Towards liquid biopsy on chip for Triple Negative Breast Cancer: preliminary results on monitoring circulating miRNA-21 using portable diagnostics.

Liquid biopsy has emerged as a promising non-invasive, cost-effective and real-time approach for cancer diagnosis and monitoring, allowing for the detection of biomarkers in bodily fluids. Among these, microRNAs (miRNAs) are a valuable choice due to their stability and ability to reflect the tumor's heterogeneity. Concerning triple negative breast cancer (TNBC), an aggressive subtype, several studies have demonstrated consistent upregulation of miRNA-21. Its elevated levels, linked to poor prognosis, make it valuable for early detection, risk stratification, and targeted therapies. While traditional miRNA quantification methods are accurate, they often require complex procedures and skilled personnel, limiting their accessibility in low-resource environments. These challenges can be addressed by electrochemical point-of-care (POC) platforms, inspired by the glucose strip, offering a good alternative by reducing matrix effects, integrating cost-effective and eco-friendly substrates. In this work, miRNA-21 was selectively detected using a complementary DNA probe modified with methylene blue, as a redox mediator, immobilized onto an AuNPs-functionalized, paper-based screen-printed electrode. Significant experimental parameters and sensor's selectivity were carefully evaluated, allowing miRNA-21 detection in both standard solution and human serum with limit of detection (LOD) 1.2 nM and satisfactory repeatability of about 8%. The platform's performance improved tenfold with an external paper-based origami pre-concentration device, enabling pM-level miRNA detection and advancing its potential for real clinical practice applications. The platform is envisioned as a starting point for developing accessible, rapid, cost-effective POC testing, with significant implications for personalized medicine and early TNBC detection.