Time-resolved studies of singlet-oxygen emission from L1210 leukemia cells labeled with 5-(N-hexadecanoyl)amino eosin. A comparison with a one-dimensional model of singlet-oxygen diffusion and quenching.

Time-resolved measurements were made of near-infrared emission from 5-(N-hexadecanoyl)amino-eosin-labeled L1210 leukemia cells following pulsed-laser excitation. The cells were suspended in phosphate-buffered saline made with deuterium oxide solvent. A significant fraction of the emission occurring 10-80 microseconds after the laser pulse was due to singlet oxygen. This singlet-oxygen emission is believed to result from singlet oxygen generated near the cell-membrane surface, where 5-(N-hexadecanoyl)amino eosin is known to concentrate, and then diffusing out into the buffer. The intensity and the kinetics of the experimentally observed singlet-oxygen emission were in excellent agreement with the predictions of a theoretical one-dimensional model of singlet-oxygen diffusion and quenching. During the 10-80 microseconds time period studied, most of the singlet oxygen was located in the buffer. Thus, the use of water-soluble singlet-oxygen quenchers, such as histidine, provide one means of separating the singlet-oxygen emission from other sources of light during this time interval.