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Global Translational Medicine SPION for cancer theranostics

Figure 3. Various surface functionalizations of super paramagnetic iron oxide nanoparticles. Reproduced from Gambhir et al. Copyright 2022 Authors.
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Abbreviations: PEG: polyethylene glycol; PVA: Polyvinyl alcohol; PVP: Polyvinylpyrrolidone.
3.2. Stabilization of SPIONs within non-polymeric ion leakage, which could otherwise cause oxidative stress.
coating The rigid silica shell enhances stability, preventing particle
SPIONs stabilized by polymers are often unstable in agglomeration and ensuring dispersibility in different
air and can be easily affected by acidic solutions, which pH environments, such as the acidic conditions found in
negatively impact their magnetic properties. As a result, tumor microenvironments. However, a major limitation of
non-polymeric or inorganic coatings are frequently this approach is the difficulty in achieving a uniform silica
preferred over polymeric coatings to achieve superior shell thickness. Inconsistent coating thickness can result
colloidal stability, enhanced functionality, and improved in irregular magnetic fields, potentially leading to uneven
biocompatibility. This method involves creating a protective heating in MHT applications.
layer of inorganic material around the SPION core, which The integration of SPIONs, either coated with Au
helps prevent aggregation, reduce surface oxidation, and NPs or decorated with Au shell, offers several benefits,
provides a flexible platform for further functionalization. including enhanced stability, improved biocompatibility,
Among the various non-polymeric coating materials, silica and the ability to functionalize the surface with a variety
and Au are the most widely studied and utilized due to of biomolecules or ligands, making them suitable for
their unique advantages and proven effectiveness. targeted drug delivery and bio-imaging applications.
Silica coating on SPIONs is a well-established These nanohybrid systems combine the unique optical and
technique that enhances their stability, functionality, chemical characteristics of Au with the magnetic properties
and biocompatibility. 27,28 The silica layer protects against of SPIONs. Au coating also improves MRI contrast and
oxidation, prevents particle aggregation and provides a provides surface plasmon resonance for optical detection,
chemically versatile surface for further modifications. In enabling dual-mode imaging. The synergistic effects of
addition, due to its hydrophilic nature, silica facilitates the these systems allow for combined MHT and photothermal
binding of various biological ligands. The silica coating therapy. Figure 4 shows spike-like Au shell crystals coated
stabilizes SPIONs by shielding magnetic dipole interactions, onto the surface of SPIONs, with the planes of both Fe O
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while its negative charge enhances coulombic repulsion and Au crystals visible in the composite’s powder X-ray
between particles, improving colloidal stability. 23,29 Silica diffraction pattern. The composite material was used for
coatings also improve cellular uptake and reduce toxicity in vivo MRI/computed tomography imaging of tumors, as
by creating a strong protective layer that prevents iron shown in Figure 5.

Volume 4 Issue 2 (2025) 37 doi: 10.36922/gtm.8464