G-Quadruplex-Rich DNA Nanowire-Functionalized Nanocarrier: From Hemin Encapsulation and Target-Triggered Release to In Situ DNAzyme Self-Assembly for Ultrasensitive miRNA Sensing.

Target-responsive "gated" nanocarriers have attracted considerable attention in biosensing owing to their controllable release of signaling molecules. However, it remains challenging to simultaneously achieve high-capacity loading with minimal leakage in complex biological media, and efficient conversion of each recognition event into a multiplied output of catalytic units for accurate detection of low-abundance targets. Herein, an electrochemical/colorimetric dual-mode biosensor for ultrasensitive miRNA-21 detection based on an integrated "Encapsulation-Release-Assembly" cascade amplification platform was reported. A gold nanocluster-decorated, ZIF-67-derived porous carbon nanocarrier (AuNCs@PC-ZIF67) is functionalized via in situ hybridization chain reaction (HCR) to grow G-quadruplex-rich DNA nanowires, which serve as both a stable biogate and a high-density reservoir for hemin encapsulation with negligible leakage. Target recognition activates an entropy-driven reaction (EDR) circuit, catalyzing target recycling and generating multiple output strands that trigger gate disassembly. The coreleased hemin and DNA nanowires spontaneously self-assemble into numerous hemin/G-quadruplex DNAzymes, converting a single binding event into amplified catalytic signals. This synergistic cascade─combining HCR-based spatial confinement gating, EDR-powered target amplification, and in situ DNAzyme self-assembly─transforms a single recognition event into multiplexed catalytic signals, enabling dual-mode readout with ultralow detection limits of 0.091 aM (electrochemical) and 2.7 aM (colorimetric). Accurate quantification in human serum and cancer cell lysates validates its clinical utility. This work establishes a cascade amplification paradigm that integrates spatial-confinement gating, entropy-driven recycling, and in situ DNAzyme assembly, providing a generalizable route for ultrasensitive biomarker detection in complex biological matrices.