of the cell.
Spectroscopic Properties of NDs for Bioimaging
NDs have been developed in many cases for bioimaging, as an alternative to fluorescent dyes and quantum dots using NDs' characteristic optical-spectroscopic properties, namely photoluminescence (PL; or fluorescence) and Raman signal. It has been well established that the main origins of the NDs' fluorescence are defects and admixtures in the particles core, formed by a diamond lattice. Different fluorescence peaks can predominate, which largely depends upon different methods of production and sizes of NDs. Different wavelengths can excite different defects. Most importantly, ND fluorescence is stable and does not photobleach, which allows for the development of ND-based fluorescence markers. In order to be able to utilize these advantages, methods have been developed to enhance ND fluorescence. Well-studied nitrogen defect color centers (namely, negatively charged nitrogen-vacancy [N-V] centers) can be created in high concentrations with proton beams followed by thermal annealing. Following this treatment, ND fluorescence can be significantly increased. Such a ND is usually defined as fluorescent ND (FND), in contrast with ND (with weak fluorescence, but is still observable and applicable). For detonation NDs, high nitrogen defects content also has been obtained and demonstrated. In addition to (N-V) centers, some other admixtures and lattice defects are used for improving NDs' fluorescence. For example, incorporation of silicon vacancy centers gives bright, narrowband single-photon emission with zero phonon line at 738 nm (lying within the near-infrared window of biological tissue), for 70–80-nm-sized NDs that were produced by bead-assisted sonic disintegration of a polycrystalline chemical vapor deposition film.
It has been reported that ND fluorescence is predominantly emitted from the diamond core and not from the surface. Nevertheless, surface also plays an important role in the fluorescence properties, as well as ND size, surface moieties of the ND host and bandgap structure of the dielectric environment. Mona et al. reported surface modification of 100-nm carboxylated NDs by gas treatments (hydrogen/argon) and significant enhancement of PL intensity and transformation of the shape of the luminescence band was also observed. Effects of NDs' surface passivation with protein molecules were observed on PL spectra owing to the energy transfer between ND cores (color defect centers), surface graphite-like nanoclusters and adsorbed macromolecules. Together with energy transfer, some surface defects and impurities, recombination of donor–acceptor pairs can determine the surface role/input in ND fluorescence.
Recently, ND fluorescence imaging has been demonstrated in a number of studies. Figure 3 shows fluorescence imaging applied in a cellular study, indicating that ND was colocalized with lysosomes after entering a macrophage cell. Imaging has been successfully applied in cellular models and, in a few cases, animal models.
(Enlarge Image)
Figure 3.
Confocal fluorescence imaging of nanodiamonds in cells. (A) The confocal fluorescence image of the mouse macrophage RAW264.7 cell after incubation with 100-nm carboxylated nanodiamonds (25 µg/ml in DMEM medium) for 6 h. The nuclei dyed with 4',6-diamidino-2-phenylindole was excited with a 405-nm wavelength and emission collected in the 415–485-nm region (blue); cytoplasm is dyed with phalloidin–Alexa Fluor® 647 (Invitrogen, CA, USA) excited at 633 nm, with signal collected in the range of 646–725 nm (cyan). (B) LysoTracker® (Sigma, MO, USA) staining lysosomes was excited at 543 nm, signal was detected in the range of 560–625 nm (red). (C) Natural fluorescence of 100-nm nanodiamonds was excited with a 488-nm wavelength and emission detected in the 500–540-nm region (green).
Reproduced with permission from [68].
Diamond has a sharp and isolated characteristic Raman peak (phonon mode of sp-bonded carbon) at 1332 cm, which can be used for spectroscopic detection of NDs in cells or in interactions with other biosystems. Therefore, NDs can also be used as a type of Raman label, which can be detected in the cells using Raman mapping techniques by mapping the distribution of the intensity of the ND Raman signal relative to the distribution of characteristic Raman peaks of the cell.
Source...