Enhanced DNA capture in silicon nitride nanopores via localized photothermal convection

Abstract

Efficient molecular capture remains a major challenge in nanopore sensing due to diffusion-limited transport. Here, we present a photothermal convection-assisted approach to enhance DNA capture using a 50 nm-thick silicon nitride (SiNₓ) membrane irradiated with a focused 532 nm laser. Local photothermal heating induces microscale convective flow at the laser focus, thereby increasing analyte transport toward the nanopore. Convection was visualized and characterized using 1-μm polystyrene beads, which exhibited aggregation patterns indicative of thermal convection rather than thermophoresis or optical trapping. COMSOL simulations confirmed the formation of vertical convective flows with velocities reaching ~1.2 × 10-5 m/s. These flows expanded the micropore capture radius to ~147 μm and significantly improved bead capture efficiency under an applied electric field. When applied to DNA sensing, this method increased capture rates by ~2-fold for 1 kbp and ~4.5-fold for 6 kbp double-stranded DNA fragments, with minimal contributions from optical pressure or thermophoresis. This strategy offers an effective means of overcoming diffusion constraints in nanopore sensing. Its compatibility with robust SiNₓ membranes underscores its potential for applications in DNA sequencing, proteomics, and real-time environmental biomarker detection.