Figure 5.

Representative X-ray photoelectron spectroscopy spectrum of AgNP embedded in the EPS matrix extracted from field biofilm samples after sputtering. The inset shows the enlargement of the Ag 3d region. The pristine sample is depicted in red, whereas the sputtered is shown in black. The peak at 368 eV is characteristic of metallic Ag, though the spectrum does not exclude the possibility of oxide layer on the surface, as the peak at 386 eV may consist of multiple overlapping signals.⁵⁷ Apart from Ag, the elements that are clearly identified by XPS are Na, C, O, and N.