CF dyes (trademarked as CF Dyes by Biotium) are a class of fluorescent dyes developed for biological research applications, including fluorescence microscopy, flow cytometry, and in vivo imaging.^[1][2] First introduced in the late 2000s, these dyes are characterized by a chemical strategy combining pegylation with sulfonation to achieve high water solubility while minimizing non-specific binding.^[3]

Varieties include 42 fluorophores spanning excitation wavelengths from 347 nm (ultraviolet) to 876 nm (near-infrared), built on four core chemical scaffolds: coumarin, pyrene, rhodamine, and cyanine.^[3] These dyes have been used in super-resolution microscopy, where several variants have been validated for techniques including STORM, MINFLUX, and STED microscopy.^[4][5]

History and development

Development began around 2007^[2][6] in response to limitations observed in existing commercial fluorophores, particularly the tendency of heavily sulfonated dyes to exhibit non-specific binding to positively charged cellular components.^[3] To address these issues, researchers developed a design strategy combining sulfonation with polyethylene glycol (PEG) modification, the details of which are described in a 2014 U.S. patent.^[3]

In 2009, researchers reported the development of a rhodamine–imidazole substitution strategy in which the benzene ring commonly used for conjugation was replaced with an imidazolium group.^[3][7] This modification produced a red shift in emission wavelength while preserving the photostability of the rhodamine xanthene core, extending the usable spectral range of rhodamine dyes toward the near-infrared region.^[7]

In 2022, a collaboration with researchers at UC Berkeley yielded CF583R and CF597R, which are rhodamine-based dyes optimized for STORM microscopy.^[7]

Chemistry

CF dyes are synthesized through chemical modifications of established coumarin, rhodamine, and cyanine dye scaffolds.^[7] The dyes employ a dual strategy of sulfonation and pegylation.^[3] Sulfonation introduces sulfonate groups (–SO₃⁻) to improve water solubility, while pegylation adds polyethylene glycol (PEG) chains that sterically shield charged groups and reduce dye aggregation.^[3]

The PEG moieties inhibit π-stacking between adjacent dye molecules, reducing H-aggregate formation. H-aggregation is a cause of fluorescence quenching when multiple dye molecules are attached to a single antibody, limiting the useful degree of labeling (DOL) in antibody conjugates.^[3]

Rhodamine-based near-infrared CF dyes (designated with an "R" suffix) utilize rhodamine–imidazole substitution chemistry, as described in Wang et al. (2022), to extend emission wavelengths beyond the traditional ~600 nm limit while retaining the photostability characteristic of the rhodamine scaffold.^[3][7] The rigid xanthene core of rhodamines confers resistance to photobleaching relative to the flexible polymethine bridge found in cyanine dyes.^[7]

Applications

Applications include immunofluorescence microscopy, flow cytometry, western blotting, in vivo imaging, fluorescence in situ hybridization, expansion microscopy, and apoptosis detection.^[8][9][10]

Patents

Key patents covering CF Dye technology include US8709830B2 ("Fluorescent dyes, fluorescent dye kits, and methods of preparing labeled molecules"), EP2223086B1 (priority date 2007), and international application WO2012129128A1.^[3][18]

See also

• Fluorophore
• Fluorescence microscopy
• Super-resolution microscopy

References