A functional nucleic acid-based amplification machine is designed for ultrasensitive biosensing of microRNA.

The machine integrates the advantages of enzymatic signal amplification and toehold initiated rolling circle amplification.

The modified molecular beacon improves the stringent target recognition and reduces background signal.

The machine leads to a mass of DNAzyme for one recognition event and thus an ultrasensitive colorimetric and visual method for detection of miRNAs.

The biosensing method shows attomolar-level detection limit, a detection range of 9 orders of magnitude for practical sample analysis.