Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains a significant global health threat because of its rapid evolution and high mutation rate, which limits the performance of existing molecular diagnostics. This study presents a dual-mode, aptamer-based detection platform that combines high sensitivity with mutation resilience. Using a computer-assisted X-aptamer Systematic Evolution of Ligands by EXponential enrichment (SELEX) approach, we identified NP14, a high-affinity, dual-target DNA aptamer that specifically binds to the SARS-CoV-2 nucleocapsid (N) protein at its N-terminal domain. Analyses via molecular docking, aptamer truncation, and targeted mutagenesis revealed that NP14 interacted with both SARS-CoV-2 and SARS-CoV N proteins and identified key nucleotides C24 and G27 of the P1 region and structural determinants critical for its high-affinity binding. Building on this discovery, we engineered a dual-mode biosensing system by integrating NP14 into a multicolor dynamic light scattering-enhanced enzyme-linked aptamer-antibody assay (MD ELAAA). MD ELAAA synergistically combines two complementary detection strategies: ⅰ) non-aggregative plasmonic colorimetry for visual signal detection and ⅱ) dynamic light scattering for ultrasensitive quantitative analysis, in which Au/Ag nanomaterials are used to amplify optical and scattering signals. This system achieves a sensitivity of 0.43 TCID₅₀/mL, representing a 47-fold improvement over standard methods. By integrating high sensitivity, specificity, variant recognition, and dual-mode signal output, the MD ELAAA platform enables reliable detection of low-abundance SARS-CoV-2 antigens. Its robust performance supports early-stage diagnostics and high-throughput variant monitoring, establishing MD ELAAA as a robust platform for next-generation viral detection and surveillance.

Aptamers, short single DNA or RNA oligonucleotides, have shown immense application potential as molecular probes for the early diagnosis and therapy of cancer. However, conventional cell-SELEX technologies for aptamer discovery are time-consuming and laborious. Here we discovered a new aptamer BC-3 by using an improved rapid X-Aptamer selection process for human bladder carcinoma, for which there is no specific molecular probe yet. We show that BC-3 exhibited excellent affinity in bladder cancer cells but not normal cells. We demonstrate that BC-3 displayed high selectivity for tumor cells over their normal counterparts in vitro, in mice, and in patient tumor tissue specimens. Further endocytosis pathway analysis revealed that BC-3 internalized into bladder cancer cells via clathrin-mediated endocytosis. Importantly, we identified ribosomal protein S7 (RPS7) as the binding target of BC-3 via an integrated methodology (mass spectrometry, colocalization assay, and immunoblotting). Together, we report that a novel aptamer BC-3 is discovered for bladder cancer and its properties in the disease are unearthed. Our findings will facilitate the discovery of novel diagnostic and therapeutic strategies for bladder cancer.