A chromogenic reaction-free distance-based paper device for facile detection of microRNA via viscosity amplification and surface hydrophobicity modulation

Distance-based microfluidic paper-based analytical devices (μPADs) are simple and user-friendly detection platforms for disease screening, environment monitoring and food safety. However, the current distance-based μPADs still face major challenges of relatively low sensitivity and accuracy. In this work, we propose a novel chromogenic reaction-free distance-based (CRFD) μPAD strategy for sensitive and accurate quantitation of microRNAs (miRNAs) via viscosity amplification and surface hydrophobicity modulations. The CRFD μPAD with sampling, indicator (with red ink), and detection zones is scaled with reference patterns. Target miRNA in sample is pre-amplified with rolling circle amplification (RCA) reaction to specifically enhance its viscosity. The difference of flow between target and control is further enlarged on CRFD μPADs whose surface hydrophobicity is rationally modulated by in situ metal-organic frameworks (MOFs) modification. Meanwhile, the repeatability and flow shape are significantly improved. For a proof-of-concept demonstration, the miR-221 and miR-222 in liver cells lysis were sensitively detected by naked-eye with limits of detection of 0.33 and 0.37 pM, respectively. A smartphone-based auto-reading system (SAS) was developed to further improve the accuracy and convenience, showing greatly reduced relative standard deviation (RSD) of assay from 12.2% to 1.0%. This facile and extensible strategy is promising for rapid detection in complex biosystem.