"One-to-many" signal-output strategy-based CRISPR/Cas12a system for sensitive label-free fluorescence detection of HBV-DNA

Although CRISPR/Cas12a systems significantly enhance the analytical accuracy and flexibility of fluorescent biosensors, their sensitivity is limited by traditional "one-to-one" mediation types and ineffective signal-output turnover routes. Herein, we demonstrate a "one-to-many" signal-output strategy-based CRISPR/Cas12a systems resembling a "seaweed" to enhance the sensitivity. Based on dendrimer DNA from high-dimensional hybridization chain (HCR) of three hairpin-free DNA building blocks, the 3D magnetic DNA machine was created. The HBV-DNA initiates the rolling circle amplification (RCA) reaction and produces DNA nanowires to activate the CRISPR/Cas12a system. The trans-cleavage of the "seaweed root" by CRISPR/Cas12a system left dendrimer DNA in solution, thus, adding SYBR Green I (SG I) to the high-density DNA duplexes, achieving multiple-turnover label-free fluorescence signal output demonstrated and a low LOD (1.502 pM). However, in the absence of target, the blocked RCA failed to activate the CRISPR/Cas12a system, resulting in complete separation from substrate and negligible fluorescence signals. Moreover, the mandatory RCA-based pre-amplification of the DNA activator could efficiently trigger the multiple-turnover trans-cleavage activity of Cas12a. it can cleave one single-stranded linker of "seaweed-like" DNA machine, thereby releasing massive DNA duplex-enriched dendrimer DNA with a "one-to-many" signal-output turnover. By coupling the periodically extended Cas12a activator generated by RCA with hyperbranched DNA duplex by high-dimensional HCR, compact 3D extension structures were formed, achieving high-density fluorescence distribution in focal volume, avoiding signal dilution and ensuring high enhancement. Additionally, spiked recoveries in physiological media exceeded 95%, demonstrating the potential application of such platforms in clinical diagnosis.