Gold Nanoparticle – Assisted Multiharmonic and Multivariate QCM Sensing of miRNA-21

MicroRNA-21 (miRNA-21) is a clinically relevant biomarker for cancer, cardiovascular, and inflammatory disorders. Conventional detection methods are laboratory-based, time-consuming, and poorly suited for point-of-care applications. Quartz Crystal Microbalance (QCM) sensors provide label-free, real-time detection, but conventional single-frequency analysis limits sensitivity and underestimates viscoelastic effects. Here, we present a multiharmonic and multivariate QCM framework combined with a gold nanoparticle (AuNP)–assisted sandwich assay to enhance miRNA detection. Frequency, amplitude, and phase features across multiple resonance modes were analyzed using a physics-informed feature selection and optimization strategy to identify the most discriminative parameters. The approach was validated experimentally for miRNA-21. Multivariate multimodal analysis reduced the detection limit from ~10 nM (single-frequency) to 100 pM. AuNP-mediated amplification further increased the effective signal by ~1.5×, yielding a final detection limit of 1 pM, corresponding to a two-order-of-magnitude improvement. Specificity assays with non-target miRNAs (miRNA-145 and miRNA-9) showed minimal cross-reactivity. These results demonstrate that combining multiharmonic signal analysis with nanoparticle-based amplification substantially enhances both sensitivity and selectivity of QCM-based miRNA detection, supporting its potential for sensitive biomarker monitoring in cancer and other pathologies.