Practice question

Alexa Fluor 488 is a sulfonated rhodamine derivative engineered for high brightness and photostability, widely used as a replacement for fluorescein isothiocyanate. Excitation near 490 nanometers promotes electrons to higher energy levels, and relaxation emits photons centred around 519 nanometers, perceived as vivid green under standard FITC filter sets. Its high quantum yield, pH insensitivity from pH 4 to 9, and minimal self-quenching make it ideal for immunolabeling, flow cytometry and green channel in multi-color confocal experiments, contrasting sharply with blue DAPI and red Alexa 568.