Abstract Fluorescence bio-imaging holds potential for new approaches for disease
detection and diagnosis. Compared with conventional clinical contrast imaging
modalities, such as X-ray and MRI, which use contrast agents that are “always
on,” fluorescence imaging contrast agents can readily be designed to be activatable
under specific circumstances and also can be used in multiplexed imaging schemes.
While a wide variety of fluorescence imaging probes have been developed, small
organic fluorescence probes have the advantages of being robustly synthesized and
characterized, as well as a track record for clinical translation. In this chapter, we
discuss organic fluorophores and highlighted some examples of their biological
applications. The aim of this chapter is to provide a literature review of the development of organic fluorescent probes for biomedical imaging and diagnosis.
Keywords Disease diagnosis, Fluorescence imaging, Fluorescence probes,
Imaging modalities, Organic fluorophores
1 Introduction
Near-infrared fluorescence imaging has developed as a powerful optical imaging
modality for visualization of molecular process and biological activities, which uses a
low-light camera to collect fluorescence emission from fluorophores [1]. The fluorescence imaging technique is based on the fact that the transillumination of light
through normal tissue is significantly different from that through an object (e.g.,
tumor or infected tissues). Compared to other well-developed imaging techniques
such as X-ray, computed tomography (CT) [2], magnetic resonance imaging (MRI),
and ultrasound [3], fluorescence imaging is advantageous because of high sensitivity,
excellent resolution, and minimum photodamage to tissues [4]. Fluorescence imaging
has been widely applied for real-time detection of biological species [5–8]. One
challenge of imaging biology in its native physiological state using fluorescence
imaging method is the autofluorescence. Scattered light generated a noise background that might even wash out the image of targets [9]. In addition, most of the
traditional fluorescent probes have absorption and emission in UV-Vis range; however, interference from absorption by hemoglobin, myoglobin, and other heme proteins is significantly high, leading to light scattering and impaired tissue penetration
[10]. Therefore, NIR (700–1,000 nm) light was recommended for wavelength selection for body imaging [11]. Meanwhile, in recent years, dyes in the second nearinfrared region (NIR-II, 1,000–1,700 nm) have been explored with a number of
merits over the NIR-I imaging modalities in terms of reduced photon scattering and
improved penetration depth [12–14], as well as good sensitivity, enhanced spatial
resolution, and better safety profile [15, 16]. A wide variety of NIR excitable
fluorescence contrast agents have been developed for targeting and diagnosis of
cancers, inflammation, and other tissue abnormalities. Representative contrast agents
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X. Yang et al.
detection and diagnosis. Compared with conventional clinical contrast imaging
modalities, such as X-ray and MRI, which use contrast agents that are “always
on,” fluorescence imaging contrast agents can readily be designed to be activatable
under specific circumstances and also can be used in multiplexed imaging schemes.
While a wide variety of fluorescence imaging probes have been developed, small
organic fluorescence probes have the advantages of being robustly synthesized and
characterized, as well as a track record for clinical translation. In this chapter, we
discuss organic fluorophores and highlighted some examples of their biological
applications. The aim of this chapter is to provide a literature review of the development of organic fluorescent probes for biomedical imaging and diagnosis.
Keywords Disease diagnosis, Fluorescence imaging, Fluorescence probes,
Imaging modalities, Organic fluorophores
1 Introduction
Near-infrared fluorescence imaging has developed as a powerful optical imaging
modality for visualization of molecular process and biological activities, which uses a
low-light camera to collect fluorescence emission from fluorophores [1]. The fluorescence imaging technique is based on the fact that the transillumination of light
through normal tissue is significantly different from that through an object (e.g.,
tumor or infected tissues). Compared to other well-developed imaging techniques
such as X-ray, computed tomography (CT) [2], magnetic resonance imaging (MRI),
and ultrasound [3], fluorescence imaging is advantageous because of high sensitivity,
excellent resolution, and minimum photodamage to tissues [4]. Fluorescence imaging
has been widely applied for real-time detection of biological species [5–8]. One
challenge of imaging biology in its native physiological state using fluorescence
imaging method is the autofluorescence. Scattered light generated a noise background that might even wash out the image of targets [9]. In addition, most of the
traditional fluorescent probes have absorption and emission in UV-Vis range; however, interference from absorption by hemoglobin, myoglobin, and other heme proteins is significantly high, leading to light scattering and impaired tissue penetration
[10]. Therefore, NIR (700–1,000 nm) light was recommended for wavelength selection for body imaging [11]. Meanwhile, in recent years, dyes in the second nearinfrared region (NIR-II, 1,000–1,700 nm) have been explored with a number of
merits over the NIR-I imaging modalities in terms of reduced photon scattering and
improved penetration depth [12–14], as well as good sensitivity, enhanced spatial
resolution, and better safety profile [15, 16]. A wide variety of NIR excitable
fluorescence contrast agents have been developed for targeting and diagnosis of
cancers, inflammation, and other tissue abnormalities. Representative contrast agents
34
X. Yang et al.