Sulfo-TAG NHS ester disodium
[CAS# 482618-42-8]

Identification

• Classification: Biochemical >> Biochemical reagent
• Name: Sulfo-TAG NHS ester disodium
• Synonyms: Disodium (2,5-dioxopyrrolidin-1-yl) 4-[2-(4-methylpyridin-2-yl)pyridin-4-yl]butanoate;ruthenium(2+);[2-[4-(sulfonatomethyl)pyridin-2-yl]pyridin-4-yl]methanesulfonate
• Molecular Formula: C₄₃H₃₉N₇Na₂O₁₆RuS₄
• Molecular Weight: 1185.12
• CAS Registry Number: 482618-42-8
• EC Number: 853-382-3
• SMILES: O=C(CCCC1=CC(C2=CC(C)=CC=[N]2[Ru+2]345([N]6=CC=C(CS(=O)([O-])=O)C=C6C7=[N]5C=CC(CS(=O)([O-])=O)=C7)[N]8=CC=C(CS(=O)([O-])=O)C=C8C9=[N]4C=CC(CS(=O)([O-])=O)=C9)=[N]3C=C1)ON%10C(CCC%10=O)=O.[Na+].[Na+]

Safety Data

• Hazard Symbols: GHS06 Danger
• Hazard Statements: H301-H311-H331
• Precautionary Statements: P261-P262-P264-P270-P271-P280-P301+P316-P302+P352-P304+P340-P316-P321-P330-P361+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	3	H301
Acute toxicity	Acute Tox.	3	H311

Discovory and Applicatios

Sulfo-TAG NHS ester disodium is a water-soluble labeling reagent used primarily in electrochemiluminescence (ECL)-based detection systems. It consists of a ruthenium(II) tris-bipyridine complex, modified with an N-hydroxysuccinimide (NHS) ester functional group and sulfonate groups for enhanced aqueous solubility. The NHS ester allows the compound to covalently attach to primary amines on biomolecules such as proteins, peptides, or nucleic acids, forming stable amide bonds. The disodium salt form ensures good solubility in aqueous buffers, facilitating its use in bioconjugation reactions under physiological conditions.

Sulfo-TAG is a proprietary label developed by Meso Scale Discovery (MSD) for use in ECL immunoassays. ECL technology is a highly sensitive detection method in which a ruthenium-based compound emits light upon electrochemical stimulation in the presence of a co-reactant such as tripropylamine. This light emission can be measured with high precision and low background, enabling sensitive quantification of target analytes in biological samples.

The NHS ester moiety of Sulfo-TAG is reactive toward lysine residues or N-terminal amines in proteins. Conjugation is typically performed in mildly basic conditions (pH 7.5–8.5), allowing selective and efficient labeling without denaturing the target molecule. After conjugation, excess unreacted Sulfo-TAG NHS ester is removed through desalting columns, dialysis, or ultrafiltration. The resulting Sulfo-TAG-labeled biomolecule can then be used in ECL-based assays, where it emits a measurable signal proportional to the amount of target analyte present.

Sulfo-TAG NHS ester disodium has found widespread use in immunoassays such as ELISA-type sandwich and competitive assays, Western blotting, and multiplex assays. It is commonly conjugated to secondary antibodies, streptavidin, or detection oligonucleotides to enable signal generation in response to the presence of a specific antigen or DNA target. Because of its strong and stable ECL signal, it allows for highly sensitive detection, often down to femtogram or attomole levels.

One of the major advantages of Sulfo-TAG labeling is its compatibility with high-throughput and multiplex formats. MSD’s ECL platform uses microplates with integrated electrodes at the bottom of each well. Upon application of an electrical potential, Sulfo-TAG-labeled molecules in proximity to the electrode surface emit light, which is captured by a photodetector. This detection is highly specific to electrode activation, minimizing background signal and increasing assay sensitivity.

Sulfo-TAG NHS ester disodium is generally stored as a lyophilized solid or frozen solution and is protected from light to prevent photodegradation. It is typically dissolved in dimethyl sulfoxide (DMSO) or water immediately prior to use. Conjugation protocols require careful control of pH and molar ratios to ensure optimal labeling efficiency without over-labeling, which could affect the biological function of the conjugated molecule.

In summary, Sulfo-TAG NHS ester disodium is a ruthenium-based labeling reagent used in electrochemiluminescence detection systems. Its NHS ester group enables covalent attachment to primary amines on biomolecules, while the sulfonated disodium form ensures water solubility. It is widely used in sensitive, multiplexed immunoassays and nucleic acid detection platforms, offering high signal-to-noise ratios, low detection limits, and compatibility with high-throughput analytical techniques.