Nanoparticles

Definition and Size

Properties of Nanoparticles

Nanoparticles show different physical and chemical properties compared to the same material in bulk form. This is mainly due to their large surface area to volume ratio and the increased proportion of atoms on the surface.

High Reactivity: Because more atoms are exposed on the surface, nanoparticles tend to be much more reactive than bulk materials. This makes them useful in chemical reactions, especially as catalysts.

Optical Properties: Nanoparticles can interact with light in unique ways. For example, gold nanoparticles appear red or purple rather than the usual metallic yellow colour. This is due to how the particles absorb and scatter light, which changes with size.

These special properties mean nanoparticles can be used in new technologies and products that bulk materials cannot achieve.

For example, silver nanoparticles have antibacterial properties because they release silver ions more effectively than bulk silver, killing bacteria more efficiently.

Uses of Nanoparticles

Nanoparticles are used in a wide range of applications due to their unique properties:

• Medical Applications: Nanoparticles can deliver drugs directly to specific cells in the body, improving the effectiveness of treatments and reducing side effects. For example, nanoparticles can carry chemotherapy drugs straight to cancer cells.
• Catalysts: Nanoparticles act as catalysts in chemical reactions because their large surface area allows more reactant particles to interact at once. This speeds up reactions and can reduce costs in industrial processes.
• Electronics: Nanoparticles are used to make smaller, faster, and more efficient electronic devices. For example, nanoparticles are used in computer chips and display screens.
• Cosmetics: Nanoparticles are found in sunscreens and moisturisers. In sunscreens, nanoparticles of zinc oxide or titanium dioxide provide UV protection without leaving a white residue on the skin.

For example, in sunscreens, nanoparticles of titanium dioxide are small enough to be transparent but still block harmful UV rays effectively.

Risks and Safety

Despite their benefits, nanoparticles may pose risks that need careful consideration:

• Potential Toxicity: Because nanoparticles can enter cells and tissues easily, they might cause harmful effects in humans or animals. Their small size allows them to cross barriers that larger particles cannot.
• Environmental Impact: Nanoparticles released into the environment (e.g., from cosmetics or industrial waste) could affect ecosystems. Their behaviour and breakdown in soil or water are not fully understood yet.
• Need for Regulation and Testing: To ensure safety, nanoparticles must be thoroughly tested for toxicity and environmental effects before widespread use. Governments and organisations such as the FDA and EU regulatory bodies are working on regulations to manage these risks.

Example: Calculating Surface Area to Volume Ratio

Calculate the surface area to volume ratio of a cube with side length 1 cm and compare it to a cube with side length 1 nm.

Surface area of a cube = $6 \times \text{side}^2$

Volume of a cube = $\text{side}^3$

For 1 cm cube:

$\text{Surface area} = 6 \times (1 \text{ cm})^2 = 6 \text{ cm}^2$

$\text{Volume} = (1 \text{ cm})^3 = 1 \text{ cm}^3$

$\text{Surface area to volume ratio} = \frac{6}{1} = 6 \text{ cm}^{-1}$

For 1 nm cube (1 nm = $1 \times 10^{-7}$ cm):

$\text{Surface area} = 6 \times (1 \times 10^{-7} \text{ cm})^2 = 6 \times 10^{-14} \text{ cm}^2$

$\text{Volume} = (1 \times 10^{-7} \text{ cm})^3 = 1 \times 10^{-21} \text{ cm}^3$

$\text{Surface area to volume ratio} = \frac{6 \times 10^{-14}}{1 \times 10^{-21}} = 6 \times 10^{7} \text{ cm}^{-1}$

This shows the surface area to volume ratio increases dramatically as size decreases.