We recommend storing secondary antibodies conjugated with fluorophores or HRP at 4 degrees C as we have found that storage at -20 degrees C and the associated continuous freeze/thaw cycles can reduce the performance of fluorescent dyes. Storage at 4 degrees C improves fluorophore stability without affecting antibody performance.
You can also prepare small aliquots to avoid freeze/thaw cycles and store them at -20 degrees C, as with each freeze/thaw step the performance of the antibody would go down.
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Antibodies and Immunoassays Support Center.