Novel psychoactive substances (NPS), as the “third generation” of illicit drugs, typically include synthetic cathinones (SCs), synthetic cannabinoids, etc. In particular, synthetic cathinones, with methcathinone as a typical representative, exhibit high addictiveness and induce irreversible physiological damage, exerting more severe social and public hazards than traditional drugs. Therefore, there is an urgent need to develop accurate on-site detection technologies to monitor and curb their abuse. Although established analytical methods such as gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-tandem mass spectrometry (LC-MS/MS) could provide high reliability, their reliance on sophisticated instrumentation makes them impractical for rapid on-site deployment. Thus, the development of a novel sensing material featuring desirable specificity based on an innovative recognition design, particularly for discriminating against structurally analogous interferents, is of great significance for the high-performance detection of SCs.

To tackle the aforementioned challenges, on the basis of the previous research on rotation-restricted emission metal-organic framework (MOF) sensing materials (Aggregate, 2025, 6, e70053), and further targeting the unique molecular structure of methcathinone, the Trace Chemical Substances Sensing Team rationally designed a fluorescent lanthanide MOF (Ln-MOF). The ingenious structural design enables efficient restriction of intramolecular ligand rotation upon specific binding with methcathinone molecules based on a single-amino-functionalized AIE ligand. Specifically, by using a carefully designed 2′-amino-5′-(4-carboxyphenyl)-[1,1′:3′,1″-terphenyl]-4,4″-dicarboxylic acid (H₃BTB-NH₂) as the AIE ligand and the lanthanide metal europium (Eu) as the metal node, a fluorescent chemical sensing Ln-MOFs was designed. Apart from the antenna effect built by the sensitization of the Eu³⁺ions through the H₃BTB-NH₂ligand, this ligand could also enable the resulting MOFs to possess an appropriate pore size for efficient diffusion. Besides, specific recognition sites for methcathinone could form strong hydrogen bonding, π-π stacking, and rich steric interactions based on the twisted molecular geometry of the ligand, enabling spatial restriction of ligand intramolecular rotation, as well as reducing the non-radiative transition and enhancing the fluorescent emission. Consequently, the Eu-BTB-NH₂ MOF probe exhibits a pronounced fluorescence emission change from red to emerald green under UV excitation, together with a fast response (< 1 s) and a desirable limit of detection (LOD) of 21 ng/mL, highlighting the sensing material’s potential for methcathinone early-warning. Furthermore, a portable sensing chip and a custom-built Drugs Analyst device are introduced, which enabled rapid, on-site methcathinone detection in various complex matrices such as urine, sewage, alcohol, etc., as well as a seized item, thereby demonstrating strong practical applicability. This work provides a mechanistically guided sensing strategy for desirable illicit drug detection in complex real-world environments and offers valuable insights into the design of rotation-restricted luminescent MOFs for optical sensing.

This research, titled “Single-Amino Group Counted Rotation-Restriction in Eu-BTB-NH₂MOF for Accurate Detection of Methcathinone”, was published in Small. It is financially supported by the National Key Research and Development Program of China, the International Science and Technology Cooperation Program of Xinjiang, the Key Research and Development Program of Xinjiang, the Youth Innovation Promotion Association, CAS, and the Tianchi Talent Plan.

Schematic illustration of the detection mechanism and sensing chip-based detection system.