Aqueous mounting media

Sections adjacent to those used for DESI-MS were stained using haematoxylin and eosin (H&E). Following submersion in xylene (Sigma-Aldrich, UK) for 2 min, slides were immersed 4 times for 2 min in industrial methylated spirit (Sigma-Aldrich, UK). Following washing in tap water, sections were stained using Harris haematoxylin (3 min; Sigma-Aldrich, UK), rinsed in hot water, and dipped for one second in eosin (Leica, UK). Following further industrial methylated spirit (4 × 2 min) and xylene (4 × 2 min) washes, slides were left to dry. Samples were mounted with coverslips using aqueous mounting media (Abcam, UK) and left overnight to dry. Images were acquired using the 3D Histech Pannoramic 250 Flash II slide scanner with [20x/0.80 Plan Apo] objective and processed using Pannoramic viewer (3D HISTECH, Hungary).

Detection of γ-glutamylcysteine synthetase (GCLM) and thioredoxin (TRX) was in CFU-f of primary MSCs cultured with Ag⁺ on glass coverslips (using a HeLa cell positive control). Slides were fixed with ice cold 100% methanol (10 min) rinsed with PBS and incubated with 5% goat serum/PBS at room temperature (1 h). Primary antibody incubation (1 h, RT) also occurred in 5% goat serum/PBS 10 μg/mL polyclonal rabbit anti-GCLM IgG (Cat: NBP1-33405, RRID: AB_2107841, Novusbio, UK) and 4 μg/mL polyclonal rabbit anti-thioredoxin IgG (Cat: NBP2-48873, RRID AB_2819005, Novusbio). Slides were rinsed before incubation with 10 μg/mL Alex fluor 647-conjugated goat anti-rabbit IgG (H + L) cross adsorbed (1 h, RT; Cat: A-21244, RRID: AB_2535812, ThermoFisher) and counterstained with 2 μg/mL DAPI. Coverslips were mounted in aqueous mounting media (Abcam, Cambridge, UK). All immunofluorescence imaging was performed using the Zeiss Axio Imager.M2 LSM 710 confocal microscope (Carl Zeiss, Cambridge, UK).