xtraFluor™ Violet 420 (XV420) is an extremely bright, violet-laser–excitable fluorophore for conventional and spectral flow cytometry. It is optimally excited by the 405 nm violet laser and emits a narrow, well-defined peak at 424 nm (Ex/Em 407/424 nm), with an extinction coefficient of 3,000,000 M⁻¹cm⁻¹ and quantum yield of 0.80 in PBS. Spectrally, it is a direct match to BV421™, substituting seamlessly into existing violet-excited panels. When labeled to antibodies, XV420 delivers a higher stain index than BV421™ and Pacific Blue™, and roughly an order of magnitude brighter signal than Alexa Fluor™ 405, for cleaner resolution of dim, low-abundance populations, while the narrow emission limits spillover into neighbouring violet detectors and supports efficient spectral unmixing on large panels.

xtraFluor™ Violet 420 is available across the full labeling workflow — as a reactive labeling dye, as ready-to-use Buccutite™ Rapid Antibody Labeling Kits, as reactive derivatives for thiol and click chemistries, and as streptavidin and biotin conjugates.

Under equivalent staining conditions, xtraFluor™ Violet 420 (XV420) conjugates demonstrate a roughly ten-fold increase in stain index compared to Alexa Fluor™ 405 and a roughly four-fold increase when compared to Pacific Blue™. Against BV421™, XV420 conjugates produce comparable performance, with Fc-specific XV420 conjugates demonstrating an approximately two-fold increase in stain index. XV420's exceptional brightness, together with its low background, cleanly separates positive from negative events, enabling improved sensitivity for low-abundance antigen detection and more reliable population discrimination.

Stain index measures how cleanly a stained population separates from background, and it scales with a fluorophore's brightness per antibody. xtraFluor™ Violet 420's high extinction coefficient (3,000,000 M⁻¹cm⁻¹) and quantum yield (0.80 in PBS) places more signal on each conjugate, which sharpens that separation. The gain is largest for dim, low-abundance antigens, where the added brightness is what resolves a weak positive population from background.

The signal must also persist through sample preparation and storage. xtraFluor™ Violet 420 conjugates retain fluorescence through routine handling, including RBC lysis and lysis/fixation, and across extended storage, so a panel reads consistently from run to run. Measured against BV421™ over nearly two years, the violet signal is retained without appreciable loss.

Buccutite™ Rapid XV420 Antibody Labeling Kits pair pre-activated xtraFluor™ Violet 420 with Buccutite™ MTA/FOL chemistry, so labeling runs at room temperature and neutral pH in two simple mixing steps, in under two hours, with minimal purification and column clean-up required. The complementary MTA and FOL handles react only with each other — there is no homo-crosslinking, no antibody-to-antibody aggregation, and no antibody reduction, unlike SMCC-based maleimide chemistry. Kits are supplied at microscale (25 µg antibody per reaction) for screening and small studies, and at production scale (1 mg per reaction) for routine or large-scale work.

For labs that prepare their own conjugates, xtraFluor™ Violet 420 comes in three reactive formats.

For biotin–streptavidin detection, xtraFluor™ Violet 420 is available pre-conjugated to streptavidin and as a fluorescent biotin derivative. The streptavidin conjugate detects biotinylated antibodies, peptides, and oligonucleotides; the biotin conjugate labels streptavidin- and avidin-based systems, with minimal spillover into the Pacific Orange™ and Brilliant Violet 510™ channels.