Fig. 2

Complete characterization of exfoliated graphene nanoflakes in 100% v/v HS. a Raman spectrum, laser excitation at 514 nm, showing the typical D, G, and 2D peak at ~1350 cm⁻¹, ~1580 cm⁻¹, and ~2750 cm⁻¹, respectively, is consistent with a graphene material; b AFM scans of 5 µm × 5 µm (left) and 1 µm × 1 µm (right) showing the nanoflakes topography. The presence of proteins on the nanoflakes can be noticed at higher magnification. High scales are, respectively, 50 nm (left) and 30 nm (right). c DCS analysis and AFM larger lateral size statistical analysis of graphene nanoflakes. The two methods resulted reasonably consistent between them, giving a main peak at about 200–300 nm. d Graphene nanoflakes stability over time (24 and 48 h) in cell culture media with (CMEM) and without (MEM) proteins as measured by DCS. The curves show that in the presence of protein-supplemented media, the graphene dispersion keeps its colloidal stability ove time with negligible aggregation