Fig. 2

UV–vis spectra. For GO, GO-POAA, GO-chitosan, POAA and chitosan dissolved in a, b PBS and c, d nutrient medium. The AFM image of e GO on mica and the height difference between the two arrows (the GO and mica) is 1.16 nm, which is consistent with the thickness of a single layer GO (up to 20 μm wide). The one-layer thicknesses of f GO-POAA and g GO-chitosan respectively increased to 1.45 and 1.66 nm, respectively