Sulfo-NHS sodium salt | CAS 106627-54-7 | ≥97%

Sulfo-NHS (N-hydroxysulfosuccinimide sodium salt; sodium 1-hydroxy-2,5-dioxopyrrolidine-3-sulfonate) is the water-soluble, sulfonated analogue of NHS and a standard additive for carbodiimide-mediated amide-bond formation and bioconjugation. Paired with a carbodiimide such as EDC, it converts a carboxylic acid into a water-soluble, amine-reactive sulfo-NHS ester: EDC first forms a short-lived O-acylisourea, which sulfo-NHS intercepts before hydrolysis or rearrangement to the unreactive N-acylurea. The resulting sulfo-NHS ester is more persistent than the O-acylisourea intermediate and remains reactive toward primary amines, improving productive EDC-mediated coupling. Two properties distinguish it from NHS: the charged sulfonate makes sulfo-NHS and its active esters directly water-soluble, allowing many labelling and coupling workflows to run in aqueous buffer without the organic cosolvent often needed for non-sulfonated NHS-ester reagents; and that same charge makes sulfo-NHS esters membrane-impermeant, restricting modification to cell-surface or otherwise solvent-exposed amines. Sulfo-NHS is supplied as a crystalline solid, soluble in water, and should be stored cold and dry.

Carbodiimide-mediated carboxyl-to-amine conjugation

• With EDC, sulfo-NHS traps the O-acylisourea before hydrolysis or N-acylurea formation, diverting the activated acid into a more persistent, water-soluble sulfo-NHS ester and improving productive amide formation.
• The sulfo-NHS ester acylates primary amines — lysine ε-amines and N-terminal α-amines — under mild conditions, giving stable amide bonds; EDC/sulfo-NHS is a standard zero-length carboxyl-to-amine conjugation system.
• Carboxyl activation is typically run near pH 5–6 and amine coupling near neutral to mildly alkaline pH; because the ester is more persistent and water-soluble, activation and amine-coupling can be separated into a two-step procedure in fully aqueous media.

Protein labelling and cell-surface modification

• Amine-reactive sulfo-NHS-ester reagents — sulfo-NHS-biotin and its longer-spacer and cleavable-disulfide variants — acylate solvent-accessible lysine ε-amines and N-termini of antibodies and proteins, core chemistry for antibody biotinylation and protein labelling.
• Because the charged sulfonate prevents sulfo-NHS ester reagents from crossing the plasma membrane, they label only the exterior proteins of intact cells, enabling selective cell-surface biotinylation and surface-proteome capture; cleavable disulfide-spacer variants release captured proteins on reduction.
• Water solubility allows labelling in aqueous buffer without organic cosolvent, suited to cells and proteins that do not tolerate DMSO or DMF.

Surface functionalisation and biosensors

• EDC/NHS or EDC/sulfo-NHS activation of carboxylated surfaces — carboxymethyl-dextran sensor coatings and carboxyl-terminated self-assembled monolayers — covalently immobilises protein ligands on SPR and related optical biosensors.
• The same chemistry functionalises carboxylated nanoparticles, microspheres and microarray slides through stable amide linkages; residual activated surface esters are capped with ethanolamine after ligand immobilisation.

Crosslinking and structural biology

• The water-soluble homobifunctional crosslinker BS3 (sulfo-DSS) bridges proximal lysine ε-amines across an 11.4 Å spacer; being charged and membrane-impermeant, it is confined to the surface of intact cells, complementing membrane-permeant DSS for mapping inside-versus-outside topology.
• Heterobifunctional sulfo-SMCC carries a sulfo-NHS ester at one end and a maleimide at the other, joining a protein amine to a second molecule's thiol in a controlled, two-step amine-to-thiol sequence that limits self-conjugation — used for antibody–enzyme and immunogen–carrier conjugates.
• EDC/sulfo-NHS forms zero-length amide crosslinks between protein carboxylates and lysine amines for protein–protein interaction studies; water-soluble NHS-ester crosslinkers such as BS3 are used in lysine-directed crosslinking mass spectrometry (XL-MS).

Further Reading

For guidance on selecting between carbodiimides, aminium/uronium salts, phosphonium salts and other reagent classes for amide and peptide bond formation, see NorrChemica's Lab Journal guide: Choosing a Coupling Reagent for Amide and Peptide Bond Formation.