Chemiluminescence imaging for microRNA detection based on cascade exponential isothermal amplification machinery

A novel G-quadruplex DNAzyme-driven chemiluminescence (CL) imaging method was developed for ultrasensitive and specific detection of miRNA based on the cascade exponential isothermal amplification reaction (EXPAR) machinery. A structurally tailored hairpin probe switch was designed to selectively recognise miRNA and form hybridisation products to trigger polymerase and nicking enzyme machinery, resulting in the generation of product I, which was complementary to a region of the functional linear template. Then, the response of the functional linear template to the generated product I further activated the exponential isothermal amplification machinery, leading to synthesis of numerous horseradish peroxidase mimicking DNAzyme units for CL signal transduction. The amplification paradigm generated a linear response from 10 fM to 100 pM, with a low detection limit of 2.91 fM, and enabled discrimination of target miRNA from a single-base mismatched target. The developed biosensing platform demonstrated the advantages of isothermal, homogeneous, visual detection for miRNA assays, offering a promising tool for clinical diagnosis.