Nanoparticles are particles of matter that range in size from 1 to 100 nanometres (nm) in diameter¹³. They are larger than atoms and simple molecules, but much smaller than the width of a human hair⁴. Due to their small size, nanoparticles often have unique physical and chemical properties compared to their larger material counterparts³.

Nanoparticles can be found naturally in the environment, but they can also be manufactured for use in various fields, including medicine, engineering, catalysis, and environmental remediation². For instance, in medicine, nanoparticles are used in drug delivery systems to target specific cells or tissues, thereby reducing side effects and improving the efficacy of treatments².

The properties of nanoparticles can be significantly influenced by their surface layer, as a large fraction of the nanoparticle’s material lies within a few atomic diameters of its surface¹. This effect is particularly strong for nanoparticles dispersed in a medium of different composition, as the interactions between the two materials at their interface also become significant¹.

It’s important to note that nanoparticles are so small that they cannot be seen with ordinary optical microscopes and require the use of electron microscopes or microscopes with laser¹. Dispersions of nanoparticles in transparent media can be transparent, whereas suspensions of larger particles usually scatter some or all visible light incident on them¹.