CF® dye with methyltetrazine reacts with cyclooctene (TCO, methylcyclopropene) containing molecules via copper free click chemistry. This copper free bioorthogonal reaction is useful for labeling live cells, or when there are concerns about native protein function loss with copper in cell extracts. Methyltetrazine has improved chemical stability compared to tetrazine. CF® dyes are Biotium's line of next-generation fluorescent dyes with advantages in brightness, photostability, and conjugate specificity compared to other fluorescent dyes. Red fluorescent CF®568 dye has excitation/emission at 562/583 nm.