A foldable isothermal amplification microdevice for fuchsin-based colorimetric detection of multiple foodborne pathogens
In this study, we have developed a foldable microdevice fully integrating DNA purification, amplification, and detection processes for detecting multiple foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with a fuchsin-based direct DNA colorimetric detection method. The microdevice was composed of three parts: a sample zone, reaction zone, and detection zone. A sealing film attached to the sample, reaction, and detection zones served as a bottom layer to make the microdevice foldable. The detection zone was made up of paper strips attached to the sticky side of the sealing film, and fuchsin-stained lines were drawn on the paper strips. The microdevice can be folded to directly transfer the DNA template solution from the sample chambers to the reaction chambers. In this manner, fluid manipulation was readily realized and the use of a bulky instrument such as a pump or rotator was completely dispensed with. After the LAMP reaction, the detection zone was folded so that the fuchsin-stained lines were completely soaked into the reaction chambers. Genomic DNAs of Salmonella spp. and Escherichia coli O157:H7 were first successfully purified from thermally-lysed milk using polydopamine-coated paper, amplified by LAMP, and directly identified by the naked eye using fuchsin within 65 min. Using this microdevice, approximately 102 CFU per mL of Salmonella spp. was detected. These results indicate the significant potential of this microdevice for the sample-in-answer-out genetic analysis of multiple foodborne pathogens in resource-limited environments.