Practical High-Performance Lateral Flow Assay Based on Autonomous Microfluidic Replacement on a Film

Although paper-based microfluidic devices are an ideal platform for point-of-care (POC) diagnostics, it is difficult to achieve microfluidic control required for sensitive analyses such as ELISA on a paper substrate. Here, we present a novel lateral-flow test chip that can perform operations similar to a pump, such as flowing, stopping, and replacing a solution, just by adding the solution onto an inlet port. The chip was fabricated by laminating paper, film, and adhesive tape. For sensitive and accurate detection in an immunoassay, the transparency and flatness of the substrate is crucial for precise analysis of weak light generated by a specific antigen-antibody reaction; however, paper is not flat and is opaque. Therefore, transparent film was applied to the detection area of the chip in this study. The chip showed a good correlation at 0.1 - 100 ng ml^-1 concentrations of C-reactive protein, demonstrating high quantitative analysis of CRP in serum suitable for clinical trials. The signal intensity of the novel chip was higher than that of a chip made of nitrocellulose membrane, and the variation was smaller. The limit of detection of the chip was 0.1 ng ml^-1, whereas that of the nitrocellulose membrane was 100 ng ml^-1. This novel chip can be used for sensitive sandwich immunoassays just by adding solutions.