What Is the AF680 Antibody Labeling Kit and How Does It Work?

The AF680 Antibody Labeling Kit (SKU: A1491940DT) enables researchers to directly conjugate an AF680 near-infrared fluorescent dye to antibodies of their choice without requiring specialized equipment. The kit uses NHS ester chemistry: the reactive AF680 dye forms stable amide bonds with primary amine groups (predominantly lysine residues and the N-terminus) present on the antibody. The result is a bright, photostable, near-infrared fluorescent antibody conjugate that performs well in demanding assays such as flow cytometry, immunofluorescence microscopy, and small-animal in vivo imaging.

Certain reagent components within the kit are temperature-sensitive and must be stored at -20°C to preserve NHS ester reactivity. Other components (such as reaction buffers) may be stored at a different temperature as specified in the product insert. Always consult the kit's package insert for definitive storage and handling instructions.

Storage, Handling, and Stability

Which components require -20°C storage? The temperature-sensitive components—typically including the lyophilized or dissolved NHS ester-activated AF680 dye—must be stored at -20°C, protected from light and moisture. Exposure to ambient temperatures or humidity can hydrolyze the NHS ester and significantly reduce labeling efficiency.

How should I handle the dye vial? Allow the -20°C components to equilibrate to room temperature inside their sealed vial or desiccated container before opening, to prevent condensation. Minimize the number of freeze-thaw cycles; if repeated use is anticipated, consider preparing single-use aliquots.

What is the shelf life? Shelf life information is provided on the Certificate of Analysis (CoA) and product label. Typical NHS ester dye reagents are stable for 6–12 months when stored correctly at -20°C. Consult your CoA for lot-specific expiry dates.

Protocol Overview and Optimization Tips

General labeling workflow: (1) Buffer-exchange the antibody into a recommended amine-free conjugation buffer (e.g., 0.1 M sodium bicarbonate, pH 8.0–8.5) to remove primary amines such as Tris or glycine that would compete with antibody labeling. (2) Reconstitute the AF680 NHS ester dye as directed. (3) Add the dye to the antibody at the recommended molar ratio and incubate at room temperature with gentle mixing. (4) Purify the labeled antibody by the recommended method (e.g., spin column, gel filtration) to remove unconjugated dye. (5) Determine the degree of labeling (DOL) spectrophotometrically.

Optimization tips: Antibody concentration should typically be ≥1 mg/mL for efficient labeling. The dye-to-antibody molar ratio can be adjusted to achieve the desired DOL; for most applications, a DOL of 2–5 moles of dye per mole of IgG is optimal. Over-labeling can quench fluorescence and impair antigen binding.

Note: Always refer to the kit's package insert for the exact, validated protocol specific to this product lot.

Troubleshooting Common Issues

Low labeling efficiency or no fluorescence signal: This is most often caused by NHS ester hydrolysis due to improper storage, the presence of primary amines in the antibody buffer, or a reaction pH that is too low. Verify that the antibody has been buffer-exchanged into an amine-free buffer at pH 8.0–8.5, that the dye reagent was stored correctly at -20°C and used promptly after reconstitution, and that the reaction was performed at the recommended temperature and incubation time.

High background or aggregation: Over-labeling (excessive DOL) can cause antibody aggregation and non-specific binding. Reduce the dye-to-antibody molar ratio and ensure thorough removal of free dye by purification. Aggregates can be removed by centrifugation (10,000 × g, 5 min) prior to use.

Loss of antigen-binding activity: Labeling at a very high DOL can block the antibody's binding site. Optimize the molar ratio to achieve a DOL in the recommended range, and consider using site-specific labeling strategies if antigen binding is critical.

Ordering, Compatibility, and Support

How do I order? The AF680 Antibody Labeling Kit (-20°C Components) is available from Aladdin Scientific under SKU A1491940DT. Orders can be placed through the Aladdin Scientific website, by contacting your local sales representative, or via your institution's procurement system.

Is this kit compatible with all antibody isotypes? The NHS ester chemistry is broadly applicable to IgG, IgM, IgA, and other antibody classes, as well as other proteins containing accessible lysine residues. Performance may vary depending on antibody format (e.g., F(ab') fragments have fewer lysines). Confirm suitability for non-IgG formats with the technical team.

Technical support: For protocol questions, troubleshooting assistance, or lot-specific data, contact Aladdin Scientific technical support. Please have your SKU (A1491940DT) and lot number available when reaching out.