Using the membrane filter method, a sample is filtered through a TRAKETCH® membrane. All microorganisms in a 100 ml sample solution are concentrated and retained completely (100%) on the membrane surface.
Detection is performed directly on the membrane by adding a fluorescent dye which can only penetrate through intact cell walls (living organisms). To ensure adequate measurement of the emitted fluorescence after stimulation by a laser, the membrane should have a low fluorescence. Otherwise we would see "a white image on a white background", i.e. we would only see a fluorescence of the entire surface.
To avoid this, SABEU stains this membrane in deep black to quench the fluorescence in defined ranges of wavelengths. This entire microbiological detection method is called solid phase cytometry, in which the membrane represents the solid phase. This method is not only rapid, but also in real time, i.e. within just 1–2 hours. In comparison, the growth of microcolonies takes 1–2 days, whereas growing visible colonies takes 1–2 weeks, depending on the microorganism.