Alexa Fluor® 488 is a bright, green-fluorescent dye with excitation ideally suited for 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).
The NHS ester (or succinimidyl ester) of Alexa Fluor® 488 is the most popular tool for conjugating this dye to a protein or antibody. NHS esters can be used to label to the primary amines (R-NH2) of proteins, amine-modified oligonucleotides, and other amine-containing molecules. The resulting Alexa Fluor® conjugate will exhibit brighter fluorescence and greater photostability than the conjugates of other spectrally similar fluorophores.
Detailed information about this AlexaFluor® NHS ester:
Fluorophore label: Alexa Fluor® 488 dye Reactive group: NHS ester Reactivity: Primary amines on proteins and ligands, amine-modified oligonucleotides Ex/Em of the conjugate: 494/517 nm Extinction coefficient: 73,000 cm-1M-1 Spectrally similar dyes: FITC, Oregon Green 488 Molecular weight: 643.4
Typical Conjugation Reaction You can conjugate amine-reactive reagents with virtually any protein or peptide (the provided protocol is optimized for IgG antibodies). You can scale the reaction for any amount of protein, but the concentration of the protein should be at least 2 mg/mL for optimal results. We recommend trying three different degrees of labeling, using three different molar ratios of the reactive reagent to protein.
The Alexa Fluor® NHS ester is typically dissolved in high-quality anhydrous dimethylformamide (DMF) or dimethylsulfoxide (DMSO) (D12345), and the reaction is carried out in 0.1–0.2 M sodium bicarbonate buffer, pH 8.3, at room temperature for 1 hour. Because the pKa of the terminal amine is lower than that of the lysine epsilon-amino group, you may achieve more selective labeling of the amine terminus using a buffer closer to neutral pH.
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)
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.
For Research Use Only. Not for use in diagnostic procedures.