Breaking the "Industrial Vitamin" Paradigm: La-N₄ Single-Atom Sites Enable Highly Active Multicomponent...

Rare-earth materials are commonly described as "industrial vitamins" since they are mainly employed as structural or electronic modifiers rather than as direct catalytic centers. This is because their highly shielded 4f electrons prevent them from effectively participating in interfacial charge transfer. In this work, we break this long-standing limitation by engineering atomically dispersed lanthanum (La) on nitrogen-doped carbon (NC), where it is stabilized in a La-N₄ coordination environment to form a new material denoted as La-NC. The resulting La-NC electrode functions as a highly active single-atom electrochemical sensing platform, enabling the selective and simultaneous detection of ascorbic acid, dopamine, and uric acid in tear fluid. Synchrotron X-ray absorption spectroscopy and aberration-corrected electron microscopy confirm the formation of isolated La single atoms with a well-defined La-N₄ configuration. Density functional theory calculations reveal that the La-N₄ sites circumvent 4f-electron shielding by promoting molecular adsorption. This facilitates interfacial charge transfer, thereby accounting for the observed electrochemical activity and molecular discrimination. This work identifies rare-earth single-atom sites as intrinsically active electrochemical centers, making them beneficial for use as biosensors in multicomponent environments such as tear fluid.