| Synonyms: | Equivalent of Cy7 |
| CAS #: | 943298-08-6 |
| Molecular Formula: | C35H42N2O8S2 |
| Molecular Weight: | 682.8 |
| The Cy7 fluorescent dye is a powerful and versatile tool in molecular and cellular biology, primarily valued for its properties in the near-infrared (NIR) spectrum. As a member of the cyanine family of fluorophores, Cy7 represents an advancement over its shorter-wavelength relatives, enabling deeper tissue penetration and reduced background signal in a wide range of bio-imaging applications. 1. Fundamental Photophysical Properties Cy7 is a heptamethine cyanine dye, characterized by a polymethine chain with seven carbon atoms. This structural feature is responsible for its spectral properties, which are significantly red-shifted compared to dyes like Cy3 and Cy5. • Excitation/Absorption Maximum (λex): Approximately 750–770 nm • Emission Maximum (λem): Approximately 775–800 nm • Spectral Range: Near-Infrared (NIR) This spectral window is particularly advantageous for biological studies because it coincides with the “near-infrared window” of biological tissues. In this range, both the absorption by hemoglobin and water and the autofluorescence of biological samples are at their minimum, leading to significantly clearer and more sensitive detection. 2. Primary Applications Due to its unique spectral characteristics, Cy7 is predominantly used in applications where deep-tissue imaging and a high signal-to-background ratio are paramount. 2.1 In Vivo and Deep-Tissue Imaging This is the most significant application of Cy7. By conjugating Cy7 to antibodies, peptides, or other biomolecules, researchers can create probes to track specific targets in live animal models. Applications include: • Drug Distribution and Pharmacokinetics: Real-time monitoring of how a drug is distributed and cleared from the body. • Tumor Imaging and Theranostics: Cy7 is widely used for non-invasive tumor detection. In a more advanced application known as theranostics, Cy7 derivatives are being explored not only for imaging tumors but also for their photothermal and photodynamic therapeutic capabilities, where they can be used to destroy cancer cells with laser irradiation. • Gene Expression Monitoring: Tracking the expression of specific genes tagged with Cy7-labeled probes. 2.2 Flow Cytometry Cy7 is a crucial component in multi-color flow cytometry panels. Its NIR emission allows for the addition of an extra channel to an experiment, without spectral overlap with commonly used visible-range dyes like FITC, PE, or even far-red dyes like APC. This enables more complex, multi-parametric analysis of different cell populations. 2.3 Confocal Microscopy While traditional confocal microscopy is often limited by tissue autofluorescence, the use of Cy7 allows for the acquisition of high-resolution, three-dimensional images of tissues and cells with minimal background noise. This is especially useful for imaging thicker samples where the NIR signal can penetrate more deeply. 2.4 Immunoassays and Protein Detection Cy7-labeled antibodies are used in various immunoassays, including Western blotting, ELISA, and immunohistochemistry. Its use in the NIR range allows for multiplexing, where multiple targets can be detected simultaneously on the same blot or slide using different fluorophores with non-overlapping emission spectra. 3. Advantages of Cy7 • Reduced Autofluorescence: The most critical advantage is its emission in the NIR spectrum, where biological tissues exhibit low intrinsic fluorescence. This dramatically improves the signal-to-noise ratio. • Deeper Tissue Penetration: NIR light scatters and is absorbed less by tissue components like hemoglobin and water, allowing for non-invasive imaging of deep tissues and organs in vivo. • Multiplexing Potential: Cy7’s distinct emission profile makes it an excellent candidate for multi-color experiments, allowing researchers to study multiple targets simultaneously without spectral bleed-through. • High Molar Extinction Coefficient: Cy7 is a very bright dye, meaning it has a high capacity to absorb light at its excitation wavelength, which translates to a strong fluorescent signal. 4. Limitations and Considerations While highly effective, Cy7 is not without its drawbacks, which are important to consider for experimental design. • Photostability: Some Cy7 derivatives, especially tandem dyes like APC-Cy7, are known to have limited photostability and can degrade when exposed to light, heat, or certain fixatives. This can lead to a loss of signal or, in the case of tandem dyes, spillover into the parent dye’s detection channel. • Aggregation: Like other cyanine dyes, Cy7 can have a tendency to aggregate in aqueous solutions, which can lead to fluorescence quenching and a reduction in signal. Newer, sulfonated or PEGylated derivatives have been developed to address this issue by improving water solubility. • Instrumentation: To fully utilize the benefits of Cy7, specialized imaging equipment with NIR lasers and detectors (e.g., a 750 nm laser for excitation and a detector optimized for the 780 nm range) is required, which may not be available in all research labs. 5. Cy7 vs. Cy5: A Brief Comparison Cy5 and Cy7 are often used in similar contexts but serve different purposes due to their different spectral properties. • Spectral Range: Cy5 is a far-red dye with emission around 670 nm. Cy7 is a near-infrared dye with emission around 780 nm. Cy7’s longer wavelength gives it a distinct advantage in deep-tissue imaging. • Autofluorescence: Both dyes benefit from reduced tissue autofluorescence compared to visible dyes, but Cy7 operates in an even more optimal window, offering a greater reduction in background. • Applications: While Cy5 is excellent for many standard microscopy and flow cytometry applications, Cy7 is the dye of choice when the experimental conditions demand maximum tissue penetration and the highest possible signal-to-background ratio, such as in whole-animal imaging. Cy7 is an indispensable fluorescent dye for modern biological research, particularly in the fields of in vivo imaging, cancer theranostics, and advanced multiplexing. Its ability to function effectively in the near-infrared spectrum provides a crucial advantage for overcoming the challenges of tissue autofluorescence and light scattering. While considerations regarding its photostability and the need for specialized equipment are important, continuous development of new, more robust Cy7 derivatives ensures its continued relevance as a cornerstone of high-sensitivity bio-imaging. References: 1. Overview of Fluorescent Dyes 2. Cyanine 3. Dye Directory 4. Cy7 Dye Profile |
|
Cyanine 7
For Research & Development use only. Not for testing and/or use on humans.
