What is RLU?
RLUs measure the light emitted when ATP interacts with the luciferase enzyme, producing a bioluminescent reaction. Since ATP is present in all living cells, RLU values give a relative measure of biological activity on a surface or in a liquid sample. However, RLUs alone do not directly quantify microbial load or ATP concentration; they simply provide a light measurement that indicates potential contamination levels. To accurately interpret ATP levels, RLUs must be converted to specific ATP concentrations using an UltraCheck Standard provided with your testing kit. This conversion provides consistency, allowing you to confidently assess microbial cleanliness and contamination across samples.
Why do I need to convert RLU to ATP concentrations?
RLUs alone are not an indicator of microbial activity - they are relative units that vary based on the activity of the enzyme. For a reliable assessment of contamination, it’s essential to convert RLUs to ATP concentrations. This conversion can be done automatically using Census or manually by following the equation provided in your test kit instructions. It is recommended to convert RLU values to ATP concentrations before storing or making process decisions based on these values.
Why does my RLU drop the longer I let an assay tube sit?
The ATP-luciferase interaction decreases over time as the enzyme and ATP are consumed in the reaction. The light production is stable for ~30 seconds after mixing; therefore, readings should be taken in the PhotonMaster within 5-15 seconds.