Sem stubs

Each nanowire chip was put into the well of a 96-well plate (Corning, USA). Then, 200 μL per well of Dulbecco's phosphate-buffered saline (DPBS, Gibco, USA) were added, used either as purchased, or pH-adjusted with 2 M NaOH and 5 M HCl aqueous solutions. At each time point, the liquid was removed, the chip taken out of the well, and blow-dried with a gentle stream of dry N₂ gas. The chips were then mounted onto scanning electron microscopy (SEM) stubs (Electron Microscopy Sciences, USA) with carbon tape (Agar Scientific, UK) and imaged in an electron microscope (Zeiss, Germany), without any coating. The height, diameter and spacing of patterned nanowires were measured and analysed using the software packages FIJI and R respectively (R Foundation for Statistical Computing, Vienna, Austria), with the package “tidyverse”.^{37,38 (link)}

Lcr BT-1 cells, OMVs and BM7 medium (control) were observed using scanning electron microscope (SEM). A 20 μl aliquot of the bacteria samples was pipetted on pieces of fractured microscope slides and allowed to dry at room temperature. Samples were fixed in a 4% paraformaldehyde solution buffered with 1x phosphate-buffered saline (PBS) and incubated overnight. The next day samples were dehydrated in an ethanol series (30, 50, 70, 85, 95, and 100%) and then incubated in 100% ethanol overnight at 4°C. The samples were then dried using a Ladd 28,000 critical point dryer (Ladd Research Industries, Williston, VT, United States), mounted on double-sided 12 mm carbon stickers on SEM stubs (Electron Microscopy Sciences, Hatfield, PA, United States), and sputter-coated using a Ladd 30,800 sputter coater (Ladd Research Industries) with a gold/palladium target. Samples were observed using a Hitachi S4000 SEM (Hitachi, Tokyo, Japan) and images were captured with PCI imaging software (Quartz Imaging Corp., Vancouver, BC, United States).