Hierarchical Nucleic Acid Amplification-Driven DNA Hydrogel Interface for Label-Free, Ultratrace PFOA Monitoring.

Per- and polyfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA), represent persistent environmental contaminants that require sensitive and reliable analytical methods for monitoring. However, the efficient conversion of molecular recognition events into amplified analytical signals remains challenging. Herein, we report a label-free electrochemical impedance spectroscopy (EIS) sensing platform based on a target-triggered DNA hydrogel signal amplification interface for ultratrace PFOA detection. Upon specific recognition of PFOA by an aptamer probe, a strand displacement amplification (SDA) circuit is activated to generate abundant DNA signal strands. These amplified DNA strands subsequently hybridize with the preassembled hybridization chain reaction (HCR) structures on the electrode surface and promote cross-linking between adjacent HCR assemblies, leading to the formation of a highly interconnected three-dimensional DNA hydrogel network. The assembled DNA hydrogel significantly increases interfacial steric hindrance and charge-transfer resistance, enabling the conversion of molecular recognition events into amplified impedance responses. The proposed sensor achieves a wide linear range from 1 aM to 10 pM with a detection limit of 0.35 aM, while exhibiting excellent selectivity toward PFOA over structurally related perfluorinated compounds. Furthermore, the platform enables the accurate detection of PFOA in complex samples with satisfactory recoveries. This work establishes a programmable DNA hydrogel-based signal amplification strategy for ultratrace contaminant analysis and provides a versatile framework for developing advanced nucleic acid-based sensing systems.