Whether a surface looks clean to the unaided eye will not reveal whether it is clean at the microscopic level. For that, a test is required. The ATP test fulfills this role. Where a particular surface has previously been visibly contaminated biologically, or indeed invisibly contaminated, and then cleaned, the ATP test can indicate the degree of thoroughness of the cleaning that has been undertaken, so providing a means of clearance verification.
Domestic indoor surfaces that are vertical or horizontal or any angle in between, and which have been affected in any way from any source by moisture, or by pollutants, or by touching, or by any type of macro- or micro- nutrients being present, may be suitable candidate surfaces for conducting an ATP swab test. Notable examples of suitable uses are where organic material has been shown to have visually affected the surface such as mould growth, sewerage ingress, bacterial biofilm etc., and also surfaces where quarantining humans have touched, coughed on, breathed on etc. Human cough droplets are a relatively invisible example material, and do contain traces of ATP regardless of whatever other contaminants may also be present in the cough. This is because cough droplets are made of mucus and saliva, both of which contain ATP.
ATP is derived exclusively from cellular materials (an example being the human body), so an ATP surface-cleanliness test is a “life-sign specific” test, and accordingly is both a surface test for microbially derived materials, and also for human, plant and animal derived liquids, and human plant and animal derived greases/dirts. Since even touch can transfer ATP to a surface, the test can serve as a sensitive test of how much a surface has been touched by certain categories of dirty hands (i.e. transfer of body liquids to the surface via the hands, and transfer of body liquids from other parts of body to the hands and then via the hands to the surface).
ATP is relatively stable in the environment even though it can be partially degraded by UV if exposed for sufficient time. The most efficient degraders of ATP are biological enzymes, generally in the presence of divalent cations usually Mg2+. This generally happens inside living cells. As such ATP is relatively persistent in indoor environments over hours, days and weeks. Drying in complex mixtures may sequester ATP and hence inactivate it in relative terms.
ATP initially became a standard test for surfaces in the area of healthy food preparation facilities, because all foods have some level of ATP present, and because all bacteria and all fungi -such as ones that may exploit unfully cleaned food spills- also contain abundant ATP. Thus, testing for ATP reveals traces of non-fully-cleaned recent food spills, since the food itself contains ATP, and it simultaneous reveals any older spills in which cellular microbes have already begun to grow and exploit, which happens very quickly.
Adaptation of the ATP test principle to a remediation environment was obvious and readily achieved. In fact, ATP testing in the remediation industry uses the exact same type of kit that is used in the food hygiene industry.
ATP is the energy currency of living cells and is detectable by a luminescence assay, if using the correct equipment and consumables. The assay can be used to detect the relative level of freed biological material not bound in cells, and present on a surface. ATP levels are reported in terms of Relative Light Units (RLU). The ATP Surface Cleanliness report references selected sections of applicable Manufacturer's Guidelines, and draws on Empirical Principles. See References section.