Violet-excited blue-emitting fluorophores, such as violetFluor™ 450, are labels designed for excitation by the 405 nm violet diode laser and emission at approximately 450 nm. They enable direct single-step immunolabeling in multicolor flow cytometry and fluorescence microscopy.

Photophysical Properties

The dye has an excitation maximum at 405 nm, emission at 450 nm, and a Stokes shift of about 45 nm. Emission is collected through a 450/50 nm bandpass filter. Moderate brightness (about 2/5) makes it best suited to antigens with moderate to high expression, such as CD45, CD3, CD4, and Ly-6G. The spectral window is well separated from FITC, PE, and APC channels.

Applications

Applications include direct immunophenotyping, confocal analysis of fixed tissue, and fluorescence plate assays. Direct conjugation avoids secondary-reagent background in mouse-on-mouse studies. The dye contributes an additional independent channel to high-parameter panels without requiring extra laser lines.

Specificity

Specificity is determined entirely by the antibody clone, not the dye. Controlled conjugation preserves antigen-binding affinity. Isotype and fluorescence-minus-one controls, plus titration, are essential because blue-region autofluorescence and spectral overlap require careful compensation.

Considerations and Limitations

Limitations include lower brightness for low-abundance targets, photobleaching, pH sensitivity of some violet dyes, and lot-to-lot spectral variation. Conjugates should be stored at 2–8°C in the dark without freezing.