AF430 is a coumarin dye identical to Alexa Fluor™ 430 with absorption
maximum at 434 nm and emission in green-yellow range (maximum at 541 nm). The dye is one
of few fluorophores that absorb in the range between UV-excited fluorophores (e.g. DAPI with an excitation
peak at 358 nm, Alexa Fluor 350 at 346 nm, AMCA/AMCA-X at ~350 nm) and fluorescein
(maximum at 494 nm). AF430 is a hydrophilic dye — sulfo group provides better
hydrophilicity. The dye is photostable — trifluoromethyl group in its structure reduces
photobleaching while sulfo group provides higher quantum yield in aqueous solution. Its fluorescence is independent
of pH over a wide range of pH values (from pH 4 to pH 10) and can be excited
by 405 nm violet laser.
AF430 possesses a large Stokes shift of 112 nm which makes
the dye valuable for multi-color imaging applications, including wide-field and confocal fluorescence microscopy,
STED microscopy, and flow cytometry. Fluorophores with large Stokes shift allow reducing cross-talk and the number
of excitation/detection channels.
As the dye exhibits high photostability, it is suitable
for STED microscopy where enormous light intensities are used. AF430 is applied in multicolor STED
microscopy by combining two dyes — one with a large and one with a small Stokes shift.
Depletion of both dyes can be performed with one wavelength (AF430 can be depleted by 660 nm
Due to its specific spectral properties, AF430 is often used in FRET experiments both
in material and life sciences.