Small Solutions for Greener Chemistry

Nanoparticles are generally thought of as particles that are smaller than 1μm. They can be formed of a wide range of materials, but those that are most common are metal oxides, ceramics, metals, polymers and lipids.

INORGANIC AND BIOINORGANIC NANOPARTICLES

The majority of inorganic particles have a similar fundamental structure; generally there is a central core that can be used to vary specific particle attributes such as fluorescence, optical, magnetic and electronic properties (see Figure 1, adapted from (1)).

Nanoparticles may be further modified by being coated with a protective layer to protect the particle from degradation. This layer can be functionalised so that it is able to form electrostatic or covalent bonds with biomolecules such as peptides, proteins and oligonucleotides (see Figure 1). Although the majority of nanostructures are spherical, other nanostructured morphologies such as flakes and dendritic shapes can be formulated (2).

Nanoparticles have a number of properties which can be exploited. These include very high surface area and magnetic, optical, electrical, thermal, chemical and mechanical properties. Quantum dots are nanoparticles with sizes 2-10nm, which are fluorescent and whose cores contain elements such as cadmium, zinc or selenide (see Figure 1).

They can be used for visualisation with biological applications. This is limited by the toxic effect of the metal core but often the toxicity can be ameliorated by various protective coatings. Magnetic nanoparticles are commonly produced and can be used for enhancing medical imaging, and for drug delivery when coated with organic layers for bioconjugation of drugs. Metal nanoparticles in combination with fluorescent active molecules can be used in imaging, which combines optical and magnetic methods. Metal nanoparticles can also be used for the bioseparation of nucleic acids, proteins and cells (3).

Nanoparticles are often below the critical wavelength of light and therefore their transparency can be exploited. This results in nanoparticles such as silicates being used for coatings and films. Silicate nanoparticles can also act synergistically with flame retardants due to their thermal properties. Nanosilicates are also used in composite materials to improve the mechanical strength of the material.

Finally, nanoparticles offer an extremely high surface to volume ratio, which increases with the decreasing size of the nanoparticles. This is relevant for access to surface (bio)catalysts and for sensor applications.