Rapid and ultra-low detection of cancer biomarker miRNA-133a-3p via AC electrokinetics-integrated capacitive sensing

MicroRNAs (miRNAs) are promising biomarkers for early cancer detection, but their low abundance and matrix interference continue to limit rapid, point-of-care (POC) assays. Here, we report a rapid, sensitive, and label-free biosensing platform for the detection of miRNA-133a-3p, a tumor-suppressive biomarker implicated in various cancers. The sensor operates on a non-faradaic capacitive principle, utilizing gold-plated printed-circuit-board interdigitated electrodes functionalized with thiolated single-stranded DNA capture probes. Alternating current electrokinetic (ACEK) effects are integrated with capacitive readout to achieve a single-step operation that enhances target transport to the interface, accelerates hybridization, and amplifies the capacitance transient. Assay conditions were optimized to achieve a linear dynamic range from 1 fM to 1 pM with a high sensitivity of 2.44%/min per decade and a limit of detection (LOD) as low as 0.56 fM in a standard buffer. High specificity was confirmed through selectivity tests against non-complementary miRNAs. For serum analysis, only a simple 1:100 dilution is required prior to measurement, yielding a LOD of 0.74 fM in diluted serum (equivalent to 74 fM in neat serum). This portable and cost-effective ACEK-capacitive platform enables fast and selective miRNA detection in complex matrices with minimal sample preparation.