Abstract
Because circulating microRNAs (miRNAs) have been recognized as a new class of blood-based biomarkers for various diseases, a significant challenge has been the development of point-of-care testing (POCT) systems based on detection of circulating miRNAs directly from serum. A promising approach to POCT systems is considered to be the development of enzyme-free and isothermal detection systems. Here, two types of DNA circuit system based on proportional and exponential amplification strategies were constructed using double-stranded DNA-modified magnetic beads (dsDNA-MBs) and their performances for detection of miRNA were studied comparatively. Both proportional and exponential amplification DNA circuit systems enabled the detection of target miRNA (miR-141) at room temperature without the need for additional enzymes because miR-141 acted as a catalyst for successive toehold-mediated DNA displacement reactions. A significant increase in the noise fluorescence signal was observed for the exponential amplification DNA circuit system because of the leakage (undesired DNA displacement reaction) revealed by the kinetic study on each DNA displacement reaction. Nevertheless, the exponential amplification DNA circuit system showed a lower limit of detection (LOD: 46 pM) and shorter assay time (15 min) compared to those of the proportional amplification DNA circuit system (LOD: 103 pM at 180 min). It is most likely that the exponential amplification DNA circuit system enabled amplification of both the signals and target miR-141, whereas the proportional amplification DNA circuit system enabled amplification of the signals alone. In addition, the exponential amplification DNA circuit system was able to discriminate between mismatched base sequences in miR-200 family members and specifically detect miR-141 even in the presence of serum. These findings are important for the rational design for POCT systems.