With the advent of nanotechnology the interaction of nanoparticles (NPs) and nano-structured surfaces with biological systems including living cells has become one of the most intriguing areas of basic and applied research at the interface to biology. As nanoparticles are of the same size scale as typical cellular components and proteins, such particles are suspected to evade the natural defences of the human organism and may lead to permanent cell damages. An important aspect in understanding the fate of NPs in biological systems is their behaviour towards proteins. The efficiency of this interaction can be a decisive factor for the fate of a nanoparticle within a biological system.
Nanoparticles are used in a large variety of scientific and industrial application and their chemical behaviour has begun to be well studied on the nano-scale.
In most interactions with nanoparticles the protein undergoes structural changes and an effect of ligand chemistry on the quantity of adsorbed protein and the extent of denaturation has been previously demonstrated. These structural changes upon adsorption to a surface may result in the loss of biological activity and hence activation of immune response.
Furthermore, the adsorption of protein molecules on the NP surface changes the surface functionality and hence may strongly influence the translocation behaviour in biological systems. However, the mechanistic steps involved in these processes are still far from being understood. In addition it should be noted that, even though the synthesized NPs may be rather insoluble in aqueous solvents, the interactions with proteins may change this behaviour.
The desire to control and utilize the biological effects of NPs has sparked the development of a number of NP biomolecular conjugates including functionalisations with DNA, peptides and proteins. Furthermore, NP-protein conjugates are used in many applications from sensing and nanobiotechnology. A number of experimental methods has been utilised in studying protein structures in solution including circular dichroism, Fourier transform infrared spectroscopy, Raman spectroscopy / SERS and fluorescence spectroscopy. The structure of the BSA molecule is well characterised making BSA a convenient model system for the study of NP / protein interactions.
The secondary structure of the BSA molecule is highly α-helical and the overall structure consists of three domains. All three domains contain different amounts of different amino acids several of which also contain oxygen, nitrogen and sulphur with the ability to stabilise the NP surface. The potentially strongest interactions with metallic NP surfaces are expected from the thiol groups of the cystein residues.