Table 1.

Main forces governing the interfacial interaction between NM and biomolecule [5].

Force	origin and nature	range (nm)	Possible impact on the interface
Hydrodynamic interactions	Convective drag, shear, lift and Brownian diffusion are often hindered or enhanced at nanoscale separations between interacting interfaces	102 to 106	Increase the frequency of collisions between nanoparticles and other surfaces responsible for transport
Electrodynamic interactions	VDW interactions arising from each of the interacting materials and the intervening media	1 to 100	Universally attractive in aqueous media; substantially smaller for biological media and cells owing to high water content
Electrostatic interactions	Charged interfaces attract counter–ions and repel co–ions through Coulombic forces, giving rise to the formation of an electrostatic double layer	1 to 100	Overlapping double layers are generally repulsive as most materials acquire negative charge in aqueous media, but can be attractive for oppositely charged materials
Solvent interactions	Lyophilic materials interact favourably with solvent molecules	1 to 10	Lyophilic materials are thermodynamically stable in the solvent and do not aggregate
	Lyophobic materials interact unfavourably with solvent molecules		Lyophobic materials are spontaneously expelled from the bulk of the solvent and forced to aggregate or accumulate at an interface
Steric interactions	Polymeric species adsorbed to inorganic particles or biopolymers expressed at the surfaces of cells give rise to spring–like repulsive interactions with other interfaces	1 to 100	Generally, increase stability of individual particles but can interfere in cellular uptake, especially when surface polymers are highly water-soluble
Polymer bridging interactions	Polymeric species adsorbed to inorganic particles or biopolymers expressed at the surfaces of cells containing charged functional groups can be attracted by oppositely charged moieties on a substrate surface	1 to 100	Generally, promote aggregation or deposition, particularly when charge functionality is carboxylic acid and dispersed in aqueous media containing calcium ions