This problem occurs in all detection systems. Measurement of light intensity is relatively simple, requiring only a photomultiplier or photodiode and the associated electronics to convert and record signals. The lack of inherent background and the ability to easily measure very low and very high light intensities with simple instrumentation provide a large potential dynamic range of measurement. A common means for generating chemiluminescence is to use a label enzyme to catalyze a chemiluminescent reaction. The chemiluminescent compound is supplied as the enzyme substrate in excess to assure saturation kinetics.
Light intensity is a linear function of the amount of label enzyme.
The absence of a steady plateau value indicates either substrate depletion or inactivation of the enzyme. Detection of enzyme-generated chemiluminescence provides great flexibility in the measurement process. Light intensity at any time point through the plateau can be related to the amount of enzyme. Measurement can be made during the rising portion if speed is an issue as either a single point or a multi-point slope type measurement. For maximal sensitivity, measurement can be performed on the plateau.