Sulfo-Cyanine 3 NHS ester

A variety of cyanine dyes has been used to label biological molecules for fluorescence imaging and other fluorescence-based biochemical analysis. They are widely used for labeling peptides, proteins and oligos etc. Cy3® dyes are one type of the most common red fluorophores. These versatile fluorophores can tolerate a pH range of 3-10 for use in a variety of applications at biologically relevant pHs. The dyes are also DMSO tolerant and photostable to enable transfer from storage to assay without loss of performance. The aqueous solubility eliminates the need for organic solvents in the assay buffers. Sulfo-Cyanine 3 is an alternative dye primarily used for labeling peptides and oligos in replacing Cy3 that was originally developed by GE Healthcare (Cy3® is the trademark of GE Healthcare). NHS ester dyes are recommended for labeling amine groups and maleimide dyes are recommended for labeling thiol groups. This Cy3® NHS ester readily reacts with amino groups.

Example protocol

PREPARATION OF STOCK SOLUTIONS

Unless otherwise noted, all unused stock solutions should be divided into single-use aliquots and stored at -20 °C after preparation. Avoid repeated freeze-thaw cycles.

1. Protein stock solution (Solution A)

Mix 100 µL of a reaction buffer (e.g., 1 M sodium carbonate solution or 1 M phosphate buffer with pH ~9.0) with 900 µL of the target protein solution (e.g. antibody, protein concentration >2 mg/mL if possible) to give 1 mL protein labeling stock solution. Note: The pH of the protein solution (Solution A) should be 8.5 ± 0.5. If the pH of the protein solution is lower than 8.0, adjust the pH to the range of 8.0-9.0 using 1 M sodium bicarbonate solution or 1 M pH 9.0 phosphate buffer. Note: The protein should be dissolved in 1X phosphate buffered saline (PBS), pH 7.2-7.4. If the protein is dissolved in Tris or glycine buffer, it must be dialyzed against 1X PBS, pH 7.2-7.4, to remove free amines or ammonium salts (such as ammonium sulfate and ammonium acetate) that are widely used for protein precipitation. Note: Impure antibodies or antibodies stabilized with bovine serum albumin (BSA) or gelatin will not be labeled well. The presence of sodium azide or thimerosal might also interfere with the conjugation reaction. Sodium azide or thimerosal can be removed by dialysis or spin column for optimal labeling results. Note: The conjugation efficiency is significantly reduced if the protein concentration is less than 2 mg/mL. For optimal labeling efficiency the final protein concentration range of 2-10 mg/mL is recommended.

2. Sulfo-Cyanine 3 NHS ester stock solution (Solution B)

Add anhydrous DMSO into the vial of Sulfo-Cyanine 3 NHS ester to make a 10 mM stock solution. Mix well by pipetting or vortex. Note: Prepare the dye stock solution (Solution B) before starting the conjugation. Use promptly. Extended storage of the dye stock solution may reduce the dye activity. Solution B can be stored in freezer for two weeks when kept from light and moisture. Avoid freeze-thaw cycles.

SAMPLE EXPERIMENTAL PROTOCOL

This labeling protocol was developed for the conjugate of Goat anti-mouse IgG with Sulfo-Cyanine 3 NHS ester. You might need further optimization for your particular proteins. Note: Each protein requires distinct dye/protein ratio, which also depends on the properties of dyes. Over labeling of a protein could detrimentally affects its binding affinity while the protein conjugates of low dye/protein ratio gives reduced sensitivity.

Run conjugation reaction

Use 10:1 molar ratio of Solution B (dye)/Solution A (protein) as the starting point: Add 5 µL of the dye stock solution (Solution B, assuming the dye stock solution is 10 mM) into the vial of the protein solution (95 µL of Solution A) with effective shaking. The concentration of the protein is ~0.05 mM assuming the protein concentration is 10 mg/mL and the molecular weight of the protein is ~200KD. Note: We recommend to use 10:1 molar ratio of Solution B (dye)/Solution A (protein). If it is too less or too high, determine the optimal dye/protein ratio at 5:1, 15:1 and 20:1 respectively.
Continue to rotate or shake the reaction mixture at room temperature for 30-60 minutes.

Purify the conjugation

The following protocol is an example of dye-protein conjugate purification by using a Sephadex G-25 column.

Prepare Sephadex G-25 column according to the manufacture instruction.
Load the reaction mixture (From "Run conjugation reaction") to the top of the Sephadex G-25 column.
Add PBS (pH 7.2-7.4) as soon as the sample runs just below the top resin surface.
Add more PBS (pH 7.2-7.4) to the desired sample to complete the column purification. Combine the fractions that contain the desired dye-protein conjugate. Note: For immediate use, the dye-protein conjugate need be diluted with staining buffer, and aliquoted for multiple uses. Note: For longer term storage, dye-protein conjugate solution need be concentrated or freeze dried.

Calculators

Common stock solution preparation

Table 1. Volume of DMSO needed to reconstitute specific mass of Sulfo-Cyanine 3 NHS ester to given concentration. Note that volume is only for preparing stock solution. Refer to sample experimental protocol for appropriate experimental/physiological buffers.

	0.1 mg	0.5 mg	1 mg	5 mg	10 mg
1 mM	136.019 µL	680.096 µL	1.36 mL	6.801 mL	13.602 mL
5 mM	27.204 µL	136.019 µL	272.039 µL	1.36 mL	2.72 mL
10 mM	13.602 µL	68.01 µL	136.019 µL	680.096 µL	1.36 mL

Molarity calculator

Enter any two values (mass, volume, concentration) to calculate the third.

Mass (Calculate)		Molecular weight		Volume (Calculate)		Concentration (Calculate)		Moles
	/		=		x		=

Spectrum

Open in Advanced Spectrum Viewer

Product family

Name	Excitation (nm)	Emission (nm)	Extinction coefficient (cm ^-1 M ^-1)	Quantum yield	Correction Factor (260 nm)	Correction Factor (280 nm)	Correction Factor (482 nm)	Correction Factor (565 nm)
Sulfo-Cyanine 5 NHS ester	651	670	250000¹	0.27¹, 0.4²	0.02	0.03	0.009	0.09

Citations

View all 13 citations: Citation Explorer

Towards an Artificial Replication of the Nuclear Pore Complex
Authors: Medin, Jesper
Journal: (2022)

Thermo-sensitive hydrogel PLGA-PEG-PLGA as a vaccine delivery system for intramuscular immunization
Authors: Wang, Xiaoyan and Zhang, Yu and Xue, Wei and Wang, Hong and Qiu, Xiaozhong and Liu, Zonghua
Journal: Journal of Biomaterials Applications (2017): 923--932

Cube-shaped theranostic paclitaxel prodrug nanocrystals with surface functionalization of SPC and MPEG-DSPE for imaging and chemotherapy
Authors: Guo, Fuqiang and Shang, Jiajia and Zhao, Hai and Lai, Kangrong and Li, Yang and Fan, Zhongxiong and Hou, Zhenqing and Su, Guanghao
Journal: Colloids and Surfaces B: Biointerfaces (2017)

Light/magnetic hyperthermia triggered drug released from multi-functional thermo-sensitive magnetoliposomes for precise cancer synergetic theranostics
Authors: Guo, Yuxin and Zhang, Yang and Ma, Jinyuan and Li, Qi and Li, Yang and Zhou, Xinyi and Zhao, Dan and Song, Hua and Chen, Qing and Zhu, Xuan
Journal: Journal of Controlled Release (2017)

Affinity-Controlled Protein Encapsulation into Sub-30 nm Telodendrimer Nanocarriers by Multivalent and Synergistic Interactions
Authors: Wang, Xu and Shi, Changying and Zhang, Li and Bodman, Alexa and Guo, D and an , undefined and Wang, Lili and Hall, Walter A and Wilkens, Stephan and Luo, Juntao
Journal: Biomaterials (2016)

References

View all 21 references: Citation Explorer

Excitation of Cy5 in self-assembled lipid bilayers using optical microresonators
Authors: Freeman LM, Li S, Dayani Y, Choi HS, Malmstadt N, Armani AM.
Journal: Appl Phys Lett (2011): 143703

Theranostic cRGD-BioShuttle Constructs Containing Temozolomide- and Cy7 For NIR-Imaging and Therapy
Authors: Wiessler M, Hennrich U, Pipkorn R, Waldeck W, Cao L, Peter J, Ehemann V, Semmler W, Lammers T, Braun K.
Journal: Theranostics (2011): 381

Rational approach to select small peptide molecular probes labeled with fluorescent cyanine dyes for in vivo optical imaging
Authors: Berezin MY, Guo K, Akers W, Livingston J, Solomon M, Lee H, Liang K, Agee A, Achilefu S.
Journal: Biochemistry (2011): 2691

In vivo detection of embryonic stem cell-derived cardiovascular progenitor cells using Cy3-labeled Gadofluorine M in murine myocardium
Authors: Adler ED, Bystrup A, Briley-Saebo KC, Mani V, Young W, Giovanonne S, Altman P, Kattman SJ, Frank JA, Weinmann HJ, Keller GM, Fayad ZA.
Journal: JACC Cardiovasc Imaging (2009): 1114

Quantitative proteomics by fluorescent labeling of cysteine residues using a set of two cyanine-based or three rhodamine-based dyes
Authors: Volke D, Hoffmann R.
Journal: Electrophoresis (2008): 4516

Page updated on September 3, 2025

Ordering information

Price
Unit size	10 mg 50 mg
Catalog Number	263264
Quantity

Add to cart

Additional ordering information

Telephone	1-800-990-8053
Fax	1-800-609-2943
Email	sales@aatbio.com
International	See distributors
Bulk request	Inquire
Custom size	Inquire
Technical Support	Contact us
Purchase order	Send to sales@aatbio.com
Shipping	Standard overnight for United States, inquire for international

Request quotation

Physical properties

Molecular weight	735.19
Solvent	DMSO

Spectral properties

Correction Factor (260 nm)	0.07
Correction Factor (280 nm)	0.073
Extinction coefficient (cm ^-1 M ^-1)	150000¹
Excitation (nm)	555
Emission (nm)	569
Quantum yield	0.15¹

Storage, safety and handling

H-phrase	H303, H313, H333
Hazard symbol	XN
Intended use	Research Use Only (RUO)
R-phrase	R20, R21, R22
Storage	Freeze (< -15 °C); Minimize light exposure
UNSPSC	12171501