<p> A novel covalent organic polymer based on proflavine (COP-PF) is designed, synthetized and characterized to be used as a redox indicator in the biosensing field. COP-PF is introduced as an intrinsic redox indicator, ensuring reliable signal transduction without the need for external mediators. The platform was further reinforced with few-layer bismuthene, which is employed to structure gold screen-printed electrodes (AuSPE), improving electron transfer and DNA immobilization. Lastly, DNA nanoengineering is proposed in the shape of tetrahedral DNA nanostructures (TDNs) whose thiol-functionalized basal vertices enabled robust anchoring to FLB, while their apex carried a complementary probe to the analyte. The synergy of these materials yielded a highly robust biosensing system with exceptional sensitivity and selectivity. Biologically, the platform was applied to the detection of miRNA-27a, a clinically relevant biomarker of autism spectrum disorder (ASD), whose diagnosis has attracted the attention of the scientific community and society at large. The device achieved an ultralow detection limit of 10.3 aM, maintained high specificity in the presence of potential interferents, and demonstrated successful performance in spiked human serum samples. These results underscore the value of integrating emerging 2D nanomaterials, DNA nanotechnology, and functional organic polymers to advance medical diagnostics, offering a versatile route for nucleic acid biomarker detection in complex biological environments. Clinical trial number: not applicable.</p> Graphical abstract <p></p>