Portable visual assay of Bacillus anthracis biomarker based on ligand-functionalized dual-emission lanthanide metal-organic frameworks and smartphone-integrated mini-device

A single-functionalized ligand single-Ln(3+) based dual-emission Ln-MOF fluorescent sensor was established for portable and visual dipicolinic acid (DPA, Bacillus anthracis biomarker) detection. First, a theory calculationbased prediction model was developed for designing single-functionalized ligand single-Ln3+ dual-emission Ln-MOFs. The model consisted of three calculation modules: intramolecular hydrogen bonds, excited state energy levels, and coordination stability with Ln(3+) of ligands. Tb3+ and Eu3+ were selected as metal luminescence centers, PTA-X (PTA: p-phthalic acid, X = NH2, CH3, H, OH) with different functional groups as one-step functionalization ligands, and the luminescent feature of four Tb-MOFs and four Eu-MOFs was predicted with the model. Coupled with prediction results and experimental verification results, Tb-PTA-OH was rapidly determined to be the sole dual-emission Ln-MOF. Then, Tb-PTA-OH was applied to DPA detection by ratiometric fluorescence, and an ultra-low limit of detection (13.4 nM) was obtained, which is much lower than the lowest anthrax infectious dose (60 mu M). A portable visual assay method based on paper-microchip and smartphone integrated mini-device was further established (limit of qualification 0.48 mu M). A new sensing mechanism and a triple gates selectivity mechanism to DPA were proposed. This work reveals guidelines for material design and mini-device customization in detecting hazardous substances.

Automated summary

This study established a dual-emission Ln-MOF fluorescent sensor based on single-functionalized ligands single-Ln(3+) for the detection of dipicolinic acid (DPA) and proposed a new sensing mechanism and a triple gates selectivity mechanism towards DPA. Through prediction models and experimental verification, Tb-PTA-OH was determined to be a highly sensitive and specific sensor for DPA detection.