Layered COF@Au integrated with pH-responsive DNA triple helix to construct recyclable SERS substrate achieving ultrasensitive detection of ofloxacin

Herein, target-induced catalytic hairpin assembly (CHA) integrate with a pH-responsive DNA triple helix structure is first used to construct a recyclable layered covalent organic framework ( L -COF) @Au as a SERS substrate for the ultrasensitive detection of ofloxacin (OFL). Firstly, a large specific surface area and abundant -NH 2 groups of the L -COF serves as an ideal carrier for Au NPs, enabling the generation of a strong and uniform electromagnetic field. Meanwhile, target-triggered catalytic hairpin assembly (CHA) is utilized to activate an efficient DNA walker system, thereby achieving significant amplification of the SERS signal. Notably, pH-responsive folding and unfolding of the DNA triplex can enables capture and release of the SERS tag (Au@4-NTP@Ag) to achieve regeneration of the SERS substrate, thus allowing multiple reuse cycles. Furthermore, a synergistic plasmonic enhancement effect was realized between the COF@Au substrate and the SERS tag, resulting in a broad dynamic detection range from 1.0 × 10 −13 mol/L to 1.0 × 10 −6 mol/L and a low limit of detection (LOD) of 5.79 × 10 −14 mol/L. The biosensor demonstrates accurate quantification in real food samples, confirming its practical applicability. In addition, the methodology simplifies experimental procedures and reduces operational costs. Overall, this study presents a highly selective and responsive sensing approach for constructing renewable SERS-based biosensors, providing a robust and prospective platform for the monitoring of antibiotics in food safety applications.