Multi-Path High Electrochemiluminescence Activation Induced by SnO₂/g-C₃N₄ Heterojunction for Ultrasensitive Bioanalysis Using SDA-Mediated Reticular DNA Structure as Signal Amplifier

Here, an ultrasensitive electrochemiluminescence (ECL) biosensor for miRNA-222 detection was fabricated using a heterojunction nanomaterial composed of stannic oxide decorated graphitic carbon nitride (SnO₂/g-C₃N₄) as an efficient emitter and strand displacement amplification (SDA) mediated reticular 3D DNA structure for dual-output signal amplification. The construction of the SnO₂/g-C₃N₄ heterojunction could efficiently improve the ECL performance through multiple paths. First, it could drive the high-energy electrons in g-C₃N₄ to migrate the SnO₂ conduction band, preventing the g-C₃N₄ conduction band from accumulating excessive electrons and thereby suppressing material passivation under high-potential conditions. Moreover, the Sn²⁺/Sn⁴⁺ redox pair could provide additional charge transport channels, accelerating electron transfer and significantly enhancing the ECL emission efficiency. Meanwhile, SnO₂ could catalyze the decomposition of the coreactant H₂O₂, promoting the production of hydroxyl radicals (OH^•) and further enhancing the ECL intensity of the material. Leveraging the synergistic effects of improved electron transfer and radical generation, the ECL intensity of the SnO₂/g-C₃N₄ heterojunction exhibited 6 times enhancement in comparison with pure g-C₃N₄. Then, a simple and efficient SDA reaction was employed to construct a reticular 3D DNA structure for signal amplification. This 3D DNA structure functioned as an ideal molecular scaffold with high loading capacity, and excellent structural stability could provide abundant Nb.BbvCI restriction enzyme cleavage sites, enabling the effective release of a large amount of dual-output DNA, significantly improving signal amplification efficiency and detection accuracy. Finally, the proposed biosensor exhibited excellent detection performance, achieving a sensitive detection limit for miRNA-222 as low as 41.3 aM.