Abstract: The invention provides a method for detecting ATP in a sample, wherein the sample is contacted with a reaction mixture to effect a light signal, the reaction mixture comprising luciferin, luciferase and one or more water-soluble salts, the total salt concentration being at least 0.05 mole/liter, and wherein the light signal is measured. A kit is described for detecting ATP in a sample comprising luciferin, luciferase and a buffer solution comprising salts. A composition for detecting ATP in a sample comprising a total salt concentration of at least 0.05 mole/liter for prolonging a light signal occurring in a luciferin-luciferase reaction is also provided.

Abstract: A process is provided for using porphyrin or porphyrin derived compounds as universal labels for various assays and other quantification techniques without the need for a bridging agent to couple the label to the target particles. Particles which can be labeled include beads, microorganisms, cells, and molecules. The porphyrin label irreversibly attaches to target particles and afterwards can be detected and quantified by any number of ways, such as chemiluminometrically, fluorometrically or radiometrically in an amount which is proportional to the number of labeled particles.