# Theranostic Nanoplatforms of Thiolated Reduced Graphene Oxide Nanosheets and Gold Nanoparticles
## 3 Results and Discussions
As to the calculated spectrum of rGOSH, an absorption peak of the \(\pi\)\(\rightarrow\)\(\pi^{\bullet}\) transitions was found at 250 nm, but again no significant spectral evidence of n\(\rightarrow\)\(\pi^{\bullet}\) transitions. Table 1, which gives the molar extinction coefficients at the peak and shoulder wavelengths' positions as estimated from the experimental spectra and calculated by the computational method, confirms the qualitative trend discussed above. Thermogravirntic studies confirmed the substantial structural modification of bwGO and rGOSH compared to the pristine GO. Indeed, the TGA curves reported in Figure 2 show different ranges of temperature and weight loss in the typical three steps, namely: (1) the low-temperature region (first step, from 50 to 110 \({}^{\circ}\)C), corresponding to the loss of physiosorbed water; (2) the intermediate-temperature interval (second step, from 110 to 350 \({}^{\circ}\)C), due to the loss of the unstable oxygen moieties (i.e., carboxylic groups); (3) the high-temperature region (third step, above 360 \({}^{\circ}\)C and up to 800 \({}^{\circ}\)C), assigned to degradation of the most stable functionalities (such as residual oxygenated groups and thiolated moieties) (see the quantitative analysis in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{2}{c}{**Experimental**} & \multicolumn{2}{c}{**Theoretical**} \\
**Sample** & \(\varepsilon_{\text{peak}}\) (\(\pi\)\(\rightarrow\)\(\pi^{\bullet}\)) & \(\varepsilon_{\text{shoulder}}\) (n\(\rightarrow\)\(\pi^{\bullet}\)) & \(\varepsilon_{\text{peak}}\) (\(\pi\)\(\rightarrow\)\(\pi^{\bullet}\)) & \(\varepsilon_{\text{shoulder}}\) (n\(\rightarrow\)\(\pi^{\bullet}\)) \\  & **(mg\({}^{-1}\) mL cm\({}^{-1}\))** & **(mg\({}^{-1}\) mL cm\({}^{-1}\))** & **(mg\({}^{-1}\) mL cm\({}^{-1}\))** & **(mg\({}^{-1}\) mL cm\({}^{-1}\))** \\ \hline arGO & 71.7 & 37.0 & - & - \\ bwGO & 24.5 & 18.2 & 7.1 & 5.1 \\ rGO-SH & 47.0 & - & 6.7 & - \\ \hline \end{tabular}
\end{table} 
Table 1: Calculated molar extinction coefficients from the experimental UV-visible spectra of as-received GO (\(140\times 10^{-3}\) mg/mL in water), base-washed GO (\(20\times 10^{-3}\) mg/mL in water), and thiolated reduced GO (\(10\times 10^{-3}\) mg/mL in DMSO) and from the computational analysis. The TGA curve of pristine GO exhibited a loss of physiosorbed water corresponding to 4.2% of weight loss. The structural modification expected in GO due to the base-washing procedure was confirmed by the higher release of physiosorbed water (7.6% weight loss during the first step), which suggested a weaker interaction of the water molecules on the bwGO (more hydrophobic) purely driven by hydrogen bonds and hence a dominant role of the attractive Van der Waals dispersive interactions than arGO. Moreover, the efficient stripping of OD can be ruled out by the lower weight loss during the second step (about 22.8% and 44.5% for bwGO and arGO, respectively). As to the third degradation step, it disclosed comparable weight losses both in arGO (10.7%) and bwGO (11.6%). To note, the first step of the TGA curve for rGOSH exhibited the lowest weight loss in the adsorbed water content ('only' 2.9% desorbed mass), thus evidencing a completely different binding mode of the water molecules onto the reduced GO in comparison with arGO and bwGO samples. Also, as expected by the reduction that occurred upon the hydrobromic treatment of GO during the one-pot synthesis of thiolated GO, the second degradation step in the TGA curve for rGOSH sample was barely visible (7.6%). On the other hand, because of the presence of the sulfhydryl groups onto the reduced GO sheets, rGOSH exhibited the highest weight loss in the third degradation step (51.0%, i.e., considerably higher than the corresponding weight loss measured for arGO and bwGO), leaving a residue of 34.5%. The structural changes of bwGO and rGOSH in the comparison with arGO were confirmed by infrared spectroscopy analyses (Figure 3).