imaging setup that is determined by the imaging system design are considered
from the start, so as to design the fluorophores probes to effectively improve
detection sensitivity. For example, one of the most important hardware, the more
advanced NIR-II camera with higher sensitivity and broader spectral ranges
beyond the current NIR window should be developed. Besides the conventional
InGaAs material widely used for NIR-II fluorescence imaging, other photosensitive semiconductor materials such as indium antimonide (InSb) and mercury
cadmium telluride (HgCdTe) may provide new capabilities to NIR-II
fluorescence imaging.
In summary, the future direction of NIR-II fluorophores will be mainly focused
on the following properties, including biocompatible, high fluorescence quantum
yield, high photostability, tunable excitation and emission wavelengths, feasible
functionalization, and easy clearance. In addition, we envisage the bright future of
NIR-II fluorescence imaging potential frontier applications in brain science, stem
cells, genetic science and sensing in vivo, and so on.
7 Conclusions
NIR-II imaging has several advantages over NIR-I imaging and other current
medical imaging modalities. Owing to the reduced photon scattering and low
autofluorescence background at longer wavelengths, high imaging resolution and
depth can be achieved by NIR-II imaging. NIR-II fluorophores from small organic
molecules to organic and inorganic nanoparticles have been successfully developed,
and their wide-ranging biomedical applications such as imaging, therapy, and
guidance for intraoperative surgery have been discussed. This chapter also provides
a summary overview of experimental strategies to tailor the luminescence characteristics, as well as control the physical and surface characteristics of the NIR-II
probes. Optical (e.g., bright emissions with tunable excitation/emission) and biomedical (e.g., biocompatibility and targeting) characteristics of the NIR-II probes
must be considered during the design and synthesis phase. To date, many probes
with NIR-II emissions and large Stokes shifts have been established. The great
advancement of NIR-II fluorophores has shown high impact not only on fundamental research but on preclinical application. However, their widespread utilization to
diagnose diseased lesions has been largely limited due to the demanding challenges
of effective in vivo targeting in a complex microenvironment. The complexity of the
in vivo microenvironment (e.g., changing pH, enzymatic degradation) often results
in unintended degradation of either the chemically conjugated targeting ligands or
organic surface coatings and off-target localization of the probes due to chargedependent non-specific attachment to various sites. Furthermore, the binding effectiveness of the targeting moieties could be affected during chemical conjugation
leading to ineffectual localization and disease identification. The second concern is
that the low QYs of the NIR-II emission are largely limited by the low absorption
Advancements of Second Near-Infrared Biological Window Fluorophores:. . .
117
from the start, so as to design the fluorophores probes to effectively improve
detection sensitivity. For example, one of the most important hardware, the more
advanced NIR-II camera with higher sensitivity and broader spectral ranges
beyond the current NIR window should be developed. Besides the conventional
InGaAs material widely used for NIR-II fluorescence imaging, other photosensitive semiconductor materials such as indium antimonide (InSb) and mercury
cadmium telluride (HgCdTe) may provide new capabilities to NIR-II
fluorescence imaging.
In summary, the future direction of NIR-II fluorophores will be mainly focused
on the following properties, including biocompatible, high fluorescence quantum
yield, high photostability, tunable excitation and emission wavelengths, feasible
functionalization, and easy clearance. In addition, we envisage the bright future of
NIR-II fluorescence imaging potential frontier applications in brain science, stem
cells, genetic science and sensing in vivo, and so on.
7 Conclusions
NIR-II imaging has several advantages over NIR-I imaging and other current
medical imaging modalities. Owing to the reduced photon scattering and low
autofluorescence background at longer wavelengths, high imaging resolution and
depth can be achieved by NIR-II imaging. NIR-II fluorophores from small organic
molecules to organic and inorganic nanoparticles have been successfully developed,
and their wide-ranging biomedical applications such as imaging, therapy, and
guidance for intraoperative surgery have been discussed. This chapter also provides
a summary overview of experimental strategies to tailor the luminescence characteristics, as well as control the physical and surface characteristics of the NIR-II
probes. Optical (e.g., bright emissions with tunable excitation/emission) and biomedical (e.g., biocompatibility and targeting) characteristics of the NIR-II probes
must be considered during the design and synthesis phase. To date, many probes
with NIR-II emissions and large Stokes shifts have been established. The great
advancement of NIR-II fluorophores has shown high impact not only on fundamental research but on preclinical application. However, their widespread utilization to
diagnose diseased lesions has been largely limited due to the demanding challenges
of effective in vivo targeting in a complex microenvironment. The complexity of the
in vivo microenvironment (e.g., changing pH, enzymatic degradation) often results
in unintended degradation of either the chemically conjugated targeting ligands or
organic surface coatings and off-target localization of the probes due to chargedependent non-specific attachment to various sites. Furthermore, the binding effectiveness of the targeting moieties could be affected during chemical conjugation
leading to ineffectual localization and disease identification. The second concern is
that the low QYs of the NIR-II emission are largely limited by the low absorption
Advancements of Second Near-Infrared Biological Window Fluorophores:. . .
117