A pathogen-activated DNAzyme triggers hybridization chain reaction for ultra-sensitive salivary detection of Helicobacter pylori

Helicobacter pylori infection is a major etiological factor in chronic gastritis, peptic ulcer disease, and gastric cancer, highlighting the demand for sensitive, non-invasive, and operationally simple diagnostic strategies. Herein, we report a pathogen-activated, enzyme-free biosensing platform that directly couples target recognition with signal amplification through a single DNAzyme-hybridization chain reaction (HCR) cascade. Distinct from conventional multicomponent amplification systems, the designed DNAzyme simultaneously functions as both the recognition element and the HCR initiator, enabling a true one-step assay without auxiliary enzymes or intermediate probes. Upon specific activation by H. pylori, the DNAzyme releases an initiator strand that triggers downstream HCR amplification, generating a fluorescence signal-off response under mild isothermal conditions (37 °C). The assay exhibits a linear response over a concentration range of 10²-10⁴ CFU mL^-1 with a detection limit of 0.11 CFU mL^-1 and enables direct analysis of saliva supernatants without complex pretreatment. Recovery studies in artificially contaminated saliva samples show satisfactory accuracy (98.4-104.9%) and reproducibility (RSD < 5%). Owing to its simplified workflow, minimal equipment requirement, and modular design, this strategy provides a generalizable sensing framework for non-invasive pathogen detection.