nanoparticles - Magnetic Nanoparticles

Definition:
- Magnetic nanoparticles (MNPs) are a class of nanoparticles characterized by exhibiting superparamagnetism and responding to external magnetic fields.
Characteristics of Superparamagnetic Materials:
  - Comprise small clusters of magnetic domains that do not align in the absence of a magnetic field.
  - Under external magnetic influence, the clusters reorient to align with the magnetic field, rendering the material magnetic.
  - Effective at near room temperature and when dimensions are reduced to between 1-10 nm.

Enhanced properties compared to ferromagnetic and paramagnetic particles:
  - Easy resuspension in solutions.
  - Larger surface area for interactions.
  - Slow sedimentation rates, leading to uniform distribution within suspensions.
Comparison with Other Magnetic Materials:
  - Ferromagnetic Particles: Permanently possess a mean magnetic moment.
  - Paramagnetic Particles: Magnetizable in an external magnetic field but remain nonmagnetic otherwise.
  - Superparamagnetic Particles: Similar to paramagnetic particles, behave like small permanent magnets when subjected to a magnetic field, forming aggregates due to magnetic interactions.

Common Materials Used for Manufacturing MNPs:
  - Magnetite (Fe₃O₄): Highly magnetic iron oxide and one of the three prevalent natural iron oxides.
  - Maghemite (γ-Fe₂O₃): Similar to ferric oxide with notable remanent magnetism.
  - Greigite (Fe₃S₄) and metals such as Iron and Nickel.
  - Ferrites: Comprised of iron oxide combined chemically with other metallic components, exhibiting ferrimagnetism and electrical nonconductivity.
Magnetization Feature:
- Magnetite's magnetic moment enhances MRI signals by increasing nearby proton signal intensity.
- MNPs can be remotely manipulated by external magnetic forces, allowing for innovative applications.

Importance of Functionalization:
- High concentrations of iron ions can be toxic in vivo. Therefore, iron oxide nanoparticles (IONPs) need modification for safe biomedical use.
- Functionalization involves coating particles to enhance biocompatibility and solubility in aqueous environments.
Methods of Functionalization:
- PEGylation: Attachment of polyethylene glycol (PEG) chains to nanoparticles.
- Utilization of bioactive molecules that allow targeting for MRI, cellular imaging, and drug delivery systems.

Historical Context:
- First MRI images produced in 1973; first human body scan occurred on July 3rd, 1977.
- 1979 Nobel Prize awarded to Hounsfield and Cormac for developments contributing to CT scans.
Principles of MRI:
  1. Protons in the body are detected.
  2. In a strong magnetic field, protons align with this magnetic field.
  3. Radio frequency (RF) pulses turn protons 90 or 180 degrees.
  4. Upon RF removal, protons realign, releasing electromagnetic energy that is detected to form images.
Explanation of MRI Image Formation:
- Protons resonate at specific frequencies, and after excitation, relax while emitting energy (electromagnetic radiation).
- Different tissues have varying concentrations of protons, aiding in tissue differentiation based on energy emission.
Types of MRI Images:
  - T1-weighted Images: Bright appearance of fat, dark appearance of fluids, used to analyze normal soft-tissue anatomy.
  - T2-weighted Images: Bright fluids and dark fat; optimal for visualizing tumors and inflammation.
  - The interplay of T1 and T2 images enhances the characterization of abnormalities.

Inception and Development:
- First introduced in 2005 by Gleich and Weizenecker at Philips Research Hamburg, published in Nature.
Features of MPI:
  - Utilizes superparamagnetic iron oxide (SPIO) nanofluid responsive to weak magnetic fields for image generation.
  - Key Advantages:
      - High spatial resolution (~0.4 mm)
      - Rapid imaging results (~20 ms)
      - Absence of radiation and iodine in the imaging process.
      - Improved contrast due to minimal background noise.