analytical & laboratory EquipmEnt 27
autofluorescence. The imager design supports
the requirement for wide dynamic range,
eliminating the concern of signal saturation.
The Pearl Imager NIR laser excitation
enables deeper tissue penetration and when
combined with IRDye fluorophore technology
(LI-COR Biosciences), provides exceptional
signal to background ratios.
Dyes and agents
While the development of a NIR optimised
imaging system such as the Pearl Imager
is important, the technology used for
developing optical tracking agents is another
Fig. 2. Variations in inherent autofluorescence as a function of illumination
key component required for successful in vivo
wavelength in pre-injected mice was demonstrated when mice were illuminated
imaging experimental design.
with 785nm light (Image A) and 660 nm light (Image B). Image A has a reference
A number of NIR dyes have been
vial containing 10 pmol of IRDye 800CW EGF. Image B has a reference vial
employed for in vivo imaging. Quantum
containing 10 pmol of Cy5.5 EGF. The NIR image (Image A) shows a significantly
dots, with their photostability and bright
lower level of autofluorescence from the mouse when compared to the red
emissions, have generated a great deal
fluorescent image (image B). Chlorophyll in the animal’s diet causes the bright
of interest; however, their size precludes
signal in Image B.
efficient clearance from the circulatory
and renal systems and there are questions
Data courtesy of Dr E M Sevick-Muraca, Baylor College of Medicine, Houston, TX. Comparison of visible and
about their long-term toxicity (Shah, K. and near-infrared wavelength excitable dyes for molecular imaging of cancer.
Weissleder, R. J. Amer. Soc. Exp. Neurother. 2,
Journal of Biomedical Optics 12 024017 (2007).
215 (2005). detection systems for such areas as drug discovery and
Cy5.5 has been used in the past primarily due to DNA sequencing for genomic research.
the lack of other dyes more suitable for imaging. The Founded in 1971, the privately held company is based
excitation/emission maxima for this dye (675/694 nm) in Lincoln, Nebraska, with subsidiaries in Germany and
fall in the range affected by tissue autofluorescence, the United Kingdom. LI-COR systems are used in over
impacting its overall performance. 100 countries and are supported by a global network of
distributors. u
Excitation/emission maxima
In contrast, IRDye 800CW (LI-COR Biosciences) has Enter 27 or ✔ at
www.scientistlive.com/elab
excitation/emission maxima at 774/789 nm, precisely
centred in the region known to give optimal Jeff Harford is Senior Product Manager, LI-COR Biosciences,
signal-to-background ratio for optical imaging (Fig. 1). Lincoln, NE, USA.
www.licor.com
The IRDye 800CW infrared dye has
minimal non-specific binding, excellent
water solubility and has been used for the
development of a number of tumour as well
as structural optical imaging agents.
Several Optical probes are currently
available including the IRDye 800CW EGF
Optical Probe, the IRDye 800CW 2-DG
and the IRDye BoneTag (Fig. 4) – more
information is available at
www.IRDye.com.
Additionally, IRDye 800CW labelling kits
are available for development of other optical
probes.
LI-COR Biosciences designs and
manufactures instrument systems for
biotechnology and environmental research.
LI-COR instruments for photosynthesis,
carbon dioxide analysis and light
measurement.
The company pioneers the development Fig. 4. IRDye 800CW EGF Optical Probe targeting a tumour with the IRDye 680
of infrared fluorescence labelling and BoneTag marking the bone structure of a nude mouse.
www.scientistlive.com
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