The interaction mechanism between bovine serum albumin and single-walled carbon nanotubes depending on their diameter and concentration in solid bionanocomposites

A method for formation of bionanocomposites that can be used as coatings for implantable devices interacting with blood is proposed. Such bionanocomposites are composed of albumin blood protein and single-walled carbon nanotubes (SWCNT). They are formed by evaporation of water-albumin dispersion of nanotubes by diode laser with precise temperature control. In this work influence of various types of SWCNT graphene structure defects on formation of frame structure from them and albumin was determined using Raman and FTIR spectroscopy methods. It was found that shape of graphene sheet affects the intensity of the D and D’ bands in its Raman spectrum. Strongest increase in the intensity of D band compared to G band is observed in case of partial or complete absence of hydrogen atoms at the boundary of graphene sheet, which leads to practical disappearance of G and D’ lines in Raman spectrum. Molecular modeling showed that for structural defects of graphene sheet edge there is a steric hindrance, which occurs when vibrations of neighboring hydrogen atoms moving towards each other. Possibility of SWCNT functionalization by oxygen atoms of negative amino acid residues aspartic (Asp) and glutamic (Glu), which are located on the outer surface of BSA, is demonstrated. Formation of covalent bonds between BSA and SWCNTs is confirmed by FTIR and Raman spectra. Spectra were recorded for small diameter nanotubes (1.7 nm) with various concentrations (0.01, 0.1, and 1 g/mol). An increase in concentration of nanotubes leads to saturation of functionalization of SWCNTs with oxygen atoms of amino acid residues Asp and Glu. Covalent interaction of BSA with SWCNTs disrupts secondary and tertiary albumin structure. This is confirmed by significant decrease in absorption bands intensity in high-frequency region. Formation of covalent bond between BSA and SWCNTs in composite leads to an increase in band intensity in ~1330 cm-1 region on Raman spectrum compared to the spectrum of initial nanotubes. This confirms presence of significant defects in SWCNTs caused by covalent addition of oxygen to graphene surface of nanotubes. It was found that increase in diameter of nanotubes (4 nm) and their concentration in composite practically does not affect vibrational spectra, which confirms the hydrophobic interaction of BSA and SWCNTs. Thus, two types of interactions in solid composites based on BSA with SWCNT – hydrophobic and with formation of covalent bonds – depend on the diameter of nanotubes used. This criterion makes it possible to widely use frame composites to control the state of blood cells aggregation.