The rare earth elements consist of 17 elements: scandium (Sc), yttrium (Y), and the lanthanides (Ln). These elements exhibit exceptional optical, electrical, and magnetic properties, making them indispensable and widely utilized across various modern technological and industrial applications. For instance, neodymium (Nd) and samarium (Sm), as star elements in the rare earth family, are key components in the production of high-performance permanent magnet materials, driving the development of new energy technologies. Cerium (Ce) plays a pivotal role in automotive exhaust purification, serving as an effective catalyst to significantly reduce environmental pollution from vehicle emissions. Given the immense value of rare earth elements, countries around the world have ramped up investments in mining rare earth ores. However, the similar valence electrons of these elements result in analogous chemical properties, presenting significant technical challenges in their exploration, detection, and separation.
Common methods for detecting rare earth elements each have their advantages and disadvantages. Neutron Activation Analysis (NAA) offers high sensitivity and the capability for simultaneous multi-element analysis. However, its complex equipment requirements and a long cooling time for certain elements limit its practicality for rapid on-site detection. X-ray Fluorescence Spectroscopy (XRF) is frequently used for analyzing solid samples but suffers from a poor sensitivity. Currently, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is the predominant method for detecting rare earth elements, yet it is often plagued by spectral interferences from oxides and hydroxide ions. Moreover, these detection methods share common drawbacks, such as bulky instrumentation, high costs, and operational complexity. Consequently, the development of an efficient, rapid, cost-effective, and accurate analytical method of identifying all rare earth elements remains a critical challenge to be addressed in fields such as geological sciences.
Recently, Professor Shuo Huang's group has achieved simultaneous discrimination of all rare earth elements using a hetero-octameric Mycobacterium smegmatis porin A (MspA) nanopore. In this work, they proposed two strategies, the mono-ligand strategy and the dual-ligand strategy, to optimize the differentiation of rare earth elements. In the mono-ligand strategy (Figure 1), they introduced a fixed single nitrilotriacetic acid (NTA) adapter at the pore constriction. Based on the coordination between the NTA ligand and trivalent rare earth ions, partial differentiation of rare earth elements was achieved.
Fig.1：Discrimination of rare earth elements using the mono-ligand strategy.
To further enhance the differentiation capability for rare earth elements, they introduced a second ligand, innovatively proposing a dual-ligand strategy (Figure 2). When the stationary ligand (NTA) fixed on the pore chelates a trivalent rare earth ion, the ion retains additional vacant orbitals to coordinate with the mobile ligand (N,N-bis(carboxymethyl)-L-lysine, ANTA). This interaction generates unique nanopore events corresponding to each rare earth ion, achieving an accuracy of 99.6% with machine learning. This MspA nanopore is the first nanopore in the world that can fully distinguish all rare earth elements. Additionally, they also observed the lanthanide contraction at the single-molecule level through the specific events of rare earth ions.
Fig.2：Discrimination of rare earth elements using the dual-ligand strategy.
Subsequently, they applied the dual-ligand strategy to the analysis of a real rare earth ore—bastnaesite (Figure 3). By extracting the rare earth elements from bastnaesite through acid digestion and freeze-drying, and utilizing the nanopore for identification and quantitative analysis, they successfully identified the types and abundances of rare earth elements in the ore. The nanopore detection results were consistent with those obtained by ICP-MS. This result confirms the practicality of the method and demonstrates its potential for application in the field of ore exploration.
Fig.3：Nanopore analysis of rare earth elements in bastnaesite.
The related paper entitled “Nanopore discrimination of rare earth elements” has been published on Nature Nanotechnology on February 10th, 2025 (paper link:https://doi.org/10.1038/s41565-025-01864-w). Prof. Shuo Huang from our department is the corresponding author. Ph.D. students Wen Sun, Yunqi Xiao and Kefan Wang from our department are co-first authors. This project was funded by the National Key R&D Program of China (grant no.2022YFA1304602 and no. 2023YFF1205900), National Natural Science Foundation of China (grant no. 22225405 and no. 223B2402), the Fundamental Research Funds for the Central Universities (grant no. 020514380336), Programs for high-level entrepreneurial and innovative talents introduction of Jiangsu Province (individual and group program) and the Excellent Research Program of Nanjing University (grant no. ZYJH004).