Engineering Protein-Based Nanofiltration Membranes with Sub-Nanometer Pores via Amyloid-Like Aggregation

Membrane proteins in biology achieve highly efficient selective molecular recognition and transmembrane transport by constructing sub-nanometer channels. However, achieving comparable selectivity in artificial protein-based membranes remains a formidable challenge, primarily due to the difficulty of precisely tailoring sub-nanometer pore sizes. Here, we present a breakthrough in the fabrication of proteinaceous nanofiltration membranes with precisely defined sub-nanometer pores. A robust protein membrane with pore sizes of 0.62-0.81 nm is formed at the air/water interface via a thiol-disulfide exchange reaction. Subsequent crosslinking with polyphenol further reduces the pore size to ∼0.4 nm, while simultaneously inverting surface charge from positive to negative and markedly enhancing ion sieving performance. As a proof-of-concept, the crosslinked amyloid-like protein membrane achieves 98.24% rejection of MgCl₂ and an excellent Mg²⁺/Li⁺ selectivity of 88.65 in a simulated salt-lake brine, surpassing the performance of most polymer membranes reported to date. Additionally, this membrane demonstrates versatility in separating anions with different valences, removing heavy metal ions, and eliminating persistent organic pollutants, while exhibiting excellent chemical stability and anti-fouling capability in acidic, alkaline, and organic solvent environments. By harnessing the precision of biological channels, this work offers a paradigm shift for next-generation biomimetic ion separation, environmental remediation, and water purification applications.