Fully Integrated and Foldable Microdevice Encapsulated with Agarose for Long-Term Storage Potential for Point-of-Care Testing of Multiplex Foodborne Pathogens

Abstract

In this study, we fabricated a fully integrated and foldable microdevice encapsulated with 2-hydroxyethyl agarose for long-term storage of reagents for the integration of isothermal amplification and subsequent colorimetric detection for the monitoring of multiplex foodborne pathogens. The microdevice comprises a reaction zone and a detection zone. Both zones were made of a thin polycarbonate film and sealed by an adhesive film to make the microdevice foldable. The 2-hydroxyethyl agarose with loop-mediated isothermal amplification (LAMP) reagents and silver nitrate were deposited in the reaction and detection chambers, respectively, for long-term maintenance of reagent activity. A thin graphene-based heater associated with a handheld battery was employed to supply a constant temperature for on-chip amplification for 30 min. To simplify the sample manipulation process, a folding motion was adopted to allow the loading of LAMP amplicons from the reaction to the detection chambers and a colorimetric strategy was used for simple visual read-out of the results on-site. Using the agarose, the reagents were successfully stored and the reagent activity was maintained for at least 45 days. Prior to performing multiplex detections, the spiked juice was thermally lysed and purified with polydopamine-coated paper. The amplifications of Salmonella spp. and Escherichia coli O157:H7 (E. coli O157:H7) were successfully demonstrated based on the stable isothermal condition attained by the heater. The microdevice can detect the low concentration of E. coli O157:H7 at 2.5 × 10² copies per mL. The introduced microdevice acts as a simple and user-friendly platform for the identification of foodborne pathogens, paving the way for the construction of a truly portable, read-out microdevice for use as a public healthcare monitoring device.

Keywords: colorimetric detection; foldable microdevice; foodborne pathogens; long-term storage; loop-mediated isothermal amplification; low gelling temperature agarose; thin-film graphene-based heater.