Nanoclusters Overview

Nanoclusters

• Nanoclusters are particles ranging in size from a few atoms to several thousand atoms.
• Nanoclusters are generally monodispersed particles that are less than 10 nm (100 Å) in diameter.
• High fraction of surface atoms gives them properties different from bulk materials.
• Different elements form different bonds and structures contributing to unique properties.

Nanocluster Properties

• EPR effect: A property of nanoclusters
• Renal clearance: A property of nanoclusters
• Biocompatibility: A property of nanoclusters
• Radiotherapy: A nanocluster application
• Photodynamic therapy: A nanocluster application
• Drug delivery: A nanocluster application
• Imaging-guided therapy: A nanocluster application
• Antimicrobial: Nanoclusters with antimicrobial activity (ROS)

Nanocluster Size and Structure

• Nanoclusters are smaller than nanoparticles.
• Geometric structures affect properties
• Electronic structures affect properties
• Size ranges from single atoms to 1nm to 5nm to 100 nm (nanoparticles)

Nanocluster Synthesis

• Made using laser vaporization technique.
• Laser focuses on metal sample causing evaporation.
• Atoms are cooled with inert gas flow.
• Atoms combine into clusters of varying sizes.
• Clusters are expanded into vacuum to cool further.
• Spectrometer measures the formed cluster.

Magic Numbers

• Electronic Magic Number: The energy needed to remove an outer electron from an atom.

• Highest ionization potential occurs in rare gases due to complete outer electron orbitals.

• Peaks in ionization potential occur for clusters with 2 and 8 atoms

• Structural Magic Number: Stability in larger clusters is determined by structure and magic number.

Theoretical Modeling of Nanoclusters

• Jellium Model: Nanocluster viewed as a large atom.
• Positive nuclear charge is uniformly distributed over a sphere, same size as cluster.
• Electron interaction with positive sphere is described as spherically symmetric
• Energy levels are calculated by Solving the Schrodinger Equation

Geometric Structures of Nanoclusters

• Bulk crystals may differ in lattice structures compared to smaller nanoclusters.
• Example: 80nm aluminum has Face-centered cubic (FCC) unit cell, while smaller nanoclusters may have different structure
• Gold nano-particles (3-5 nm) have icosahedral structure instead of bulk FCC

Other Properties and Applications

• Orbital calculations using density functional are applied, showing that icosahedral forms have the lowest energy in certain cases.
• Deviation from FCC (Face-centered cubic) structure occurs for clusters smaller than 8 nm in diameter
• Important to understand density of states in nanoclusters. Density of states represents number of possible electron energy levels within a range. Continuous density (found in large particle bulk materials) become a distinct set of energy levels in nanoclusters.
• Nanoclusters reactivity depends on size.
• Nanoparticles reactivity with oxygen can be studied using mass spectometer
• Reaction rate of iron with hydrogen is dependent on size
• High catalytic in nano-gold clusters (under 3-5nm) with icosahedral structure compared to bulk metals.
• Magnetic moments arise from electron spin and angular momentum in atoms.
• Atoms combine in nanoclusters resulting in a net magnetic moment
• Bulk properties appear in nanoclusters when the number of atoms exceeds a certain value (often 100+ for materials like copper and 1000+ for gold).

This quiz explores the fascinating world of nanoclusters, discussing their size, unique properties, and applications in various fields such as medicine and material science. Test your knowledge on concepts like the EPR effect, biocompatibility, and the sizes that define these remarkable particles.