Distance-based quantification of miRNA-21 by the coffee-ring effect using paper devices

Enabled by the coffee-ring effect, a paper-based signal transduce method is employed for catalytic hairpin assembly (CHA) amplification and hybridization chain reaction (HCR) to achieve miRNA quantification. Once the target miRNAs appeared, it was circularly used by CHA to initiate HCR amplification to produce a large number of G-quadruplex, which is combined with hemin to form a hemin/G-quadruplex DNAzyme. The DNAzyme catalyzes a colorimetric reaction to produce colored nanoparticles, which were converted to the end edge of the paper by evaporation-driven flow, forming a visible colored band. Higher concentration of miRNA led to more colored nanoparticles and thus a longer colored band that can simply be measured by a ruler. The results of determination of miRNA in samples demonstrate that the relative standard deviation of the proposed approach is 5.2%, highly sensitive and repeatable, with a working range 1.0 to 1000 pM and a LOD of 0.2 pM. The paper-based analytical device as a novel platform offers a new signal transduce pathway toward the detection of low-abundance biomarkers for diagnosis.