| Size | Price | Stock | Qty |
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| 5mg |
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| 10mg |
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| 50mg |
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| Other Sizes |
| Targets |
QSY 21 NHS targets primary amine groups (‑NH2) on lysine residues and the N‑terminus of peptides and proteins. The NHS ester group reacts efficiently at pH 7-9 to form covalent amide bonds. Once conjugated to a biomolecule, QSY 21 serves as a FRET acceptor, quenching the fluorescence of donor fluorophores such as Alexa Fluor 488, fluorescein, or other green‑emitting dyes when in close proximity (typically 1-10 nm).
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| ln Vitro |
In vitro, QSY 21 NHS is used to generate labeled biomolecules for FRET‑based assays. It can be conjugated to peptides, antibodies, or oligonucleotides to create FRET probes. Common applications include protease activity assays (e.g., caspases, matrix metalloproteinases), receptor dimerization studies, and molecular beacon assays for nucleic acid detection. The efficiency of quenching can be measured as a reduction in donor fluorescence. When conjugated to a peptide containing a protease‑cleavable sequence, proteolytic cleavage separates the QSY 21 acceptor from the donor fluorophore, restoring donor fluorescence.
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| ln Vivo |
Due to its high molecular weight and hydrophobicity, QSY 21 NHS is not suitable for in vivo animal experiments unless conjugated to targeting moieties. When conjugated to antibodies or other targeting proteins, it can be used in live‑cell imaging or small animal fluorescence imaging as part of activatable probes. In such applications, the probe remains quenched until it reaches the target site (e.g., tumor), where proteolytic cleavage activates the fluorescence. Such conjugates are administered intravenously at typical antibody doses of 1-10 mg/kg.
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| Enzyme Assay |
The NHS ester labeling efficiency is typically assessed by measuring the degree of labeling (DOL) of a model protein. Bovine serum albumin (BSA, 10 mg/mL in 0.1 M sodium bicarbonate buffer, pH 8.5) is incubated with 10‑fold molar excess of QSY 21 NHS (dissolved in DMSO, final concentration 1-5%) for 1 hour at room temperature with gentle agitation. Unconjugated dye is removed by size‑exclusion chromatography (e.g., Sephadex G‑25) or dialysis. The DOL is calculated from the absorbance at the dye maximum (typically around 600-650 nm, exact value from manufacturer) and protein concentration (measured by BCA or Bradford assay) using the Beer‑Lambert law.
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| Cell Assay |
Cells are treated with QSY 21‑labeled probes in culture media at 37degC for varying time points (0.5-24 hours) to study uptake, localization, and activation. For live‑cell imaging, cells are seeded in glass‑bottom dishes and incubated with 1-100 nM of labeled probe. Fluorescence is monitored using a confocal or fluorescence microscope equipped with the appropriate filter sets for the donor fluorophore (e.g., 488 nm excitation, 520 nm emission). Endocytosis can be assessed by co‑staining with endosomal markers (e.g., LysoTracker, Rab5). Cell viability can be assessed using the MTT assay to ensure that the labeled probes are not cytotoxic at the concentrations used.
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| Animal Protocol |
For in vivo imaging, QSY 21‑labeled probes are administered intravenously via tail vein injection into mice at doses of 1-10 mg/kg. Animals are anesthetized and imaged at multiple time points (1, 4, 8, 24, 48 hours post‑injection) using a fluorescence imaging system (e.g., IVIS Spectrum). At the end of the experiment, animals are euthanized, and major organs (liver, spleen, kidneys, heart, lungs) are harvested for ex vivo imaging to assess biodistribution. When proteolytic cleavage activates the fluorescence, the fold‑increase in signal intensity over baseline is calculated.
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| ADME/Pharmacokinetics |
QSY 21 NHS is typically stored at −20degC in a desiccated, light‑protected environment. NHS ester dyes are moisture‑sensitive and hydrolyze rapidly in aqueous solutions. For conjugation, the dye should be dissolved in anhydrous DMSO immediately before use. Stock solutions (10-20 mM in DMSO) can be stored at −20degC for up to 1 month if kept dry. After conjugation to a protein, the labeled conjugate should be stored at 4degC in a buffer containing a preservative (e.g., 0.02% sodium azide) and protected from light to prevent photobleaching.
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| Toxicity/Toxicokinetics |
QSY 21 NHS is a research chemical and not a drug; therefore, toxicity data are not standardized. The dye should be handled as a potential irritant. Avoid inhalation, skin contact, and eye contact; wear appropriate PPE (lab coat, gloves, safety goggles). Work in a chemical fume hood when handling the solid dye or DMSO stock solutions. While the NHS ester may react with amines on proteins in the skin or respiratory tract, acute toxicity is low. The compound is not classified as a carcinogen by IARC or NTP.
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| References | |
| Additional Infomation |
QSY 21 NHS is not a drug and is not approved for human therapeutic use. It is a biochemical assay reagent used exclusively for research applications, particularly in FRET‑based assays for biomolecular interactions, protease activity, and proximity studies. This product is sold for research use only and is not intended for diagnostic or therapeutic use. The QSY dye family includes various quenchers with different absorption spectra to match different donor fluorophores, and QSY 21 is optimized for quenching green‑emitting dyes such as Alexa Fluor 488 and fluorescein. The compound is available from specialized biochemical reagent suppliers under catalog numbers such as A10479 (Thermo Fisher) and similar designations.
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| Molecular Formula |
C45H39CLN4O7S
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|---|---|
| Molecular Weight |
815.33
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| Exact Mass |
814.223
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| CAS # |
304014-13-9
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| PubChem CID |
162310014
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| Appearance |
Purple to purplish red solid powder
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| Melting Point |
>200℃
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| Hydrogen Bond Acceptor Count |
10
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| Rotatable Bond Count |
7
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| Heavy Atom Count |
58
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| Complexity |
1790
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| Defined Atom Stereocenter Count |
0
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| SMILES |
C1CN(CCC1C(=O)ON2C(=O)CCC2=O)S(=O)(=O)C3=CC=CC=C3C4=C5C=CC(=[N+]6CCC7=CC=CC=C76)C=C5OC8=C4C=CC(=C8)N9CCC1=CC=CC=C19.[Cl-]
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| HS Tariff Code |
2934.99.9001
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| Storage |
Powder -20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month |
| Shipping Condition |
Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)
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| Solubility (In Vitro) |
May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples
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| Solubility (In Vivo) |
Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.
Injection Formulations
Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)(e.g. IP/IV/IM/SC) *Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution. Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline) Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil) Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals). View More
Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)] Oral Formulations
Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium) Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals). View More
Oral Formulation 3: Dissolved in PEG400 (Please use freshly prepared in vivo formulations for optimal results.) |
| Preparing Stock Solutions | 1 mg | 5 mg | 10 mg | |
| 1 mM | 1.2265 mL | 6.1325 mL | 12.2650 mL | |
| 5 mM | 0.2453 mL | 1.2265 mL | 2.4530 mL | |
| 10 mM | 0.1226 mL | 0.6132 mL | 1.2265 mL |
*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.
Calculation results
Working concentration： mg/mL；
Method for preparing DMSO stock solution： mg drug pre-dissolved in μL DMSO (stock solution concentration mg/mL). Please contact us first if the concentration exceeds the DMSO solubility of the batch of drug.
Method for preparing in vivo formulation:：Take μL DMSO stock solution, next add μL PEG300, mix and clarify, next addμL Tween 80, mix and clarify, next add μL ddH2O，mix and clarify.
(1) Please be sure that the solution is clear before the addition of next solvent. Dissolution methods like vortex, ultrasound or warming and heat may be used to aid dissolving.
(2) Be sure to add the solvent(s) in order.
Products are for research use only; We do not sell to patients
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