Field-compatible protocol for detecting tetracyclines with bioluminescent bioreporters without pipetting steps

Whole-cell bioreporters are living organisms and thus using them for detecting environmental contaminants would reflect biological effects of these pollutants. However, bioreporters are not widely used in field studies. Many of the bioreporter field protocols are suitable for liquid samples or include pipetting steps, which is a demanding task outside the laboratory. We present a bioreporter protocol without pipetting or sample type requirements. The protocol utilizes polyester swabs, commonly used in cleanroom technology. As an example contaminant, we used tetracycline and generated test samples with known concentrations up to the maximum tetracycline residue limit of milk set by the European Union (EU) regulation. The matrices of the test samples were Milli-Q water, milk and soil. The swabs were first dipped in the bioreporter cell cultures and then to test samples and luminescence was measured after incubation. The standard deviation of measurements from ten replicate swabs was in the same range as commonly in pipetting protocols (4-19%). The test samples with lowest tetracycline concentration (5 ng mL^-1 ) were distinguished from the control samples (0 ng mL^-1 tetracycline). Our results show that swabs can be used together with luminescent whole cell bioreporters, making it possible to conduct the measurements in field conditions.