A new sensor has been developed to detect miRNA-15 using nanoelectrodes and a hairpin DNA-based electrochemical amplification technique. By utilizing a complex DNA cylinder connected with hairpin DNA1, the sensor is able to absorb more methylene blue (MB) than simple double-stranded DNA. Another hairpin DNA2 is modified on an Au nanoelectrode surface and, when miRNA-15 is introduced, it triggers a chain reaction. This reaction unlocks two hairpins alternatively to polymerize into a complex structure that attaches more MB. The miRNA-15 is then replaced by DNA1 due to strand displacement reactions and continues to react with the next DNA2 to achieve circular amplification. The electrochemical signal from MB oxidation has a linear relationship with the miRNA-15 concentrations, making it possible to detect miRNA-15. Moreover, this method can be readily adapted for the detection of various other miRNA species. The newly devised nanosensor holds promising applications for the in vivo detection of miRNA-15 within biological systems, which is achieved by leveraging the advantageous characteristics of nanoelectrodes, including their low resistance-capacitance time constant, rapid mass transfer kinetics, and small diameter.