# Copper- and Iron-Based Nanoflowers in Cancer Theranostics
## 2 Synthesis Methods for Copper- and Iron-Based Nanoflowers
### Hydrothermal Method  
Hydrothermal synthesis involves the reaction of a solid substance with an aqueous solution at an elevated temperature and pressure within a reaction vessel, resulting in the deposition of fine particles [67]. This method is solution-based, with water serving as the solvent, hence the term \"hydrothermal\" [68]. This process takes place in a steel pressure vessel called an autoclave, where temperature and pressure are carefully regulated. The temperature is raised above the boiling point of water until vapor saturation is reached [69]. The hydrothermal method has played a crucial role in modern science and technology due to its advantages, including uniform precipitation, low cost, scalability, and the production  
Figure 4: Illustration of the sol–gel process for synthesizing nanomaterials. Reproduced with permission from Ref. [66]. of a pure final product [34]. Furthermore, the hydrothermal technique encompasses various applications, including hydrothermal synthesis, treatment, crystal growth, organic waste treatment, and the preparation of functional ceramic powders [70]. The hydrothermal method, widely used for nanoparticle synthesis, facilitates rapid nucleation and growth at various temperature and pressure levels [42]. This eco-friendly, cost-effective, and versatile approach yields pure nanoparticles with a specific morphology [71] without needing organic solvents or additional post-synthesis treatments [72; 73]. However, its limitations include an inability to produce particles smaller than 10 nm and slow reaction kinetics at high temperatures. Despite its limitations, the hydrothermal method provides excellent magnetic controllability and superior control over particle size, shape, and dispersion compared to alternative techniques [74]. [PERSON] and colleagues created a nanoflower-based therapeutic using iron ions, thioguanine (TG), and tetracarboxylic porphyrin (TCPP) through a one-step hydrothermal process for chemo/chemodynamic/photodynamic cancer therapy. The resulting nanoflowers, featuring a low-density Fe\({}_{2}\)O\({}_{3}\) core and a shell of iron complexes (Fe-TG and Fe-TCPP), show strong tumor site accumulation, favorable degradability within the tumor microenvironment (TME), the effective inhibition of tumor growth and metastasis, and the ability to boost host antitumor immunity [75]. In the acidic tumor microenvironment, the nanoflowers degrade gradually after internalization, enabling targeted drug release and catalytic reactions specifically at tumor sites. After treatment, iron ions are excreted via renal clearance. This multimodal therapy enhances antitumor immunity effectively without added toxicity. The degradable and easily manufactured nanomedicine shows strong potential for clinical precision oncology [75]. [PERSON] et al., synthesized hollow spherical and nanoflower Fe\({}_{3}\)O\({}_{4}\) structures to improve magnetothermal conversion efficiency. Using the hydrothermal method, they achieved nanoparticles with a uniform size and shape distribution. The Fe\({}_{3}\)O\({}_{4}\) nanoflowers exhibited a significantly higher intrinsic loss power (ILP) of 6.52, 1.83 times greater than that of hollow spherical Fe\({}_{3}\)O\({}_{4}\) (3.55), demonstrating their strong potential for magnetic hyperthermia therapy (MHT) in cancer treatment [76]. Intrinsic loss power (ILP) measures a material's inherent ability to convert magnetic energy into heat in an alternating magnetic field, highlighting its intrinsic properties and efficiency. Because ILP is unaffected by external magnetic field parameters, it allows for unbiased comparisons across various magnetic nanomaterials, facilitating the identification of optimal candidates for magnetothermal applications [76]. The ILP is expressed as  
\[ILP=\frac{SAR}{f\,H^{2}}\]  
where the \(f\) represents the frequency of the alternating magnetic field, and \(H\) is its amplitude. The synthesized Fe\({}_{3}\)O\({}_{4}\)-SC nanoflower nanoparticles demonstrated high ILP values compared to other magnetic materials.