Overview
Cy3.5-labeled dextran is a fluorescent tracer formed by covalently linking the cyanine dye Cy3.5 to dextran, a biocompatible polysaccharide. This conjugate is widely used in life science research due to its dual advantages: the inert, water-soluble properties of dextran and the bright, photostable fluorescence of Cy3.5. The labeling typically involves NHS ester or maleimide chemistry, with 1-3 dye molecules per dextran chain (degree of labeling, DOL). Dextran's size (10-70 kDa) determines its diffusion characteristics, making it useful for studying blood-brain barrier permeability, lymphatic drainage, or nanoparticle uptake.
Physical and Chemical Properties
The conjugate exhibits orange fluorescence with excitation/emission maxima around 550/570 nm, compatible with standard TRITC filter sets. Its quantum yield is higher than many fluorescent proteins, enabling sensitive detection. The dextran backbone provides solubility in aqueous buffers (PBS, saline) and stability across pH 4-9. Unlike free Cy3.5 dye, the dextran conjugate resists cellular uptake due to its size, making it ideal for extracellular space studies. The fluorescence intensity remains stable for hours in vivo, though prolonged exposure to light may cause photobleaching. Shelf life is typically 12-24 months when stored properly.
Main Applications
In vascular biology, Cy3.5-dextran tracks blood vessel leakage or evaluates drug delivery efficiency. Its size-exclusion properties help model macromolecular transport across endothelial barriers. Researchers also use it to label hydrogel matrices or quantify endocytosis in flow cytometry. Neuroscience applications include mapping microcirculation in brain slices or measuring interstitial fluid flow. Compared to FITC-dextran, Cy3.5 offers better tissue penetration and less interference from autofluorescence. Some formulations serve as reference standards in fluorescence microscopy calibration.
Safety and Storage
While dextran is generally non-toxic, the conjugate should be handled as a potential irritant. Avoid skin contact and use gloves/lab coats. Solutions are stable for weeks at 4°C if sterile-filtered, but repeated freeze-thaw cycles should be avoided. For long-term storage, lyophilized powder is preferred. Protect from moisture and light to prevent dye degradation. Dispose of waste according to institutional regulations for organic dyes. In vivo use may require IACUC approval depending on dosage and administration route.
B2B Procurement Guide
When sourcing Cy3.5-dextran, specify: 1) Dextran molecular weight (e.g., 40 kDa for vascular studies), 2) Degree of labeling (typically 1-3 dyes/chain), and 3) Purity (≥90% by HPLC). Bulk orders may qualify for discounts. Reputable suppliers include Sigma-Aldrich, Thermo Fisher, and TdB Labs. Request batch-specific QC data (fluorescence spectra, HPLC traces). For GMP-grade material, expect 2-4 week lead times. Small trial quantities (1-5 mg) are advisable for method validation before large-scale purchase.
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