Inquiry Basket
NHS Ester Chemistry & Amine-Reactive Labeling Support
What Are NHS Ester Reagents? Chemistry, Reactivity, and Role in Fluorescent Labeling
N-hydroxysuccinimide (NHS) ester reagents are amine-reactive compounds that form stable amide bonds with primary amines under mild aqueous conditions. They are among the most widely used tools in bioconjugation, fluorescent labeling, crosslinking, and probe construction because they react quickly, tolerate physiological buffers, and produce linkages that are resistant to hydrolysis under normal assay conditions.
This guide explains the structure and preparation of NHS esters, the reaction mechanism that drives amine acylation, the factors that control conjugation efficiency, and the role NHS ester reagents play in fluorescent dye labeling of proteins, antibodies, peptides, and nucleic acids.
What Can BOC Sciences Help You Solve?
Unsure which NHS ester reagent to use?
Compare amine-reactive dyes, crosslinkers, and activated esters based on your labeling target and assay platform.
Need to optimize conjugation efficiency?
Match pH, buffer, molar ratio, and reaction time to your protein, antibody, peptide, or oligonucleotide substrate.
Facing hydrolysis or low labeling yield?
Identify handling, storage, and buffer issues that cause NHS ester degradation and reduce labeling performance.
Planning fluorescent conjugates for assays or imaging?
Select suitable fluorescent dyes and NHS ester formats for protein, antibody, peptide, and nucleic acid labeling projects.
Need custom NHS ester reagents?
Support custom NHS ester synthesis, dye functionalization, linker design, and scaled conjugation services.
Overview: Why NHS Ester Reagents Matter in Fluorescent Labeling
NHS ester reagents, also called succinimidyl esters, are activated forms of carboxylic acids in which the acid is esterified with N-hydroxysuccinimide. This activation converts a carboxyl group into a good electrophile that reacts selectively with unprotonated primary amines, forming a stable amide linkage and releasing N-hydroxysuccinimide as a benign leaving group. Because proteins, antibodies, peptides, and amino-modified oligonucleotides all carry primary amines, NHS ester chemistry provides a general route for attaching fluorescent dyes, biotin, drugs, and crosslinkers to biological molecules.
In fluorescent labeling workflows, NHS ester derivatives of dyes such as fluorescein, rhodamine, cyanine, and BODIPY dyes are prepared so that the dye can be conjugated directly to a biomolecule of interest. The reaction is fast, typically reaching useful conversion within 30 to 120 minutes at room temperature, and it proceeds in aqueous buffers near neutral to mildly basic pH. These features make NHS ester chemistry the default starting point for most protein and antibody fluorescent labeling projects, and a common option for peptide, nucleic acid, and small molecule labeling as well.
The practical value of NHS ester reagents depends on several connected factors: the quality and stability of the reagent, the pH and composition of the reaction buffer, the molar ratio between dye and biomolecule, and the purification and characterization of the final conjugate. Understanding these factors helps researchers avoid low labeling efficiency, high background, and loss of biological activity, and it supports reproducible conjugate preparation across different laboratories and applications.
Core principle:
NHS ester chemistry converts a carboxyl group into an amine-reactive electrophile. The resulting amide bond is stable under physiological conditions,
which is why NHS ester dyes and crosslinkers are so widely used for fluorescent labeling, antibody conjugation, and probe construction. The main
practical challenge is the competing hydrolysis of the NHS ester in water, so reaction pH, buffer choice, reagent handling, and timing must be
controlled carefully.
Core Chemistry: Structure and Preparation of NHS Esters
The reactivity of an NHS ester reagent is defined by its activated ester structure and by the molecule attached to the carboxyl carbon. This section describes the structural features that make NHS esters amine-reactive, how they are prepared from carboxylic acids, and how the reactive group behaves in aqueous solution.
Activated ester structure:
In an NHS ester, the carboxyl group of a dye, drug, biotin, or linker is esterified with N-hydroxysuccinimide. The electron-withdrawing succinimide ring makes the carbonyl carbon more electrophilic than in a simple ester, so primary amines can attack it under mild conditions.
In an NHS ester, the carboxyl group of a dye, drug, biotin, or linker is esterified with N-hydroxysuccinimide. The electron-withdrawing succinimide ring makes the carbonyl carbon more electrophilic than in a simple ester, so primary amines can attack it under mild conditions.
Amine selectivity:
NHS esters react preferentially with unprotonated primary amines, such as the epsilon-amino group of lysine side chains and the N-terminal amine of proteins and peptides. Secondary amines react more slowly, and other nucleophiles react only under forcing conditions.
NHS esters react preferentially with unprotonated primary amines, such as the epsilon-amino group of lysine side chains and the N-terminal amine of proteins and peptides. Secondary amines react more slowly, and other nucleophiles react only under forcing conditions.
Preparation routes:
NHS esters are typically prepared by activating a carboxylic acid with a carbodiimide such as EDC in the presence of N-hydroxysuccinimide, or by using uronium coupling reagents such as HATU or TSTU. The isolated NHS ester can then be stored and used later.
NHS esters are typically prepared by activating a carboxylic acid with a carbodiimide such as EDC in the presence of N-hydroxysuccinimide, or by using uronium coupling reagents such as HATU or TSTU. The isolated NHS ester can then be stored and used later.
Leaving group:
During the reaction, N-hydroxysuccinimide is released. It is water soluble, generally non-toxic, and easily removed from the conjugate during purification, which simplifies downstream processing.
During the reaction, N-hydroxysuccinimide is released. It is water soluble, generally non-toxic, and easily removed from the conjugate during purification, which simplifies downstream processing.
Sulfo-NHS variants:
Sulfo-NHS esters carry a sulfonate group that improves water solubility and eliminates the need for organic co-solvents in some protocols. They react by the same mechanism but are preferred for certain protein and cell-based labeling applications.
Sulfo-NHS esters carry a sulfonate group that improves water solubility and eliminates the need for organic co-solvents in some protocols. They react by the same mechanism but are preferred for certain protein and cell-based labeling applications.
Linker integration:
NHS esters are frequently incorporated into heterobifunctional crosslinkers that carry a second reactive group, such as a maleimide, azide, alkyne, or hydrazide, enabling two-step conjugation strategies.
NHS esters are frequently incorporated into heterobifunctional crosslinkers that carry a second reactive group, such as a maleimide, azide, alkyne, or hydrazide, enabling two-step conjugation strategies.
Practical note:
NHS ester reagents are moisture sensitive. Hydrolysis converts the activated ester back to the free carboxylic acid, which is no longer reactive toward
amines. Reagents should be stored desiccated at low temperature, warmed to room temperature before opening, and dissolved in anhydrous solvent
immediately before use.
Reaction Mechanism and the Role of pH
The NHS ester reaction with a primary amine is a nucleophilic acyl substitution. The unprotonated amine attacks the carbonyl carbon of the ester, forming a tetrahedral intermediate that collapses to release N-hydroxysuccinimide and generate the amide product. Because the amine must be unprotonated to act as a nucleophile, pH strongly controls reaction rate.
Nucleophilic attack:
The lone pair of the primary amine attacks the electrophilic carbonyl carbon of the NHS ester, forming a tetrahedral intermediate.
The lone pair of the primary amine attacks the electrophilic carbonyl carbon of the NHS ester, forming a tetrahedral intermediate.
Intermediate collapse:
The tetrahedral intermediate collapses, expelling N-hydroxysuccinimide and forming a stable amide bond between the biomolecule and the dye or linker.
The tetrahedral intermediate collapses, expelling N-hydroxysuccinimide and forming a stable amide bond between the biomolecule and the dye or linker.
pH dependence:
Below pH 7, most amines are protonated and unreactive. As pH rises, the fraction of deprotonated, nucleophilic amine increases, accelerating aminolysis. The practical optimum for most NHS ester conjugations is pH 8.0 to 8.5.
Below pH 7, most amines are protonated and unreactive. As pH rises, the fraction of deprotonated, nucleophilic amine increases, accelerating aminolysis. The practical optimum for most NHS ester conjugations is pH 8.0 to 8.5.
Hydrolysis competition:
Water can also attack the NHS ester, hydrolyzing it to the free acid. Hydrolysis accelerates at higher pH, so working above pH 8.5 reduces conjugation efficiency instead of improving it.
Water can also attack the NHS ester, hydrolyzing it to the free acid. Hydrolysis accelerates at higher pH, so working above pH 8.5 reduces conjugation efficiency instead of improving it.
Temperature control:
Reactions are commonly run at room temperature for 1 to 2 hours or at 4 degrees Celsius overnight. Lower temperatures slow hydrolysis and can improve outcomes for dilute protein solutions.
Reactions are commonly run at room temperature for 1 to 2 hours or at 4 degrees Celsius overnight. Lower temperatures slow hydrolysis and can improve outcomes for dilute protein solutions.
Buffer compatibility:
Buffers containing primary amines, such as Tris and glycine, compete with the target molecule and must be avoided during conjugation. Phosphate, bicarbonate, borate, and HEPES buffers are commonly used instead.
Buffers containing primary amines, such as Tris and glycine, compete with the target molecule and must be avoided during conjugation. Phosphate, bicarbonate, borate, and HEPES buffers are commonly used instead.
| Condition | Typical Value | Effect on Reaction |
|---|---|---|
| Reaction pH | 8.0-8.5 | Balances amine nucleophilicity against NHS ester hydrolysis. |
| Temperature | Room temperature (1-2 h) or 4 degrees Celsius (overnight) | Lower temperature reduces hydrolysis but extends reaction time. |
| NHS ester hydrolysis half-life | About 4-5 h at pH 7, about 10 min at pH 8.6 (0 degrees Celsius) | Higher pH dramatically shortens reagent lifetime in water. |
| Buffer type | Bicarbonate, borate, phosphate, HEPES | Avoid primary amine buffers such as Tris and glycine. |
| Typical molar excess | 5-20 fold over biomolecule | Higher ratios raise the degree of labeling but can reduce activity. |
For researchers building click-compatible fluorescent probes, NHS ester derivatives can be combined with azide or alkyne functionalized dyes for two-step conjugation workflows. Learn how click chemistry reagents support selective fluorescent labeling.
The Role of NHS Esters in Fluorescent Labeling
Fluorescent labeling with NHS ester dyes is the most common way to prepare fluorescent protein, antibody, peptide, and nucleic acid conjugates. The dye is supplied with an NHS ester functional group, dissolved in anhydrous solvent, and mixed with the biomolecule under mildly basic conditions. The covalent amide bond that forms is stable, and the labeled molecule can be purified and characterized for downstream use.
Protein Labeling
NHS ester dyes label lysine side chains and the N-terminus of proteins. The approach is widely used for preparing fluorescent enzymes, receptors, and other proteins for binding studies, tracking, and analytical assays.
Antibody Labeling
Antibody conjugates prepared with NHS ester dyes are standard reagents for immunofluorescence, flow cytometry, and immunoblotting. Controlling the dye-to-antibody ratio preserves antigen binding and reduces background.
Peptide Labeling
Peptides can be labeled at the N-terminus or at lysine residues using NHS ester dyes, producing fluorescent peptides for receptor binding, cellular uptake, and imaging studies.
Oligonucleotide Labeling
Amino-modified oligonucleotides react with NHS ester dyes to form labeled probes for qPCR, FISH, microarrays, and other nucleic acid detection applications.
Small Molecule Labeling
NHS esters can attach fluorescent dyes, biotin, or other functional groups to amine-containing small molecules, enabling tracer synthesis and assay development.
Surface and Bead Functionalization
Amine-presenting surfaces, nanoparticles, and beads can be functionalized with NHS ester dyes or crosslinkers for capture assays and imaging applications.
Labeling efficiency note:
The efficiency of NHS ester conjugation depends on protein concentration, dye-to-protein molar ratio, pH, and the accessibility of amine groups.
Labeling efficiency is typically 20 to 35 percent for antibody conjugations at moderate protein concentrations, so an excess of dye is normally used
to reach the desired degree of labeling.
NHS Esters vs Other Amine-Reactive Reagents
NHS esters are not the only amine-reactive functional groups used for labeling. Isothiocyanates, sulfonyl chlorides, and other activated esters offer different trade-offs in reactivity, stability, and handling. The table below compares NHS esters with the alternatives most often encountered in fluorescent labeling workflows.
| Reagent Type | Target Group | Linkage Formed | Optimal pH | Notes |
|---|---|---|---|---|
| NHS ester | Primary amines | Amide | 8.0-8.5 | Fast, widely used, moisture sensitive, some hydrolysis competition. |
| Sulfo-NHS ester | Primary amines | Amide | 8.0-8.5 | Water soluble, avoids organic co-solvents, same reaction chemistry. |
| Isothiocyanate (FITC) | Primary amines | Thiourea | 9.0-9.5 | Stable in water, slower reaction, classic FITC labeling chemistry. |
| Sulfonyl chloride | Primary amines | Sulfonamide | 8.0-9.0 | Reactive but less selective, used in specialized dye chemistry. |
| TFP / STP ester | Primary amines | Amide | 7.5-8.5 | Alternative activated esters with different hydrolysis profiles. |
For labeling workflows that require site selectivity rather than random amine modification, bioorthogonal approaches provide an alternative route. Researchers developing probes, modified biomolecules, or surface-functionalized fluorescent labels may benefit from click-compatible reagents. Read how bioorthogonal labeling improves selectivity and flexibility.
Application-Based Use of NHS Ester Reagents
NHS ester reagents support a wide range of research and analytical workflows. The most appropriate reagent format, dye, and reaction condition depend on the target molecule, the detection platform, and the required conjugate quality. The table below summarizes common applications and the NHS ester reagents typically used for each.
Immunofluorescence and microscopy:
NHS ester dyes such as FITC, rhodamine, cyanine, and TAMRA derivatives label antibodies for direct immunofluorescence staining and confocal imaging.
NHS ester dyes such as FITC, rhodamine, cyanine, and TAMRA derivatives label antibodies for direct immunofluorescence staining and confocal imaging.
Flow cytometry:
Bright, water-soluble NHS ester dyes are used to prepare antibody conjugates for multicolor flow cytometry panels.
Bright, water-soluble NHS ester dyes are used to prepare antibody conjugates for multicolor flow cytometry panels.
Immunoblotting and ELISA:
Enzyme- and fluorophore-labeled antibodies prepared via NHS ester chemistry serve as detection reagents in immunoblotting and immunoassay formats.
Enzyme- and fluorophore-labeled antibodies prepared via NHS ester chemistry serve as detection reagents in immunoblotting and immunoassay formats.
Nucleic acid detection:
NHS ester dyes label amino-modified oligonucleotides for qPCR probes, FISH probes, and microarray detection.
NHS ester dyes label amino-modified oligonucleotides for qPCR probes, FISH probes, and microarray detection.
FRET probe construction:
Donor and acceptor dyes carrying NHS esters can be conjugated to peptides or nucleic acids to build FRET-based biosensors.
Donor and acceptor dyes carrying NHS esters can be conjugated to peptides or nucleic acids to build FRET-based biosensors.
Crosslinking and conjugation:
NHS ester crosslinkers, including heterobifunctional reagents, connect amine groups with thiols or click partners for probe and conjugate assembly.
NHS ester crosslinkers, including heterobifunctional reagents, connect amine groups with thiols or click partners for probe and conjugate assembly.
| Application | Typical Target | Representative NHS Ester Reagent | Key Considerations |
|---|---|---|---|
| Direct immunofluorescence | Antibodies | FITC, rhodamine, cyanine NHS esters | Control dye-to-antibody ratio, minimize background. |
| Flow cytometry | Antibodies | Bright, water-soluble NHS ester dyes | Match excitation source and minimize spectral overlap. |
| qPCR probe design | Amino-modified oligonucleotides | FAM, Cy3, Cy5 NHS esters | Label at the 5-prime or internal amino-modified site. |
| Peptide receptor studies | Peptides | TAMRA, cyanine NHS esters | Avoid labeling residues required for receptor binding. |
| Surface functionalization | Amino surfaces, beads | NHS ester crosslinkers, dye NHS esters | Control surface density and washing steps. |
Need Help Choosing an NHS Ester Reagent for Your Labeling Workflow?
BOC Sciences can support NHS ester reagent selection, dye functionalization, conjugation optimization, and custom fluorescent labeling for proteins, antibodies, peptides, oligonucleotides, and small molecules.
Request NHS Ester Labeling SupportA Practical Workflow for NHS Ester Labeling
A structured workflow helps researchers move from reagent selection to a purified, characterized fluorescent conjugate. The steps below apply broadly to protein, antibody, peptide, and oligonucleotide labeling with NHS ester dyes, and they can be adjusted for the specific biomolecule and dye.
Step 1: Select the dye and NHS ester format
Choose a fluorescent dye whose excitation and emission match the detection platform, and confirm that it is available as an NHS ester or sulfo-NHS ester. Consider brightness, photostability, solubility, and spectral compatibility with other labels.
Choose a fluorescent dye whose excitation and emission match the detection platform, and confirm that it is available as an NHS ester or sulfo-NHS ester. Consider brightness, photostability, solubility, and spectral compatibility with other labels.
Step 2: Prepare the biomolecule
Exchange the protein, antibody, peptide, or amino-modified oligonucleotide into an amine-free buffer such as 0.1 M sodium bicarbonate at pH 8.3 to 8.5. Remove Tris, glycine, ammonium salts, and other amine-containing components that would compete for the NHS ester.
Exchange the protein, antibody, peptide, or amino-modified oligonucleotide into an amine-free buffer such as 0.1 M sodium bicarbonate at pH 8.3 to 8.5. Remove Tris, glycine, ammonium salts, and other amine-containing components that would compete for the NHS ester.
Step 3: Dissolve the NHS ester reagent
Prepare the reagent fresh in anhydrous DMSO or DMF at a defined concentration. Keep the organic solvent content below 5 to 10 percent of the final reaction volume to avoid damaging the biomolecule.
Prepare the reagent fresh in anhydrous DMSO or DMF at a defined concentration. Keep the organic solvent content below 5 to 10 percent of the final reaction volume to avoid damaging the biomolecule.
Step 4: Run the conjugation reaction
Add the NHS ester solution to the biomolecule at a 5 to 20 fold molar excess, mix gently, and incubate at room temperature for 1 to 2 hours protected from light. Optimize the ratio for the desired degree of labeling.
Add the NHS ester solution to the biomolecule at a 5 to 20 fold molar excess, mix gently, and incubate at room temperature for 1 to 2 hours protected from light. Optimize the ratio for the desired degree of labeling.
Step 5: Purify the conjugate
Remove unreacted dye and released N-hydroxysuccinimide using a desalting column, size-exclusion chromatography, or dialysis. Confirm separation by monitoring absorbance at 280 nm and at the dye absorption maximum.
Remove unreacted dye and released N-hydroxysuccinimide using a desalting column, size-exclusion chromatography, or dialysis. Confirm separation by monitoring absorbance at 280 nm and at the dye absorption maximum.
Step 6: Characterize and validate
Calculate the degree of labeling from the absorbance spectrum, and verify that the conjugate retains biological activity, solubility, and stability under storage conditions appropriate for the labeled molecule.
Calculate the degree of labeling from the absorbance spectrum, and verify that the conjugate retains biological activity, solubility, and stability under storage conditions appropriate for the labeled molecule.
Common Challenges and Optimization Tips
NHS ester labeling performance is affected by reagent stability, buffer composition, reaction conditions, and conjugate quality. Recognizing common problems early helps improve yield, reduce background, and preserve biomolecule activity.
Low labeling efficiency
Check the buffer for primary amines, confirm pH 8.0 to 8.5, use freshly dissolved NHS ester, and increase the protein concentration above 1 mg/mL when possible.
High background signal
Remove free dye completely by purification, centrifuge to remove dye aggregates, and avoid over-labeling that increases nonspecific binding.
Loss of biological activity
Reduce the dye-to-biomolecule ratio, label at lower temperature, and validate activity immediately after conjugation. Site-selective strategies can preserve critical binding or catalytic regions.
Reagent hydrolysis
Store NHS esters desiccated at low temperature, avoid aqueous stock solutions, and prepare reaction mixtures quickly to minimize hydrolysis before conjugation.
Protein precipitation
Hydrophobic dyes or excessive organic solvent can cause precipitation. Use sulfo-NHS ester dyes or water-soluble derivatives, and keep the organic solvent fraction low.
Inconsistent labeling
Variability often comes from reagent age, buffer pH drift, or batch differences. Use fresh reagents, verify pH, and standardize the reaction protocol across experiments.
How BOC Sciences Supports NHS Ester Labeling Research
BOC Sciences provides NHS ester reagents, amine-reactive fluorescent dyes, custom NHS ester synthesis, and fluorescent labeling services for research and analytical development. The service scope can support reagent selection, dye functionalization, biomolecule conjugation, and application-oriented optimization.
NHS Ester Reagent Supply
Researchers can access NHS ester dyes, crosslinkers, and activated reagents for labeling and conjugation workflows.
- Fluorescent dye NHS esters
- Sulfo-NHS ester reagents
- NHS ester crosslinkers
- Biotin and hapten NHS esters
Custom NHS Ester Synthesis
Custom synthesis supports dye functionalization, linker design, and NHS ester activation for specialized reagents.
- Dye carboxylate activation
- Linker and spacer design
- Sulfo-NHS modification
- Scaled reagent production
Fluorescent Labeling Services
Custom labeling support is available for proteins, antibodies, peptides, oligonucleotides, and small molecules.
- Protein and antibody labeling
- Peptide and oligonucleotide labeling
- Degree of labeling control
- Conjugate purification
Conjugation Optimization
Reaction condition optimization helps improve labeling yield, reduce background, and preserve biomolecule activity.
- Buffer and pH selection
- Molar ratio optimization
- Hydrolysis control
- Troubleshooting support
Crosslinker Application Support
NHS ester crosslinkers can be applied to connect amines with thiols or click partners for probe and conjugate assembly.
- Heterobifunctional reagent selection
- Two-step conjugation design
- Surface functionalization
- Probe construction
Application Development
Application-focused support aligns NHS ester chemistry and conjugate design with assay, imaging, and diagnostic goals.
- Immunoassay reagent preparation
- Imaging probe development
- Biosensor construction
- Custom fluorescent probes
Start Your NHS Ester Conjugation Project with BOC Sciences
Whether you need a standard NHS ester dye, a custom amine-reactive reagent, a labeled antibody, a nucleic acid probe, or a complete fluorescent labeling workflow, BOC Sciences can help identify suitable reagents and strategies for your research goals.
Send Your Project RequirementsRecommended NHS Ester Products
The following products are recommended for researchers working with NHS ester chemistry, amine-reactive labeling, bioconjugation, and conjugate preparation. The selection includes fluorescent NHS esters, cyanine and BODIPY derivatives, biotinylation reagents, click chemistry building blocks, and other activated esters for protein, antibody, peptide, and nucleic acid modification.
| Catalog | Product Name | CAS | Inquiry |
|---|---|---|---|
| R01-0029 | Sulfo-Cyanine3 NHS ester | Bulk Inquiry | |
| R01-0035 | Sulfo-Cyanine7 NHS ester | Bulk Inquiry | |
| R01-0032 | Sulfo-Cyanine5 NHS ester | Bulk Inquiry | |
| R01-0037 | TAMRA NHS ester, 5-isomer | 321862-17-3 | Bulk Inquiry |
| R01-0036 | Sulfo-Cyanine7.5 NHS ester | Bulk Inquiry | |
| R01-0034 | Sulfo-Cyanine7 bis-NHS ester | Bulk Inquiry | |
| R01-0033 | Sulfo-Cyanine5.5 NHS ester | Bulk Inquiry | |
| R01-0031 | Sulfo-Cyanine5 bis-NHS ester | Bulk Inquiry | |
| R01-0028 | ROX NHS ester, 6-isomer | 117491-83-5 | Bulk Inquiry |
| F02-0030 | Cy3-NHS ester | 146368-16-3 | Bulk Inquiry |
| R01-0019 | Cyanine5 NHS ester | 350686-88-3 | Bulk Inquiry |
| R01-0476 | Digoxigenin NHS-ester | 129273-26-3 | Bulk Inquiry |
| R01-0024 | DBCO-C6-NHS ester | 1384870-47-6 | Bulk Inquiry |
| R01-0023 | Cyanine7.5 NHS ester | Bulk Inquiry | |
| R01-0020 | Cyanine5 NHS ester minimal dye | Bulk Inquiry | |
| R01-0018 | Cyanine3.5 NHS ester | 2231670-85-0 | Bulk Inquiry |
| R01-0030 | sulfo-Cyanine3.5 NHS ester | Bulk Inquiry | |
| R01-0016 | Cyanine3 NHS ester | Bulk Inquiry | |
| R01-0017 | Cyanine3 NHS ester minimal dye | Bulk Inquiry | |
| R01-0015 | Cyanine2 NHS ester minimal dye | Bulk Inquiry | |
| R01-0438 | Cy5-NHS ester tetrafluoroborate | 1263093-76-0 | Bulk Inquiry |
| R01-0441 | Cy5.5 NHS ester (potassium salt) | 910482-46-1 | Bulk Inquiry |
| R01-0014 | Coumarin 343 X NHS ester | 946123-12-2 | Bulk Inquiry |
| R01-0012 | BDP TR NHS ester | 150152-65-1 | Bulk Inquiry |
| R01-0011 | BDP TMR NHS ester | 485397-12-4 | Bulk Inquiry |
| R01-0010 | BDP R6G NHS ester | 335193-70-9 | Bulk Inquiry |
| R01-0007 | BDP 630/650 X NHS ester | 2213445-35-1 | Bulk Inquiry |
| R01-0006 | BDP 581/591 NHS ester | 654651-21-5 | Bulk Inquiry |
| R01-0022 | Cyanine7 NHS ester | 1432019-64-1 | Bulk Inquiry |
| R01-0003 | Alkyne-PEG3-NHS ester | Bulk Inquiry | |
| R01-0001 | AF488 NHS ester | Bulk Inquiry | |
| R01-0005 | BDP 558/568 NHS ester | 150173-73-2 | Bulk Inquiry |
| R01-0474 | Biotin-PEG4-NHS ester | 459426-22-3 | Bulk Inquiry |
| R01-0439 | 6-Azidohexanoic acid sulfo-NHS ester | Bulk Inquiry | |
| R01-0002 | 5-hexynoic NHS ester | 906564-59-8 | Bulk Inquiry |
| R01-0440 | 3-Azidopropionic Acid Sulfo-NHS ester | 2055198-09-7 | Bulk Inquiry |
Explore More NHS Ester Resources
Continue exploring NHS ester chemistry, reaction mechanisms, reagent selection, and labeling strategies through our related technical resources. These guides cover NHS and Sulfo-NHS esters, fluorescent dye selection, biomolecule labeling, conjugation chemistry, and reagent stability.
- NHS Ester Reaction Mechanism: Acylation of Primary Amines and Hydrolysis Kinetics
- NHS vs Sulfo-NHS Esters: Water Solubility and Conjugation Performance
- How to Choose the Right NHS Ester Dye for Your Labeling Experiment
- NHS Ester Labeling of Proteins and Antibodies: Protocols and Optimization
- NHS Ester vs Maleimide vs Click Chemistry: Choosing the Right Conjugation Chemistry
- What Are NHS Ester Reagents? Chemistry, Reactivity, and Role in Fluorescent Labeling
- NHS Ester Labeling of Peptides, Oligonucleotides, and Small Molecules
- NHS Ester Crosslinkers for Bioconjugation: Homo- and Heterobifunctional Reagents
- NHS Ester Storage, Stability, and Quality Control: Preventing Hydrolysis and Failed Labeling
- Custom NHS Ester Synthesis and Fluorescent Conjugation Services
Frequently Asked Questions
These questions address common decision points in NHS ester reagent selection, amine-reactive labeling, and custom conjugation project planning.
What is an NHS ester reagent and how does it work?
An NHS ester is an activated carboxylic acid esterified with N-hydroxysuccinimide. It reacts with unprotonated primary amines, such as lysine side chains and N-terminal amines, to form a stable amide bond and release N-hydroxysuccinimide. This makes NHS esters useful for attaching fluorescent dyes, biotin, drugs, and crosslinkers to proteins, antibodies, peptides, and amino-modified nucleic acids.
What is the optimal pH for NHS ester conjugation?
The practical optimum is pH 8.0 to 8.5. At lower pH, amines are protonated and react slowly. At higher pH, hydrolysis of the NHS ester becomes a significant competing reaction that reduces conjugation efficiency. Bicarbonate, borate, phosphate, and HEPES buffers are commonly used.
Why is hydrolysis important in NHS ester labeling?
NHS esters hydrolyze in water, converting back to the unreactive free carboxylic acid. The hydrolysis half-life is about 4 to 5 hours at pH 7 but only about 10 minutes at pH 8.6 at 0 degrees Celsius. Reagents should be stored dry, dissolved immediately before use, and reacted promptly at controlled pH.
What is the difference between NHS ester and sulfo-NHS ester?
Sulfo-NHS esters carry a sulfonate group that improves water solubility, allowing labeling without organic co-solvents in many protocols. The reaction chemistry is the same. Sulfo-NHS reagents are often preferred for protein labeling, cell-based applications, and workflows where organic solvent tolerance is limited.
Can BOC Sciences provide custom NHS ester synthesis and labeling?
Yes. BOC Sciences can support custom NHS ester synthesis, dye functionalization, linker design, and fluorescent labeling for proteins, antibodies, peptides, oligonucleotides, and small molecules. Services may include reagent preparation, conjugation, purification, and project-specific optimization.
Request NHS Ester Reagent or Custom Labeling Support
Share your target molecule, dye requirements, and labeling goals with BOC Sciences. Our team can help you evaluate suitable NHS ester reagents, reactive groups, conjugation strategies, and custom synthesis options.
Reagent recommendation
Compare NHS ester dyes, sulfo-NHS reagents, crosslinkers, and activated esters for your application.
Compare NHS ester dyes, sulfo-NHS reagents, crosslinkers, and activated esters for your application.
Custom labeling support
Discuss protein, antibody, peptide, oligonucleotide, small molecule, or surface-based fluorescent labeling.
Discuss protein, antibody, peptide, oligonucleotide, small molecule, or surface-based fluorescent labeling.
Conjugation optimization
Optimize pH, buffer, molar ratio, and reaction conditions to improve labeling efficiency and preserve activity.
Optimize pH, buffer, molar ratio, and reaction conditions to improve labeling efficiency and preserve activity.
Bulk product inquiry
Request pricing, availability, packaging, and project-specific supply information.
Request pricing, availability, packaging, and project-specific supply information.
