Amino acid side chain-like surface modification on magnetic nanoparticles for highly efficient separation of mixed proteins

► Various surface modifications were introduced for mixed proteins separation. ► Systematic characterization was achieved by solid-state NMR, BET, FT-IR, and XPS. ► Protein separation efficiency was calculated at each pH. ► Adsorption of mixed proteins onto Si-MNPs@SH was governed not by pH but by Mw. This work reports on the realization of specific functionalized silica-coated magnetic nanoparticles (Si-MNPs) for effective protein separation through surface modification with various amino acid side chain-like functional groups such as thiol (SH), disulfide (SS), carbon chain (Cn), carboxyl (COOH), amine (NH2), and aldehyde (CHO). This study also suggests an improved and convenient method for the synthesis of functionalized Si-MNPs by hydrolysis condensation with silan-coupling agents. The protein adsorption effects in a coexistent mixed state are explored using various proteins, which have different isoelectric point (pI) values and molecular weights, in order to elucidate the binding performance of different proteins one solution. The adsorption efficiency of bovine serum albumin (BSA; 66kDa; pI=4.65) and lysozyme (LYZ; 14.3kDa; pI=11) is 70–100% with various amino acid side chain-like functional groups. However, the adsorption efficiency of a mixed protein solution of BSA and LYZ was different. Although the relatively bulky BSA molecule displayed 50% and 20% adsorption corresponding to pH 4.65, and pH 11, respectively, the smaller LYZ provided almost 100% adsorption at both pH 4.65 and pH 11.