Ligand-Free Fe3 O4 /CMCS Nanoclusters with Negative Charges for Efficient Structure-Selective Protein Adsorption

The easy and effective capture of a single protein from a complex mixture is of great significance in proteomics and diagnostics. However, adsorbing nanomaterials are commonly decorated with specific ligands through a complicated and arduous process. Fe3 O4 /carboxymethylated chitosan (Fe3 O4 /CMCS) nanoclusters are developed as a new nonligand modified strategy to selectively capture bovine hemoglogin (BHB) and other structurally similar proteins (i.e., lysozyme (LYZ) and chymotrypsin (CTP)). The ligand-free Fe3 O4 /CMCS nanoclusters, in addition to their simple and economical two-step preparation process, possess many merits, including uniform morphology, high negative charges (-27 mV), high saturation magnetization (60 emu g(-1) ), and high magnetic content (85%). Additionally, the ligand-free Fe3 O4 /CMCS nanoclusters are found to selectively capture BHB in a model protein mixture even within biological samples. The reason for selective protein capture is further investigated from nanomaterials and protein structure. In terms of nanomaterials, it is found that high negative charges are conducive to selectively adsorb BHB. In consideration of protein structure, interestingly, the ligand-free magnetic nanoclusters display a structure-selective protein adsorption capacity to efficiently capture other proteins structurally similar to BHB, such as LYZ and CTP, showing great potential of the ligand-free strategy in biomedical field.