Reversible and irreversible changes of protein by NP interaction. Nanoparticle (NP) induced protein structural changes may result in reversible and irreversible conformational changes. The mechanism is controlled by the degree of protein structural modification. Minute structural changes of protein by NPs, which would be regained by removal of NPs, can be considered as reversible mechanism. Again significant NP-induced changes of protein structure (loss of β-sheets, α-helix), which will never be restored by removing NPs, may be termed as irreversible changes.