## 3 Results and Discussion
### Experimental Results
The current study mainly focused on the shift of LSPR of GNR and aggregations and although DDA can underestimate the broadening of the absorption spectra, the method has been proved sufficiently accurate by previous research studies [63, 64, 65, 24], for predicting the wavelength of longitudinal surface plasmonic resonance (LSPR). The light source applied in this work had a bandpass filter that only allowed light from 770 nm to 790 nm wavelength be transmitted, thus underestimated broadening from DDA would not significantly affect result of the temperature increase. Table 2 shows the results of absorbance and temperature increase in the solutions of the optical and thermal experiments obtained at 780 nm wavelength. The averaged values of local temperature increases were recorded after a 300 s exposure to the filtered light source. The averaged results were obtained after three measurements of each sample. The measured temperature change of Sample A (pure water) was 0.05 K. Note that the Hydrosun(r) 750 (Mullheim, Germany) light source contains a water filter, so the remaining spectrum has minimal energy left for pure water absorption. As a baseline, however, 0.05 K has been deducted from the measured temperature increase of Samples D, E and F in Table 2. A correlation with the absorbed intensity measured in the optical experiment can be seen in Table 2. When the volume fraction of GNRs in the samples changed from \(0.93\times 10^{-6}\)  
Figure 5: GNR solutions of various concentrations (refer to Table 1). **(A)** 0 GNRs/mL, **(B)** 1.04 \(\times\) 10\({}^{11}\) GNRs/mL, **(C)** 2.08 \(\times\) 10\({}^{11}\) GNRs/mL, **(D)** 3.12 \(\times\) 10\({}^{11}\) GNRs/mL, **(E)** 4.16 \(\times\) 10\({}^{11}\) GNRs/mL and **(F)** 5.20 \(\times\) 10\({}^{11}\) GNRs/mL. Figure 6: Measured absorbance of GNR solutions with various concentrations (see Table 1). to \(1.24\times 10^{-6}\), both the absorption and heat generation showed obvious increases. In Sample E the absorbance increased by 12% causing temperature increase 0.25 K higher than in the solution with lower concentration, whereas in Sample F the absorbance increased by 16% causing a temperature increase 0.1 K higher than in Sample E. One possible reason of the insignificant increase of temperature in Sample F was that there was more light scattered by Sample F than by Sample E. The results of the optical and thermal experiments confirm that the heat generated in the solutions depends on the light energy, which could be potentially absorbed by the GNRs. As can be seen from Table 2, in Sample E the temperature increase was around 0.4 K, which was only 0.1 K lower than in the reference solution (Sample F). The GNRs solution with a volume fraction of \(1.24\times 10^{-6}\) was, therefore, the most appropriate solution in this case, because it could generate a similar amount of heat as the reference solution with less material, which was beneficial in terms of cost and possible toxicity. The expected temperature for hyperthermia was not reached because of the low intensity of the lamp utilized in the experiment. An alternative light source, such as a continuous wave (CW) NIR laser with adjustable intensity, can be applied to ensure a higher temperature increase, without exceeding the therapeutic intensity limit.