# Theranostic Nanoplatforms of Thiolated Reduced Graphene Oxide Nanosheets and Gold Nanoparticles
## 3 Results and Discussions

Table 3: Optical parameters of wavelength at the maximum of absorbance (\(\lambda_{max}\)) full width at half maximum (FWHM), optical diameter (D) and aspect ratio (R) calculated from the surface plasmon (SP) bands of AuNS, AuNR, and their hybrids with bwGO and rGOSH, according to Equations (1)–(5) in Materials and Methods section. Figure 5: UV-VIS spectra of the different nanocomposite dispersions, before and after the two centrifugation steps for (**a**) AuNS (wine), (**b**) bwGO@AuNS (red), (**c**) rGOSH@AuNS (orange), (**d**) AuNR (cyan), (**e**) bwGO@AuNR (light blue), (**f**) rGOSH@AuNR (navy). The spectra in Figure 5 demonstrate: (1) The efficiency of the methodology, which collected most of the plasmonic particles in the pellets, while the supernatants were optically transparent; (2) the general stability of the prepared particles upon aggregation, with minor shifts (bathochromic for AuNS and GO@AuNS, hypsochromic for AuNR and GO@AuNR, respectively) in the plasmon wavelengths measured for most of the tested conditions. Figure 6 illustrates the morphology of GO@AuNP nanocomposites, with spherical and rod-like nanoparticles detected most preferentially at the basal plane and at the edge of the nanosheets, respectively. The cross-sectional view of the typical AFM height images indicated a length over the longitudinal and transversal axes of AuNRs, respectively, of about 70 and 28 nm, while for AuNS a diameter of about 30 nm was measured, according to the electronic spectroscopy analyses. Moreover, substrate-dependent effects in the size and circularity of the nanoparticles grown in the presence of bwGO or rGOSH were disclosed by the quantitative study of the AFM height micrographs, as estimated by the values of particle average height, z, and aspect ratio, r, respectively (Table 4). In particular, an opposite size change trend but a similar increase in circularity were displayed both by bwGO@AuNS (Figure 6b) and rGOSH@AuNS (Figure 6c), compared to the citrate-capped gold nanospheres (Figure 6a). On the other hand, a bimodal distribution of circularity was found for AuNRs with both rod-like and spherical-grown seeds (Figure 6d), which was maintained in bwGO@AuNR (Figure 6e) but not on rGOSH@AuNR (Figure 6f), where mostly spherical nanoparticles were detected. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **z (nm)** & **r** \\ \hline
**AuNS** & \(14\pm 2\) & \(0.75\pm 0.02\) \\
**bwGO@AuNS** & \(12\pm 2\) & \(0.98\pm 0.02\) \\
**rGOH@AuNS** & \(15\pm 2\) & \(0.88\pm 0.02\) \\
**AuNR** & \(6\pm 2\) & \(0.60\pm 0.02\) \\  & \(6\pm 2\) & \(0.88\pm 0.02\) \\
**bwGO@AuNR** & \(8\pm 2\) & \(0.60\pm 0.02\) \\
**rGOSH@AuNR** & \(7\pm 2\) & \(0.84\pm 0.02\) \\
**rGOSH@AuNR** & \(7\pm 2\) & \(0.98\pm 0.02\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average height (z, in nm) and aspect ratio (r) values calculated from the atomic force microscopy (AFM) micrographs images recorded in AC mode in air for the different samples. Figure 6: AFM micrographs of amplitude (top panels), height (middle panels, z scale = 15 nm), and section analysis curves (bottom panels) of: (**a**) AuNS, (**b**) bwGO@AuNS, (**c**) rGOSH@AuNS, (**d**) AuNR, (**e**) bwGO@AuNR, (**f**) rGOSH@AuNR. Arrows point to surfactant residues adsorbed on the mica substrates. To note, residues of the CTAB used to assist the seed-mediated growth of the nanorods were clearly detected, especially for the sample of AuNR (see arrows in Figure 6d), since the cationic surfactant strongly interacted. The infrared spectra analyses also confirmed the strong association of the gold nanoparticles to the GO substrates in the GO@AuNP nanocomposites (Figure 7). As to the hybrids of GO and AuNS, the experimental spectra in Figure 7a disclose significant shifts in the bands associated to the asymmetric and symmetric stretching modes of the citrate carboxylate (-COO-) moieties, interpreted as due to the unidentate covalent bond formation between oxygen atom of citrate -COO- moieties and gold atoms on the nanoparticle surface [95].