Removable Nanopore Sealing and In Situ Iron Oxide Nanoparticle Synthesis on Thin Silicon Nitride Membranes

We report in situ synthesis of iron oxide particles inside silicon nitride nanopores via a chemical reaction, monitored by current readout. Nanopores were formed by electroporation on glass chips (diameters from 1.7 to 11.3 nm), transmission electron microscopy (TEM) drilling (diameters from 6.5 to 64.6 nm), or hydrofluoric acid etching (diameters from 12.6 to 36.2 nm) in 5–20 nm thick membranes. Nanopores seal on time scales from ∼1 ms to ∼3.6 s, across a range of sizes and concentrations. We show single and ∼5-pore arrays, as fabricated, after sealing, and after cleaning and pore recovery. These results are independent of the fabrication method. Energy-dispersive X-ray spectroscopy, aberration-corrected scanning TEM, and powder X-ray diffraction verify the synthesis of mixed magnetite and maghemite iron oxide. This work advances nanoparticle–nanopore chips for applications in biosensing, plasmonics, and photonics, where position and size control is required.