468
H. M. Heise
20.5 Applications of NIR-Fluorescence in Biomedicine
Near-infrared fluorescence probes (NIFPs) have often been used in immunoassays,
bio-imaging and medical diagnosis. These fluorescent compounds have a characteristic molecular structure with highly conjugated polyene systems for enabling long
emission wavelengths between 650 nm up to 900 nm. In this region, lower tissue
autofluorescence exists with deep tissue penetration and minimal background interference. Its high sensitivity and selectivity is remarkable with the consequence of
fluorescence spectroscopy, finding a broad range of applications also in bioanalytical
chemistry and, in particular, for imaging applications [68]. As most biomolecules
show no or only weak fluorescence, their detection sensitivity is rather low. For
improvement, fluorescent labeling has been used in the past, and near-infrared (NIR)
fluorescence detection shows obvious advantages in biological material analysis. The
potential of cancer NIR imaging can certainly be realized with NIR dyes in conjugation with tumor specific ligands [69]. A recent review on near-infrared fluorescent
dyes and their classification, providing a fine overview on the current state of the
art with applications, has been published [70]. Besides several organic fluorescent
dyes such as cyanine dyes, rhodamine, thiazine and oxazine dyes from past developments (indocyanine green must especially be noticed for measurements with the
vascular system involved), also the synthesis of new classes has been introduced
such as fluorescent quantum dots or rare earth complexes and even single-walled
nanotubes (SWNT) must be mentioned. One wide area is the use within immunoassays, where these dyes are used as marker molecules in medical diagnostics. For
further details, the reader is referred to the recent review [69]. Several studies have
been carried out for indocyanine green enhanced near-infrared optical imaging of
acutely damaged muscle, for which often animal models have been applied. For
imaging applications, nanofluorophores have also been presented that are applicable
within the so-called second near-infrared window (1000–1700 nm), thus providing
high spatial resolution, low background and deep tissue penetration. There are further
recent studies, e.g., for tumor imaging, which could be achieved by using a hypoxiatriggered single molecule probe for background-free NIR II fluorescent imaging with
deep tissue penetration at the centimeter level, providing in addition possibilities in
photothermal therapy for curative tumor treatment [71].
20.6 Concluding Remarks
There are many interdisciplinary research activities worldwide, searching for new
and more efficient analytical methods and techniques for expanding the field of
medical diagnostics. Upgraded technology for clinical chemistry should be based
on reagent-free and automation-capable NIR spectroscopy and the recent advent
of hand-held instrumentation will be widening the application range. For example,
personal measurements on cholesterol and triglycerides in blood have been suggested
H. M. Heise
20.5 Applications of NIR-Fluorescence in Biomedicine
Near-infrared fluorescence probes (NIFPs) have often been used in immunoassays,
bio-imaging and medical diagnosis. These fluorescent compounds have a characteristic molecular structure with highly conjugated polyene systems for enabling long
emission wavelengths between 650 nm up to 900 nm. In this region, lower tissue
autofluorescence exists with deep tissue penetration and minimal background interference. Its high sensitivity and selectivity is remarkable with the consequence of
fluorescence spectroscopy, finding a broad range of applications also in bioanalytical
chemistry and, in particular, for imaging applications [68]. As most biomolecules
show no or only weak fluorescence, their detection sensitivity is rather low. For
improvement, fluorescent labeling has been used in the past, and near-infrared (NIR)
fluorescence detection shows obvious advantages in biological material analysis. The
potential of cancer NIR imaging can certainly be realized with NIR dyes in conjugation with tumor specific ligands [69]. A recent review on near-infrared fluorescent
dyes and their classification, providing a fine overview on the current state of the
art with applications, has been published [70]. Besides several organic fluorescent
dyes such as cyanine dyes, rhodamine, thiazine and oxazine dyes from past developments (indocyanine green must especially be noticed for measurements with the
vascular system involved), also the synthesis of new classes has been introduced
such as fluorescent quantum dots or rare earth complexes and even single-walled
nanotubes (SWNT) must be mentioned. One wide area is the use within immunoassays, where these dyes are used as marker molecules in medical diagnostics. For
further details, the reader is referred to the recent review [69]. Several studies have
been carried out for indocyanine green enhanced near-infrared optical imaging of
acutely damaged muscle, for which often animal models have been applied. For
imaging applications, nanofluorophores have also been presented that are applicable
within the so-called second near-infrared window (1000–1700 nm), thus providing
high spatial resolution, low background and deep tissue penetration. There are further
recent studies, e.g., for tumor imaging, which could be achieved by using a hypoxiatriggered single molecule probe for background-free NIR II fluorescent imaging with
deep tissue penetration at the centimeter level, providing in addition possibilities in
photothermal therapy for curative tumor treatment [71].
20.6 Concluding Remarks
There are many interdisciplinary research activities worldwide, searching for new
and more efficient analytical methods and techniques for expanding the field of
medical diagnostics. Upgraded technology for clinical chemistry should be based
on reagent-free and automation-capable NIR spectroscopy and the recent advent
of hand-held instrumentation will be widening the application range. For example,
personal measurements on cholesterol and triglycerides in blood have been suggested