Singlet oxygen fluorescent probe is a highly selective detection of singlet oxygen Reagents. Unlike other available fluorescent and chemiluminescent singlet oxygen detection reagents, singlet oxygen fluorescent probes do not respond significantly to hydroxyl radicals or superoxide. The indicator initially emits weak blue fluorescence, but in the presence of singlet oxygen, it emits green fluorescence similar to fluorescein (maximum excitation/emission wavelength ∼504/525 nm). Singlet oxygen fluorescent probes are cell-impermeable.