Luo et al. demonstrated a locked nucleic acid (LNA) aided strand displacement reaction-based ratiometric electrochemical biosensor with greater repeatability to detect exosomal miR-21 originating from cancer with an LOD of 2.3 fM.180 Human epidermal growth factor receptor 2 (+) BT 474 (HER-2 (+) BT 474), a well-known BC biomarker, was easily identified from the first collected population using its complementary HER-2 antibody. The gene discussed is ERBB2; the disease is breast cancer.