Bilayer Adsorption of Lysozyme on Nanodiamonds in Aqueous Suspensions

The interactions of one of the most famous enzymes, lysozyme, with carboxylated nanodiamonds in water were studied. It was found that stable complexes are formed as a result of lysozyme adsorption on the surface of nanodiamonds. Based on the obtained adsorption isotherms and change in the fluorescence of nanodiamonds during the adsorption of lysozyme on them, it is concluded that lysozyme is adsorbed on carboxylated nanodiamonds in two layers. Numerical estimates and IR absorption spectroscopy data showed that the lysozyme has different adsorption orientations in the first and second layers, with preferential side-on and end-on orientations, correspondingly. Moreover, in the first layer, lysozyme undergoes significant conformational changes. The enzymatic activity of adsorbed lysozyme in both layers is discussed.