Dyestuff Intermediates :
Near-Infrared dyes for Sensing of Biological Targets
Near-infrared dyes materials are promising labeling reagents for sensitive determination and imaging of biological targets. In the near-infrared region biological samples have low background fluorescence signals, providing high signal to noise ratio. Meanwhile, near-infrared radiation can penetrate into sample matrices deeply due to low light scattering. Thus, in vivo and in vitro imaging of biological samples can be achieved by employing the NIR dyes probes. To take full advantage of NIR dyes materials in the biological and biomedical field, one of the key issues is to develop intense and biocompatible NIR dye probes. A number of NIR dye materials are there including traditional NIR dye molecules, newly developed NIR dye quantum dots and single-walled carbon nanotubes, as well as rare earth metal compounds.The major advantage of NIR dye lies in a high signal to noise ratio and thereby achieving low detection limits. Recently, research interests on the near-infrared (NIR) portion of the electromagnetic spectrum (700 – 1000 nm) have increased tremendously. Thus, a high background signal appears in the detection of biological samples when visible fluorescence spectra are used. However, the absorption of the radiation and autofluorescence of these biosamples are at their lowest in the NIR region.
Therefore, the NIR region often is referred to as the “Biological Window”. It is expected that NIR optical imaging will make a significant impact in disease detection and staging, drug development, and treatment assessment.
Biological tissues possess “near infrared window” of transparency above 700 nm (actual value depends on tissue type). This allows for in-depth imaging of organisms in real-time, non-destructive fashion. Labeling of a biomolecule (peptide, protein, or other) with NIR dye makes it possible to track it, and study distribution of the molecule in organism. This type of imaging is a great tool for life science and drug design.
The dyes are of cyanine class. Both possess high extinction coefficients. Internal polymethyne chain contains cyclohexane moiety to increase rigidity and quantum yield. Fluorescence quantum yield is thus improved by 20% comparatively to parent structures.
Succinimide esters are most useful for the labeling of amino groups in various biomolecules, such as proteins and peptides. Azides and alkynes are reactive dyes for advanced and efficient Click Chemistry reaction. We also recommend preparing NIR dye labeled oligonucleotides through post-synthetic Click Chemistry labeling of alkynylated oligos with dye azides.