Oxygen vacancy-rich SnO2/CdIn2S4 heterojunction with self-primed multi-cycle amplification for sensitive ctDNA detection

Currently, sensitive detection of circulating tumor DNA (ctDNA) serves as a critical indicator for tumor diagnosis and therapeutic assessment. Therefore, we have developed a signal quenching photoelectrochemical (PEC) sensor that integrates novel photoactive materials and DNA conformation transformation assistance to initiate self-primed multi-cycle strand displacement amplification (MC-SDA), achieving sensitive detection of ctDNA. The oxygen vacancy-rich SnO₂ (SnO₂-OV) forms an S-scheme heterojunction with CdIn₂S₄, serving as a photoelectrochemical (PEC) active material and providing excellent initial photocurrent signals. In the presence of the ctDNA, triggering the conformational transformation of the template chain (HP) initiates the MC-SDA reaction, resulting in exponential amplification and generating abundant S2 chains. On the electrode surface, the introduction of S2 triggers hybridization chain reaction, leading to the formation of numerous G4@hemin composite structures with peroxidase-like activity. This structure catalyzes the oxidation of 3-amino-9-ethylcarbazole by H₂O₂, performing the biocatalytic precipitation reaction on the electrode surface. This effectively impedes electron transfer, ultimately causing the quenching of the photocurrent signal. Under optimal conditions, this PEC sensor exhibits highly efficient and sensitive detection performance, with a wide linear range for ctDNA from 0.1 fM-100 pM and a low detection limit of 21.8 aM. Additionally, this biosensor can be applied to analyze ctDNA concentrations in real serum samples. Therefore, this PEC sensor holds potential as a promising alternative tool for tumor diagnosis and assessment.