# Research Progress of Polysaccharide-Gold Nanocomplexes in Drug Delivery
## 3 Preparation of polysaccharide Gold Nanoparticles
Additionally, considerable effort has been dedicated to understanding the nucleation mechanism and gold nanoscale growth [68]. [PERSON] et al. [69] pointed out that the hydroxyl group in the citrate is in the \(\alpha\)-position with a carboxylate, which allows the formation of a cyclic pentameric complex in the construction of intermediates, i.e., cyclic five-membered complexes, in the rate-determining step [69]. The Brust-Schiffrin (BBS) method is a highly effective technique for synthesizing thiol-functionalized AuNPs, known for their stability. The BBS method involves the transfer of AuCl\({}_{4}\) from the water phase to toluene phase, reducing Au(iii) to Au metal and stabilizing the generated AuNPs. The AuNPs synthesized by this method usually have a small size (2-6 nm) and narrow size distribution, and the obtained AuNPs can be easily functionalized and modified by subsequent ligand exchange, while it can synthesize many AuNPs [70]. Seed-mediated synthesis strategies, in which small gold nanoparticle precursors are added to a growth solution to initiate heterogeneous nucleation, are among the most prevalent, simple, and productive methodologies for generating well-defined colloidal anisotropic nanostructures [71]. Biosynthesis of AuNPs is considered a safe, dynamic, and energy-efficient method (Figure 4). Compared to other methods, AuNPs produced through biological means exhibit enhanced stability. This stability is attributed to the presence of metabolites, including proteins, fatty acids, sugars, enzymes, and phenolic compounds, produced by various organisms. These metabolites have a dual role in both the formation of AuNPs and the maintenance of their stability. Cyanobacteria, for instance, can synthesize AuNPs both intracellular and extracellularly. It is postulated that the reduction of Au ions by cyanobacteria during biosynthesis leads to the formation of AuNPs. Moreover, extensive studies have demonstrated that the AuNPs produced by cyanobacteria do not exhibit toxicity towards normal and cancerous human cells [49; 72; 73]. CAO extracted from red algae has a dual role as a reducing and stabilizing agent and can be used to synthesize AuNPs. Carrageenan oligosaccharidesacharide (CAO) reduced Au3+ions and capped gold nanoparticles (AuNPs) and, subsequently, the cytotoxicity of CAO-AuNPs on cancer cells (HCT-116 cells and MDA-MB-231 cells) (Figure 4A). This study provides a reference for green preparation of AuNPs from marine carbohydrates [74]. Figure 3: Synthesis of gold nanoparticles. (**A**): Turkevich–Frens method. (**B**): UV synthesis of gold nanoparticles. (**C**): Ultrasonic, laser ablation, and plant extract-based AuNPs. Reproduced with permission from Ref. [64]. Fungi contain enzymes and proteins as reducing agents, so they can always be used to synthesize metal nanoparticles from their salts, but care needs to be taken with their pathogenicity in experiments. These AuNPs can be synthesized directly on the surface of mycelium when fungus is present [18]. [PERSON] et al. successfully biosynthesisized gold nanoparticles (AuNPs) and platinum nanoparticles (PtNPs) using yeast microcapsules. These nanoparticles were employed to stimulate the immune response and improve the efficacy of antitumor treatment. This approach was supplemented with chemodynamic therapy (CDT) and photothermal therapy (PTT), leading to a synergistic effect. Nevertheless, the therapeutic impact and range of tumor treatment could be further improved, and this experimental protocol requires further optimization [77]. A wide range of gold nanomaterials with varying sizes and shapes, such as gold nanospheres, gold nanorods (AuNRs), gold nanoshells, gold nanocages, gold nanoclters (AuNCs), and nanostars, have been fabricated [78]. Different morphologies dictate distinct properties, and AuNPs with anisotropic shapes (e.g., AuNRs and gold nanostra) or hollow structures (e.g., gold nanoshells and gold nanocages) can exhibit LSPR peaks in the near-infrared (NIR) region [79].