Optical characteristics of avidin-conjugated BODIPY, FITC, OreG and RhodG. 5 μg Av-BODIPY, Av-FITC, Av-OreG or Av-RhodG in 390 μL PBS (pH 7.4) or the mixture of sodium dihydrogen phosphate and phosphate (pH 3.3) were placed in a nonfluorescent 96-well plate and spectral fluorescence image was obtained. The ratio of BODIPY, FITC, OreG or RhodG molecules to avidin was 0.8 in all cases a: Emission spectra. All 4 dyes had the same emission peak at a wavelength of 550 nm but the fluorescence intensity was different with Av-FITC the highest followed by Av-OreG, Av-RhodG and Av-BODIPY. b: Fluorescence intensities of Av-BODIPY (B), Av-FITC (F), Av-OreG (O) and Av-RhodG (R) were 28, 238, 170 and 159, respectively, in arbitrary units (a.u.) with Av-FITC the highest and Av-BODIPY the lowest under pH 7.4. However, under the acidic condition (pH 3.3), fluorescence intensities of Av-BODIPY, Av-FITC, Av-OreG and Av-RhodG were 35, 33, 122 and 199 (a.u.), respectively, with Av-FITC the lowest and Av-RhodG the highest.