# Preparation and Characterization of Gold Nanorods Coated with Gellan Gum and Lipoic Acid
## 3 Results and Discussion
### Preparation and Characterization of Coated AuNRs
Finally, with the subsequent coating by gellan gum, a reversal of the sign of the Zeta potential was registered, reaching the maximum value for AuNRs/GG-LA. The data collected indicate that the starting nanorods have been successfully coated. To evaluate the hyperthermia capabilities of gold nanorods after coating, the temperature variations of AuNRs/LA, AuNRs/LA,GG, and AuNRs/GG-LA dispersions were recorded during laser (810 nm) treatment. The study examined 3 different gold concentrations of nanosystems (10, 20, 35 \(\upmu\)g\(\cdot\)mL\({}^{-1}\)) setting the laser power of \(3.5\times 10^{-3}\), \(7\times 10^{-3}\), and \(14\times 10^{-3}\) W/mm\({}^{3}\), in order to analyze the thermal behavior as a function of the irradiation time, the gold concentration, and the energy supplied (Figure 5). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Size (nm)** & **PDI** & **Zeta Potential (mV)** \\ \hline CTAB-AuNRs & 61.1 \(\pm\) 26 & 0.55 & \(+\)41 \(\pm\) 12.1 \\ AuNRs/LA & 97.5 \(\pm\) 34 & 0.64 & \(+\)19.5 \(\pm\) 6.76 \\ AuNRs/LA,GG & 146.7 \(\pm\) 12 & 0.50 & \(-\)17.1 \(\pm\) 4.96 \\ AuNRs/GG-LA & 173.0 \(\pm\) 18 & 0.47 & \(-\)25.6 \(\pm\) 5.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dynamic light scattering measurements. Hydrodynamic diameters (numeric), polydispersity index (PDI) and \(\zeta\) potentials of hexadecyltrimethylammonium bromide (CTAB)-AuNRs, AuNRs/LA, AuNRs/LA,GG, and AuNRs/GG-LA. The hyperthermia profiles of AuNRs/LA and AuNRs/LA,GG turned out to be quite similar under the same concentration and set power. AuNRs/GG-LA samples, although able to reach temperatures suitable for cancer PTT (powers \(\geq 7\times 10^{-3}\) W/mm\({}^{3}\)), registered a slightly lower ability to increase the temperature of the surrounding medium. This finding could be explained by the presence of GG-LA, potentially capable of assuming a less deployed conformation compared to the GG sodium salt, acting presumably as a shield towards laser radiation. In this case, the energy absorbed by the systems would be reduced, consequently decreasing its transformation into thermal energy. It can be noted that the application of the minimum laser power (\(3.5\times 10^{-3}\) W/mm\({}^{3}\)) allowed to reach temperatures exploitable in photothermal therapy (45 and 50 \({}^{\circ}\)C, respectively) only for the highest concentrations of AuNRs/LA and AuNRs/LA,GG, in opposition to what occurs for AuNRs/GG-LA (maximum temperature reached: 37 \({}^{\circ}\)C). Analyses conducted at \(7\times 10^{-3}\) W/mm\({}^{3}\) showed optimal results for AuNRs/LA and AuNRs/LA,GG regardless of the concentration tested, while AuNRs/GG-LA displayed good efficiency only at the highest concentration. Finally, the maximum power investigated (\(14\times 10^{-3}\) W/mm\({}^{3}\)) returned exaggerated temperature values for AuNRs/LA and AuNRs/LA,GG, reaching 75 and 80 \({}^{\circ}\)C, respectively. Once again, AuNRs/GG-LA demonstrated a milder hyperthermia effect, reaching 70 \({}^{\circ}\)C at the maximum concentration analyzed and remaining in the range suitable for PTT at lower concentrations. Considering the data collected, the power of \(7\times 10^{-3}\) W/mm\({}^{3}\) appear the most suitable to obtain  
Figure 5: Time-dependent thermal rising of AuNRs/LA(left), AuNRs/LA,GG (center), and AuNRs/GG-LA (right) aqueous dispersions, at concentrations of 35, 20, and 10 \(\upmu\)g\(\cdot\)mL\({}^{-1}\), during 300 s of 810 nm laser treatment with power of \(3.5\times 10^{-3}\) (first line), \(7\times 10^{-3}\) (second line), and \(14\times 10^{-3}\) W/mm\({}^{3}\) (third line). effective treatment at the concentrations used, without incurring possible side effects due to the excessive induced thermal rise. Taking into account the previous experiment, a new hyperthermia study was performed reproducing the setting of the future cellular experiment, but in absence of cell cultures.