Polydopamine aggregation: A novel strategy for power-free readout of loop-mediated isothermal amplification integrated into a paper device for multiplex pathogens detection

Loop-mediated isothermal amplification (LAMP) has been widely used for detecting pathogens. However, power-free and clear visualization of results still remain challenging. In this study, we developed a paper device integrated with power-free DNA detection strategy realized by polydopamine aggregation. In the presence of DNA amplicons, the polymerization of dopamine into aggregated polydopamine was hindered, while in the absence of DNA amplicons, polydopamine aggregation is facilitated. The porosity of the paper enabled the capillary flow of dispersed polydopamine for positive sample, while aggregated polydopamine remained at the bottom of the paper strip due to large size of the aggregates for negative sample. Based on this mechanism, we fabricated a slidable paper device integrating LAMP with dopamine polymerization for the naked-eye detection, operated in a seamless manner. Moreover, the introduced paper device was successfully used to detect DNA extracted from Escherichia coli O157:H7 and SARS-CoV-2 within 25 min, as well as Enterococcus faecium within 35 min. The detection limits of both Escherichia coli O157:H7 and SARS-CoV-2 were 10^-4 ng/μL. The introduced paper device can be used as a simple and sensitive tool for detecting multiple infectious pathogens, making it an ideal tool particularly for resource-limited environment.