Figure 4.

SERS spectra of starch (cyan) and AgNP stabilized by citrate (red), field EPS (blue), starch/Glc (black), and colonized EPS (green) systems. The starch peak at 2911 cm^–1 (assigned as CH stretching vibrations) can be used as a reference: in the presence of AgNP (starch/Glc) system, the intensity of otherwise prominent CH peak is negligible compared to highly amplified signals at 1362 and 1573 cm^–1 (assigned as COO^– stretching vibrations).³⁶ The amplification of the signal is due to the SERS effect, signifying close proximity of the COO^– functional groups to the AgNP surface. The prominent amplification of the COO^– groups is also observed in AgNP stabilized by citrate (known to be stabilized by COO^–; used as reference), as well as colonized and field EPS. This suggests that EPS supports the formed NP primarily by COO^– functional groups.