Dual-Band Multigap Resonator Integrated With Spiral Inertial Microfluidics for Simultaneous Label-Free and High-Throughput Biomolecular Detection

Microwave resonator sensors exhibit three distinctive advantages over conventional analytical methods: real-time monitoring capacity, label-free detection mechanism, and high integration with microfluidic systems. The working principle exploits dielectric characterization through measurable resonant frequency shifts caused by dielectric constant variations in biological analytes. In this paper, an integrated microwave microfluidic sensing chip is proposed for the detection of white blood cells (WBCs, THP-1) and circulating cancer cells (CTCs, MCF-7). The proposed dual-band multi-gap coupled resonator (DMCR) is constructed on a glass substrate with copper structure gaps to generate resonance, exhibiting high sensitivity at both resonance frequency. The polydimethylsiloxane (PDMS)-based microfluidic chip employs a spiral channel architecture to achieve continuous cell separation through the synergistic effects of inertial lift forces and Dean vortices. The spiral microfluidic device achieves 74.13% separation efficiency for WBCs and 84.6% for CTCs at designated outlets, with detection sensitivities of 3.51 MHz/(10⁴ cells/mL) and 11.6 MHz/(10⁴ cells/mL) for MCF-7 and THP-1 cell lines, respectively. This label-free platform demonstrates a certain degree of specificity through the integration of microwave resonator sensors and microfluidic sorting mechanisms, showing significant potential for clinical liquid biopsy applications requiring non-invasive analysis of circulating tumor cells.