A Reciprocal-Amplifiable Fluorescence Sensing Platform via Replicated Hybridization Chain Reaction for Hosting Concatenated Multi-Ag Nanoclusters as Signal Reporter.

Exploring the replication of hybridization chain reaction HCR (HCR) for reciprocal amplification is intriguing in biosensing and bioanalysis. Herein, we develop a HCR-based fluorescence platform that is manipulated by the combination of a specific DNA trigger () and a -analogous amplicon (), thereby concatenating multi green-emissive Ag nanoclusters (AgNCs) for amplifiable signal readout. Four well-designed hairpins (H1 recognizing , H2, H3, and H4) with sequential complements are executed to operate HCR. The termini of H1/H3 are merged to hybridize an inhibiting strand (). The parent scaffold for AgNCs is separated into two splits (CACT and CGT) that are individually overhung in H2/H4. The presence of activates the first HCR amplifier through cross-hybridization of four reactive hairpins for forming HCR duplexes. The next invasion of a complex () drives to hybridize the tandem repeats in H1/H3, so that the displaced functions as to catalyze the second amplifier HCR for feeding back more hairpin assemblies with rapid reaction kinetics. In the shared HCR polymers, the parent scaffolds (CACTCGT) in H2/H4 are collectively concatenated for the preferential clustering of AgNCs adducts, which cooperatively emit enormous -responsive fluorescence signal. Because of the localization of in HCR products, an alternative amplicon is introduced to drive HCR progress via DNA strand displacement, generating more nucleating sites of emitters. Thus, the rational combination of nonenzymatic HCR and label-free fluorescent concatemers would create a reciprocal signal amplification, achieving a simplified, rapid, and highly sensitive assay down to femtomolar concentrations.