A Direct Near-Infrared Photocage-Blocked Methylation Gate Integrated with an Ultrasensitive Triple-Loop Self-Boosted Exponential Amplification DNA Nanocircuit for High-Fidelity Molecular Imaging

Fluorescent biosensors constructed from sensitive DNA nanocircuits for high-fidelity imaging in live biological samples are in high demand for disease diagnosis. In this contribution, we present a direct near-infrared (NIR) photocage-blocked methylation gate that integrates with an ultrasensitive triple-loop self-boosted exponential amplification DNA nanocircuit. For one thing, a methylation gate is incorporated as a specific component to enhance biorecognition capability, which is then directly blocked by an NIR photocage comprising an upconverting nanoparticle and a photolytic 6-nitropiperonyloxymethyl (NPOM) group. Under exogenous 980 nm NIR-light-transformed ultraviolet upconverting luminescence, the linkage between the NPOM group and adenine is photolytically cleaved to controllably expose the m⁶A site. For another, by cascading an iterative catalytic hairpin assembly hybridization chain reaction cycle with a self-actuated DNAzyme cleavage that triggers fluorescence output, a robust DNA nanocircuit with triple-loop self-boosted exponential amplification is built. When a model microRNA biomarker (miRNA-155) with elevated expression across various malignant tumors is used for proof-of-concept validation, we show the ultrahigh sensitivity and strong specificity of this fluorescent biosensor. More importantly, the bioanalytical toolbox enables high-fidelity molecular imaging in live-cell and in vivo scenarios, paving the way for the deployment of DNA nanocircuits in disease diagnosis.