nanomaterials based on their optical excitations, the current utility in high-resolution
(preclinical) in vivo imaging, and the underlying issues for future clinical
translations.
Keywords Fluorescence, In vivo, Molecular imaging, Nanomaterials, Optical
imaging, Quantum dots
1 Overview
Most clinical optical imaging agents are organic fluorescent dyes (e.g., cyanine,
rhodamine, oxazine dyes). However, these suffer from several drawbacks such as
photo-bleaching and short blood circulation, which limit their repeated use for longterm imaging of cellular and molecular processes in living systems. In the last two
decades, many efforts have been devoted to developing inorganic (metal-containing)
nanoparticles as targetable optical probes with superior photostability. In this chapter, we will discuss several types of inorganic nanoparticles that use fluorescence.
We will also introduce some recent studies to validate their interesting features as
contrast agents in preclinical in vivo imaging. Finally, we will address the potential
issues for each type of fluorescent nanomaterials to attain better sensitivity and lower
toxicity for potential clinical translations.
2 Quantum Dots
Quantum dots (QDs; semiconductor nanoparticles) are composed of II–VI, III–V,
and IV–VI group elements of the periodic table and are representative inorganic
fluorescent nanomaterials (CdSe, CdS, CdTe, ZnS, InP, InAs, etc.). Their fluorescence is induced from the quantum confinement effect, which occurs when the QD
radius is smaller than the exciton Bohr radius (5.3 nm) of the original material [1].
QDs have many photo-physical advantages. QDs display narrower emission
bands than the traditional organic fluorophores. QDs have high photostability that
preclude the fast quenching of emissive light after repeated, high-intensity light
excitations. Therefore, these highly bright and photostable QDs offer fluorescence
imaging of live cells and in vivo animal imaging for long time periods [2]. QDs
have multiplexed imaging for simultaneous detection of multiple distinctive biological species due to their unique size-dependent light emission [3]. This is
because QDs follow the quantum behaviors of a particle in a box (the smaller the
box is, the larger is the separation between energy levels); for example, while the
larger CdSe QDs (5–6 nm) emit red light (relatively long wavelength), smaller
CdSe QDs (2–3 nm) have blue-shifted (short) emission (higher photon energies)
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T. Kim and J. V. Jokerst
(preclinical) in vivo imaging, and the underlying issues for future clinical
translations.
Keywords Fluorescence, In vivo, Molecular imaging, Nanomaterials, Optical
imaging, Quantum dots
1 Overview
Most clinical optical imaging agents are organic fluorescent dyes (e.g., cyanine,
rhodamine, oxazine dyes). However, these suffer from several drawbacks such as
photo-bleaching and short blood circulation, which limit their repeated use for longterm imaging of cellular and molecular processes in living systems. In the last two
decades, many efforts have been devoted to developing inorganic (metal-containing)
nanoparticles as targetable optical probes with superior photostability. In this chapter, we will discuss several types of inorganic nanoparticles that use fluorescence.
We will also introduce some recent studies to validate their interesting features as
contrast agents in preclinical in vivo imaging. Finally, we will address the potential
issues for each type of fluorescent nanomaterials to attain better sensitivity and lower
toxicity for potential clinical translations.
2 Quantum Dots
Quantum dots (QDs; semiconductor nanoparticles) are composed of II–VI, III–V,
and IV–VI group elements of the periodic table and are representative inorganic
fluorescent nanomaterials (CdSe, CdS, CdTe, ZnS, InP, InAs, etc.). Their fluorescence is induced from the quantum confinement effect, which occurs when the QD
radius is smaller than the exciton Bohr radius (5.3 nm) of the original material [1].
QDs have many photo-physical advantages. QDs display narrower emission
bands than the traditional organic fluorophores. QDs have high photostability that
preclude the fast quenching of emissive light after repeated, high-intensity light
excitations. Therefore, these highly bright and photostable QDs offer fluorescence
imaging of live cells and in vivo animal imaging for long time periods [2]. QDs
have multiplexed imaging for simultaneous detection of multiple distinctive biological species due to their unique size-dependent light emission [3]. This is
because QDs follow the quantum behaviors of a particle in a box (the smaller the
box is, the larger is the separation between energy levels); for example, while the
larger CdSe QDs (5–6 nm) emit red light (relatively long wavelength), smaller
CdSe QDs (2–3 nm) have blue-shifted (short) emission (higher photon energies)
56
T. Kim and J. V. Jokerst