Nanoparticles (NPs) are classed as single particles with size diameters in the nanometre range, typically less than 100 nm. In cell biology, many molecules are measured in the nanoscale range, such as proteins and DNA. It is established that NPs less than several hundred nanometres can easily enter cells (with less than 50 nm entering most cells), whereas those under 20 nm can move through the blood vessels and permeate adjacent tissue, and also cross the blood–brain barrier1, thus NPs hold great promise regarding applications in biomedicine. Aside from this advantage of ubiquitous tissue accessibility, NPs also benefit from their large surface area to volume ratio, which, alongside ease of chemical functionalization, permits attachment of a multifunctional cargo payload (such as a fluorescent moiety or cell targeting molecules), as illustrated in Figure 12.

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