## 3 Results and Discussion
Figure 1: Absorption spectra of gold nanoparticles (AuNPs) fabricated using (**a**) green method and (**b**) standard (conventional) method with sodium citrate as the reducing agent. Spectra I, II, and III indicate the as-prepared AuNPs dissolved in a water solution, the water solution after centrifugation, and the absorption spectrum of redispersed AuNPs in the water solution, respectively. AuNPs prepared with sodium citrate exhibited no redispersion ability, whereas AuNPs prepared with the apple extract exhibited dispersion ability where spectra I and III overlap (**a**). A hydrothermal process was further conducted to heat the pectin-capped AuNPs in a Teflon-lined autoclave. Carbonization under a low-temperature (120 \({}^{\circ}\)C) or a high-temperature (180 \({}^{\circ}\)C) protocol was adopted to fabricate carbon dots with partial crystallinity and unique photoluminescence. As displayed in Figure 4, the LSPR absorption bands observed for the pectin-capped AuNPs remained nearly unchanged after the hydrothermal treatment process conducted under the two protocols. Moreover, the absorption maximum was centered at approximately 530 nm, suggesting that the size and morphology of nanoclusters remained unaltered after heating in the autoclave. Figure 5a-c presents the TEM images of the AuNPs, indicating that most of the hybrid nanoclusters exhibited spherical morphologies after the hydrothermal treatment process; however, the particle size distribution of the AuNPs, calculated by manually measuring 100 AuNPs, decreased slightly at elevated temperatures (Figure 5d). Notably, all AuNPs were embedded within an irregular carbon nanosheet, confirming that the hybrid nanoclusters comprised two components: an organic component and AuNPs. The high thermal stability of the pectin-capped AuNPs may be attributable to the formation of a rigid  
Figure 3: SEM image and corresponding elemental analysis, EDS, of pectin-capped AuNPs on a silicon substrate. Figure 2: (a) Time-dependent absorbance of AuNPs in the water solution under 80 \({}^{\circ}\)C and (b) TGA analysis of pectin-capped AuNPs. carbon-based network against thermal-induced aggregation [27]. Figure 6a depicts high-resolution TEM images of the pectin-capped AuNPs, revealing organic (carbon) and inorganic (AuNPs) components and a clear boundary between the crystalline AuNPs and amorphous carbon. Moreover, the darker spots against the carbon background in these images (Figure 6a) represent the crystal lattice of AuNPs with a size distribution of \(<20\) nm. We also subjected the AuNPs to electron energy-loss spectroscopy (EELS). Figure 6b presents the EELS results, confirming the presence of carbon and gold elements. Overall, the TEM results reveal that organic extracts from red apples were wrapped around the nanoparticles rather than being deposited as a thin layer on the particle surface. We speculate that this carbon-based feature can render AuNPs extremely stable under conditions of temperature fluctuations. The fabricated hybrid materials composed of pectin extracts and metal nanoparticles have a potential for biological applications in which toxic and oxidant issues may hinder the practical use of metal nanoparticles [33]. Figure 4: Absorption spectra of pectin-capped AuNPs before and after the hydrothermal process at different temperatures. Inserts are images of pectin-capped AuNPs under different conditions. Figure 5: TEM images of (**a**) as-prepared AuNPs; (**b**) autoclaved pectin-capped AuNPs at 120 \({}^{\circ}\)C, and (**c**) autoclaved pectin-capped AuNPs at 180 \({}^{\circ}\)C; (**d**) Particle size distribution of as-prepared AuNPs, and pectin-capped AuNPs under hydrothermal process at different temperatures. Apple extracts with antioxidant and anti-inflammatory effects may be possibly responsible for the potential cancer-preventive candidates [34].