Fabrication of Patterned PVDF Membranes for Hybrid Nanomaterial Devices

Hydrophilic PVDF membranes (0.22 μm pore size, Millipore) were patterned with ma-N 490 photoresist (micro resist technology GmbH) according to previously published protocol.^{[25 (link)]} Au-TiO₂NW dispersion (1.8 mL, 92 mm² open filter area) followed by PBS buffer (10 mL) was vacuum filtered through the patterned membrane. PDMS was spin-coated (Sylgard 184, 1 krpm spin speed, 30 s) onto a silanized 2 inch glass wafer and semi-cured (70 °C, 6 min). The dried membrane was put in contact with the PDMS under pressure (80 °C, 10 min) and peeled off after being soaked in DI water. A diluted PDMS solution (PDMS:heptane 1:20) was spin coated (6 krpm 60 s) and cured (80 °C, 20 min), followed by another spin-coated PDMS layer (6 krpm, 120 s) and curing (80 °C, 16 h). After 10 min UV ozone treatment, a poly(vinyl alcohol) (PVA) layer was spin-coated on top (10%, 3 krpm, 60 s). A dry film resist layer was laminated on top (LP Dry Film Photopolymer), exposed, and developed. The substrate was dry etched (RIE, 250 W, 100 mTorr, O₂/CF₄, 400 s) and the PVA and dry resist stripped in boiling DI water. The SEG was cut out with a scalpel and clamped on a custom-made printed circuit board connector. Finally, a thin layer of platinum was electroplated onto the electrodes (Sigma-Aldrich, chloroplatinic acid solution 0.8 wt% in DI water, pulsed −1.5 V, 20 Hz, 10% duty cycle).