Nanocomposite capsules containing magnetite nanoparticles (MNPs) are promising multifunctional drug delivery systems for various biomedical applications. The presence of MNPs allows one to visualize these capsules via magnetic resonance imaging (MRI) and optoacoustic (photoacoustic) imaging. Moreover, we can ensure precise navigation and remote release via a magnetic field gradient and alternating magnetic fields, respectively. Magnetic dipole-dipole interaction between single capsules is important when a magnetic field is applied, and it is determined by a magnetic moment of each individual capsule. However, there is a lack of experimental data on the magnetic moment of a single capsule. Physical properties of capsules vary due to the change in the volume fraction of MNPs, as well as the capsule shell architecture. Therefore, two types of submicron capsules with different amounts of MNPs were synthesized. The first type of capsules was prepared by freezing-induced loading and layer-by-layer (LbL) assembly. The amount of MNPs varied by the number of freezing-induced loading cycles: two, four, and six. The second type of capsules is a nanocomposite shell formed using the LbL assembly of the oppositely charged polyelectrolytes and MNPs. Structural properties of both types of submicron capsules and MNPs were studied using transmission electron microscopy. Magnetic moments of nanocomposite shells placed in an external magnetic field were directly measured by optical tweezers and calculated based on vibrating-sample magnetometer measurements of the water suspension of nanocomposite shells. The magnetic moment of an individual shell depends on the amount of MNPs and increases as the number of MNPs per shell grows. Magnetic coupling parameters and the specific absorption rate were calculated. The obtained results can be applied while preparing drug carrier systems sensitive to alternating magnetic fields and navigated by gradient magnetic fields. They can also be taken into account in device development for navigating drug delivery systems and for the treatment based on alternating magnetic field-induced hyperthermia.
- freezing-induced loading
- layer-by-layer assembly
- magnetic moment of a single capsule
- magnetite nanoparticles
- optical tweezers
- specific absorption rate
- vibrating-sample magnetometer magnetic measurements