Nanomaterials for Medical Imaging …
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diagnostics [4, 277]. The following are some of the important characteristics of NP’s
required for biomedical imaging should be dissolvable and stable in diverse native
environments, good signal-to-background-noise ratio, no toxicity, exhibit strong nonspecific binding and uptake, superior blood half-life and should avoid clearance by
the reticuloendothelial system [277–280]. Some of the most widely exploited NPs
in optical imaging include quantum dots, upconverting NPs, persistent luminescent
NPs, metal, and carbon nanoparticles [281, 282]. Here we will be presenting a brief
description of quantum dots, upconverting NPs, and persistent luminescent NPs in
detail.
9.1 Quantum Dots
Quantum dots (QDs) are a group of semiconductor nanoparticles sized in the range
between 6 mm and 20 nm with a very high quantum yield and possess excellent
photo- and chemical-stability characteristics in comparison with organic fluorescent
dyes [283–285]. QDs are usually composed of elements from groups II-VI elements
(e.g., CdS, CdSe, ZnS, MgSe, etc.), III-VI elements (e.g., GaAs, InP, InGaAs, etc.),
IV-VI elements (e.g., PbSe, PbS, PbTe) and ternary QDs are I–III-VI (I = Cu, Ag; III
= In, Sn, Ga, Al and VI = S, Se, Te, etc.) [286, 287]. In this context, Han et al. [288]
implemented a lattice-mismatch strain tuning theory to characterize highly luminescent NIR CdTe/CdS QDs. The small shells were efficiently compressed by lattice
strain attributed to growing thicker shell and transition of a transition of bandgap
offset from type-I to type-II nanocrystals that happened during the well-controlled
gradual growth of the shell, allowing largest spectral shifts tuning from the visible
to the NIR spectral region. This study demonstrated that QDs developed using this
approach were highly fluorescent, extraordinarily small, and better tumor-targeting
ability. A select type of QDs are graphene quantum dots (GQDs) were developed by
Ashwin et al. by changing oxygen contents that enhance the fluorescence in red to
NIR region. GQDs loaded into muscle gel and excited with green LED via transillumination method obtained red emission in vivo. Our work enables us to develop
nanomaterials developed using pulsed laser ablation for in vivo imaging [289].
ZnS shell grown over CdTe x Se 1-x NIR QDs alloy nanocrystals have been developed to provide a quantum yield of around 80% in chloroform [290]. Also, the aspect
ratio and emission range of the quantum dots can be varied by changing the Te and
Se mole ratio. They found that the composition of Se played a vital role in controlling the rod shape whole Te plays an essential role in the fluorescence emission. In
recent times, fluorescence imaging in the NIR II region has been gaining momentum.
In this wavelength region, tissue absorption by endogenous chromophores such as
oxyhemoglobin, deoxyhemoglobin, and melanin are limited [291]. Additionally, in
this region, there is an increased signal-to-background ratio due to reduced photon
scattering, improved penetration depth, and reduced interference from fluorescence
[292, 293]. Ag 2 S QDs conjugated with Tat peptide, which is used as a targeting
ligand have been implemented for the tracking of human mesenchymal stem cells
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diagnostics [4, 277]. The following are some of the important characteristics of NP’s
required for biomedical imaging should be dissolvable and stable in diverse native
environments, good signal-to-background-noise ratio, no toxicity, exhibit strong nonspecific binding and uptake, superior blood half-life and should avoid clearance by
the reticuloendothelial system [277–280]. Some of the most widely exploited NPs
in optical imaging include quantum dots, upconverting NPs, persistent luminescent
NPs, metal, and carbon nanoparticles [281, 282]. Here we will be presenting a brief
description of quantum dots, upconverting NPs, and persistent luminescent NPs in
detail.
9.1 Quantum Dots
Quantum dots (QDs) are a group of semiconductor nanoparticles sized in the range
between 6 mm and 20 nm with a very high quantum yield and possess excellent
photo- and chemical-stability characteristics in comparison with organic fluorescent
dyes [283–285]. QDs are usually composed of elements from groups II-VI elements
(e.g., CdS, CdSe, ZnS, MgSe, etc.), III-VI elements (e.g., GaAs, InP, InGaAs, etc.),
IV-VI elements (e.g., PbSe, PbS, PbTe) and ternary QDs are I–III-VI (I = Cu, Ag; III
= In, Sn, Ga, Al and VI = S, Se, Te, etc.) [286, 287]. In this context, Han et al. [288]
implemented a lattice-mismatch strain tuning theory to characterize highly luminescent NIR CdTe/CdS QDs. The small shells were efficiently compressed by lattice
strain attributed to growing thicker shell and transition of a transition of bandgap
offset from type-I to type-II nanocrystals that happened during the well-controlled
gradual growth of the shell, allowing largest spectral shifts tuning from the visible
to the NIR spectral region. This study demonstrated that QDs developed using this
approach were highly fluorescent, extraordinarily small, and better tumor-targeting
ability. A select type of QDs are graphene quantum dots (GQDs) were developed by
Ashwin et al. by changing oxygen contents that enhance the fluorescence in red to
NIR region. GQDs loaded into muscle gel and excited with green LED via transillumination method obtained red emission in vivo. Our work enables us to develop
nanomaterials developed using pulsed laser ablation for in vivo imaging [289].
ZnS shell grown over CdTe x Se 1-x NIR QDs alloy nanocrystals have been developed to provide a quantum yield of around 80% in chloroform [290]. Also, the aspect
ratio and emission range of the quantum dots can be varied by changing the Te and
Se mole ratio. They found that the composition of Se played a vital role in controlling the rod shape whole Te plays an essential role in the fluorescence emission. In
recent times, fluorescence imaging in the NIR II region has been gaining momentum.
In this wavelength region, tissue absorption by endogenous chromophores such as
oxyhemoglobin, deoxyhemoglobin, and melanin are limited [291]. Additionally, in
this region, there is an increased signal-to-background ratio due to reduced photon
scattering, improved penetration depth, and reduced interference from fluorescence
[292, 293]. Ag 2 S QDs conjugated with Tat peptide, which is used as a targeting
ligand have been implemented for the tracking of human mesenchymal stem cells