Enhanced DNA capture in silicon nitride nanopores via localized photothermal convection

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 30 nm-thick silicon nitride (SiN_x) 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^-1. 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 SiN_x membranes underscores its potential for applications in DNA sequencing, proteomics, and real-time environmental biomarker detection.