Cascade DNA system-based ratiometric electrochemical/electrochemiluminescent biosensor for Alzheimer’s disease biomarker

Detecting amyloid- β oligomer (A β O) in a sensitive and reliable manner is crucial for the early diagnosis of Alzheimer’s disease (AD). Here, a ratiometric electrochemical/electrochemiluminescent (EC/ECL) biosensor sensitized with a cascade DNA system was designed for A β O assay, an AD biomarker. Benefited from the strong binding of aptamer to target A β O, this system not only exhibited excellent identification to A β O in interfering substrates, but also achieved the signal transduction from A β O to nucleic acid (M). The releasing M strands triggered the upstream entropy-driven DNA circuit (EDC), which could directly initiate the downstream hybridization chain reaction (HCR). The continuous programmability of cascade DNA system achieved a one-to-multiple amplification effect, enhancing the assembly amount of ferrocene (Fc). The electron transfer and energy transfer between Ru(bpy)₃²⁺-conjugated silica nanoparticles (RuSi NPs) and Fc improved the sensitivity for A β O detection. The reverse change of signals between EC (Fc) and ECL (Ru) introduced intrinsic self-calibration and ensured the reliability of the biosensor. Taking the above advantages, the proposed method exhibited a high sensitivity for A β O quantification in the range of 50 fM to 10 nM and a detection limit of 14 fM. The proposed sensing strategy was also validated using real serum samples, offering a sensitive and efficient approach for AD diagnosis.