Shop All Labels & Labeling Kits

CMNB-Caged Carboxyfluorescein, SE (5-Carboxyfluorescein-Bis-(5-Carboxymethoxy-2-Nitrobenzyl) Ether, β-Alanine-Carboxamide, Succinimidyl Ester) Invitrogen™

Conjugation of the succinimidyl ester of the water-soluble, CMNB-caged carboxyfluorescein, SE to a primary amine on a biomolecule of interest produces an essentially nonfluorescent probe that yields a green-fluorescent fluorescein-labeled product only after ultraviolet illumination and removal of the caging group.

Alexa Fluor™ 568 C5 Maleimide Invitrogen™

Alexa Fluor® 568 is a bright, orange/red fluorescent dye with excitation ideally suited for the 568 nm laser line on the Ar-Kr mixed-gas laser. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 568 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 568 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

The maleimide derivative of Alexa Fluor® 568 is the most popular tool for conjugating the dye to a thiol group on a protein, oligonucleotide thiophosphate, or low molecular weight ligand. The resulting Alexa Fluor® 568 conjugates exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® maleimide:

Fluorophore label: Alexa Fluor® 568 dye
Reactive group: maleimide
Reactivity: thiol groups on proteins and ligands, oligonucleotide thiophosphates
Ex/Em of the conjugate: 575/600 nm
Extinction coefficient: 92,000 cm-1M-1
Spectrally similar dyes: Rhodamine red
Molecular weight: 880.92

Typical Conjugation Reaction
The protein should be dissolved at a concentration of 50-100 µM in a suitable buffer (10-100 mM phosphate, Tris, or HEPES) at pH 7.0-7.5. In this pH range, the protein thiol groups are sufficiently nucleophilic that they react almost exclusively with the reagent in the presence of the more numerous protein amine groups, which are protonated and relatively unreactive. We recommend reducing any disulfide bonds at this point using a 10-fold molar excess of reducing agent such as DTT or TCEP. Excess DTT must be removed by dialysis and subsequent thiol-modification should be carried out under oxygen-free conditions to prevent reformation of the disulfide bonds; these precautions are not necessary when using TCEP prior to maleimide conjugation.

The Alexa Fluor® maleimide is typically dissolved in high-quality anhydrous dimethylsulfoxide (DMSO) at a concentration of 1-10 mM immediately prior to use, and stock solutions should be protected from light as much as possible. Generally, this stock solution is added to the protein solution dropwise while stirring to produce approximately 10-20 moles of reagent per mole of protein, and the reaction is allowed to proceed at room temperature for 2 hours or at 4°C overnight, protected from light. Any unreacted thiol-reactive reagent can be consumed by adding excess glutathione, mercaptoethanol, or other soluble low molecular weight thiol.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Alexa Fluor™ 405 Cadaverine Invitrogen™

Alexa Fluor® 405 Cadaverine is useful as a polar tracer and as a reactive dye for labeling proteins via a carboxylic acid moiety. Alexa Fluor® 405 is a bright, violet dye with excitation ideally suited to the 405 nm laser line. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 405 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 405 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

Detailed information about this AlexaFluor® cadaverine:

• Fluorophore label : Alexa Fluor® 405 dye
• Reactive group: cadaverine
• Reactivity: carboxylic acids, aldehydes, and ketones (and glutamine residues through an enzyme-catalyzed transamidation reaction)
• Ex/Em of the conjugate: 399/422 nm
• Extinction coefficient: 29,000 cm-1M-1
• Spectrally similar dyes: Cascade Blue
• Molecular weight: 666.58

Cell Tracking and Tracing Applications
Alexa Fluor® cadaverines make excellent fluorescent polar tracers because they are bright, small, and water soluble. Since they contain an aldehyde-fixable functional group, they can be fixed in cells by treatment with formaldehyde or glutaraldehyde. They are easily loaded into cells by microinjection, infusion from patch pipette, or uptake induced by our Influx™ Pinocytic Cell-Loading Reagent. Learn more about cell tracking and tracing.

Protein Labeling Applications
Alexa Fluor® cadaverines can be used as reactive molecules for adding a fluorescent label to carboxylic acids using a coupling agent such as a carbodiimide; they do not spontaneously react with carboxylic acids in solution. They do, however, react spontaneously with the common amine-reactive functional groups, including succinimidyl esters and isothiocyanates. The amine-containing Alexa Fluor® cadaverines can also be used to label glutamine residues in some proteins and peptides via an enzyme-catalyzed transamidation reaction.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Related Products
DMSO (dimethylsulfoxide) (D12345)
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Biotin-XX Microscale Protein Labeling Kit Invitrogen™

Microscale Protein Labeling Kits provide a convenient means for attaching a fluorescent label to a small amount of antibody or protein (20–100 µg). The kits are available in four Alexa Fluor® colors (or biotin) and supply everything needed for three labeling and separation reactions.

Important Features of Microscale Protein Labeling Kits:

• Labeled proteins typically ready to use typically in 2 hours (~30 minutes hands-on time)
• Optimized for 20–100 µg of protein with molecular weights between 12 and 150 kDa
• Purified using convenient spin filters with yields between 60 and 90%
• Stabilizing proteins must be removed from the sample before labeling


Stable Reaction Chemistry and Superior Alexa Fluor® Dyes
In this Microscale Protein Labeling Kit, the reactive label contains a succinimidyl (NHS) ester moiety that reacts with primary amines of proteins to form stable dye-protein conjugates. Compared to traditional dyes, Alexa Fluor® dyes are brighter, more photostable, and more pH resistant between pH 4 and 10. And generally when using Alexa Fluor® dyes, higher degrees of labeling can be achieved without intramolecular quenching. For details see Alexa Fluor® Dyes Spanning the Visible and Infrared Spectrum—Section 1.3.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See Antibody Labeling from A to Z or use our Labeling Chemistry Selection Tool for other choices. To learn more about our various kits read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in the Molecular Probes® Handbook.

We'll Make a Custom Antibody Conjugate for You
If you can't find what you're looking for in our stocked list, we'll prepare a custom antibody conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

For Research Use Only. Not intended for animal or human therapeutic or diagnostic use.

Alexa Fluor™ 633 Hydrazide Invitrogen™

Alexa Fluor® 633 Hydrazide is useful as a cell tracer and as a reactive dye for labeling aldehydes or ketones in polysaccharides or glycoproteins. Alexa Fluor® 633 is a bright, far red fluorescent dye with excitation ideally suited to the 633 nm laser line. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 633 dye is water soluble and pH-insensitive from pH 4 to pH 10.

Detailed information about this AlexaFluor® hydrazide:

• Fluorophore label : Alexa Fluor® 633 dye
• Reactive group: hydrazide
• Reactivity: Aldehydes or keytones in polysaccharides or glycoproteins
• Ex/Em of the conjugate: 624/643 nm
• Extinction coefficient: 110,000 cm-1M-1
• Spectrally similar dyes: Cy5
• Molecular weight: ~1,150

Cell Tracking and Tracing Applications
Alexa Fluor® hydrazides and hydroxlamines are useful as low molecular weight, membrane-impermeant, aldehyde-fixable cell tracers, exhibiting brighter fluorescence and greater photostability than cell tracers derived from other spectrally similar fluorophores. They are easily loaded into cells by microinjection, infusion from patch pipette, or uptake induced by our Influx™ Pinocytic Cell-Loading Reagent. Learn more about cell tracking and tracing.

Glycoprotein and Polysaccharide Labeling Applications
The Alexa Fluor® hydrazides and hydroxlamines are reactive molecules that can be used to add a fluorescent label to biomolecules containing aldehydes or ketones. Aldehydes and ketones can be introduced into polysaccharides and glycoproteins by periodate-mediated oxidation of vicinal diols. Galactose oxidase can also be used to oxidize terminal galactose residues of glycoproteins to aldehydes.

Hydrazide vs Hydroxylamine
Hydrazine derivatives react with ketones and aldehydes to yield relatively stable hydrazones. Hydroxylamine derivatives (aminooxy compounds) react with aldehydes and ketones to yield oximes. Oximes are superior to hydrazones with respect to hydrolytic stability. Both hydrazones and oximes can be reduced with sodium borohydride (NaBH4) to further increase the stability of the linkage.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Related Products
DMSO (dimethylsulfoxide) (D12345)
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Alexa Fluor™ 633 C5 Maleimide Invitrogen™

Alexa Fluor® 633 is a bright, red fluorescent dye with excitation ideally suited to the 633 nm laser line. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 633 dye is water soluble and pH-insensitive from pH 4 to pH 10.

The maleimide derivative of Alexa Fluor® 633 is the most popular tool for conjugating the dye to a thiol group on a protein, oligonucleotide thiophosphate, or low molecular weight ligand. The resulting Alexa Fluor® 633 conjugates exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® maleimide:

Fluorophore label: Alexa Fluor® 633 dye
Reactive group: maleimide
Reactivity: thiol groups on proteins and ligands, oligonucleotide thiophosphates
Ex/Em of the conjugate: 622/640 nm
Extinction coefficient: 143,000 cm-1M-1
Molecular weight: ~1300

Typical Conjugation Reaction
The protein should be dissolved at a concentration of 50-100 µM in a suitable buffer (10-100 mM phosphate, Tris, or HEPES) at pH 7.0-7.5. In this pH range, the protein thiol groups are sufficiently nucleophilic that they react almost exclusively with the reagent in the presence of the more numerous protein amine groups, which are protonated and relatively unreactive. We recommend reducing any disulfide bonds at this point using a 10-fold molar excess of reducing agent such as DTT or TCEP. Excess DTT must be removed by dialysis and subsequent thiol-modification should be carried out under oxygen-free conditions to prevent reformation of the disulfide bonds; these precautions are not necessary when using TCEP prior to maleimide conjugation.

The Alexa Fluor® maleimide is typically dissolved in high-quality anhydrous dimethylsulfoxide (DMSO) at a concentration of 1-10 mM immediately prior to use, and stock solutions should be protected from light as much as possible. Generally, this stock solution is added to the protein solution dropwise while stirring to produce approximately 10-20 moles of reagent per mole of protein, and the reaction is allowed to proceed at room temperature for 2 hours or at 4°C overnight, protected from light. Any unreacted thiol-reactive reagent can be consumed by adding excess glutathione, mercaptoethanol, or other soluble low molecular weight thiol.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Alexa Fluor™ 488 Cadaverine Invitrogen™

Alexa Fluor® 488 Cadaverine is useful as a polar tracer and as a reactive dye for labeling proteins via a carboxylic acid moiety. Alexa Fluor® 488 is a bright, green-fluorescent dye with excitation ideally suited to the 488 nm laser line. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 488 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 488 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

Detailed information about this AlexaFluor® cadaverine:

• Fluorophore label : Alexa Fluor® 488 dye
• Reactive group: cadaverine
• Reactivity: carboxylic acids, aldehydes, and ketones (and glutamine residues through an enzyme-catalyzed transamidation reaction)
• Ex/Em of the conjugate: 493/516 nm
• Extinction coefficient: 73,000 cm-1M-1
• Spectrally similar dyes: FITC, GFP
• Molecular weight: 640.61

Cell Tracking and Tracing Applications
Alexa Fluor® cadaverines make excellent fluorescent polar tracers because they are bright, small, and water soluble. Since they contain an aldehyde-fixable functional group, they can be fixed in cells by treatment with formaldehyde or glutaraldehyde. They are easily loaded into cells by microinjection, infusion from patch pipette, or uptake induced by our Influx™ Pinocytic Cell-Loading Reagent. Learn more about cell tracking and tracing.

Protein Labeling Applications
Alexa Fluor® cadaverines can be used as reactive molecules for adding a fluorescent label to carboxylic acids using a coupling agent such as a carbodiimide; they do not spontaneously react with carboxylic acids in solution. They do, however, react spontaneously with the common amine-reactive functional groups, including succinimidyl esters and isothiocyanates. The amine-containing Alexa Fluor® cadaverines can also be used to label glutamine residues in some proteins and peptides via an enzyme-catalyzed transamidation reaction.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Related Products
DMSO (dimethylsulfoxide) (D12345)
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

D-Biotin Invitrogen™

D-biotin binds with high affinity to streptavidin, avidin and NeutrAvidin® biotin-binding proteins.

Pierce™ Biotin Quantitation Kit Thermo Scientific™

Thermo Scientific Pierce Biotin Quantitation Kit includes aliquots of HABA reagent and biotinylated protein standard for convenient colorimetric determination of biotinylation levels in labeled antibodies and other proteins.

Features of the Biotin Quantitation Kit:

Colorimetric – requires a plate reader or spectrophotometer set to measure at 500nm
Reliable – proven, well-characterized method for determination of biotinylation levels
Convenient – kit provides the essential reagents and standards to perform the assay with ease
Flexible – adaptable to spectrophotometer cuvettes or standard plate readers with 96-well microplates
Options – calculate results directly from absorbance values based on extinction coefficients using the procedure outlined in the instructions
Robust – supplied HABA-avidin complex can be used over a wide range of pH and salt concentrations

HABA dye (4'-hydroxyazobenzene-2-carboxylic acid) is a reagent that enables quick estimation of the mole-to-mole ratio of biotin to protein in a solution. The Pierce Biotin Quantitation Kit contains a premix of HABA and avidin and a biotinylated horseradish peroxidase (HRP) positive control. The HABA-Avidin Premix is supplied in convenient Thermo Scientific No-Weigh Microtube packaging, which eliminates the difficulties associated with weighing small quantities of reagent.

To quantitate biotinylation, a solution containing the biotinylated protein is added to a mixture of HABA and avidin. Because of its higher affinity for avidin, biotin displaces the HABA and the absorbance at 500nm decreases proportionately. By this method, an unknown amount of biotin present in a solution can be quantitated in a single cuvette by measuring the absorbance of the HABA-avidin solution before and after addition of the biotin-containing sample. The change in absorbance relates to the amount of biotin in the sample by the extinction coefficient of the HABA-avidin complex. View online HABA Calculator.

EZ-Link™ Sulfo NHS-LC-LC-Biotin, No-Weigh™ Format Thermo Scientific™

Thermo Scientific EZ-Link Sulfo-NHS-LC-LC-Biotin enables simple and efficient biotin labeling of antibodies, proteins, and any other primary amine–containing macromolecules. Specific labeling of cell surface proteins is another common application for these uniquely water-soluble and membrane impermeable reagents.

Thermo Scientific No-Weigh products are specialty reagents provided in a pre-aliquoted format. The pre-weighed packaging prevents the loss of reagent reactivity and contamination over time by eliminating the repetitive opening and closing of the vial. The format enables use of a fresh vial of reagent each time, eliminating the hassle of weighing small amounts of reagents and reducing concerns over reagent stability.

Features of EZ-Link Sulfo-NHS-LC-LC-Biotin:

Protein labeling—biotinylate antibodies to facilitate immobilization, purification or detection using streptavidin resins or probes
Cell surface labeling—biotinylates only surface proteins of whole cells because the negatively charged reagent does not permeate cell membranes
Amine-reactive—reacts with primary amines (-NH2), such as the side-chain of lysines (K) or the amino-termini of polypeptides
Soluble—charged sulfo-NHS group increases reagent water solubility compared to ordinary NHS-ester compounds
Irreversible—forms permanent amide bonds; spacer arm cannot be cleaved
Doubly long —spacer arm (total length added to target) is 22.4 angstroms; this extended arm helps to minimize steric hindrance for biotin binding

Sulfo-NHS-LC-LC-Biotin is the longest of three very similar EZ-Link Reagents that are water-soluble, non-cleavable, and enable simple and efficient biotinylation of antibodies, proteins and any other primary amine-containing macromolecules in solution. Specific labeling of cell surface proteins is another common application for these uniquely water-soluble and membrane impermeable reagents. Differing only in their spacer arm lengths, the three Sulfo-NHS-ester reagents offer the possibility of optimizing labeling and detection experiments where steric hindrance of biotin binding is an important factor.

We manufacture biotin reagents to ensure the highest possible overall product integrity, consistency, and performance for the intended research applications.

N-Hydroxysulfosuccinimide (NHS) esters of biotin are the most popular type of biotinylation reagent. NHS-activated biotins react efficiently with primary amino groups (-NH2) in alkaline buffers to form stable amide bonds. Proteins (e.g., antibodies) typically have several primary amines that are available as targets for labeling, including the side chain of lysine (K) residues and the N-terminus of each polypeptide.

Varieties of biotin NHS-ester reagents differ in length, solubility, cell permeability and cleavability. Non-sulfonated NHS-biotins are cell permeable but must be dissolved in organic solvent such as DMSO or DMF. Sulfo-NHS biotins (and those with pegylated spacers) are directly water soluble but not membrane permeable. Varieties containing disulfide bonds can be cleaved using reducing agents, enabling the biotin group to be disconnected from the labeled protein.

Alexa Fluor™ 660 C2 Maleimide Invitrogen™

Alexa Fluor® 660 is a bright, far-red fluorescent dye. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 660 dye is water soluble and pH-insensitive from pH 4 to pH 10.

The maleimide derivative of Alexa Fluor® 660 is the most popular tool for conjugating the dye to a thiol group on a protein, oligonucleotide thiophosphate, or low molecular weight ligand. The resulting Alexa Fluor® 660 conjugates exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.

Detailed information about this AlexaFluor® maleimide:

Fluorophore label: Alexa Fluor® 660 dye
Reactive group: maleimide
Reactivity: thiol groups on proteins and ligands, oligonucleotide thiophosphates
Ex/Em of the conjugate: 668/697 nm
Extinction coefficient: 112,000 cm-1M-1
Molecular weight: ~1000

Typical Conjugation Reaction
The protein should be dissolved at a concentration of 50-100 µM in a suitable buffer (10-100 mM phosphate, Tris, or HEPES) at pH 7.0-7.5. In this pH range, the protein thiol groups are sufficiently nucleophilic that they react almost exclusively with the reagent in the presence of the more numerous protein amine groups, which are protonated and relatively unreactive. We recommend reducing any disulfide bonds at this point using a 10-fold molar excess of reducing agent such as DTT or TCEP. Excess DTT must be removed by dialysis and subsequent thiol-modification should be carried out under oxygen-free conditions to prevent reformation of the disulfide bonds; these precautions are not necessary when using TCEP prior to maleimide conjugation.

The Alexa Fluor® maleimide is typically dissolved in high-quality anhydrous dimethylsulfoxide (DMSO) at a concentration of 1-10 mM immediately prior to use, and stock solutions should be protected from light as much as possible. Generally, this stock solution is added to the protein solution dropwise while stirring to produce approximately 10-20 moles of reagent per mole of protein, and the reaction is allowed to proceed at room temperature for 2 hours or at 4°C overnight, protected from light. Any unreacted thiol-reactive reagent can be consumed by adding excess glutathione, mercaptoethanol, or other soluble low molecular weight thiol.

Conjugate Purification
Labeled antibodies are typically separated from free Alexa Fluor® dye using a gel filtration column, such as Sephadex™ G-25, BioGel® P-30, or equivalent. For much larger or smaller proteins, select a gel filtration media with an appropriate molecular weight cut-off or purify by dialysis. We offer several purification kits optimized for different quantities of antibody conjugate:
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Alexa Fluor™ 555 Cadaverine Invitrogen™

Alexa Fluor® 555 Cadaverine is useful as a polar tracer and as a reactive dye for labeling proteins via a carboxylic acid moiety. Alexa Fluor® 555 is a bright, orange dye. Used for stable signal generation in imaging and flow cytometry, Alexa Fluor® 555 dye is water soluble and pH-insensitive from pH 4 to pH 10. In addition to reactive dye formulations, we offer Alexa Fluor® 555 dye conjugated to a variety of antibodies, peptides, proteins, tracers, and amplification substrates optimized for cellular labeling and detection (learn more).

Detailed information about this AlexaFluor® cadaverine:

• Fluorophore label : Alexa Fluor® 555 dye
• Reactive group: cadaverine
• Reactivity: carboxylic acids, aldehydes, and ketones (and glutamine residues through an enzyme-catalyzed transamidation reaction)
• Ex/Em of the conjugate: 555/572 nm
• Extinction coefficient: 155,000 cm-1M-1
• Spectrally similar dyes: TRITC
• Molecular weight: ~950

Cell Tracking and Tracing Applications
Alexa Fluor® cadaverines make excellent fluorescent polar tracers because they are bright, small, and water soluble. Since they contain an aldehyde-fixable functional group, they can be fixed in cells by treatment with formaldehyde or glutaraldehyde. They are easily loaded into cells by microinjection, infusion from patch pipette, or uptake induced by our Influx™ Pinocytic Cell-Loading Reagent. Learn more about cell tracking and tracing.

Protein Labeling Applications
Alexa Fluor® cadaverines can be used as reactive molecules for adding a fluorescent label to carboxylic acids using a coupling agent such as a carbodiimide; they do not spontaneously react with carboxylic acids in solution. They do, however, react spontaneously with the common amine-reactive functional groups, including succinimidyl esters and isothiocyanates. The amine-containing Alexa Fluor® cadaverines can also be used to label glutamine residues in some proteins and peptides via an enzyme-catalyzed transamidation reaction.

Learn More About Protein and Antibody Labeling
We offer a wide selection of Molecular Probes® antibody and protein labeling kits to fit your starting material and your experimental setup. See our Antibody Labeling kits or use our Labeling Chemistry Selection Tool for other choices. To learn more about our labeling kits, read Kits for Labeling Proteins and Nucleic Acids—Section 1.2 in The Molecular Probes® Handbook.

We’ll Make a Custom Conjugate for You
If you can’t find what you’re looking for in our online catalog, we’ll prepare a custom antibody or protein conjugate for you. Our custom conjugation service is efficient and confidential, and we stand by the quality of our work. We are ISO 9001:2000 certified.

Related Products
DMSO (dimethylsulfoxide) (D12345)
Antibody Conjugate Purification Kit for 0.5-1 mg (A33086)
Antibody Conjugate Purification Kit for 20-50 µg (A33087)
Antibody Conjugate Purification kit for 50-100 µg (A33088)

Pierce™ Streptavidin, Maleimide-Activated Thermo Scientific™

Thermo Scientific Pierce Maleimide-Activated Streptavidin conjugate include streptavidin in a purified form, activated for crosslinking to sulfhydryl groups containing molecules.

Related Products
Pierce™ Streptavidin
Pierce™ Streptavidin, Horseradish Peroxidase Conjugated
Pierce™ Streptavidin, Alkaline Phosphatase Conjugated
Pierce™ Streptavidin, Hydrazide-Activated

DyLight™ 650-4xPEG Maleimide Thermo Scientific™

Thermo Scientific DyLight 650-4xPEG Sulfhydryl-Reactive Dye is a maleimide-activated derivative of our high-performance DyLight 650 Dye used to fluorescently label cysteine-containing peptides, proteins, or other biomolecular probes.

The DyLight 650-4xPEG Dye contains 4 polyethylene glycol (PEG) chains that are non-toxic, enhance fluorescence, and reduce nonspecific binding of conjugates made with them. Conjugates made with DyLight 650-4xPEG Dye can be used as molecular probes for cellular and in vivo imaging, flow cytometry, IHC, and other fluorescence detection methods. The PEG chains also improve solubility of the dyes and labeled molecules in aqueous solution, aid in cell permeability, and improve tissue retention.

Features of DyLight 650-4xPEG Maleimide:

High fluorescence intensity—significantly brighter fluorescence than Alexa Fluor™ 647
PEGylated—improves solubility in aqueous solution and aids in cell permeability
Specific—maleimide-activated dye labels proteins and other molecules at reduced sulfhydryls (-SH)

Applications:
• Fluorescence microscopy
In vivo or ex vivo imaging
• Cell-based assays
• Flow cytometry/fluorescence-activated cell sorting (FACS)

DyLight 650-4xPEG Sulfhydryl-Reactive Dye is activated with a maleic acid imide (maleimide) moiety to form a reactive alkylation reagent. Labeling occurs through reaction of the maleimide-activated dye with reduced sulfhydryl groups (-SH) to form stable thioether bonds. Maleimides are specific for sulfhydryl groups between pH 6.5–7.5. Learn more about maleimide chemistry.

Biotin-X Cadaverine (5-(((N-(Biotinoyl)Amino)Hexanoyl)Amino)Pentylamine, Trifluoroacetic Acid Salt) Invitrogen™

The primary aliphatic amine of biotin-X cadaverine can be reversibly coupled to aldehydes and ketones to form a Schiff base - which can be reduced to a stable amine derivative by sodium borohydride (NaBH4) or sodium cyanoborohydride (NaCNH3) to form new biotinylated probes. Carboxylic acids of proteins and other water-soluble biopolymers can be coupled to this molecule in aqueous solution using water-soluble carbodiimides such as EDAC (E2247).
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