There are two possible basic approaches for rapid measurements of microbiological contamination.
- Examine the individual target organisms
- Measure a signal produced by the total population of target organisms
Culture based lab methods are combining both by cultivating individuals to receive a huge number (an amplification of the signal) which can be seen with the naked eye.
Due to the time required for cultivation, culture-based approaches are not suitable for rapid microbiology.
As per microbiological measurements, it is very important that the technology can distinguish between viable and dead organisms. This is necessary to measure the effects of disinfection or other treatment steps.
In order to measure viability, some time and reagent is required. This can be done by observing a biochemical reaction (using some kind of reagent) which is only occurring in living organisms.
A second theoretical possibility would be the observation of movements of organisms that clearly demonstrate their viability – the disadvantage of this approach is that no movement does not necessarily indicate a dead organism.
Conclusion: Measuring viability requires some time and reagent.