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

Nature possesses protein-based membranes that exhibit exceptional selectivity in ion transport. However, replicating such natural phenomena in a laboratory setting often involves a costly and intricate synthesis of nanocomposites, which face challenges such as multicomponent integration and compatibility/stability issues. As a potential alternative, due to a high water content and the likelihood of long-range proton diffusion, we propose the use of a protein (bovine serum albumin, BSA)-based self-standing biopolymer membrane. Herein, for the first time, we have introduced the BSA membrane as a novel material for selective ion transport, and this property is established by myriad use of various techniques, such as electrical study, radiotracer method, and electrodriven ion-permeation experiments. Furthermore, optical and surface characterization techniques have been utilized to explore the axial ion-transport mechanism within the BSA membrane, revealing a “vehicle mechanism” for ion transport. This membrane has shown transport selectivity factors of approximately 9 and 14 for Cs⁺ over Ba²⁺ and Eu³⁺, respectively. Additionally, due to its biological nature, the membrane exhibits a high ion flux. This work represents a significant stride toward the advancement of ion-selective membranes based on biopolymers, taking inspiration from the natural world.