microscopy cannot resolve whether the particles are internalized or well-dispersed/
aggregated due to the diffraction-limited image resolutions; however, STED microscopy images successfully identified the individual nano-diamond in the cytoplasm
(Fig. 8c). This not only identifies the cellular process, but the nano-diamonds
(ND) can also provide further information on cellular function in disease diagnostics.
For example, a ND-based tracking assay was recently developed to observe
intraneuronal transport abnormalities with a spatial resolution of 12 nm and a
temporal resolution of 50 ms. [84] Figure 8d shows that when NDs were internalized
to primary hippocampal neuron cells, they could be tracked in real time using
pseudo-total internal reflection fluorescence video microscopy (pseudo-TIRF).
Here, the overlay images (BF and FL) can display the precise localization of ND
overall trajectories and movement throughout the microtubules. Therefore, using the
primary hippocampal neurons treated with amyloid-β 1–42 peptide, the authors successfully found the decreased transport velocities of ND – this indicates abnormal
intraneuronal transport in Alzheimer’s disease.
In addition, exceptionally biocompatible and photostable, fluorescent nanodiamonds (NDs) can allow the monitoring of the long-term fate of stem cells
in vivo. In a recent study, Wu et al. delivered ND-labelled lung stem cells (LSCs)
by intravenous injection and observed their engraftment and regenerative capabilities with single-cell resolution through time-gated fluorescence (TGF) imaging and
immunostaining [85]. Here, the authors first demonstrated that fluorescent nanodiamond labelling did not impair the lung stem cells’ self-renewal and differentiation
into type I and type II pneumocytes. Since the regenerative capacity of LSCs could
be activated after tissue injury, using naphthalene-injured mice, they found that the
transplanted LSCs migrated and integrated into bronchiolar epithelium of the murine
lungs to successfully regenerate the damaged epithelial linings (Fig. 8e, f). However,
this still required a sufficiently large number of photoluminescent nitrogen-vacancy
(NV) centers to increase the optical cross sections for fluorescent nano-diamonds.
Unfortunately, the use of nano-diamonds is still limited in multiplexed imaging.
Persistent luminescent nanoparticles store energy by pre-charging with UV
excitations and gradually releasing the photon energies. The emission is steady for
several hours or days with no additional input of energies. Therefore, there is no need
for external continuous excitation – this approach can lead to sensitive imaging
without background autofluorescence [86]. Scherman and coworkers prepared silicate crystals doped with Eu
2+ , Dy
3+ , and Mn
2+ ions via a sol-gel process followed by
successive high temperature calcination. These nanoparticles possess energy traps
where the excited lights can be non-radiatively captured to induce persistent luminescence. They found that these particles can successfully emit light at 700 nm with
a long-lasting luminescence for more than 1 h upon excitation ex vivo by UV light
(6 W UV lamp, <5 min). The authors have also shown that when such particles were
pre-excited and implanted to BALB/c mice, the sensitive fluorescent signals could
be easily detected in real time using a photon counting system [87]. However, these
probes could only be excited ex vivo by UV lights, which prevent long-term imaging
in vivo.
Inorganic Fluorescent Nanomaterials
69
aggregated due to the diffraction-limited image resolutions; however, STED microscopy images successfully identified the individual nano-diamond in the cytoplasm
(Fig. 8c). This not only identifies the cellular process, but the nano-diamonds
(ND) can also provide further information on cellular function in disease diagnostics.
For example, a ND-based tracking assay was recently developed to observe
intraneuronal transport abnormalities with a spatial resolution of 12 nm and a
temporal resolution of 50 ms. [84] Figure 8d shows that when NDs were internalized
to primary hippocampal neuron cells, they could be tracked in real time using
pseudo-total internal reflection fluorescence video microscopy (pseudo-TIRF).
Here, the overlay images (BF and FL) can display the precise localization of ND
overall trajectories and movement throughout the microtubules. Therefore, using the
primary hippocampal neurons treated with amyloid-β 1–42 peptide, the authors successfully found the decreased transport velocities of ND – this indicates abnormal
intraneuronal transport in Alzheimer’s disease.
In addition, exceptionally biocompatible and photostable, fluorescent nanodiamonds (NDs) can allow the monitoring of the long-term fate of stem cells
in vivo. In a recent study, Wu et al. delivered ND-labelled lung stem cells (LSCs)
by intravenous injection and observed their engraftment and regenerative capabilities with single-cell resolution through time-gated fluorescence (TGF) imaging and
immunostaining [85]. Here, the authors first demonstrated that fluorescent nanodiamond labelling did not impair the lung stem cells’ self-renewal and differentiation
into type I and type II pneumocytes. Since the regenerative capacity of LSCs could
be activated after tissue injury, using naphthalene-injured mice, they found that the
transplanted LSCs migrated and integrated into bronchiolar epithelium of the murine
lungs to successfully regenerate the damaged epithelial linings (Fig. 8e, f). However,
this still required a sufficiently large number of photoluminescent nitrogen-vacancy
(NV) centers to increase the optical cross sections for fluorescent nano-diamonds.
Unfortunately, the use of nano-diamonds is still limited in multiplexed imaging.
Persistent luminescent nanoparticles store energy by pre-charging with UV
excitations and gradually releasing the photon energies. The emission is steady for
several hours or days with no additional input of energies. Therefore, there is no need
for external continuous excitation – this approach can lead to sensitive imaging
without background autofluorescence [86]. Scherman and coworkers prepared silicate crystals doped with Eu
2+ , Dy
3+ , and Mn
2+ ions via a sol-gel process followed by
successive high temperature calcination. These nanoparticles possess energy traps
where the excited lights can be non-radiatively captured to induce persistent luminescence. They found that these particles can successfully emit light at 700 nm with
a long-lasting luminescence for more than 1 h upon excitation ex vivo by UV light
(6 W UV lamp, <5 min). The authors have also shown that when such particles were
pre-excited and implanted to BALB/c mice, the sensitive fluorescent signals could
be easily detected in real time using a photon counting system [87]. However, these
probes could only be excited ex vivo by UV lights, which prevent long-term imaging
in vivo.
Inorganic Fluorescent Nanomaterials
69