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NHS Ester Crosslinker Chemistry & Bioconjugation Support
NHS Ester Crosslinkers for Bioconjugation: Homo- and Heterobifunctional Reagents
NHS ester crosslinkers are bifunctional molecules that carry an amine-reactive N-hydroxysuccinimide (NHS) ester on at least one end and a second reactive group, which may be the same or different. The NHS ester reacts rapidly with primary amines to form a stable amide bond, while the second group can target thiols, azides, alkynes, or aldehydes. This makes crosslinkers versatile tools for covalently joining proteins, peptides, nucleic acids, dyes, surfaces, and nanoparticles in a defined and reproducible way.
This guide explains how NHS ester crosslinkers are designed and used for bioconjugation. It covers homobifunctional crosslinkers that link two amines, heterobifunctional reagents such as NHS-maleimide, NHS-azide, and NHS-hydrazide crosslinkers, spacer arms, PEG linkers, cleavable bonds, and two-step conjugation strategies. Selection criteria, reaction conditions, and applications, including antibody-drug conjugate constructs and surface immobilization, are described throughout.
What Can BOC Sciences Help You Solve?
Unsure which crosslinker format to use?
Compare homobifunctional and heterobifunctional NHS ester crosslinkers based on your available functional groups and application goals.
Need to design a two-step conjugation?
Plan sequential amine-to-thiol or amine-to-azide workflows with matched pH, buffer, and purification steps.
Facing hydrolysis or low coupling yields?
Identify reagent handling, buffer composition, and molar ratio issues that reduce crosslinking efficiency.
Building probes or functionalized surfaces?
Select spacer arm length, PEG linkers, and cleavable options that fit your conjugate geometry and solubility.
Need custom crosslinker reagents?
Support custom NHS ester crosslinker synthesis, linker design, and scaled conjugation services.
Overview: NHS Ester Crosslinkers as Controlled Bioconjugation Tools
A crosslinker is a small molecule with two reactive groups separated by a spacer arm, allowing two molecules to be joined covalently. NHS ester crosslinkers use an N-hydroxysuccinimide ester as the amine-reactive end, which targets primary amines such as lysine side chains and N-terminal groups. When both ends are NHS esters, the crosslinker joins two amines; when the second end is a maleimide, azide, alkyne, or hydrazide, the partners are joined through different chemistries stepwise.
NHS ester chemistry is a natural fit for crosslinking because the reaction is fast, proceeds in aqueous buffers, and forms an amide bond stable under most assay conditions. The practical optimum is pH 8.0 to 8.5 with a reagent molar excess of 5 to 20 fold. Because hydrolysis competes with aminolysis, pH, buffer, and handling strongly influence efficiency.
Choosing between homobifunctional and heterobifunctional reagents depends on the functional groups available, conjugate geometry, and whether a cleavable linkage is required. This guide walks through that decision from reagent selection and linker design to sequential reaction planning and characterization. For more on amine-reactive labeling, see the guide to NHS Ester Reagents for Fluorescent Labeling, and for the broader context, review our bioconjugation solutions.
Core principle:
An NHS ester crosslinker forms an amide bond at its amine-reactive end and a second, defined linkage at the other end. Because the two groups usually
have different pH optima and stabilities, heterobifunctional reagents are handled as two sequential reactions, with purification or buffer exchange
between steps.
Crosslinker Basics: Molecules with Two Reactive Groups
A crosslinker's behavior is defined by its two reactive groups, the distance between them, and the spacer chemistry. Understanding each component helps predict how a crosslinker will behave with a given pair of molecules.
Two reactive groups:
A crosslinker carries one reactive group at each end. The groups may be identical, as in homobifunctional reagents, or different, as in heterobifunctional reagents.
A crosslinker carries one reactive group at each end. The groups may be identical, as in homobifunctional reagents, or different, as in heterobifunctional reagents.
NHS ester end:
The NHS ester reacts with unprotonated primary amines, mainly lysine epsilon-amino groups and the N-terminus, forming an amide bond and releasing N-hydroxysuccinimide. The reaction runs at pH 8.0 to 8.5 in buffers without competing amines such as Tris or glycine.
The NHS ester reacts with unprotonated primary amines, mainly lysine epsilon-amino groups and the N-terminus, forming an amide bond and releasing N-hydroxysuccinimide. The reaction runs at pH 8.0 to 8.5 in buffers without competing amines such as Tris or glycine.
Second reactive group:
Common partners include maleimide for thiols, azide and alkyne for click chemistry, hydrazide for aldehydes and ketones, and a second NHS ester for amine-to-amine linking.
Common partners include maleimide for thiols, azide and alkyne for click chemistry, hydrazide for aldehydes and ketones, and a second NHS ester for amine-to-amine linking.
Spacer arm:
The spacer separates the two reactive groups and controls the distance and flexibility between the conjugated molecules. Short arms bring partners close; longer arms reduce steric hindrance.
The spacer separates the two reactive groups and controls the distance and flexibility between the conjugated molecules. Short arms bring partners close; longer arms reduce steric hindrance.
Bond stability:
Amide and thioether bonds are stable under most physiological conditions. Disulfide and hydrazone linkages can be cleaved deliberately.
Amide and thioether bonds are stable under most physiological conditions. Disulfide and hydrazone linkages can be cleaved deliberately.
Orientation and selectivity:
Homobifunctional crosslinkers react with both partners in one step but give random orientation. Heterobifunctional reagents allow each end to be reacted separately, giving more control.
Homobifunctional crosslinkers react with both partners in one step but give random orientation. Heterobifunctional reagents allow each end to be reacted separately, giving more control.
Homobifunctional NHS Crosslinkers: Linking Amines to Amines
Homobifunctional NHS ester crosslinkers, such as the classic DSS and BS3 reagents, carry an NHS ester at both ends of a spacer arm. Both ends react with primary amines, so the crosslinker bridges two amine-bearing molecules through amide bonds. The chemistry is simple and fast, and it has long been used to study protein complexes.
In practice, one NHS end attaches to an amine-bearing molecule and the second NHS end reacts with an amine on a partner. Because the two ends are identical, both reactions occur under the same conditions, and the product distribution depends mainly on the molar ratio of crosslinker to protein. A large excess favors conjugates with only one end attached, while equimolar conditions favor direct bridging. DSS is soluble in organic solvents such as DMSO and DMF, while its sulfonated analog BS3 is water soluble and needs no co-solvent.
Amine-to-amine linkage:
Both ends react with primary amines, forming two amide bonds at lysine residues and N-terminal groups on proteins, peptides, and amino-modified surfaces.
Both ends react with primary amines, forming two amide bonds at lysine residues and N-terminal groups on proteins, peptides, and amino-modified surfaces.
Common applications:
Homobifunctional NHS crosslinkers stabilize protein-protein complexes, crosslink subunits in multimeric assemblies, immobilize proteins on amine-presenting surfaces, and prepare immunogen reagents.
Homobifunctional NHS crosslinkers stabilize protein-protein complexes, crosslink subunits in multimeric assemblies, immobilize proteins on amine-presenting surfaces, and prepare immunogen reagents.
Simple reaction conditions:
A single step at pH 8.0 to 8.5 in an amine-free buffer is sufficient. Reaction time is 30 to 120 minutes at room temperature or overnight at 4 degrees Celsius.
A single step at pH 8.0 to 8.5 in an amine-free buffer is sufficient. Reaction time is 30 to 120 minutes at room temperature or overnight at 4 degrees Celsius.
No orientation control:
Because the reactive groups are identical, conjugation is random with respect to which lysine residues are modified. This can affect activity if critical binding sites are labeled.
Because the reactive groups are identical, conjugation is random with respect to which lysine residues are modified. This can affect activity if critical binding sites are labeled.
Molar ratio control:
A 5 to 20 fold molar excess of crosslinker limits the number of crosslinks and reduces over-crosslinking and aggregation.
A 5 to 20 fold molar excess of crosslinker limits the number of crosslinks and reduces over-crosslinking and aggregation.
Water-soluble variants:
Sulfonated analogs such as BS3 dissolve directly in aqueous buffer, simplifying protocols for sensitive proteins and cell-surface work.
Sulfonated analogs such as BS3 dissolve directly in aqueous buffer, simplifying protocols for sensitive proteins and cell-surface work.
Heterobifunctional Crosslinkers: NHS Plus a Second Reactive Group
Heterobifunctional crosslinkers carry two different reactive groups, so each end can be reacted with a different partner in a defined order. The NHS end attaches to an amine, and the second end is selected for a thiol, azide, alkyne, or aldehyde. This design underlies most modern bioconjugation workflows.
NHS-maleimide (SMCC-type)
The NHS end reacts with an amine at pH 8.0 to 8.5, and the maleimide end reacts with a sulfhydryl group at pH 6.5 to 7.5 to form a stable thioether. This is the classic architecture for joining an antibody to an enzyme, peptide, or payload.
NHS-azide
The NHS end attaches to an amine, leaving an azide available for click chemistry. The azide can then react with an alkyne- or BCN-functionalized partner, enabling two-step fluorescent labeling.
NHS-alkyne
An NHS ester paired with a terminal alkyne supports copper-catalyzed click reactions with azide partners. This format is often chosen for probe construction and for conjugations needing a small, stable linker.
NHS-hydrazide
After the NHS end reacts with an amine, the hydrazide end reacts with aldehydes or ketones, including aldehydes from periodate oxidation of glycans, forming a hydrazone linkage. This is a common route for labeling glycoproteins.
NHS-pyridyldithiol
The pyridyldithiol end reacts with thiols to form a cleavable disulfide. The NHS end provides the amine attachment, giving a cleavable heterobifunctional option.
NHS-PEG-maleimide
A PEG spacer between the NHS ester and maleimide improves water solubility, reduces aggregation, and increases the distance between partners, which is useful for large biomolecules and nanoparticles.
| Crosslinker Type | Reactive Groups | Target Groups | Linkage Formed | Typical Application |
|---|---|---|---|---|
| Homobifunctional NHS (NHS-NHS) | NHS ester + NHS ester | Amine + amine | Amide + amide | Protein-protein crosslinking, surface immobilization |
| NHS-maleimide (SMCC-type) | NHS ester + maleimide | Amine + thiol | Amide + thioether | Antibody-enzyme and antibody-payload constructs |
| NHS-azide | NHS ester + azide | Amine + azide partner (alkyne or BCN) | Amide + triazole | Two-step fluorescent labeling, click conjugation |
| NHS-alkyne | NHS ester + alkyne | Amine + azide | Amide + triazole | Two-step labeling, probe construction |
| NHS-hydrazide | NHS ester + hydrazide | Amine + aldehyde or ketone | Amide + hydrazone | Glycoprotein and oxidized carbohydrate labeling |
| NHS-pyridyldithiol | NHS ester + pyridyldithiol | Amine + thiol | Amide + disulfide | Cleavable conjugation and reversible crosslinking |
For crosslinkers that rely on azide, alkyne, or BCN chemistry, the second step follows the rules of click reactions. Review the guide to click chemistry for fluorescent labeling, plus the pages on Alkyne Reagents for Fluorescent Labeling, Azide Reagents for Fluorescent Labeling, and BCN Reagents for Fluorescent Labeling.
Spacer Arm and Linker Design: Length, PEG, and Cleavability
The spacer arm between the two reactive groups determines the distance and flexibility around the conjugation site. Choosing the right spacer affects steric accessibility, solubility, aggregation, and cleavability.
Spacer arm length:
Short arms of a few atoms hold the conjugated molecules close together, useful for proximity capture. Longer arms reduce steric clash and give large biomolecules room to interact normally.
Short arms of a few atoms hold the conjugated molecules close together, useful for proximity capture. Longer arms reduce steric clash and give large biomolecules room to interact normally.
PEG spacers:
Polyethylene glycol spacers are hydrophilic, reducing aggregation and nonspecific binding. They improve solubility and range from short PEG2 to long PEG24 and beyond, letting researchers tune the arm length.
Polyethylene glycol spacers are hydrophilic, reducing aggregation and nonspecific binding. They improve solubility and range from short PEG2 to long PEG24 and beyond, letting researchers tune the arm length.
Cleavable linkers:
Disulfide linkers are cleaved by reducing agents such as DTT or TCEP, and hydrazone linkers are acid labile. These suit conjugates that must be released after delivery or analysis.
Disulfide linkers are cleaved by reducing agents such as DTT or TCEP, and hydrazone linkers are acid labile. These suit conjugates that must be released after delivery or analysis.
Non-cleavable linkers:
Amide and thioether linkages are stable under physiological conditions. Non-cleavable crosslinkers are preferred for permanent conjugates used in assays and imaging.
Amide and thioether linkages are stable under physiological conditions. Non-cleavable crosslinkers are preferred for permanent conjugates used in assays and imaging.
Water solubility:
Sulfonated (sulfo-NHS) variants dissolve in aqueous buffer without organic co-solvents, protecting sensitive proteins. Hydrophobic crosslinkers are added from concentrated DMSO or DMF stock solutions.
Sulfonated (sulfo-NHS) variants dissolve in aqueous buffer without organic co-solvents, protecting sensitive proteins. Hydrophobic crosslinkers are added from concentrated DMSO or DMF stock solutions.
Rigid versus flexible arms:
Alkyl and PEG chains are flexible, while aromatic or cyclic spacers provide rigidity. Rigid arms position partners at a defined distance and angle, which matters in FRET pairs and structured probes.
Alkyl and PEG chains are flexible, while aromatic or cyclic spacers provide rigidity. Rigid arms position partners at a defined distance and angle, which matters in FRET pairs and structured probes.
The selection criteria below summarize the main decision points when choosing a crosslinker.
| Criterion | What to Consider | Practical Guidance |
|---|---|---|
| Target functional groups | Which groups are available on each molecule | Use homobifunctional if both partners have amines; use heterobifunctional for amine-to-thiol or amine-to-click routes. |
| Spacer arm length | Distance and steric access between conjugates | Longer PEG spacers reduce steric clash; short arms suit proximity capture and structural studies. |
| Solubility | Aqueous versus organic solubility needs | Choose sulfo-NHS variants for water solubility; keep organic solvent below 5 to 10 percent of the reaction volume. |
| Cleavability | Whether the conjugate must be released later | Disulfide linkers are reducible; non-cleavable amide and thioether bonds give permanent conjugates. |
| Reaction pH compatibility | pH optima of both reactive ends | React the NHS end at pH 8.0 to 8.5 and the maleimide end at pH 6.5 to 7.5 in sequence. |
| Conjugate stability | Storage and assay conditions | Amide bonds are stable, thioethers are stable, and hydrazone bonds are acid sensitive. |
Linker design note:
There is no single best spacer. A short, non-cleavable arm may suit a stable enzyme conjugate, while a long PEG arm often suits a nanoparticle or large
antibody conjugate. When in doubt, test two spacers and compare yield, solubility, and activity.
Two-Step Conjugation Strategies: Sequential Reactions
Heterobifunctional crosslinkers work best when the two ends are reacted in sequence, because the NHS ester and the second group often have different pH optima and stabilities. A typical workflow reacts the NHS end first at pH 8.0 to 8.5, removes excess crosslinker, then reacts the second end.
The most common two-step route is amine-to-thiol conjugation with an NHS-maleimide crosslinker such as an SMCC-type reagent. The NHS end couples to a lysine amine on the first molecule, and the product is purified or buffer exchanged to remove unreacted crosslinker. The maleimide end then reacts with a free sulfhydryl on the partner at pH 6.5 to 7.5, where maleimide is stable and thiols are reactive. If the partner lacks a native thiol, one can be introduced by reducing disulfides or thiolating lysines.
The second common route is amine-to-azide click conjugation. An NHS-azide crosslinker couples to an amine-bearing molecule, and the azide later reacts with an alkyne- or BCN-functionalized partner. Copper-catalyzed cycloaddition needs a copper catalyst, while strain-promoted reactions with BCN partners proceed without catalyst. This route is widely used to attach dyes, biotin, and other reporters in a very selective step.
Step 1: Couple the NHS end
React the crosslinker with an amine-bearing molecule at pH 8.0 to 8.5 in an amine-free buffer. A 5 to 20 fold molar excess favors mono-attachment.
React the crosslinker with an amine-bearing molecule at pH 8.0 to 8.5 in an amine-free buffer. A 5 to 20 fold molar excess favors mono-attachment.
Step 2: Remove excess crosslinker
Purify or buffer exchange the modified molecule so unreacted crosslinker cannot bridge partners nonspecifically in the second step.
Purify or buffer exchange the modified molecule so unreacted crosslinker cannot bridge partners nonspecifically in the second step.
Step 3: Adjust conditions for the second end
Exchange into a thiol-compatible buffer at pH 6.5 to 7.5 for maleimide chemistry, or a click-compatible buffer for azide or alkyne reactions.
Exchange into a thiol-compatible buffer at pH 6.5 to 7.5 for maleimide chemistry, or a click-compatible buffer for azide or alkyne reactions.
Step 4: React the second end
Add the thiol-bearing or click-partner molecule. Maleimide forms a thioether, and azide-alkyne pairs form a triazole, both stable linkages.
Add the thiol-bearing or click-partner molecule. Maleimide forms a thioether, and azide-alkyne pairs form a triazole, both stable linkages.
Step 5: Control stoichiometry
Use the second partner in slight excess over the activated intermediate and monitor conjugation by gel analysis.
Use the second partner in slight excess over the activated intermediate and monitor conjugation by gel analysis.
Step 6: Purify and characterize
Remove small molecule byproducts and characterize the conjugate by mass spectrometry, spectrophotometry, and functional assays.
Remove small molecule byproducts and characterize the conjugate by mass spectrometry, spectrophotometry, and functional assays.
pH guidance:
The NHS ester end is most efficient at pH 8.0 to 8.5, where lysine amines are deprotonated but hydrolysis is manageable. The maleimide end is most
efficient and stable at pH 6.5 to 7.5; above pH 8 the maleimide ring hydrolyzes and loses reactivity. Running the two ends in sequence avoids the
conflict.
Click-based second steps follow the principles of click chemistry for fluorescent labeling. For strain-promoted routes, BCN Reagents for Fluorescent Labeling pair with azide-modified molecules.
Applications of NHS Ester Crosslinkers in Research and Development
NHS ester crosslinkers appear wherever two molecules must be joined covalently. The examples below cover common research uses, from antibody-drug conjugate constructs to surface and nanoparticle functionalization.
Antibody-drug conjugate constructs:
Heterobifunctional NHS-maleimide crosslinkers attach payloads or reporters to antibodies through defined amine-to-thiol chemistry. The sequential workflow preserves antigen binding.
Heterobifunctional NHS-maleimide crosslinkers attach payloads or reporters to antibodies through defined amine-to-thiol chemistry. The sequential workflow preserves antigen binding.
Fluorescent probe construction:
Crosslinkers connect dyes, peptides, proteins, and small molecule ligands into probes for imaging and assays. Two-step click routes allow the dye to be added last, minimizing photo-damage.
Crosslinkers connect dyes, peptides, proteins, and small molecule ligands into probes for imaging and assays. Two-step click routes allow the dye to be added last, minimizing photo-damage.
Surface immobilization:
Amine-presenting surfaces, slides, and beads are treated with NHS crosslinkers and then reacted with thiol- or click-modified capture molecules, producing stable surfaces for capture assays and biosensors.
Amine-presenting surfaces, slides, and beads are treated with NHS crosslinkers and then reacted with thiol- or click-modified capture molecules, producing stable surfaces for capture assays and biosensors.
Nanoparticle functionalization:
PEG-spaced NHS crosslinkers attach antibodies, peptides, or dyes to nanoparticles while reducing aggregation and nonspecific uptake.
PEG-spaced NHS crosslinkers attach antibodies, peptides, or dyes to nanoparticles while reducing aggregation and nonspecific uptake.
Protein-protein interaction studies:
Homobifunctional NHS crosslinkers stabilize weak or transient complexes for pull-down and identification, and help map interaction interfaces.
Homobifunctional NHS crosslinkers stabilize weak or transient complexes for pull-down and identification, and help map interaction interfaces.
Assay reagent preparation:
Crosslinker chemistry prepares enzyme-antibody conjugates, hapten-carrier immunogens, and labeled detection reagents for immunoassay workflows.
Crosslinker chemistry prepares enzyme-antibody conjugates, hapten-carrier immunogens, and labeled detection reagents for immunoassay workflows.
These applications build on a broader set of conjugation workflows. See our bioconjugation solutions, Drug Delivery solutions, and Fluorescent Nanoparticle Services for related support.
Need Help Selecting an NHS Ester Crosslinker for Your Conjugation Workflow?
BOC Sciences can support crosslinker selection, spacer arm design, two-step conjugation planning, and custom crosslinker synthesis for proteins, peptides, antibodies, surfaces, and nanoparticles.
Request Crosslinker Selection SupportA Practical Workflow for Selecting and Using an NHS Ester Crosslinker
The workflow below guides researchers from the conjugation goal to a purified and validated conjugate, with each decision following logically.
Step 1: Define the conjugation goal
Identify the two molecules to be joined, the groups available on each, and the final use of the conjugate. This determines whether a homobifunctional or heterobifunctional crosslinker is appropriate.
Identify the two molecules to be joined, the groups available on each, and the final use of the conjugate. This determines whether a homobifunctional or heterobifunctional crosslinker is appropriate.
Step 2: Choose the crosslinker type
If both partners have accessible amines, a homobifunctional NHS crosslinker can bridge them directly. If one partner has a thiol, azide, or aldehyde, select a heterobifunctional reagent with the matching second group.
If both partners have accessible amines, a homobifunctional NHS crosslinker can bridge them directly. If one partner has a thiol, azide, or aldehyde, select a heterobifunctional reagent with the matching second group.
Step 3: Select the spacer arm
Pick a spacer length and composition that fit the molecule sizes and assay geometry. Use PEG spacers to improve solubility and reduce aggregation, and choose a cleavable linker if release is needed.
Pick a spacer length and composition that fit the molecule sizes and assay geometry. Use PEG spacers to improve solubility and reduce aggregation, and choose a cleavable linker if release is needed.
Step 4: Prepare the reaction buffers
Use amine-free buffers such as bicarbonate, borate, phosphate, or HEPES for the NHS step at pH 8.0 to 8.5, and thiol- or click-compatible buffers for the second step.
Use amine-free buffers such as bicarbonate, borate, phosphate, or HEPES for the NHS step at pH 8.0 to 8.5, and thiol- or click-compatible buffers for the second step.
Step 5: Run sequential reactions
React the NHS end first, remove excess crosslinker, exchange the buffer, and then react the second end under its optimal conditions.
React the NHS end first, remove excess crosslinker, exchange the buffer, and then react the second end under its optimal conditions.
Step 6: Purify and validate
Purify by desalting, size-exclusion chromatography, or dialysis, confirm conjugation by gel analysis or mass spectrometry, and verify biological activity.
Purify by desalting, size-exclusion chromatography, or dialysis, confirm conjugation by gel analysis or mass spectrometry, and verify biological activity.
Common Challenges and Optimization Tips
Crosslinker conjugation is sensitive to reagent stability, buffer, pH, and stoichiometry. Recognizing common failure modes early improves reproducibility and conjugate quality.
NHS ester hydrolysis
NHS esters hydrolyze in water, with a half-life of about 4 to 5 hours at pH 7 and about 10 minutes at pH 8.6 at 0 degrees Celsius. Store reagents dry, dissolve immediately before use, and react promptly.
Maleimide instability at high pH
The maleimide ring hydrolyzes above pH 8, reducing thiol reactivity. Keep the maleimide step at pH 6.5 to 7.5 and avoid a single high-pH reaction for both ends.
Buffer interference
Primary amine buffers such as Tris and glycine compete with the target molecule for the NHS ester. Exchange into phosphate, bicarbonate, borate, or HEPES before conjugation.
Unintended bridging and aggregation
If excess crosslinker is not removed, the second reactive end can bridge molecules randomly. Purify the intermediate before the second step and control the molar ratio.
Poor solubility and precipitation
Hydrophobic crosslinkers and dyes can precipitate proteins. Use sulfo-NHS variants, keep organic solvent below 5 to 10 percent of the reaction volume, and consider PEG-spaced reagents.
Lack of orientation control
Amine targeting modifies lysines randomly, which can disrupt binding sites. For critical conjugates, use click-based two-step strategies that place the reactive handle at a defined site.
How BOC Sciences Supports Crosslinker Supply and Conjugation Design
BOC Sciences provides NHS ester crosslinker reagents, custom linker design, and conjugation services for research and analytical development. The scope spans reagent supply, sequential reaction planning, and conjugate construction.
Heterobifunctional Crosslinker Supply
Access NHS-maleimide, NHS-azide, NHS-alkyne, and NHS-hydrazide crosslinkers with defined spacer arms.
- NHS-maleimide crosslinkers
- NHS-azide and NHS-alkyne reagents
- NHS-hydrazide and cleavable options
- Sulfo-NHS water-soluble variants
Homobifunctional NHS Crosslinker Supply
Supply of NHS-NHS crosslinkers, including PEG-spaced and sulfonated versions, for amine-to-amine bridging.
- DSS and BS3-type reagents
- PEG-spaced NHS crosslinkers
- Cleavable disulfide variants
- Bulk packaging and custom quantities
Spacer Arm and Linker Design
Custom design of spacer arms and linkers to control distance, solubility, and cleavability in conjugates.
- PEG spacer selection and synthesis
- Cleavable versus non-cleavable linkers
- Water solubility tuning
- Geometry and rigidity optimization
Two-Step Conjugation Design
Planning and optimization of sequential conjugation workflows, including amine-to-thiol and amine-to-azide routes.
- Sequential reaction protocols
- pH and buffer optimization
- Intermediate purification guidance
- Stoichiometry and ratio control
Custom Crosslinker Synthesis
Custom synthesis of crosslinkers with tailored reactive groups, spacers, and dye-functionalized ends.
- Custom reactive group pairing
- Dye-crosslinker conjugates
- Cleavable linker synthesis
- Scale-up and QC support
Conjugate and Probe Construction
Assembling crosslinked conjugates, fluorescent probes, functionalized surfaces, and nanoparticle reagents for research use.
- Antibody and protein conjugates
- Fluorescent probe construction
- Surface and bead immobilization
- Nanoparticle functionalization
Start Your Crosslinker Conjugation Project with BOC Sciences
Whether you need a standard NHS ester crosslinker, a custom heterobifunctional reagent, a two-step protocol, or a complete conjugation workflow, BOC Sciences can help identify the right chemistry for your research goals.
Send Your Project RequirementsRecommended NHS Ester and Bioconjugation Products
The following products are recommended for researchers working with NHS ester chemistry, amine-reactive bioconjugation, crosslinking, and functional group installation. The selection includes biotinylation reagents, azide- and alkyne-functionalized NHS esters, DBCO reagents, maleimide-containing crosslinkers, homobifunctional NHS esters, and fluorescent bis-NHS ester derivatives for protein, antibody, peptide, and other biomolecule modification.
| Catalog | Product Name | CAS | Inquiry |
|---|---|---|---|
| R01-0475 | N-Succinimidyl 6-Biotinamidohexanoate | 72040-63-2 | Bulk Inquiry |
| R01-0474 | Biotin-PEG4-NHS ester | 459426-22-3 | Bulk Inquiry |
| R01-0004 | succimimidyl-4-azidobutyrate | 943858-70-6 | Bulk Inquiry |
| R01-0439 | 6-Azidohexanoic acid sulfo-NHS ester | Bulk Inquiry | |
| R01-0440 | 3-Azidopropionic Acid Sulfo-NHS ester | 2055198-09-7 | Bulk Inquiry |
| R01-0003 | Alkyne-PEG3-NHS ester | Bulk Inquiry | |
| R01-0002 | 5-hexynoic NHS ester | 906564-59-8 | Bulk Inquiry |
| R01-0024 | DBCO-C6-NHS ester | 1384870-47-6 | Bulk Inquiry |
| R01-0473 | N-Succinimidyl 3-maleimidopropionate | 55750-62-4 | Bulk Inquiry |
| R01-0444 | Disuccinimidyl glutarate | 79642-50-5 | Bulk Inquiry |
| R01-0034 | Sulfo-Cyanine7 bis-NHS ester | Bulk Inquiry | |
| R01-0031 | Sulfo-Cyanine5 bis-NHS ester | Bulk Inquiry |
Explore More NHS Ester Resources
Explore additional resources on NHS ester reactivity, crosslinking chemistry, reactive-group selection, and bioconjugation strategies. These guides provide useful context for understanding amine-reactive chemistry and comparing NHS ester crosslinkers with other conjugation approaches.
- NHS Ester Reaction Mechanism: Acylation of Primary Amines and Hydrolysis Kinetics
- 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
Frequently Asked Questions
These questions address common decision points in NHS ester crosslinker selection, two-step conjugation planning, and custom design.
What is the difference between homobifunctional and heterobifunctional NHS ester crosslinkers?
A homobifunctional crosslinker carries two identical NHS ester groups and joins two amines in one reaction. A heterobifunctional crosslinker carries an NHS ester plus a second group such as a maleimide, azide, alkyne, or hydrazide, joining two molecules through different chemistries in sequential steps.
Why do the two ends of a heterobifunctional crosslinker require different pH conditions?
The NHS ester reacts most efficiently at pH 8.0 to 8.5, where lysine amines are deprotonated. The maleimide end reacts with thiols at pH 6.5 to 7.5 and hydrolyzes above pH 8. Running the two reactions in sequence satisfies both optima.
What should I consider when choosing a spacer arm?
Consider the size of the conjugated molecules, the distance between them, solubility, and cleavability. PEG spacers improve solubility, short arms bring partners close, and disulfide or hydrazone arms allow controlled release.
When should I use a cleavable crosslinker?
Use a cleavable crosslinker when the conjugate must be separated after delivery, analysis, or purification, or when you want to confirm that an effect depends on the intact conjugate. Disulfide linkers are cleaved by reducing agents, and hydrazone linkers are acid labile.
Can BOC Sciences provide custom crosslinker synthesis and conjugation services?
Yes. BOC Sciences can support custom NHS ester crosslinker synthesis, spacer arm and linker design, two-step conjugation optimization, and conjugate construction for proteins, peptides, antibodies, surfaces, and nanoparticles.
Request Crosslinker Reagent or Conjugation Design Support
Share your target molecules, available functional groups, and conjugation goals with BOC Sciences. Our team can help evaluate crosslinker types, spacer arms, sequential strategies, and custom synthesis options.
Crosslinker recommendation
Compare homobifunctional and heterobifunctional NHS ester crosslinkers.
Compare homobifunctional and heterobifunctional NHS ester crosslinkers.
Two-step conjugation support
Plan sequential amine-to-thiol or amine-to-azide workflows with matched conditions.
Plan sequential amine-to-thiol or amine-to-azide workflows with matched conditions.
Linker design guidance
Choose spacer length, PEG, and cleavable options that fit your conjugate.
Choose spacer length, PEG, and cleavable options that fit your conjugate.
Bulk product inquiry
Request pricing, availability, and project-specific supply information.
Request pricing, availability, and project-specific supply information.
