We have developed a simple, user-friendly, and highly sensitive Zika virus (ZIKV) detection method by incorporating optimized reverse transcription loop-mediated isothermal amplification (RT-LAMP) and a lateral flow assay (LFA). The optimized RT-LAMP reaction was carried out using Bst 3.0 polymerase, which has robust and fast isothermal amplification performance even in the presence of high concentrations of inhibitors; this permitted the amplification of ZIKV RNA in pure water and human whole blood. In addition, the strong reverse transcription activity of Bst 3.0 polymerase enabled specific ZIKV RNA amplification without extra addition of reverse transcriptase. The RT-LAMP condition was optimized by adjusting the Mg and dNTP mix concentration to extirpate nontarget amplification, which is caused by nonspecific primer dimers amplification. After 30 min of RT-LAMP reaction, the resultant amplicons were simply and rapidly analyzed by the LFA test in less than 5 min. The optimized RT-LAMP combined with the LFA allowed specific ZIKV RNA detection down to the single copy level within 35 min.

Microfluidic paper-based analytical devices (μPADs) for molecular detection have great potential in the field of point-of-care diagnostics. Currently, a critical problem being faced by μPADs is improving their detection sensitivity. Various preconcentration processes have been developed, but they still have complicated structures and fabrication processes to integrate into μPADs. To address this issue, we have developed a novel paper-based preconcentrator utilizing ion concentration polarization (ICP) with minimal addition on lateral-flow paper. The cation selective membrane (i.e., Nafion) is patterned on adhesive tape, and this tape is then attached to paper-based channels. When an electric field is applied across the Nafion, ICP is initiated to preconcentrate the biomolecules in the paper channel. Departing from previous paper-based preconcentrators, we maintain steady lateral fluid flow with the separated Nafion layer; as a result, fluorescent dyes and proteins (FITC-albumin and bovine serum albumin) are continuously delivered to the preconcentration zone, achieving high preconcentration performance up to 1000-fold. In addition, we demonstrate that the Nafion-patterned tape can be integrated with various geometries (multiplexed preconcentrator) and platforms (string and polymer microfluidic channel). This work would facilitate integration of various ICP devices, including preconcentrators, pH/concentration modulators, and micro mixers, with steady lateral flows in paper-based platforms.

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