Intramolecular DNA Machine Coupled with Catalytic Redox-Recycling Amplification for Highly Efficient Electrochemical Detection of Dipicolinic Acid

The accurate and timely determination of dipicolinic acid (DPA) is of great concern to prevent an anthrax epidemic. However, conventional methods suffer from poor detection efficiency and limited signal amplification. Herein, we report a highly efficient electrochemical biosensor for DPA analysis, which is based on two core conceptual and mechanistic breakthroughs: (i) a confined intramolecular DNA machine amplification paradigm that replaces the traditional intermolecular diffusion-driven design and (ii) the synergistic coupling of target-triggered intramolecular DNA machine activation with CeO₂ catalytic redox-recycling amplification. The sensor designs a sandwich-structured complex (SSC) as the recognition component, and DNA circuit probes are assembled in the X-shaped probe (XSP) structure. The disassembly of the SSC triggered by the strong chelation function between DPA and Zr⁴⁺ results in the release of the trigger probe and the initiation of the intramolecular DNA machine on the XSP nanostructure. Nanoceria (CeO₂) nanoparticles move close to the sensing electrode, catalyzing the conversion of <i>p</i>-aminophenylphosphate to <i>p</i>-aminophenol to amplify current responses during the potential sweep in the presence of the co-reactant nicotinamide adenine dinucleotide. The reported sensing strategy allows for effective determination of DPA with a limit of detection down to 7.4 pM within a reaction time of just 40 min. Significantly, the sensitivity of the intramolecular DNA machine surpassed that of the intermolecular DNA machine sensor by up to 3 orders of magnitude. Furthermore, the sensor has proven to effectively and consistently monitor bacterial spore samples, which demonstrates a wide applicability in hazardous pathogens on site analysis and biomedical research.