Synthesis of fluorescent terbium-based metal-organic framework for quantitative detection of nitrite and ferric ions in water samples

Colorimetric detection of Fe2+ and Cr2O72- in environmental water samples based on dual-emitting RhB-embedded Zr-MOFs

Three dye-loaded tunable dual-emission colorimetric fluorescent probes RhB@UiO-66-Ph (R@U-P) were prepared by in-situ encapsulation method under solvothermal conditions. The resonance energy transfer between UiO-66-Ph and RhB made the dual emission of R@U-P easily tunable with the embedded dye content changing. The R@U-P composites achieved emission from purple light to red light, and served as probes to realize comparative detection of Fe3+, Fe2+ and Cr2O72- in water through colorimetric or quenching detection mode. Mechanism study indicates that the resonance energy transfer or electron transfer interactions between R@U-P composites and inorganic ions resulted in the relative changes of the two emission peaks and realized the selective detection of analytes. The preparation and application of R@U-P probes provide a promising strategy for the in-situ encapsulation dye to obtain two dual-emission composites for the comparative detection of Fe3+, Fe2+ and Cr2O72- in water samples.

Synchronous fluorescence detection of nitrite in meat products based on dual-emitting dye@MOF and its portable hydrogel test kit

A novel ratiometric fluorescent nanoprobe (Rh6G@UIO-66-NH2) was fabricated for efficient nitrite (NO2-) detection in the present study. When NO2- was introduced, it interacted with the amino groups on the surface of Rh6G@UIO-66-NH2, forming diazonium salts that led to the quenching of blue fluorescence. With this strategy, a good linear relationship between NO2- concentration and the fluorescent intensity ratio of the nanoprobe in the range of 1-100 μM was established, with a detection limit of 0.021 μM. This dual-readout nanosensor was applied to analyze the concentration of NO2- in real meat samples, achieving satisfactory recovery rates of 94.72-104.52%, highlighting the practical potential of this method. Furthermore, a portable Gel/Rh6G@UIO-66-NH2 hydrogel test kit was constructed for on-spot dual-mode detection of NO2-. This kit allows for convenient colorimetric analysis and fluorometric detection when used in conjunction with a smartphone. All the photos taken with the portable kit was converted into digital information using ImageJ software. It provides colorimetric and fluorescent visual detection of NO2- over a range of 0.1-1.5 mM, achieving a direct quantitative tool for NO2- identification. This methodology presents a promising strategy for NO2- detection and expands the application prospects for on-spot monitoring of food safety assessment.

Solvothermal synthesis and device fabrication of a Eu3+-based metal-organic framework as a turn-on and blue-shift fluorescence sensor toward Cr3+, Al3+ and Ga3

A novel three-dimensional Eu³⁺-based metal-organic framework with the formula {[(CH₃)₂NH₂][Eu(BTDI)]·H₂O·DMF}_n (JXUST-25) was prepared by solvothermal method based on Eu³⁺ and 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H₄BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu³⁺ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr³⁺, Al³⁺ and Ga³⁺ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr³⁺/Al³⁺/Ga³⁺. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr³⁺, Al³⁺ and Ga³⁺ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M³⁺ ions may be caused by the host-guest interaction and the absorbance caused enhancement mechanism.

Dual-Color 2D Lead-Organic Framework with Two-Fold Interlocking Structures for the Detection of Nitrofuran Antibiotics and 2,6-Dichloro-4-nitroaniline

The misuse of organic pollutants such as nitrofuran antibiotics (NFAs) and 2,6-dichloro-4-nitroaniline (DCN) has become a hot topic of global concern, and developing rapid, efficient, and accurate techniques for detecting NFAs and pesticides in water is a major challenge. Here, we designed a novel lead-based anion 2D metal-organic framework (MOF){[(CH₃)₂NH₂]₂[Pb(TCBPE)(H₂O)₂]}_n (F3) with interlocking structures, in which TCBPE stands for 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene. Powder X-ray diffraction and thermogravimetric analysis revealed that F3 has excellent chemical and solvent stability. It is worth noting that F3 has a grinding discoloration effect. The solvent-protected grinding approach achieved F3B with a high quantum yield (QY = 73.77%) and blue fluorescence, while the direct grinding method produced F3Y with a high quantum yield (QY = 37.27%) and yellow-green fluorescence. Importantly, F3B can detect NFAs in water rapidly and sensitively while remaining unaffected by other antibiotics. F3Y can identify DCN in water quickly and selectively while remaining unchanged by other pesticides. F3B demonstrated high selectivity and rapid response to NFAs at a limit of detection (LOD) as low as 0.26 μM, while F3Y indicated high selectivity and responded quickly to DCN in water at an LOD as low as 0.14 μM. The method was successfully applied to detect NFAs in actual water samples of the fish tanks and ponds as well as the pesticide DCN in soil samples. The recovery rates were 97.0-105.15% and 102.2-106.48%, and the relative standard deviations were 0.63-1.45% and 0.29-1.69%, respectively. In addition, F3B and F3Y can be made into fluorescent test papers for the visual detection of NFAs and DCN, respectively. Combined with experiments and density functional theory calculations, the mechanism of fluorescence quenching of MOFs by target analytes was also revealed.

Construction of an ultra-small hydrazone-linked covalent organic polymer for selective fluorescent detection of ferric ion in aqueous solution

A novel ultra-small hydrazone-linked covalent organic polymer (UHCOP) was synthesized based on the Schiff-base reaction between 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde and 1,4-benzenedicarbohydrazide at room temperature and utilized as a sensitive fluorescent sensor for rapid (<2 min) and selective detection of Fe³⁺ in aqueous solution. The prepared UHCOP displayed ultra-small size with the diameter of 7.98 ± 0.97 nm and gave a stable fluorescent emission at 510 nm. UHCOP exhibited good sensitivity and highly selectivity towards Fe³⁺. The coordination interaction between UHCOP and Fe³⁺ resulted in the obviously aggregation-caused quenching response of UHCOP. The linear range was from 5.0 μM to 1.4 mM (R² = 0.999) with the detection limit of 2.5 μM. Finally, UHCOP has been successfully applied in the detection of Fe³⁺ in real water samples, proving the fabricated UHCOP is promising as a sensitive fluorescent sensor for selective detection of Fe³⁺ in aqueous solution.

Partnered Excited-State Intermolecular Proton Transfer Fluorescence (P-ESIPT) Signaling for Nitrate Sensing and High-Resolution Cell-Imaging

Nitrite (NO₂⁻) is a common pollutant and is widely present in the environment and in human bodies. The development of a rapid and accurate method for NO₂⁻ detection is always a very important task. Herein, we synthesized a partnered excited-state intermolecular proton transfer (ESIPT) fluorophore using the “multi-component one pot” method, and used this as a probe (ESIPT-F) for sensing NO₂⁻. ESIPT-F exhibited bimodal emission in different solvents because of the solvent-mediated ESIPT reaction. The addition of NO₂⁻ caused an obvious change in colors and tautomeric fluorescence due to the graft of NO₂⁻ into the ESIPT-F molecules. From this basis, highly sensitive and selective analysis of NO₂⁻ was developed using tautomeric emission signaling, achieving sensitive detection of NO₂⁻ in the concentration range of 0~45 mM with a detection limit of 12.5 nM. More importantly, ESIPT-F showed the ability to anchor proteins and resulted in a recognition-driven “on-off” ESIPT process, enabling it to become a powerful tool for fluorescence imaging of proteins or protein-based subcellular organelles. MTT experimental results revealed that ESIPT-F is low cytotoxic and has good membrane permeability to cells. Thus, ESIPT-F was further employed to image the tunneling nanotube in vitro HEC-1A cells, displaying high-resolution performance.

Visual Hg(II) sensing in aqueous solution via a new 2,5-Bis(4-pyridyl)thiazolo[5,4-d]thiazole-based fluorescence coordination polymer

A new fluorescence coordination polymer [Zn(Py₂TTz)(5-OH-IPA)]_n (1) (Py₂TTz = 2,5-bis(4-pyridyl)thiazolo[5,4-d]thiazole, 5-OH-IPA = 5-hydroxyisophthalic acid dianion) was synthesized, which exhibited the characteristics of fluorescence quenching and bathochromic shift toward Hg(II) in aqueous solution at pH 7.00. Mechanism study showed that the interactions between Hg(II) ions and Py₂TTz ligands in 1 were responsible for the fluorescence emission change. Thanks to the specific interactions between 1 and Hg(II), excellent selectivity was achieved both in aqueous solution and in solid test paper. The detection limit of 1 for Hg(II) sensing was 125.76 nmol L^-1 and a linear rang was 1.00-10.00 μmol L^-1. More importantly, satisfactory recovery and accuracy of 1 for Hg(II) sensing were also obtained in buffer-free real water samples.

Luminescent binuclear Zinc(II) organic framework as bifunctional water-stable chemosensor for efficient detection of antibiotics and Cr(VI) anions in water

To achieve the ultrastable LMOFs with predominant luminescent sensing performances, the aromatic π-electron mixed ligands strategy was introduced, and the ternary LMOF of {[Zn₂(HDDB)(bib)_1.5]·3H₂O}_n (1), was fabricated based on 3,5-di(2',4'-dicarboxylphenyl)benozoic acid (H₅DDB) and the N-donor of meta-bis(imidazol-1-yl)benzene (bib) under mixed solvothermal condition. LMOF 1 features the first reported 3D 3,4,4-c {6².8³.10}{6².8}₂{6³.8².10}₂ framework with 21.2 % porosity as well as high thermal and chemical stability. Further luminescent sensing showed that LMOF 1 as a bifunctional chemosensor possessing predominant detectability for sensitive detect the hexavalent chromates and nitroimidazoles/nitrofurans antibiotics in water through strong luminescent quenching effects, with excellent reusability as well as trace detection limits. Moreover, luminescent quenching mechanisms were further investigated from electron transfer and energy transfer viewpoints.

A colorimetric and fluorescent dual-readout probe based on red emission carbon dots for nitrite detection in meat products

Nitrite (NO₂^-) is widely present in the human environment and accurate, sensitive and selective detecting of nitrite is of vital significance for food safety and water quality. Herein, a novel red emission carbon dots (r-CDs) fluorescent probe was fabricated for dual-mode detection of nitrite, which was capable of both convenient colorimetric analysis and accurate fluorometric detection. When NO₂^- is added to the rose-red r-CDs solution, NO₂^- interacts with the amino groups which on the surface of r-CDs to form diazotized substance, resulting in that the colorimetric color of r-CDs solution realizes the transition from rose red to light purple, and the red fluorescence is gradually quenched. The detection limits of colorimetric and fluorescence for NO₂^- were 0.193 μM and 0.149 μM, respectively. Furthermore, the dual-readout probe revealed satisfactory recovery and reliability when analyzing the concentration of NO₂^- in ham and bacon samples..

Synthesis of bifunctional fluorescent nanohybrids of carbon dots-copper nanoclusters via a facile method for Fe3+ and Tb3+ ratiometric detection

In this work, a dual-emission ratiometric fluorescent probe of carbon dots-copper nanoclusters (CDs-Cu NCs) nanohybrids with bifunctional features was successfully assembled through mechanical mixing. The CDs were synthesized using ascorbic acid as a carbon source, and Cu NCs were prepared using d-penicillamine as the stabilizer and reducing agent. The as-prepared CDs-Cu NCs displayed two emission peaks (blue at 424 nm and red at 624 nm) when excited at 360 nm, and showed great stability. Interestingly, trace amount of Fe³⁺ could lead to the aggregation of Cu NCs, and induce a drastic static fluorescence quenching at 624 nm because of the electrostatic combination between them, while the fluorescence of the emission peak at 424 nm remained constant. Moreover, an attractive fluorescence enhancement phenomenon at 424 nm was observed when trace Tb³⁺ was added to the above system, which may due to the combination of fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) mechanisms. Thus, CDs-Cu NCs were applied for the ratiometric detection of Fe³⁺ and Tb³⁺ in aqueous solution, and the detection limit (3σ/slope) was 45 nM and 62 nM with the linear range from 0.01 to 40 μM and 0.1 to 50 μM, respectively. Furthermore, the developed sensor was successfully applied for the detection of Fe³⁺ and Tb³⁺ in real-water samples.