A novel Tb-doped Eu-based metal–organic framework (Eu-MOF@Tb) has been developed by incorporating hexanuclear europium cluster and 2,2′-bipyridine-5,5′-dicarboxylic acid as well as coordination with Tb(III). Owing to the diverse coordination status of Tb(III) and Eu(III) in MOF, antenna effect emission from Tb(III) can be invoked by dipicolinic acid (DPA), but the luminescence originating from Eu(III) remains unchanged. Taking advantage of this phenomenon, a ratiometric luminescent method for detection of DPA, a biomarker for Bacillus subtilis spores, was developed through differential sensitization toward lanthanide ions. This analysis method allowed for the detection of DPA in the 0.2–10 μM concentration range, with a detection limit of 60 nM. It was further validated by spiked recoveries (89.3–110%) of real-world samples with RSD values in the range 3.9–11%. Alongside this, a paper indicator test was prepared for naked-eye detection of DPA via a dose-sensitive color evolution from red to green under UV light. The effectiveness of the proposed approach was explored in the detection of bacterial spores in real biological and environmental samples and indicated great potential for applications as a real-time monitoring system against the anthrax threat. Graphical Abstract
Yuqi Huang,Tiange Li,Mengmeng Lei,Xianqing Huang,Tianlin Wang
In the present investigation, we demonstrated a simple approach for the reproducible synthesis of cerium(III)-based blue phosphor, which provides versatile applications in the construction of warm white-light-emitting diodes (WLEDs) and anticounterfeiting patterns. It is found that the mixture of dipicolinic acid (DPA) with Ce3+ in ethanol (DPA-Ce) emits blue fluorescence under the assistance of ultraviolet (UV) induction. The quantum yield of the DPA-Ce phosphor reaches 44% and is improved to 52% by combining with guanosine 5′-monophosphate (GMP). The obtained DPA-Ce-GMP emits blue fluorescence in both a solid powder and aqueous solution, having advantages of long luminescence lifetimes, ultralong stability, and outstanding antitemperature bleaching. With DPA as a universal ligand, DPA-Tb with green fluorescence and DPA-Eu with red fluorescence are integrated with the blue fluorescence of DPA-Ce-GMP to construct full-color and white-light-emitting devices. The as-prepared warm WLED with a quantum yield of 64% presents an excellent stability and high quality with a color rending index of up to 90, CIE color coordinates of (0.37, 0.36), a correlated color temperature of 3950 K, and a luminous efficiency of 37.8 lm W–1. Multiple anticounterfeiting patterns are further encoded with the as-prepared lanthanide-based phosphors. The investigation offers a simple assay for the cost-effective, large-scale synthesis of phosphors, with great promise in diverse applications including the lighting industry and anticounterfeiting technology.
Spore counting in probiotic Bacillus cultures using dipicolinic acid (DPA) as a marker was studied for developing a rapid and simple detection method. The newly developed method is based on the fluorescence enhancement by a new chelating agent, which forms a complex with EuCl 3 and DPA. The results showed that 1,2-cyclohexanediamine-N,N,N′N′-tetraacetic acid (CyDTA) greatly enhanced the fluorescence intensity in all selected chelating agents. The optimal composition of the fluorescence complex DPA-Eu-CyDTA had a detection limit of 0.3 nM of DPA. Metal ions in high concentrations, including Cu 2+ , Fe 2+ , Fe 3+ , Al 3+ , and Zn 2+ , might lower the detection sensitivity, which could be eliminated by diluting the sample with the metal ions below 10 μM. The maximum release of DPA was achieved by heating treatments at 121 °C for at least 10 min for two types of Bacillus endospores. The spore concentrations and corresponding released DPA fluorescence intensities were linearly associated (coefficient R 2 = 0.9993 and 0.9995 for Bacillus subtilis MA139 and Bacillus licheniformis BL20386, respectively). The detection limit for both strains reached approximately 6800 spores/mL. The verification results showed that the DPA fluorimetry assay developed in the present study was fully consistent with the plate-counting assay. The study shows that the fluorescence complex DPA-Eu-CyDTA can be reliably used for the detection of endospores in Bacillus fermentation for the production of probiotics.
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