Paper/PMMA hybrid device with a microvalve-controlled design for exosome isolation and analysis

This study proposes a paper/PMMA hybrid device designed to isolate exosomes and extract exosomal miRNA, followed by quantitative analysis. It aims to provide simplified and convenient sample preparation for potential point-of-care testing (POCT) processes. In contrast to previous work conducted by our research team, which focused on isolating exosomes and exosomal nucleic acids, this study introduces a novel approach by integrating paper and a PMMA mold with a microvalve controlled design. This innovative method enables the entire process to be performed on paper. The pressure on the paper could be adjusted by turning the screw upon the valve to change the pore size and permeability of the paper, which achieved the effect of controlling the flow rate of fluids. The paper was designed to have an immunoaffinity area for capturing exosomes and a sol-gel silica coating area for extracting miRNA. The paper-based ELISA (p-ELISA) exhibited a limit of detection and a limit of quantitation of 6 × 10⁷ and 5.4 × 10⁸ particles/mL, respectively, for exosome measurement. The reverse transcription quantitative polymerase chain reaction (RT-qPCR) revealed that the Ct (threshold cycle) value for quantifying the miR-21 in the miRNAs extracted by the proposed paper/PMMA hybrid device was comparable to the Ct value of the commercial extraction kit. The developed paper/PMMA hybrid device with a microvalve-controlled design should be incorporated into the POCT system to extract exosomal miRNAs.