a , Scanning electron microscopy (SEM) of the morphology of untreated biofilm and (b) treated with CAT-NP (CAT-NP bound; see arrows). Magnified view of CAT-NP in the selected area (b1). SEM/EDS images showing iron (pink) distribution on biofilms (b2). c, CAT-NP bound on biofilm as determined by measuring iron amounts with ICP-MS. d, 3D architecture of untreated biofilm. e, Spatial distribution of CAT-NP in treated biofilm: f, CAT-NP (white); g, bacteria (green); h, EPS (red) are observed with confocal microscopy. i, Cross-sectional merged images of top and middle areas of the biofilm. j, Orthogonal distribution of CAT-NP, and (k) bacteria and EPS across biofilm thickness