Samarium-Based Turn-Off Fluorescence Sensor for Sensitive and Selective Detection of Quinolinic Acid in Human Urine and Serum

Weak Coupling Strategy to Construct High-Performance Sm/Tb-Doped Lanthanide Coordination Polymer Luminescent Sensor for D2O Detection

Accurate measurement of the purity and content of heavy water is of great concern in nuclear energy, the chemical industry, and biomedicine. Since the physical and chemical properties of D2O and H2O are very similar, achieving luminescent detection is challenging. Due to the difference in the vibrational frequency of the O-D and the O-H bonds, the quenching efficiency of the excited state of Ln3+ is different, which leads to a significant difference in the optical properties of Ln3+. Based on this theory, we composed a weak coupling strategy to strengthen the luminescence difference of Ln3+. Then, we demonstrated the weak coupling effect and how to improve detection performance by analyzing L1-Eu0.14Tb0.86(C22H20Eu0.14Tb0.86N3O10) and L1-Sm0.45Tb0.55(C22H20Sm0.45Tb0.55N3O10). The structure and performance of the two sensors were characterized in detail. A series of heavy water detection luminescence sensing experiments show that L1-Sm0.45Tb0.55 and L1-Eu0.14Tb0.86 can not only qualitatively distinguish D2O and H2O with the naked eye but also quantitatively detect any concentration of H2O in D2O. The prepared composite films L1-Sm0.45Tb0.55@PMMA and L1-Eu0.14Tb0.86@PMMA have practical application value. The application of Sm/Tb-doped lanthanide coordination polymers for detecting the H2O content in D2O has not been reported.

Fluorescence Visualization Quantitative Detection of Tetracycline and Nitrofurantoin in Food and Natural Water by Zn2+@Eu-bpdc Composite

Quantitative detection of tetracycline (TC) and nitrofurantoin (NFT) in food and water is of importance for food safety and environmental protection. Herein, Zn2+ was introduced into a europium metal-organic framework Eu-bpdc (H2bpdc = 2,2'-bipyridyl-5,5'-dicarboxylic acid) to prepare a composite of Zn2+@Eu-bpdc, which was developed as a fluorescence sensor for TC and NFT. The fluorescence mechanism concerns with bpdc2- ligand-to-Eu(III) charge transfer, and the detection mechanism is the inner filter effect. Zn2+@Eu-bpdc is a ratiometric fluorescence sensor for TC with the linear fitting equation of I520/I618 = 1.94 × 104 M-1CTC, whose limit of detection (LOD) is 0.148 μmol·L-1 (μM); it is also a fluorescence "turn-off" sensor for NFT with the fitting equation of (I0-I)/I = 3.62 × 104 M-1CNFT and LOD = 0.0792 μM. Zn2+@Eu-bpdc can detect TC or NFT in lake water, honey, and milk with high accuracy. The emission color changes of paper-based Zn2+@Eu-bpdc depending on CTC or CNFT reveal the visualization detections of TC and NFT. With the red and green values as input signals, smartphone-assisted on-site detection is utilized to recognize the antibiotic residuals of TC and NFT by a self-programmed APP. Zn2+@Eu-bpdc is promising in a smartphone-assisted intelligent platform for on-site detection of TC and NFT.

Impedimetric detection of gut-derived metabolites using 2D Germanene-based materials

Apart from the extensively researched graphene under the Group 14 2D materials, monolayered germanene and its derivatives have been gaining interest lately as alternative class of 2D materials owing to their facile synthesis, and attractive electronic and optical properties. Herein, three different functionalized germanene-based nanomaterials, namely Ge-H, Ge-CH3 and Ge-C3-CN were investigated on their novel incorporation in impedimetric immunosensors for the detection of gut-derived metabolites associated with neurological diseases, such as kynurenic acid (KA) and quinolinic acid (QA). The designed germanene-based immunosensor relies on an indirect competitive mechanism using disposable electrode printed chips. The competition for a fixed binding site of a primary antibody occurs between the bovine serum albumin-conjugated antigens on the electrode surface and the free antigens in the solution. Among the three materials, Ge-H displayed superior bioanalytical performance in KA and QA detection. Lower limits of detection of 5.07-11.38 ng/mL (26.79-68.11 nM) were attained for KA and QA with a faster reaction time than previously reported methods. Also, minimal cross-reactivity with interfering compounds, good reproducibility in impedimetric responses (RSD = 2.43-7.51 %) and long-term stability up to a month at 4 °C were the other attributes that the proposed Ge-H competitive impedimetric immunosensor has accomplished. The application of the developed Ge-H immunosensor to serum samples allowed an accurate KA and QA quantification at physiologically relevant levels. This work serves as a stepping-stone in the development of germanene-based nanomaterials for their implementation into cost-effective, miniaturized, portable and rapid impedimetric immunosensors, which are highly desirable for point-of-care testing in clinical settings.

Fluorescence sensing and device fabrication with luminescent metal-organic frameworks

Metal-organic frameworks (MOFs) are a novel class of hybrid porous multi-functional materials consisting of metal ions/clusters and organic ligands. MOFs have exclusive benefits due to their tunable structure and diverse properties. Luminescent MOFs (LMOFs) exhibit both porosity and light emission. They display abundant host and guest responses, making them conducive to sensing. Currently, LMOF sensing research is gaining more depth, with attention given to their device and practical applications. This work reviews recent advancements and device applications of LMOFs as chemical sensors toward ions, volatile organic compounds, biomolecules, and environmental toxins. Furthermore, the detection mechanism and the correlation between material properties and structure are elaborated. This analysis serves as a valuable reference for the preparation and efficient application of targeted LMOFs.