A unique and convenient electrochemical biosensor for sodium based on a Na+-pumping rhodopsin

Abstract

Sodium ion (Na+) detection plays a crucial role in various fields, including clinical diagnostics, environmental monitoring, and food quality control. However, existing techniques often lack sensitivity, selectivity, or practicality. This study presents a novel protein-based electrochemical biosensor for selective and quantitative Na+ detection, utilizing the microbial rhodopsin Nonlabens dokdonensis rhodopsin 2 (NdR2) reconstituted into liposome nanoparticles and immobilized on indium tin oxide (ITO) electrodes. Upon light illumination, the biosensor generates photocurrents proportional to the Na+ concentration in the sample. Extensive characterization unveiled the biosensor’s remarkable selectivity towards Na+ over other cationic species, including K+, Ca2+, Mg2+, and Cs+. Quantitative analysis revealed two linear response ranges: 2–50 mM and 50–200 mM, with a detection limit of 75 μM. The biosensor demonstrated exceptional thermal stability, withstanding 50 °C for 90 min with minimal signal deterioration. Long-term storage stability tests further highlighted its robustness, with consistent Na+ response for up to 17 days. Furthermore, the biosensor successfully detected Na+ in fetal bovine serum, although with a distinct photocurrent profile potentially influenced by interfering components. This pioneering work introduces a highly selective, sensitive, and stable protein-based biosensor for Na+ detection, offering promising implications for diverse applications in clinical diagnostics, environmental monitoring, and quality control, while paving the way for further advancements in biosensing technologies.