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NHS Ester Dye Selection & Fluorescent Labeling Support
How to Choose the Right NHS Ester Dye for Your Labeling Experiment
NHS ester dyes are among the most widely used tools for attaching fluorescent labels to proteins, antibodies, peptides, and amino-modified nucleic acids. Because every NHS ester dye reacts with primary amines through the same well-understood mechanism, the conjugation step is not where most experiments go wrong. The critical decisions happen before the reaction starts: which dye family, which wavelength range, which solubility profile, and how much dye to add.
This guide walks through the dye selection process in the order you will actually face it. You will learn how to match dye excitation and emission to your instrument, how the main dye families available as NHS esters compare, how to balance brightness against photostability, when to choose water-soluble sulfo versions, how linker design affects conjugate behavior, and how to plan the degree of labeling for your specific application.
What Can BOC Sciences Help You Solve?
Unsure which dye family fits your instrument?
Compare excitation and emission profiles of NHS ester dyes against the lasers and filter sets in your lab.
Struggling to control the degree of labeling?
Optimize dye-to-biomolecule molar excess, buffer, and reaction conditions to hit your target DOL.
Facing weak signal or rapid photobleaching?
Balance brightness and photostability across dye families to match the demands of your assay.
Planning a multicolor panel?
Select spectrally separated NHS ester dyes for flow cytometry and multiplex imaging workflows.
Need a water-soluble or custom NHS ester dye?
Review sulfo versions, linker options, custom dye functionalization, and scaled supply.
Overview: Why Dye Selection Comes First in NHS Ester Labeling
Every NHS ester dye works by the same chemistry: the activated ester reacts with unprotonated primary amines, such as the epsilon-amino group of lysine residues and the N-terminal amine, to form a stable amide bond while releasing N-hydroxysuccinimide. The labeling reaction is forgiving, typically run at pH 8.0 to 8.5 in an amine-free buffer with a modest molar excess of dye. What the reaction chemistry cannot fix is a dye that is poorly matched to the experiment. If the dye is not excited by your laser, emits outside your filter window, self-quenches at the loading you need, or precipitates in your reaction buffer, no amount of protocol tuning will produce good data.
Treat dye selection as a sequence of constraints. The instrument defines the usable wavelength range, the application defines the required brightness, photostability, and solubility, and the biomolecule defines how much modification it can tolerate. When a dye satisfies all three, the remaining variables, such as molar excess and reaction time, are straightforward to optimize.
The goal is a conjugate that is bright enough to detect, stable enough to measure, and biologically active enough to report what you are studying. Reaching that goal is what the rest of this guide covers. For the conjugation chemistry itself, including pH control and hydrolysis behavior, see the companion material on NHS ester dyes and related labeling protocols.
Core principle:
All NHS ester dyes conjugate through the same amine-reactive mechanism, so the chemistry rarely limits the outcome. Selection is driven by the
photophysical and physical properties of the dye core, the excitation and detection hardware available, and the constraints of the biomolecule and
assay. Match the dye to the instrument and the application first, then control molar excess to reach the intended degree of labeling.
Spectral Matching: Aligning Excitation and Emission with Your Instrument
The first filter in dye selection is the instrument. A dye is only useful if your microscope, cytometer, or plate reader can excite it and collect its emission. For laser-based detection, such as flow cytometry, the laser lines are fixed and the dye must fit them; for lamp-based microscopy, filter sets play the same role. Working through the points below before considering brightness or cost prevents the most common cause of weak or missing signal.
Match absorption to the excitation source:
Choose a dye whose absorption maximum sits close to an available laser line. A 405 nm source suits coumarin dyes, 488 nm suits fluorescein and FAM, 561 nm suits rhodamine, TAMRA, and Cy3, and 633 to 640 nm suits Cy5.
Choose a dye whose absorption maximum sits close to an available laser line. A 405 nm source suits coumarin dyes, 488 nm suits fluorescein and FAM, 561 nm suits rhodamine, TAMRA, and Cy3, and 633 to 640 nm suits Cy5.
Check emission against the detector window:
The emission peak must fall inside the bandpass filter or detector range. Avoid dyes whose emission lands at the edge of a filter, where signal drops sharply.
The emission peak must fall inside the bandpass filter or detector range. Avoid dyes whose emission lands at the edge of a filter, where signal drops sharply.
Respect the excitation filter for microscopy:
With lamp-based illumination, confirm that the dye absorption overlaps the excitation filter window; otherwise the dye will be dim even with a perfect emission match.
With lamp-based illumination, confirm that the dye absorption overlaps the excitation filter window; otherwise the dye will be dim even with a perfect emission match.
Space emission peaks for multiplexing:
In multicolor panels, choose dyes with emission separated by roughly 40 to 60 nm to keep compensation manageable. FITC with TAMRA and Cy3 with Cy5 are common pairings.
In multicolor panels, choose dyes with emission separated by roughly 40 to 60 nm to keep compensation manageable. FITC with TAMRA and Cy3 with Cy5 are common pairings.
Consider sample autofluorescence:
Biological samples emit background in the green range. Far-red dyes such as Cy5 often give a better signal-to-background ratio despite lower absolute brightness.
Biological samples emit background in the green range. Far-red dyes such as Cy5 often give a better signal-to-background ratio despite lower absolute brightness.
Confirm the source exists:
A coumarin dye is useless if the cytometer only provides 488 nm and 633 nm lasers. Verify hardware before selecting a dye family.
A coumarin dye is useless if the cytometer only provides 488 nm and 633 nm lasers. Verify hardware before selecting a dye family.
| Excitation Source | Compatible NHS Ester Dye Families | Typical Emission Range | Common Applications |
|---|---|---|---|
| 405 nm laser | Coumarin NHS esters | 430-500 nm | Blue channel labeling, nuclear counterstain channels. |
| 488 nm laser | FITC, FAM, fluorescein NHS esters | 510-540 nm | Immunofluorescence, flow cytometry, reporter assays. |
| 561 nm laser | Rhodamine, TAMRA, ROX NHS esters | 580-620 nm | Orange channel detection, FRET acceptors. |
| 633-640 nm laser | Cyanine Cy5 NHS esters | 660-680 nm | Far-red detection in low-autofluorescence samples. |
Dye Families Available as NHS Esters: A Practical Comparison
Once the wavelength range is fixed, compare the dye families that cover it. Each family has a characteristic balance of brightness, photostability, solubility, and spectral width, and most are available in NHS ester or sulfo-NHS ester format. The six families below cover the visible spectrum and near-infrared.
Fluorescein and FITC Family
FAM and FITC derivatives emit near 520 nm and are the classic green labels for 488 nm excitation. They are bright and inexpensive, but emission is pH sensitive below pH 7 and photostability is moderate. Compare fluorescein dyes when green signal is required.
Rhodamine Family
Rhodamine derivatives, including TAMRA, ROX, and Texas Red, emit from orange to red. They are notably more photostable and less pH sensitive than fluorescein, making them reliable for imaging and FRET. Review rhodamine dyes for stable orange-red labeling.
Cyanine Family
Cy3, Cy5, and Cy7 cover green through near-infrared emission. Cy5 is the workhorse far-red label, and sulfo-cyanine versions are water soluble. Explore cyanine dyes for multiplex and low-background detection.
BODIPY Family
BODIPY dyes offer narrow, sharp emission bands and high quantum yields, useful when spectral separation matters. Many BODIPY derivatives are hydrophobic, so sulfo variants or careful solvent handling are often required. See BODIPY dyes for narrow-spectrum options.
Coumarin Family
Coumarin NHS esters are small, violet-excited dyes that emit in the blue range near 450 to 500 nm. They are useful for blue channels and FRET donors, though brightness is lower than fluorescein. Browse coumarin dyes for violet-excited labeling.
TAMRA Family
TAMRA emits near 580 nm and is a standard orange label, a common FRET acceptor for FITC or FAM donors, and a routine dye for immunofluorescence. It is photostable and easy to work with. Check TAMRA dyes for orange-channel probes.
| Dye Family | Example NHS Ester Formats | Peak Emission | Typical Strengths | Watch Out For |
|---|---|---|---|---|
| Fluorescein | FAM NHS ester, FITC | ~520 nm | Bright, standard for 488 nm, low cost | pH-sensitive emission, moderate photostability |
| Rhodamine | Rhodamine NHS ester, TAMRA, ROX, Texas Red | ~580-620 nm | Photostable, pH insensitive, versatile | Some derivatives are hydrophobic |
| Cyanine | Cy3, Cy5, Cy7 NHS esters | ~570-780 nm | Red to near-infrared coverage, multiplex friendly | Aggregation, hydrophobicity without sulfo groups |
| BODIPY | BODIPY NHS esters | ~500-670 nm | Sharp spectra, high quantum yield | Limited water solubility |
| Coumarin | Coumarin NHS esters | ~450-500 nm | Small size, violet-excited, FRET donors | Lower brightness, narrow usable range |
| TAMRA | TAMRA NHS ester | ~580 nm | Standard FRET acceptor, photostable | Overlaps other orange labels in panels |
Brightness and Photostability: Managing the Trade-Off
After spectral fit, the next decision is how much signal the dye delivers and how long it survives illumination. Brightness is the product of the extinction coefficient and the fluorescence quantum yield; photostability is resistance to irreversible photobleaching. The two often trade off, and the right balance depends on whether you use brief detection or long illumination.
Brightness is a product, not a single number:
A dye with a very high extinction coefficient and a quantum yield near 1 is bright. Fluorescein combines both, which is why it remains a reference for green signal.
A dye with a very high extinction coefficient and a quantum yield near 1 is bright. Fluorescein combines both, which is why it remains a reference for green signal.
Fluorescein: bright but fragile:
FAM and FITC are bright and cheap, but they photobleach noticeably and their emission drops at low pH. They suit brief measurements, not extended time-lapse imaging.
FAM and FITC are bright and cheap, but they photobleach noticeably and their emission drops at low pH. They suit brief measurements, not extended time-lapse imaging.
Rhodamine and TAMRA: stable workhorses:
These dyes are less pH sensitive and much more photostable than fluorescein. TAMRA and rhodamine derivatives tolerate repeated scans and long exposures.
These dyes are less pH sensitive and much more photostable than fluorescein. TAMRA and rhodamine derivatives tolerate repeated scans and long exposures.
Cyanine: strong and low background:
Cy3 is robust and often brighter than FITC in practice, while Cy5 benefits from reduced autofluorescence in the far-red, improving signal-to-noise in cells and tissue.
Cy3 is robust and often brighter than FITC in practice, while Cy5 benefits from reduced autofluorescence in the far-red, improving signal-to-noise in cells and tissue.
BODIPY: bright per molecule:
BODIPY dyes have high quantum yields and narrow emission, but some derivatives self-quench at high labeling density, so DOL must be controlled.
BODIPY dyes have high quantum yields and narrow emission, but some derivatives self-quench at high labeling density, so DOL must be controlled.
Choose for the assay, not the dye:
For time-lapse or 3D imaging, prioritize photostable rhodamine or cyanine dyes. For quick endpoint reads where maximum signal matters, fluorescein or BODIPY derivatives are acceptable.
For time-lapse or 3D imaging, prioritize photostable rhodamine or cyanine dyes. For quick endpoint reads where maximum signal matters, fluorescein or BODIPY derivatives are acceptable.
Water Solubility: NHS Ester Dyes and Sulfo-NHS Versions
Many dye cores are aromatic and hydrophobic, which becomes a practical problem when the NHS ester is mixed with an aqueous protein solution. Hydrophobic dyes can precipitate, stick to surfaces, and label unevenly. The standard solution is a sulfo derivative, whose sulfonate groups make the dye water soluble without changing its wavelengths.
Why solubility matters:
A dye that is not fully soluble in the reaction buffer will form aggregates, reduce labeling efficiency, and cause speckled background in imaging.
A dye that is not fully soluble in the reaction buffer will form aggregates, reduce labeling efficiency, and cause speckled background in imaging.
Sulfo-NHS ester dyes:
Sulfo-cyanine dyes such as sulfo-Cy3 and sulfo-Cy5 are standard water-soluble options, and sulfo-NHS esters react by the same mechanism with the same optimal pH of 8.0 to 8.5.
Sulfo-cyanine dyes such as sulfo-Cy3 and sulfo-Cy5 are standard water-soluble options, and sulfo-NHS esters react by the same mechanism with the same optimal pH of 8.0 to 8.5.
Avoiding organic co-solvents:
Sulfo versions allow conjugation in purely aqueous buffers, which matters for antibodies and enzymes that are destabilized by DMSO or DMF.
Sulfo versions allow conjugation in purely aqueous buffers, which matters for antibodies and enzymes that are destabilized by DMSO or DMF.
When standard NHS esters are fine:
If the biomolecule tolerates a small amount of organic solvent, standard NHS esters dissolved in anhydrous DMSO at 5 to 10 percent of the final volume remain a convenient option.
If the biomolecule tolerates a small amount of organic solvent, standard NHS esters dissolved in anhydrous DMSO at 5 to 10 percent of the final volume remain a convenient option.
Charge and nonspecific binding:
Additional sulfonate groups increase negative charge, which can reduce electrostatic nonspecific binding in some cell-based assays.
Additional sulfonate groups increase negative charge, which can reduce electrostatic nonspecific binding in some cell-based assays.
Storage and reconstitution:
Sulfo reagents are hygroscopic. Store them desiccated at low temperature, warm to room temperature before opening, and dissolve immediately before use to limit hydrolysis.
Sulfo reagents are hygroscopic. Store them desiccated at low temperature, warm to room temperature before opening, and dissolve immediately before use to limit hydrolysis.
Practical note:
The hydrolysis half-life of an NHS ester is about 4 to 5 hours at pH 7 but only about 10 minutes at pH 8.6 at 0 degrees Celsius. For water-soluble
sulfo-NHS ester dyes, prepare the reaction promptly after reconstitution and keep the pH near 8.0 to 8.5 so that labeling proceeds faster than
hydrolysis.
Linker and Spacer Design: Distance, Solubility, and Sterics
The NHS ester is usually attached to the dye through a linker, and this short chemical bridge has a disproportionate effect on conjugate quality. Linker length controls how far the dye sits from the biomolecule surface, and linker chemistry controls solubility and sterics. Choosing the right linker is especially important for antibodies, enzymes, and small peptides.
Short linkers for compact conjugates:
C2 to C4 spacers keep the dye close to the biomolecule. They are suitable when the labeled region is not part of the binding or catalytic surface.
C2 to C4 spacers keep the dye close to the biomolecule. They are suitable when the labeled region is not part of the binding or catalytic surface.
Long linkers reduce steric clash:
C6 and PEG-based spacers push the dye away from the protein surface, helping preserve epitope binding on antibodies and active site access in enzymes.
C6 and PEG-based spacers push the dye away from the protein surface, helping preserve epitope binding on antibodies and active site access in enzymes.
PEG spacers aid solubility:
Polyethylene glycol linkers add aqueous solubility to hydrophobic dye cores and reduce aggregation of the final conjugate.
Polyethylene glycol linkers add aqueous solubility to hydrophobic dye cores and reduce aggregation of the final conjugate.
Linkers can alter spectra:
Very short linkers occasionally allow intramolecular interactions that shift or quench emission. Compare the conjugate spectrum to the free dye.
Very short linkers occasionally allow intramolecular interactions that shift or quench emission. Compare the conjugate spectrum to the free dye.
Match spacer to target size:
Small peptides and aptamers often benefit from longer spacers to avoid burying the recognition site, while antibodies generally tolerate short to medium spacers.
Small peptides and aptamers often benefit from longer spacers to avoid burying the recognition site, while antibodies generally tolerate short to medium spacers.
Linker length controls FRET:
In FRET probes, the spacer sets donor-acceptor distance. Too short causes direct quenching, and too long reduces energy transfer efficiency.
In FRET probes, the spacer sets donor-acceptor distance. Too short causes direct quenching, and too long reduces energy transfer efficiency.
Degree of Labeling: Planning Dye Loading for Your Application
The degree of labeling (DOL) is the average number of dye molecules attached to each biomolecule. It is the most important quality parameter of a conjugate, balancing signal intensity against biological function. DOL is calculated from the absorbance of the purified conjugate at 280 nm and at the dye absorption maximum. The right target depends on the application, and the same logic used for fluorescent dyes for antibody labeling applies to most protein conjugates.
Antibody immunostaining: DOL 2-4:
Keeping loading low preserves antigen binding and keeps background low. Heavily labeled antibodies bind more weakly and stain more nonspecifically.
Keeping loading low preserves antigen binding and keeps background low. Heavily labeled antibodies bind more weakly and stain more nonspecifically.
Flow cytometry: DOL 3-6:
Higher loading increases signal for low-abundance antigens. Because cytometers detect quickly, the modest loss of activity at higher DOL is usually acceptable.
Higher loading increases signal for low-abundance antigens. Because cytometers detect quickly, the modest loss of activity at higher DOL is usually acceptable.
Enzyme studies: DOL 1-3:
Protect lysines near the active site by keeping labeling light, then verify that catalytic activity is preserved after conjugation.
Protect lysines near the active site by keeping labeling light, then verify that catalytic activity is preserved after conjugation.
Over-labeling causes self-quenching:
Beyond a certain density, dye molecules quench each other. Total signal falls even as DOL rises, so more dye is not always brighter.
Beyond a certain density, dye molecules quench each other. Total signal falls even as DOL rises, so more dye is not always brighter.
Control molar excess, not guesswork:
Use a dye-to-protein molar excess of 5 to 20 fold, then measure the resulting DOL spectrophotometrically and adjust for the next batch.
Use a dye-to-protein molar excess of 5 to 20 fold, then measure the resulting DOL spectrophotometrically and adjust for the next batch.
Labeling efficiency is not 100 percent:
Antibody conjugations typically achieve only a fraction of theoretical incorporation, so plan the dye excess with the target DOL and the expected efficiency in mind.
Antibody conjugations typically achieve only a fraction of theoretical incorporation, so plan the dye excess with the target DOL and the expected efficiency in mind.
| Application | Typical Target DOL | Dye-to-Protein Molar Excess | Primary Consideration |
|---|---|---|---|
| Antibody immunostaining | 2-4 | 5-10 fold | Preserve antigen binding, minimize background. |
| Flow cytometry | 3-6 | 8-20 fold | Maximize signal for low-abundance targets. |
| Enzyme activity studies | 1-3 | 3-8 fold | Protect lysines near the active site. |
| Peptide receptor binding | 1-2 | 2-5 fold | Avoid labeling residues required for recognition. |
| FRET probe construction | 1 per probe | 1-3 fold | Control donor-acceptor distance and stoichiometry. |
Still Unsure Which NHS Ester Dye Fits Your Experiment?
BOC Sciences can help you compare dye families, check spectral compatibility with your instrument, plan the degree of labeling, and select water-soluble sulfo-NHS ester dyes for your protein, antibody, or peptide labeling project.
Request Dye Selection SupportA Step-by-Step Workflow for Selecting an NHS Ester Dye
The process below condenses this article into six ordered steps. Following them in sequence prevents choosing a dye for popularity or cost before confirming it works with your instrument and application.
Step 1: Define the application and instrument
Record the laser lines or filter sets available, the assay format, and whether the experiment is single-color or multiplex. This defines the usable wavelength range.
Record the laser lines or filter sets available, the assay format, and whether the experiment is single-color or multiplex. This defines the usable wavelength range.
Step 2: Shortlist dye families by spectral match
Select the families whose absorption and emission fit the instrument. Confirm that excitation overlaps an available source and emission overlaps the detector window.
Select the families whose absorption and emission fit the instrument. Confirm that excitation overlaps an available source and emission overlaps the detector window.
Step 3: Compare brightness and photostability
Balance signal strength against illumination time. Prefer photostable rhodamine or cyanine dyes for imaging, and brighter fluorescein or BODIPY derivatives for quick endpoint reads.
Balance signal strength against illumination time. Prefer photostable rhodamine or cyanine dyes for imaging, and brighter fluorescein or BODIPY derivatives for quick endpoint reads.
Step 4: Check solubility and choose sulfo versions
For proteins and antibodies in aqueous buffers, prefer sulfo-NHS ester dyes to avoid precipitation and organic co-solvents.
For proteins and antibodies in aqueous buffers, prefer sulfo-NHS ester dyes to avoid precipitation and organic co-solvents.
Step 5: Plan DOL and molar excess
Set the target DOL for the application, such as 2-4 for antibody immunostaining or 3-6 for flow cytometry, and plan a 5 to 20 fold molar excess of dye.
Set the target DOL for the application, such as 2-4 for antibody immunostaining or 3-6 for flow cytometry, and plan a 5 to 20 fold molar excess of dye.
Step 6: Validate with a small pilot run
Label a small sample at pH 8.0 to 8.5, purify away free dye, measure the DOL by absorbance, and confirm signal and activity before scaling up.
Label a small sample at pH 8.0 to 8.5, purify away free dye, measure the DOL by absorbance, and confirm signal and activity before scaling up.
Common Dye Selection and Labeling Challenges
Even with a sound selection process, experiments fail in predictable ways. Recognizing these failure modes helps you decide whether the fix is a different dye, a different loading, or a different reaction condition.
Spectral bleed-through in multiplex
Dyes with overlapping emission spill into neighboring channels. Choose emission peaks separated by 40 to 60 nm or accept larger compensation in flow cytometry.
Photobleaching during long imaging
Fluorescein and some BODIPY derivatives fade quickly under repeated illumination. Switch to photostable rhodamine or cyanine dyes for time-lapse and 3D imaging.
Precipitation and aggregates
Hydrophobic dye cores precipitate in aqueous buffer. Use sulfo-NHS ester dyes, keep organic solvent below 10 percent, and centrifuge to remove aggregates.
Over-labeling and self-quenching
Excess dye loading lowers effective brightness through self-quenching and raises background. Reduce the molar excess and confirm the measured DOL.
Loss of activity after conjugation
Random lysine modification can disrupt binding or catalysis. Lower the target DOL, use a longer spacer, and validate activity immediately after purification.
Batch-to-batch variability
Reagent age, buffer pH drift, and storage conditions cause inconsistent DOL. Use fresh, desiccated NHS esters, verify pH, and standardize the protocol.
How BOC Sciences Supports NHS Ester Dye Selection
BOC Sciences supports the full dye selection and labeling workflow, from spectral compatibility consulting to custom NHS ester dye supply and conjugate characterization. The service scope is tailored to researchers who need practical guidance as much as reagents.
Dye Selection Consultation
Application-focused guidance for choosing among NHS ester dye families and formats.
- Instrument profile and wavelength review
- Dye family shortlist for your assay
- Excitation and emission compatibility check
- Application-based recommendation report
Spectral Compatibility Assessment
Systematic evaluation of dye spectra against lasers, filters, and detector windows.
- Laser and bandpass filter mapping
- Spectral overlap and bleed-through analysis
- Multiplex panel planning
- FRET donor-acceptor pair selection
Degree of Labeling Optimization
Design and verification support for controlling dye loading on biomolecules.
- DOL target planning by application
- Dye-to-protein molar ratio design
- Spectrophotometric DOL measurement
- Labeling protocol refinement
Water-Soluble Dye Guidance
Help selecting sulfo-NHS ester dyes and designing aggregation-free aqueous labeling.
- Sulfo-NHS ester dye selection
- Solubility and aggregation troubleshooting
- Organic solvent reduction strategies
- Buffer and pH protocol design
Custom NHS Ester Dye Supply
Custom synthesis of NHS ester dyes with tailored linkers and solubility profiles.
- Custom dye functionalization
- Linker and spacer design
- Sulfo modification for solubility
- Scaled reagent production
Conjugate Characterization
Analytical support for verifying the quality of your labeled conjugate.
- Absorbance-based DOL analysis
- Purity and aggregate assessment
- Stability and storage testing
- Lot-to-lot consistency support
Start Your NHS Ester Dye Selection Project with BOC Sciences
Whether you need help choosing between dye families, a water-soluble sulfo-NHS ester for a challenging protein, a custom linker design, or a complete labeling and characterization workflow, BOC Sciences can match reagents and strategies to your research goals.
Send Your Project RequirementsRecommended Dyes and NHS Ester Reagents for Labeling Experiments
The products below are commonly used in NHS ester and amine-reactive fluorescent labeling, including FAM, rhodamine, BODIPY, coumarin, and cyanine derivatives and related conjugates. They are a useful starting set for building your own labeling workflow.
| 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
Learn more about NHS ester labeling chemistry, fluorophore selection, conjugation conditions, and substrate-specific considerations. Explore related guides covering proteins, antibodies, peptides, oligonucleotides, reagent solubility, reaction mechanisms, and NHS ester stability.
- NHS vs Sulfo-NHS Esters: Water Solubility and Conjugation Performance
- NHS Ester Labeling of Proteins and Antibodies: Protocols and Optimization
- What Are NHS Ester Reagents? Chemistry, Reactivity, and Role in Fluorescent Labeling
- NHS Ester Labeling of Peptides, Oligonucleotides, and Small Molecules
- 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 the decisions researchers most often face when choosing NHS ester dyes and planning fluorescent labeling experiments.
What is the most important factor when choosing an NHS ester dye?
Spectral compatibility with your instrument comes first. If the dye is not excited by an available laser line and its emission falls outside your detector window, no other property matters. Once the spectrum fits, consider brightness, photostability, water solubility, and target degree of labeling.
Why should I use a sulfo-NHS ester dye for protein labeling?
Sulfo-NHS ester dyes carry sulfonate groups that make the dye water soluble, so labeling proceeds in purely aqueous buffers without organic co-solvents. This reduces precipitation, avoids destabilizing antibodies and enzymes, and often produces cleaner conjugates with less background.
How do I calculate the degree of labeling of my conjugate?
Measure the absorbance of the purified conjugate at 280 nm and at the dye absorption maximum. Correct the 280 nm reading for the dye contribution, then divide the dye concentration by the protein concentration using the respective extinction coefficients. Most labeling protocols include the correction factor for this calculation.
What molar excess of dye should I use for antibody labeling?
A dye-to-antibody molar excess of 5 to 20 fold is typical. For a target DOL of 2 to 4 in immunostaining, start near the lower end of the range and increase only if signal is too low. Measure the resulting DOL and adjust for subsequent batches.
Can I combine several NHS ester dyes in a multicolor flow cytometry panel?
Yes. Choose dyes whose emission peaks are separated by roughly 40 to 60 nm, such as FITC with TAMRA or Cy3 with Cy5, so that spectral overlap is manageable. Confirm that each dye is excited by a laser present on your cytometer and that the sulfo versions you select are water soluble.
Request NHS Ester Dye Selection Support
Share your target biomolecule, instrument configuration, and labeling goals with BOC Sciences. Our team can recommend suitable dye families, sulfo versions, linker options, and DOL targets for your experiment.
Dye recommendation
Compare fluorescein, rhodamine, cyanine, BODIPY, coumarin, and TAMRA NHS ester dyes for your application.
Compare fluorescein, rhodamine, cyanine, BODIPY, coumarin, and TAMRA NHS ester dyes for your application.
Spectral check
Confirm excitation and emission compatibility with your lasers, filters, and detectors.
Confirm excitation and emission compatibility with your lasers, filters, and detectors.
DOL planning
Define target degree of labeling and molar excess for antibodies, proteins, peptides, or probes.
Define target degree of labeling and molar excess for antibodies, proteins, peptides, or probes.
Bulk product inquiry
Request pricing, availability, packaging, and custom synthesis options for NHS ester dyes.
Request pricing, availability, packaging, and custom synthesis options for NHS ester dyes.
