Magnetic Particles 

Gold particles, particularly in the form of gold nanoparticles (AuNPs), are colloidal gold structures ranging from 1 to 100 nanometers in diameter. Their nanoscale size leads to unique optical, electronic, and chemical properties that differ significantly from bulk gold, making them central to applications in sensing, medicine, catalysis, and electronics.

Technical Content

• Structure and Composition:
  • Atomic Arrangement: Gold nanoparticles consist of crystalline gold atoms arranged in face-centered cubic (fcc) structures. Their size and shape (spherical, rod-like, star-shaped, etc.) influence their physical and chemical behavior.
• Optical Properties – Surface Plasmon Resonance (SPR):
  • Localized SPR: AuNPs exhibit localized surface plasmon resonance, a collective oscillation of conduction electrons excited by incident light at specific wavelengths. SPR leads to strong absorption and scattering of light, and the resonance frequency depends on particle size, shape, dielectric environment, and inter-particle interactions.
• Synthesis and Surface Engineering:
  • Synthesis Methods: Common methods include the Turkevich method (citrate reduction of gold salts), Brust-Schiffrin method (two-phase reduction using thiols), and seed-mediated growth for anisotropic shapes.

Applications

• Sensing and Diagnostics:
  • Colorimetric Assays: SPR sensitivity to environmental changes allows AuNPs to serve as colorimetric sensors. Aggregation or binding events lead to shifts in SPR, visible as color changes.
• Medicine and Biotechnology:
  • Drug Delivery: AuNPs can be functionalized with therapeutic agents and targeting ligands for controlled drug delivery, leveraging their biocompatibility and ease of surface modification.
• Catalysis:
  • Chemical Reactions: AuNPs catalyze reactions under mild conditions, with applications in environmental remediation and chemical synthesis. Their catalytic activity is size- and support-dependent, often enhanced at edges, corners, and defect sites.

Gold nanoparticles exemplify how nanoscale dimensions drastically alter material properties. Their unique optical response via surface plasmon resonance, coupled with tunable surface chemistry and catalytic capabilities, makes them versatile tools across multiple disciplines.