Laser photoacoustic trace gas detection, an extremely sensitive technique applied in biological research

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis bf two examples. A CO2 laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6.10(12)), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation.