Selective Ion Transport through a Self-Standing Protein-Based Biopolymer

Nature possesses protein-based membranes that exhibitexceptionalselectivity in ion transport. However, replicating such natural phenomenain a laboratory setting often involves a costly and intricate synthesisof nanocomposites, which face challenges such as multicomponent integrationand compatibility/stability issues. As a potential alternative, dueto a high water content and the likelihood of long-range proton diffusion,we propose the use of a protein (bovine serum albumin, BSA)-basedself-standing biopolymer membrane. Herein, for the first time, wehave introduced the BSA membrane as a novel material for selectiveion transport, and this property is established by myriad use of varioustechniques, such as electrical study, radiotracer method, and electrodrivenion-permeation experiments. Furthermore, optical and surface characterizationtechniques have been utilized to explore the axial ion-transport mechanismwithin the BSA membrane, revealing a "vehicle mechanism"for ion transport. This membrane has shown transport selectivity factorsof approximately 9 and 14 for Cs+ over Ba2+ andEu(3+), respectively. Additionally, due to its biologicalnature, the membrane exhibits a high ion flux. This work representsa significant stride toward the advancement of ion-selective membranesbased on biopolymers, taking inspiration from the natural world.