## 3 Results
### UV-Vis Spectral Analysis of EGCG-Modified Magnetic Beads2  
To investigate the optical properties and confirm the surface modification of the magnetic beads with EGCG, UV-Vis absorption spectroscopy was performed on T-Fe\({}_{3}\)O\({}_{4}\), pure EGCG, and the two types of EGCG-coated magnetic beads (EGCG@T beads_1 and EGCG@T beads_2) (Figure 3). The T-Fe\({}_{3}\)O\({}_{4}\) sample exhibited a broad absorption band in the 550-900 nm region, which is characteristic of iron oxide nanoparticles. This peak was retained in both EGCG@T beads_1 and EGCG@T beads_2, indicating that the core magnetic properties of Fe\({}_{3}\)O\({}_{4}\) were maintained after EGCG surface modification. Figure 2: Results of chemical composition and molecular structure analyses using FT-IR. **(A)** Overall analysis results for T-Fe\({}_{3}\)O\({}_{4}\), EGCG, EGCG@T Beads_1, and EGCG@T Beads_2; **(B)** magnification of the red dashed box region. Pure EGCG showed a sharp and intense absorption peak near 270-280 nm, corresponding to the \(\pi\)-\(\pi^{*}\) transition of aromatic rings in its polyphenic structure. This prominent peak was also observed in both EGCG@T bead samples, confirming the presence of EGCG molecules on the bead surface. Notably, EGCG@T beads_1 showed a relatively higher absorption intensity at \(\sim\)280 nm compared to EGCG@T beads_2, suggesting a denser or more homogeneous EGCG coating. Meanwhile, EGCG@T beads_2 displayed enhanced absorbance in the visible region (600-900 nm), likely due to changes in the nanoparticle aggregation state or surface plasmon interactions after modification. These UV-Vis spectral features collectively support the successful conjugation of EGCG onto the magnetic beads and the retention of optical properties from both EGCG and T-Fe\({}_{3}\)O\({}_{4}\) components. The T-Fe\({}_{3}\)O\({}_{4}\), EGCG, and EGCG@T complexes were analyzed using TG-DTA at NICEM. It was confirmed that the peak in EGCG@T bead spectra was due to the 100 nm peak of EGCG. In addition, it was confirmed that the EGCG@T beads' peaks were shifted compared to the T-Fe\({}_{3}\)O\({}_{4}\) peak due to the 280 nm peak of EGCG. Therefore, it was confirmed once again that T-Fe\({}_{3}\)O\({}_{4}\) and EGCG were present in a complex form. Effect of EGCG Concentration on Surface Morphology, Elemental Composition, and Colloidal Properties of Magnetic Beads  
To evaluate the influence of the EGCG concentration on the bead surface characteristics and physicochemical properties, scanning electron microscopy (SEM), elemental analysis, zeta potential, and dynamic light scattering (DLS) measurements were performed under three conditions: 0.1\(\times\), 1\(\times\), and 10\(\times\) EGCG treatment (Figure 4). Figure 3: Results of molecular structure analysis using TG-DTA. It is difficult to distinguish between the different concentrations in the SEM image, but it can be confirmed that the overall shape showed a globular geometry for the nanoparticle beads. While specific comparative studies between beads with spherical and other nanoparticle shapes (like cubic or rod-shaped) in the context of exosome isolation are limited, the general consensus in the literature suggests that spherical magnetic beads offer superior performance due to their uniform magnetic field distribution and improved colloidal stability. These characteristics are advantageous for reproducible bead recovery and consistent exosome isolation performance. The elemental analysis showed a clear decrease in carbon content (C) with decreasing EGCG concentration, confirming successful coating of the surface. At the atomic level, the C content peaked at 66.53% in the 0.1\(\times\) condition and gradually decreased with higher concentrations of beads (61.86% at 1\(\times\) and 31.14% at 10\(\times\)). Meanwhile, the Fe and O signals shifted accordingly, reflecting changes in the surface exposure of the magnetic core.