Target-Induced 3D DNA Network Structure as a Novel Signal Amplifier for Ultrasensitive Electrochemiluminescence Detection of MicroRNAs

Here, a target-induced three-dimensional DNA network structure (T-3D Net) produced by catalytic hairpin assembly (CHA) was proposed as a novel signal amplifier to fabricate an ultrasensitive electrochemiluminescence (ECL) biosensor for microRNAs detection. Usually, conventional CHA can produce only one output DNA in each target cycle, while the proposed strategy could produce multiple output DNA by using DNA-functionalized magnetic beads (MBs) and gold nanoparticles (AuNPs) to form T-3D Net. Then, the T-3D Net with high loading capacity could be completely collapsed by dissolving AuNPs to efficiently convert trace microRNA-21 into a large amount of output DNA. Furthermore, the nanocomposite containing Ru­(bpy)₃²⁺ as luminophore and boron nitride quantum dots (BNQDs) as coreactant provided a strong initial ECL response owing to the short electron transfer distance between luminophore and coreactant (signal-on). Next, the DNA duplex probes labeled with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and dopamine (DA) (S1-ABEI/S2-DA) were further immobilized on the nanocomposite to reduce the background signal due to the double quenching effect of DA for both ABEI and Ru­(bpy)₃²⁺ (signal-off). In the presence of the output DNA with enzyme-assisted self-recycling, S2-DA was displaced and detached from the electrode surface to achieve ECL signal recovery. Simultaneously, S1-ABEI restored a stable hairpin structure, making ABEI close to the electrode surface for more effective resonance energy transfer (RET) between ABEI and Ru­(bpy)₃²⁺, which greatly improved the final ECL response (signal-super on). Thus, the ECL biosensor demonstrated superior performance for ultrasensitive detection of microRNA-21 with low detection limit (0.33 aM) and was successfully applied to monitor the expression of microRNA-21 in human cancer cell lysates. This strategy provided an ultrasensitive way for the detection of biomolecules and revealed an effective avenue for diseases diagnosis.