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# ULTRAWEAK CHEMILUMINESCENCE FROM HUMAN BLOOD PLASMA R.N. Tilbury , D.J. Gregg, J.M. Percival, and A.J. Matich Chemistry, Victoria University of Wellington P.O. Box 600, Wellington, New Zealand # ABSTRACT Ultraweak biological chemiluminescence is extremely weak light emitted by living organisms, or their components, at photon fluxes below about 104 photons cm-2 s-1. It is finding application as a very sensitive and non-invasive analytical tool in biochemistry, medicine and agriculture. It appears that electronically excited oxygen species, which are of interest in a variety of cellular processes in normal and pathological conditions, give rise to most of the chemiluminescence in biological systems. Spontaneous ultraweak light emission, which was oxygen dependent, was detected from human blood plasma with a photon counter sensitive in the wavelength range 200-630 nm. This light emission was also found to be dependent on a number of other factors, such as smoking, the length of time between the donor's last meal and the sampling of the blood, and to a lesser extent, diet and age of donor. Separation of the plasma chylomicrons and lipoprotein fractions by ultracentrifugation showed that these constituents could only account for less than 15% of the total light emission. Salt fractionation and chromatographic fractionation of the plasma showed that the albumin fraction accounted for the majority of the total light emission. Removal of the free fatty acids bound to albumin by charcoal treatment produced a marked decrease in the intensity of chemiluminescence. It was thus concluded that the free fatty acids in complex with albumin are the major source of the ultraweak chemiluminescence originating from human blood plasma.