Highly integrated and one-step triggered cascade DNA walker based on entropy-driven catalytic and DNAzyme amplification

As an amplification tool, DNA walker nanomachine exhibits promising potential in the fields of biosensing. To further improve amplification efficiency of DNA walker, a number of cascade amplification systems have been developed, but they still suffer from separated steps and long reaction time. Herein, by combining entropy-driven catalytic (EDC) amplification with DNAzyme reaction, a highly integrated cascade three-dimensional (3D) DNA walker is constructed, which allows the autonomous DNA circuit to be completed in one step. Further combined with element tag and inductively coupled plasma mass spectrometry (ICP-MS) detection, the cascade walker can be used for quantification of miRNA-21. Specifically, the reactant of EDC (WLT complex) and the substrate of DNAzyme (Substrate-Tb) are both fixed on magnetic beads (MBs) to assemble the track of walker. Once cascade DNA walker is triggered by target miRNA, EDC amplification runs first and keeps circulating to liberate many DNAzyme strands. DNAzyme can repeatedly cleave Substrate-Tb with autonomously walking along the substrate on MBs. As a result, a great number of fragments of Substrate-Tb, as output signal, are generated within 1 h, resulting in elemental signal response in ICP-MS and reflecting the amount of miRNA-21. A good linear relationship was obtained with miRNA-21 concentration in the range of 0.02−1 nmol L−1, and the detection limit of 5 pmol L−1 was achieved. The recoveries of miRNA-21 in human serum were 92.0–107 %. The developed method provided a novel idea for constructing highly integrated and efficient cascade DNA walker with ICP-MS strategy for bioanalysis.