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 interfaces102 to 106Increase 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 media1 to 100Universally 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 layer1 to 100Overlapping 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 molecules1 to 10Lyophilic materials are thermodynamically stable in the solvent and do not aggregate
Lyophobic materials interact unfavourably with solvent moleculesLyophobic 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 interfaces1 to 100Generally, 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 surface1 to 100Generally, promote aggregation or deposition, particularly when charge functionality is carboxylic acid and dispersed in aqueous media containing calcium ions