Scalable fabrication and mechanistic understanding of horizontally aligned MWCNT nanochannel devices for ionic current-based DNA biosensing.

Carbon nanotube (CNT)-based ionic nanochannels offer a powerful platform for controlling ion transport at the nanoscale, enabling highly sensitive biosensing modalities based on molecularly gated ion transport. In this work, we design, fabricate, simulate, and experimentally characterize a multi-walled carbon nanotube (MWCNT)-based ionic nanochannel functionalized with single-stranded DNA for label-free detection of complementary nucleic acids. Devices fabricated via CVD growth, mechanical transfer, and microfabrication of integrated reservoirs and electrodes exhibit stable and reproducible ionic transport in KCl electrolytes. Conductance strongly depends on electric double-layer structure and ion-surface interactions, as shown by systematic variation of electrolyte concentration. Covalent attachment of 15A capture strands to CNT termini reduces channel resistance, whereas hybridization with complementary 30T targets results in reproducible, concentration-dependent resistance increases. The sensor exhibits a linear detection regime from 2 to 20 μM with a sensitivity of 1.86 MΩ μM-1 (R2 ≈ 0.99). These results demonstrate a deterministic, tunable MWCNT ionic nanochannel platform for quantitative, label-free nucleic acid detection, providing a scalable foundation for next-generation nanofluidic biosensors and molecular diagnostics.