A portable test strip based on fluorescent europium-based metal-organic framework for rapid and visual detection of tetracycline in food samples

Highly selective and visual detection of vanillin based on fluorescence Cd-MOF sensor in milk powders

Vanillin is a commonly used synthetic flavoring agent in daily life. However, excessive intake of vanillin may pose risks to human health. Therefore, there is an urgent need for rapid and sensitive detection methods for vanillin. In this study, we developed a fluorescent sensor based on Cd-MOF for the sensitive and selective recognition of vanillin. The presence of vanillin leads to significant fluorescence quenching of Cd-MOF due to competitive absorption and photoinduced electron transfer (PET). The limit of detection was determined to be 39.6 nM, which is the lowest-among the reported fluorescent probes. The sensor was successfully applied for the detection of vanillin in real samples such as powdered milk and milk, with a recovery rate ranging from 96.88 % to 104.83 %. Furthermore, by immobilizing the Cd-MOF probe into a polyvinyl alcohol (PVA) film, we achieved a portable and visual detection composite materials for vanillin.

A rapid and accurate fluorescent sensor array based on lanthanide metal-organic framework for identification and determination of perfluorinated compounds

Perfluorinated compounds (PFCs), as an important class of environmental pollutants, have chemical and structural similarities that make their detection a great technical challenge. This study synthesized three species of metal-organic frameworks (MOFs) using different lanthanide metal ions or organic ligands, which were integrated into a fluorescent sensor array. This innovative approach offers a straightforward, rapid, and precise detection strategy for PFCs. Different ionization properties and fluorinated hydrophobic tails of PFCs lead to different electrostatic attraction and hydrophobic effects between PFCs and sensing elements, which become the basis for differential sensing. Furthermore, the fluorescence signal is more convenient to collect, making the sensor array simple to complete the identification. Combined with pattern recognition methods, the array successfully identified seven kinds of PFCs and mixtures with a classification accuracy of 100 % and a detection limit as low as 51 nM. Finally, the utility of the sensor array in river water sample analysis was verified. The strategy provides an effective method for identifying and determining PFCs and offers new opportunities for developing sensor arrays based on lanthanide MOFs.

Luminol-Eu3+-Gd3+-functionalized mesoporous silica for ultrasensitive detection of tetracycline antibiotics and smartphone-assisted sensing analysis

An organic-inorganic hybrid nanoprobe, namely LML-D-SBA@Eu3+-Gd3+, was constructed, with SBA-15 acting as the carrier material, and luminol and Eu3+ acting as fluorescence channels to achieve ratiometric signals that eliminate external interference (accurate detection). Gd3+ was used as a sensitizer to amplify the red emission of Eu3+ (ultrasensitive detection). In TCs detection, the luminol emission at 428 nm was quenched due to the photoinduced electron transfer mechanism, and the Eu3+ emission at 617 nm was sensitized due to the synergistic energy transfer from TCs and Gd3+ to Eu3+. The fluorescence intensity at 617 and 428 nm showed ratiometric changes as indicated by notable color changes from blue to red. The detection limits for TC and OTC were 0.21 and 0.08 ng/mL, respectively. To realize a facile, rapid, and cost-effective detection, we constructed a portable intelligent sensing platform based on smartphones, and it demonstrated great potential for on-site detection of TCs.

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.

Bimetallic metal-organic frameworks (BMOFs) for dye removal: a review

Safe drinking water and a clean living environment are essential for good health. However, the extensive and growing use of hazardous chemicals, particularly carcinogenic dyes like methylene blue, methyl orange, rhodamine B, and malachite green, in both domestic and industrial settings, has led to a scarcity of potable water and environmental challenges. This trend poses a serious threat to human society, sustainable global development, and marine ecosystems. Consequently, researchers are exploring more advanced methods beyond traditional wastewater treatment to address the removal or degradation of these toxic dyes. Conventional approaches are often inadequate for effectively removing dyes from industrial wastewater. In this study, we investigated bimetallic metal-organic frameworks (BMOFs) as a solution to these limitations. BMOFs demonstrated outstanding dye removal and degradation capabilities due to their multifunctionality, water stability, large surface area, adjustable pore size, and recyclability. This review provides a comprehensive overview of research on dye removal from wastewater using BMOFs, including their synthesis methods, types of dyes, and processes involved in dye removal, such as degradation and adsorption. Finally, the review discusses the future potential and emerging opportunities for BMOFs in sustainable water treatment.

Dual-State Red-Emitting Zinc-Based MOF Accompanied by Dual-Mode and Dual-State Detection: Color Tonality Visual Mode for the Detection of Tetracycline

Red-emitting metal-organic frameworks (MOFs) are still mostly based on the use of lanthanides or functionalization with red fluorophores. However, production of transition-metal-based MOFs with red-emitting is scarce. This work reports on the synthesis of a novel dual-state red-emitting Zn-based MOF (denoted as UoZ-7) with the capability to detect target molecules in dual state, in solution, and as solid on paper. UoZ-7 gives strong red emission when excited in the solution and in the solid state with 365 nm ultraviolet (UV) lamp irradiation. Coordination-induced emission is the mechanism for the red emission enhancement in the MOF as a restriction of intramolecular rotation occurred to the ligand within the framework structure. UoZ-7 was successfully used for tetracycline (TC) using dual-mode detection, fluorescence-based ratiometry, and color tonality, in the dual state, in solution, and on the paper. TC molecules adsorb on the red-emitting UoZ-7 surface, and a yellow-greenish color emerges due to aggregation-induced emission between TC and UoZ-7. Concurrently, the inner filter effect diminishes the red emission of UoZ-7. The dual-mode or dual-state detection platform provides a simple and reliable fast method for the detection of TC on-site in various environmental and biomedical applications. Moreover, red-emitting UoZ-7 will have further luminescence-based biomedical applications.

A LMOF/MIP paper-based chip and analysis of tetracycline in foodstuff with sample-to-answer performance

The development of high-performance specific sensors is promising for the rapid detection of harmful residues in animal-derived foods. Recently, luminescent metal-organic framework/molecularly imprinted polymer (LMOF/MIP) materials have been developed as ideal candidates for the analysis of harmful residues. Here, we reported a simple fabrication protocol of paper-based chip through in-situ growth of LMOF on a negatively charged modified filter paper, a paper-based molecularly imprinting layer (FP@BA-Eu@MIP) was thereafter successfully prepared via the boronate affinity-based controllable oriented surface imprinting strategy. The paper-based chips obtained were used to construct a rapid test strip of tetracycline (TC). After addition of TC, significant fluorescence changes on the surface of the FP@BA-Eu@MIP paper-based chip could be observed from blue to red via inner filter effect and photo-induced electron transfer under the excitation of 360 nm. The adsorption kinetics was explored in detail. The presented strip exhibited satisfied selectiveness and sensitivity with a limit of detection of 8.47 μg L-1 for TC. It was confirmed that LMOF/MIP as a biomimetic recognition module can play a crucial role in enrichment and fluorescence response. This study provided a real application case for an in-situ fabricated fluorescence paper-based chip in rapidly detecting harmful residues.

Heterometallic Eu/Zn-MOF-based ratiometric sensing platform: Highly sensitive fluorescence / second-order scattering identification of tetracycline analogs and its molecular informatization applications

The traditional preparation method of ratiometric probes faces challenges such as cumbersome preparation and low sensitivity. Thus, there is an urgent need to provide a simple method of preparing a highly sensitive ratiometric probe. Here, Eu3+-doped zinc-based organic framework (Eu/Zn-MOF) was prepared through hydrothermal method for the detection of tetracycline analogs (TCs). Under the same excitation conditions, the probe can simultaneously display valuable fluorescence and second-order scattering signals. The developed probe enabled specific identification and fast detection (1 min) of TCs, including tetracycline, oxytetracycline, doxycycline, and chlortetracycline. The linear detection ranges of tetracycline, oxytetracycline, doxycycline and chlortetracycline were respectively 100 nM - 200 μM, 100 nM - 200 μM, 98 nM - 195 μM, and 97 nM - 291 μM, and the corresponding detection limits were respectively 15.79 nM, 20.83 nM, 15.31 nM, and 28.30 nM. The developed sensor was successfully applied to detect TCs in real samples, and the recovery rate was from 92.54 % to 109.69 % and the relative standard deviation was from 0.04 % to 2.97 %. Moreover, the heterometallic Eu/Zn-MOF was designed as a ratiometric neuron for Boolean logic computing and information encryption based on the specific identification of TCs. As a proof of concept, molecular steganography was successfully employed to encode, store, and conceal information by transforming the specific identification patterns of Eu/Zn-MOF into binary strings. This study is anticipated to advance the application of metal-organic frameworks in logic detection and information security, and bridging the gap between molecular sensors and the realm of information.

Shaping Phenolic Resin-Coated ZIF-67 to Millimeter-Scale Co/N Carbon Beads for Efficient Peroxymonosulfate Activation

Catalytic performance decline is a general issue when shaping fine powder into macroscale catalysts (e.g., beads, fiber, pellets). To address this challenge, a phenolic resin-assisted strategy was proposed to prepare porous Co/N carbon beads (ZACBs) at millimeter scale via the phase inversion method followed by confined pyrolysis. Specially, p-aminophenol-formaldehyde (AF) resin-coated zeolitic imidazolate framework (ZIF-67) nanoparticles were introduced to polyacrylonitrile (PAN) solution before pyrolysis. The thermosetting of the coated AF improved the interface compatibility between the ZIF-67 and PAN matrix, inhibiting the shrinkage of ZIF-67 particles, thus significantly improving the void structure of ZIF-67 and the dispersion of active species. The obtained ZACBs exhibited a 99.9% removal rate of tetracycline (TC) within 120 min, with a rate constant of 0.069 min-1 (2.3 times of ZIF-67/PAN carbon beads). The quenching experiments and electron paramagnetic resonance (EPR) tests showed that radicals dominated the reaction. This work provides new insight into the fabrication of high-performance MOF catalysts with outstanding recycling properties, which may promote the use of MOF powder in more practical applications.

Recent progress in lanthanide-based fluorescent nanomaterials for tetracycline detection and removal

Tetracycline (TC) has been widely used in clinical medicine and animal growth promotion due to its broad-spectrum antibacterial properties and affordable prices. Unfortunately, the high toxicity and difficult degradation rate of TC molecules make them easy to accumulate in the environment, which breaks the ecological balance and seriously threatens human health. Rapid and accurate detection of TC residue levels is important for ensuring water quality and food safety. Recently, fluorescence detection technology of TC residues has developed rapidly. Lanthanide nanomaterials, based on the high luminescence properties of lanthanide ions and the high matching with TC energy levels, are favored in the real-time trace detection of TC due to their advantages of high sensitivity, rapidity, and high selectivity. Therefore, they are considered potential substitutes for traditional detection methods. This review summarizes the synthesis strategy, TC response mechanism, removal mechanism, and applications in intelligent sensing. Finally, the development of lanthanide nanomaterials for TC fluorescence detection and removal is reasonably summarized and prospected. This review provides a reference for the establishment of a method for the accurate determination of TC content in complex food matrices.

Magnetic Immunoassay Based on Au Pt Bimetallic Nanoparticles/Carbon Nanotube Hybrids for Sensitive Detection of Tetracycline Antibiotics

Misusage of tetracycline (TC) antibiotics residue in animal food has posed a significant threat to human health. Therefore, there is an urgent need to develop highly sensitive and robust assays for detecting TC. In the current study, gold and platinum nanoparticles were deposited on carbon nanotubes (CNTs) through the superposition method (Au@Pt/CNTs-s) and one-pot method (Au@Pt/CNTs-o). Au@Pt/CNTs-s displayed higher enzyme-like activity than Au@Pt/CNTs-o, which were utilized for the development of sensitive magnetic immunoassays. Under the optimized conditions, the limits of detection (LODs) of magnetic immunoassays assisted by Au@Pt/CNTs-s and Au@Pt/CNTs-o against TCs could reach 0.74 ng/mL and 1.74 ng/m, respectively, which were improved 6-fold and 2.5-fold in comparison with conventional magnetic immunoassay. In addition, the measurement of TC-family antibiotics was implemented by this assay, and ascribed to the antibody used that could recognize TC, oxytetracycline, chlortetracycline, and doxycycline with high cross-reactivity. Furthermore, the method showed good accuracy (recoveries, 92.1-114.5% for milk; 88.6-92.4% for pork samples), which also were applied for determination of the targets in real samples. This study provides novel insights into the rapid detection of targets based on high-performance nanocatalysts.

Three in one: coordination-induced emission for inherent fluorescent Al-MOF synthesis combined with inner filter effect@aggregation-induced emission mechanisms for designing color tonality and ratiometric sensing platforms

Three phenomena, namely coordination-induced emission (CIE), aggregation-induced emission (AIE), and inner filter effect (IFE), were incorporated into the design of a ratiometric and color tonality-based biosensor. Blue fluorescent Al-based metal-organic frameworks (FMIL-96) were prepared from non-emissive ligand and aluminum ions via CIE. Interestingly, the addition of tetracycline (TC) led to ratiometric detection and color tonality, as the blue emission at 380 nm was quenched (when excited at 350 nm) due to IFE, while the green-yellowish emission at 525 nm was enhanced due to AIE. Based on that, an ultra-sensitive visual-based color tonality mode with smartphone assistance was developed for detection of TC. The sensor exhibited a linear relationship within a broad range of 2.0 to 85.0 μM TC with a detection limit of 68.0 nM. TC in milk samples was quantified with high accuracy and precision. This integration of smartphone and visual fluorescence in solution is accurate, reliable, cost-effective, and time-saving, providing an alternative strategy for the semi-quantitative determination of TC on-site.

A novel fluorescence platform for specific detection of tetracycline antibiotics based on [MQDA-Eu3+] system

Tetracycline antibiotics (TCs) are extensively used in clinical medicine, animal husbandry, and aquaculture because of their cost-effectiveness and high antibacterial efficacy. However, the presence of TCs residues in the environment poses risks to humans. In this study, an inner filter effect (IFE) fluorescent probe, 2,2'-(ethane-1,2-diylbis((2-((2-methylquinolin-8-yl)amino)-2-oxoethyl)azanediyl))diacetic acid (MQDA), was developed for the rapid detection of Eu3+ within 30 s. And its complex [MQDA-Eu3+] was successfully used for the detection of TCs. Upon coordination of a carboxyl of MQDA with Eu3+ to form a [MQDA-Eu3+] complex, the carboxyl served as an antenna ligand for the effective detection of Eu3+ to intensify the emission intensity of MQDA via "antenna effect", the process was the energy absorbed by TCs via UV excitation was effectively transferred to Eu3+. Fluorescence quenching of the [MQDA-Eu3+] complex was caused by the IFE in multicolor fluorescence systems. The limits of detection of [MQDA-Eu3+] for oxytetracycline, chlorotetracycline hydrochloride, and tetracycline were 0.80, 0.93, and 1.7 μM in DMSO/HEPES (7:3, v/v, pH = 7.0), respectively. [MQDA-Eu3+] demonstrated sensitive detection of TCs in environmental and food samples with satisfactory recoveries and exhibited excellent imaging capabilities for TCs in living cells and zebrafish with low cytotoxicity. The proposed approach demonstrated considerable potential for the quantitative detection of TCs.

Construction of a novel Eu-MOF material based on different detection mechanisms and its application in sensing pollutants aniline, F- and Hg2

Aniline is an organic pollutant with carcinogenicity and teratogenicity, while F- and Hg2+ are toxic ions that are easily soluble in water. When they are released to the environment, they will pose a threat to human health. Designing a material that can simultaneously detect three types of pollutants is of great significance. In this paper, a novel rare earth metal organic framework material (Eu-MOF) with three-dimensional structure based on 1-methylimidazole-4,5-dicarboxylic acid was synthesized for the first time through solvent thermal method. It has excellent luminescent performance and can be used as a multifunctional fluorescent probe to detect aniline, F-, and Hg2+ based on photoinduced electron transfer, energy competitive absorption, and ion exchange mechanisms, with detection limits of 1.79 × 10-8, 8.13 × 10-8, and 8.83 × 10-7 M, respectively. It is worth noting that Eu-MOF can detect F- and Hg2+ in real water samples, such as lake water and green tea water, with favorable recovery rates.

Construction of a Colorimetric and Near-Infrared Ratiometric Fluorescent Sensor and Portable Sensing System for On-Site Quantitative Measurement of Sulfite in Food

Sulfites play imperative roles in food crops and food products, serving as sulfur nutrients for food crops and as food additives in various foods. It is necessary to develop an effective method for the on-site quantification of sulfites in food samples. Here, 7-(diethylamino) quinoline is used as a fluorescent group and electron donor, alongside the pyridinium salt group as an electron acceptor and the C=C bond as the sulfite-specific recognition group. We present a novel fluorescent sensor based on a mechanism that modulates the efficiency of intramolecular charge transfer (ICT), CY, for on-site quantitative measurement of sulfite in food. The fluorescent sensor itself exhibited fluorescence in the near-infrared light (NIR) region, effectively minimizing the interference of background fluorescence in food samples. Upon exposure to sulfite, the sensor CY displayed a ratiometric fluorescence response (I447/I692) with a high sensitivity (LOD = 0.061 μM), enabling accurate quantitative measurements in complex food environments. Moreover, sensor CY also displayed a colorimetric response to sulfite, making sensor CY measure sulfite in both fluorescence and colorimetric dual-signal modes. Sensor CY has been utilized for quantitatively measuring sulfite in red wine and sugar with recoveries between 99.65% and 101.90%, and the RSD was below 4.0%. The sulfite concentrations in live cells and zebrafish were also monitored via fluorescence imaging. Moreover, the sulfite assimilated by lettuce leaves was monitored, and the results demonstrated that excessive sulfite in leaf tissue could lead to leaf tissue damage. In addition, the sulfate-transformed sulfite in lettuce stem tissue was tracked, providing valuable insights for evaluating sulfur nutrients in food crops. More importantly, to accomplish the on-site quantitative measurement of sulfite in food samples, a portable sensing system was prepared. Sensor CY and the portable sensing system were successfully used for the on-site quantitative measurement of sulfite in food.

Sensitive dual-signal detection and effective removal of tetracycline antibiotics in honey based on a hollow triple-metal organic framework nanozymes

In this work, a colorimetric/fluorescent dual-signal mode sensor is proposed for the sensitive, selective and accurate detection and removal of tetracycline antibiotics (TCs). A triple-metal MOF of NiCoFe is successfully synthesized and controllable adjusted the shape of the hollow structure for the first time, and then modified with TCs aptamer. The as-prepared triple-atom MOF (apt-NiCoFe-MOF-74) exhibits well-defined hollow morphology, high crystallinity, and high surface areas endow their alluring adsorption and removal performances for TCs. More attractively, this triple-metal MOF show a good peroxidase-like activity and strong fluorescence property at 540 nm of apt-NiCoFe-MOF-74 when excitation wavelength was 370 nm. Inspire by this, a dual-signal output biosensor is constructed and the linear absorbance response is well correlated with wide range and low LOD for TCs. The biosensor provided an universal method with satisfactory sensitivity and accuracy for TCs analysis in real food samples.

Visualized detection of water by modified metal organic framework-199 and its portable test paper with reversible color change

Herein, we fabricate a melamine modified metal organic framework-199 composite (MOF-199@melamine), of which the structure is affected by the dynamics of the guest H2O molecule with significant color change. It realizes the visualized quantitative detection of water in a variety of organic solvents within 30 s. Moreover, DMF restored the original structure by replacing H2O molecules, realizing the regeneration of the materials. On this basis, PTFE-MOF-199@melamine test paper is developed to portably detect water content in organic solvents (maximum 0 %-98 % (v/v) water content) and ambient relative humidity (11-85 %). The test paper can be recycled four times with a regeneration rate higher than 90 %. The results are expected to solve the problems of existed electrochemical or fluorescence strategy such as the complicated operation process and signal output/reading system.

Ratiometric fluoroprobe based on Eu-MOF@Tb3+ for detecting tetracycline hydrochloride in freshwater fish and its application in rapid visual detection

Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380-75 μM, with a low limit of detection (LOD) at 0.115 μM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

Exosome, a Rising Biomarkers in Liquid Biopsy: Advances of Label-Free and Label Strategy for Diagnosis of Cancer

Cancer is commonly considered as one of the most severe diseases, posing a significant threat to human health and society due to various serious challenges. These challenges include difficulties in accurate diagnosis and a high propensity to form metastasis. Tissue biopsy remains the gold standard for diagnosing and subtyping cancer. However, concerns arise from its invasive nature and the potential risk of metastasis during these complex diagnostic procedures. Meanwhile, liquid biopsy has recently witnessed the rapid advancements with the emergence of three prominent detection biomarkers: circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), and exosomes. Whereas, the very low abundance of CTCs combined with the instability of ctDNA intensify the challenges and decrease the accuracy of these two biomarkers for cancer diagnosis. While exosomes have gained widespread recognition as a promising biomarker in liquid biopsy due to their relatively low-invasive detection method, excellent biostability, rich resources, high abundance, and ability to provide valuable information about cancer. Therefore, it is crucial to systematically summarize recent advancements mainly in exosome-based detection methods for early cancer diagnosis. Specifically, this review will primarily focus on label-based and label-free strategies for detecting cancer using exosomes. We anticipate that this comprehensive analysis will enhance readers' understanding of the significance and value of exosomes in the fields of cancer diagnosis and therapy.

A portable smartphone-assisted Tb-MOF-based agar-slice probe for the rapid and on-site fluorescence assay of malachite green in aquatic products

In this study, a new Tb-MOF fluorescence probe was developed for the detection of malachite green (MG) in real aquatic products. Fluorescence sensing experiments revealed that MG can effectively quench the green fluorescence of Tb-MOF suspensions, and the detection process exhibits the advantages of high sensitivity, a wide linear range (0-80 μM), a low detection limit (10.8 nM) and a rapid response time. Selective detection of MG is achieved primarily through fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) mechanisms. Furthermore, a smartphone-assisted Tb-MOF-based agar slice detection platform was constructed for the visual and quantitative detection of MG. Additionally, the on-site detection of MG in crucian and shrimp samples was accomplished with high recoveries (99.8 %-107.99 %) and low relative standard deviations (RSD < 2.2 %). This developed detection platform introduced a low-cost, portable and user-friendly approach for MG detection.

A smartphone sensing platform for the sensitive and selective detection of clothianidin based on MIP-functionalized lanthanide MOF

A novel molecularly imprinted nanomaterial (Eu (BTC)-MPS@MIP) was synthesized on the surface of silanized europium-based metal-organic frameworks (Eu (BTC)-MPS) using 1, 3, 5-benzotrioic acid (H3BTC) as a ligand. The resulting Eu (BTC)-MPS@MIP was applied to constructing a smartphone sensing platform for the sensitive and selective detection of clothianidin (CLT) in vegetables. The synthesized Eu (BTC)-MPS@MIP demonstrated the successful formation of a typical core-shell structure featuring a shell thickness of approximately 70 - 80 nm. The developed sensing platform based on Eu (BTC)-MPS@MIP exhibited sensitivity in CLT detection with a detection limit of 4 µg/L and a linear response in the range 0.01 - 10 mg/L at excitation and emission wavelengths of 365 nm and 617 nm, respectively. The fluorescence sensing platform displayed excellent specificity for CLT detection, as evidenced by a high imprinting factor of 3.1. This specificity is primarily attributed to the recognition sites in the molecularly imprinted polymer (MIP) layer. When applied to spiked vegetable samples, the recovery of CLT ranged from 78.9 to 102.0%, with relative standard deviation (RSD) values falling between 2.2 and 6.2%. The quenching mechanism of Eu (BTC)-MPS@MIP toward CLT can be attributed to the inner filter effect (IFE), resulting from the optimal spectral overlap between the absorption spectrum of CLT and the excitation spectra of Eu (BTC)-MPS@MIP. The proposed method has the potential for extension to the detection of other pesticides by replacing the MIP recognition probes.

Pyrene and Eu3+ modified mesoporous silica used as a fluorescent probe for ratiometric detection of tetracycline antibiotics

The detection of residual tetracycline antibiotics (TCs) in the aquatic environment is important because of the irreversible damage of TCs to the ecosystem and human health. Considering the photostability, sensitivity, and accuracy of the detection systems, mesoporous SBA-15 silica material was an ideal support matrix for improving photostability because it can protect the optical properties of fluorescent signals. To achieve ratiometric detection (with sensitivity and accuracy), pyrene and Eu3+ as two fluorescent signals were implemented into SBA-15, and an organic-inorganic hybrid fluorescent nanoprobe Py/EDTA-SBA-15@Eu3+ was constructed. In the presence of TCs, the red emission of Eu3+ in the nanoprobe was sensitized, and the fluorescence resonance energy transfer occurred from pyrene to Eu3+, resulting in the increased emission of Eu3+ at 617 nm and the decreased emission of pyrene at 384 nm. By monitoring the fluorescent intensity changes at 617 and 384 nm (F617/F384), the nanoprobe achieved the ratiometric detection of oxytetracycline (OTC) and tetracycline (TC) in the range of 0.20-80 and 0.40-80 μM, respectively, with detection limits of 0.18 nM for OTC and 5.83 nM for TC. In addition, the practical application of the nanoprobe was validated in tap water and honey samples.

Dual-emissive europium doped UiO-66-based ratiometric light-up biosensor for highly sensitive detection of histidinemia biomarker

BACKGROUND

Lanthanide metal-organic frameworks (Ln-MOFs) are a kind of emerging crystalline porous materials with high fluorescence and easy-to-tunable properties, making them ideal for sensing applications. However, current Ln-MOFs based fluorescent probes are primarily single-emissive or fluorescence-quenched, which greatly limited the detection performances such as sensitivity, accuracy and repeatability, thereby hindering their applications in efficient target monitoring and related disease diagnosis. To address these issues, the reasonable design of Ln-MOFs equipped with dual fluorescence emissions and light-up mode is urgently needed for a high-performance biosensor.

RESULTS

A dual-emissive europium doped UiO-66 (Eu@UiO-66-NH2-PMA)-based ratiometric fluorescent biosensing platform was constructed for highly sensitive and selective detection of the histidinemia biomarker-histidine (His). Eu@UiO-66-NH2-PMA (pyromellitic acid abbreviated as PMA) was synthesized utilizing a post-synthetic modification method via coordination interactions between the free -COOH of UiO-66-NH2-PMA and Eu3+, which exhibited characteristic peaks of broad ligand emission and sharp Eu3+ emissions simultaneously. Considering that Cu2+ had the excellent fluorescence quenching ability toward Eu3+ and superior affinity with His, it was deliberately introduced into the Eu@UiO-66-NH2-PMA, acting as active sites for target His responsiveness. The Eu@UiO-66-NH2-PMA/Cu2+/His ternary competition system demonstrated a low detection limit of 74 nM, excellent selectivity and good anti-interference capability that allowed for sensitive analysis of His levels in milk and human serum samples.

SIGNIFICANCE

Attributing to the superior luminescent properties, good stability and self-calibration capability of Eu@UiO-66-NH2-PMA, the developed ratiometric light-up sensing platform enabled sensitive, selective and credible analysis of His in complex practical samples, which might provide an available tool for food nutrition guideline and diagnostic applications of His related diseases.

Fluorescent and smartphone imaging detection of tetracycline residues based on luminescent europium ion-functionalized the regular octahedral UiO-66-NH2

Antibiotic residues cause extensive damage to food security, thus arousing serious concerns. Hence, rapid and sensitive detection of antibiotic residues is crucial to food safety. This study aimed to propose a portable, visual, intelligent and rapid method for tetracycline detection. We developed a ratiometric fluorescent sensor based on the Eu3+-functionalized regular octahedral UiO-66-NH2 material. The developed sensor could quantify tetracycline in the concentration range of 0.5-200 μM with a detection limit as low as 0.2 μM under the optimum conditions. Furthermore, the analytical results obtained using the designed sensor in the actual samples were basically consistent with those obtained using high-performance liquid chromatography. Based on these achievements, a smartphone application-integrated fluorescent testing paper was designed for facile, intelligent, and visual detection of tetracycline. The integrated portable sensor not only saved cost and time for testing but also provided a forward-looking approach to fast, sensitive detection of antibiotic residues.

Eu MOF-enhanced FeNCD nanozymes for fluorescence and highly sensitive colorimetric detection of tetracycline

The constrained enzymatic activity and aggregation challenges encountered by small-sized nanozymes pose obstacles to their practical utility, necessitating a strategy to mitigate aggregation and boost enzymatic catalytic efficiency. In this work, a negatively charged Eu MOF was utilized as the encapsulation matrix, encapsulating the small-sized nanozymes FeNCDs into the Eu MOF to synthesize an FeNCDs@Eu MOF. The dispersibility of the encapsulated FeNCDs was increased, and owing to the negative charge of the FeNCDs@Eu MOF, electrostatic pre-concentration of the positively charged target molecule tetracycline (TC) was facilitated, thereby amplifying the enzymatic catalytic efficiency of the FeNCDs. The response of the FeNCDs to TC increased by nearly 6 times upon encapsulation. The TC detection limit (LOD) of the FeNCDs@Eu MOF-based sensor is as low as 11.63 nM. The incorporation of fluorescence detection expanded the linear range of the sensor, rendering it more suitable for practical sample detection.

A Recent Advancement in Food Quality Assessment: Using MOF-Based Sensors: Challenges and Future Aspects

Monitoring food safety is crucial and significantly impacts the ecosystem and human health. To adequately address food safety problems, a collaborative effort needed from government, industry, and consumers. Modern sensing technologies with outstanding performance are needed to meet the growing demands for quick and accurate food safety monitoring. Recently, emerging sensors for regulating food safety have been extensively explored. Along with the development in sensing technology, the metal-organic frameworks (MOF)-based sensors gained more attention due to their excellent sensing, catalytic, and adsorption properties. This review summarizes the current advancements and applications of MOFs-based sensors, including colorimetric, electrochemical, luminescent, surface-enhanced Raman scattering, and electrochemiluminescent sensors. and also focused on the applications of MOF-based sensors for the monitoring of toxins such as heavy metals, pesticide residues, mycotoxins, pathogens, and illegal food additives from food samples. Future trends, as well as current developments in MOF-based materials.

Zinc-doped carbon quantum dots-based ratiometric fluorescence probe for rapid, specific, and visual determination of tetracycline hydrochloride

In this work, a rapid, specific, and visual ratiometric fluorescence probe was constructed for tetracycline hydrochloride (TCH) determination based on zinc-doped carbon quantum dots (Zn-CDs). In the presence of TCH, the blue fluorescence at 440 nm originating from Zn-CDs was quenched, and the green fluorescence at 515 nm stemming from TCH was enhanced. The inner filter effect (IFE) and the chelation between Zn and tetracycline are the main mechanisms for the conversion of spectra. The spectrum and color change completed and stabilized within 1 min, indicating the possibility of real-time detection of TCH. The detection range for TCH is 0.1-50 μM, and the low detection limit is 61.1 nM. In addition, Zn-CDs-based test strips were successfully applied to direct visual identification of TCH in actual samples of river water and milk, indicating the possibility of their practical application.

Detection mechanism and the outlook of metal-organic frameworks for the detection of hazardous substances in milk

Milk has a high nutritional value. However, milk is easily contaminated in the production, processing, and storage processes, which harms consumers' health. Therefore, the harmful substances' detection in milk is important. Metal-organic frameworks (MOFs) have proven high potential in food safety detection due to their unique porous structure, large effective surface area, large porosity, and structural tunability. This article systematically describes the detection mechanism of fluorescence, electrochemical, colorimetric, and enzyme-linked immunosorbent assay based on MOFs. The progress of the application of MOFs in the detection of antibiotics, harmful microorganisms and their toxins, harmful ions, and other harmful substances in milk in recent years is reviewed. The structural tunability of MOFs enables them to be functionalized, giving the ability to be applied to different detection methods or substances. Therefore, MOFs can be used as an advantageous sensing material for detecting harmful substances in the complex environment of milk.

Novel dual-emission fluorescence imprinted sensor based on Mg, N-CDs and metal-organic frameworks for rapid and smart detection of 2, 4, 6-trinitrophenol

Rapid and real-time detection of 2, 4, 6-trinitrophenol (TNP) is of great importance for the living environment and human health. Herein, we constructed an innovative ratiometric fluorescence imprinted sensor with fast response and high selectivity based on magnesium and nitrogen co-doped carbon dots (Mg, N-CDs) and chromium telluride quantum dots (r-CdTe) self-assembled in zirconium-based metal organic frameworks (UiO-66) combined with imprinted polymers for the detection of TNP. In the protocol, the introduction of UiO-66 with large specific surface area and porosity using as carrier material significantly enhanced the mass transfer rate, which improved the sensitivity of the Mg, N-CDs/r-CdTe@UiO-66@MIP (LHU@MIP). And the Mg, N-CDs with high quantum yields and r-CdTe were selected as fluorescence emitting elements to yield fluorescence signal, achieving signal amplification. The dual-channel strategy enabled the sensor to not only display a fast fluorescence response, but also generate a dual-response signal under the action of internal filtering effect (IFE). Combining these advantages, the LHU@MIP had a wide linear range (1-100 μM), good detection sensitivity (0.56 μM), and a distinct color change (from blue to pink). Meanwhile, for accurate on-site analysis, we designed a portable smart sensing platform with a color recognizer application. The smartphone enabled visual sensing of TNP by capturing fluorescent images and converting them into digital values. More importantly, the platform was successfully utilized for the analysis of TNP in the simulated actual samples with considerable results. Therefore, the developed platform was characterized by low cost, portability, ideal specificity, and provided a strategy for on-site monitoring of TNP.

Rapid and sensitive detection of tetracycline residue in food samples using Cr(III)-MOF fluorescent sensor

As tetracycline antibiotics were used in the poultry sector, their residue in edible animal products may adversely affect food safety and human health. The development of selective and sensitive tetracycline sensors has garnered a lot of interest due to the complexity of food samples. Therefore, a fluorescent sensing probe based on chromium(III)-metal-organic framework was developed for the rapid detection of tetracycline. After the addition of tetracycline, blue emission at λem 410 nm was effectively quenched by the interaction between TC and Cr(III)-metal-organic framework material. Under optimized conditions (sensor concentration: 30 mg/L and pH: 10.0), the sensing probe showed a fast response time (1 min), and low detection limit (0.78 ng/mL) with a linear range (5-45 ng/mL). Interestingly, the Cr(III)-metal-organic framework was successfully applied to quantity tetracycline residue in chicken meat and egg samples with recoveries of 95.17-06.93%. To deduce, our work can provide a new strategy for the direct detection of tetracycline in food samples.

Dual-state dual emission from precise chemically engineered bi-ligand MOF free from encapsulation and functionalization with self-calibration model for visual detection

Synthesis of dual-state dual emitting metal-organic frameworks (DSDE-MOFs) is uncommon and challenging. Additionally, DSDE-MOFs can fulfil the expanding need for on-site detection due to their stability and self-reference for a variety of non-analyte variables. In the present work, a novel intrinsic DSDE of chemically engineered bi-ligand Eu-based MOF (UoZ-1) was designed. The prepared UoZ-1 spherical particles were small-sized around 10-12 nm and displayed blue (425 nm) and red fluorescence (620 nm) at both states, dispersed in liquid and in solid state, when excited at 250 nm. A ratiometry platform was developed since the red emission was quenched by the addition of folic acid and the blue emission was almost remained unaffected. In the fluorometric ratiometric-mode, a dynamic linear range was recorded from 10 to 200 µM with LOD about 0.4 µM. Visual-based detection with assistance of smartphone was developed for quantification based on RGB analysis using Color Grab App. In the visual-mode, LOD as small as 2.3 µM was recorded. By utilizing the intrinsic dual-emitting UoZ-1, highly stable, recyclable, sensitive, and selective on-site visual detection of folic acid can be achieved. UoZ-1, a DSDE-MOF with no encapsulation or functionalization requirements, exhibits great potential for diverse applications.

A dual-mode green emissive fluorescent probe for real-time detection of doxycycline in milk using a smartphone sensing platform

Real-time quantitative analysis of tetracyclines is urgently needed to provide consumers with early warning of potential risks. Herein, we report a dual-mode green emissive fluorescent probe, which refers to the liquid mode and the solid mode of electrospun films doped with nitride-doped carbon nanosheets (NCNSs) for real-time detection of doxycycline (DOX). Highly fluorescent NCNSs were prepared by low-temperature solid treatment of urea and sodium citrate. With the addition of DOX, the green emission intensity of NCNSs at 475 nm can be obviously reduced. Method validation exhibited a good linear relationship in 0.05-150 μM between the fluorescence quenching of NCNSs and the concentration of DOX with a limit of detection (LOD) of 0.0127 μM. Furthermore, the immobilization of NCNSs in PAN carriers forming electrospun films stabilizes the green fluorescence of NCNSs. Additionally, electrospun films integrated into a smartphone were developed for real-time detection of DOX with LOD of 0.285 μM. Additionally, DOX in milk was monitored with satisfactory recoveries. Therefore, the integration of the smartphone and electrospun film provides a promising and convenient method for real-time identification of DOX in food analysis.

An intelligent smartphone-test strip detection platform for rapid and on-site sensing of benzoyl peroxide in flour samples

Benzoyl peroxide (BPO) is a commonly used flour whitener, but its excessive usage can have adverse effects on human health, such as nutrient loss, vitamin deficiencies and certain diseases. In this study, a europium metal organic framework (Eu-MOF) fluorescence probe was prepared, which exhibited a strong fluorescence emission at 614 nm upon excitation at 320 nm, with a high quantum yield of 8.11%. The red fluorescence of the probe could be effectively quenched by BPO through the inner filter effect (IFE) and photoinduced electron transfer (PET) mechanism. The detection process offered several advantages, including a wide linear range of 0-0.95 mM, a low detection limit of 66 nM and a fast fluorescence response of 2 min. Furthermore, an intelligent detection platform was designed to enhance the practical application of the detection method. This platform combined the portability and visuality of a traditional test strip with the color recognition capability of a smartphone, allowing for the visualization and quantitative detection of BPO in a convenient and user-friendly manner. The detection platform was successfully applied to the analysis of BPO in real flour samples with satisfactory recoveries (99.79%-103.94%), suggesting a promising strategy for the rapid and on-site detection of BPO in food samples.

A smartphone-assisted paper-based ratio fluorescent probe for the rapid and on-site detection of tetracycline in food samples

Rapid, sensitive and portable analytical methods for on-site detection of tetracycline (TC) in food samples is of critical importance for food safety and public health. In this study, a dual-emission ratio fluorescent probe (Gd0.9@Eu0.1) was prepared and utilized for the detection of tetracycline (TC) by observing the fluorescence color change from blue to red. The detection process exhibits a wide linear range (0-52.0 μM), good selectivity and low detection limit (14 nM). A paper-based probe and a colorimetric card was constructed for the visual detection of TC. Furthermore, a novel and portable detection platform combining smartphone and test strip was exploited for the quantitative and on-site detection of TC in real pork sample. The developed method was validated through intra- (n = 5) and inter-day (n = 2) measurements, as well as comparison with a traditional HPLC method. These statistical result validate the reliability and accuracy of the developed method. This intelligent detection platform represents a promising approach for the rapid, sensitive and visual detection of TC in food samples.

Intrinsic Dual-State Emission Zinc-Based MOF Rodlike Nanostructures with Applications in Smartphone Readout Visual-Based Detection for Tetracycline: MOF-Based Color Tonality

Dual-state emitters (DSEs) are entities that exhibit fluorescence in both the solution and solid state, which open up a wide range of possibilities for their utilization in various fields. The development of detection platforms using intrinsic luminescent metal-organic frameworks (LMOFs) is highly desirable for a variety of applications. DSE MOFs as a subclass of intrinsic LMOFs are highly attractive due to no need for encapsulation/functionalization by fluorophores and/or using luminescent linkers. Herein, a highly stable intrinsic dual-state blue emission (λem = 425 nm) zinc-based MOF with rodlike nanostructures (denoted as UoZ-2) was synthesized and characterized. To the best of our knowledge, intrinsic DSE of Zn-MOFs with blue emission in the dispersed form in solution and solid-state fluorescence have not been reported yet. When tetracycline (TC) was added, a continuous color evolution from blue to greenish-yellow with dramatic enhancement was observed due to aggregation induced emission (AIE). Thus, a sensitive ratiometry-based visual detection platform, in solution and on paper independently, was designed for detection of TC exploiting the DSE and AIE properties of UoZ-2 alone and UoZ-2:TC. The detection limit was estimated to be 4.5 nM, which is considered to be one of the most sensitive ratiometric fluorescent probes for TC sensing. The ratiometry paper-based UoZ-2 sensor displays a reliable TC quantitative analysis by recognizing RGB values in the on-site TC detection with satisfactory recoveries.

An indirect competitive assay-based method for the sensitive determination of tetracycline residue using a real-time fluorescence-based quantitative polymerase chain reaction

Tetracycline (TC) is an effective antibiotic used to treat humans and livestock, but its inappropriate use imposes toxic effects, including pollution, on environmental ecology and food. Currently, sensitive, accurate, and cost-effective methods that can detect lower concentrations of TC residues in environmental and food samples are needed. In this study, a novel indirect competitive assay-based aptamer method was developed for detecting TC residues through signal amplification by real-time fluorescence-based quantitative polymerase chain reaction. The response surface methodology was introduced to optimize the optimal concentrations (influencing factors) of the three types of single-stranded DNA in the competitive assay process. The optimal conditions for the three types of ssDNA were 112 nM for the specific aptamer of TC (Apt40), 115 nM for the signal DNA, and 83 nM for the DNA catcher. As expected, under optimal conditions, the Ct value was linearly related to the logarithm of TC concentration. The calibration curve equation was Ct = -0.34516 log[TC] + 9.9345 (R2 = 0.998) in the range of 10-3-103 ng mL-1, and the limit of detection was 7.02 × 10-5 ng mL-1. The new method was effectively applied to detect TC residues in wastewater, honey, and milk samples. It achieved an average recovery rate of 101.19% with a small variation of 5.16%. The validation was carried out using an enzyme-linked immunosorbent assay. This approach demonstrates high sensitivity and selectivity, making it well suited for detecting leftover antibiotics in food when using suitable aptamers.

Stable Europium(III) Metal-Organic Framework Demonstrating High Proton Conductivity and Fluorescence Detection of Tetracyclines

A europium(III) metal-organic framework (MOF), namely, {[[(CH₃)₂NH₂]₃Eu₂(DTTP-2OH)₂(HCOO)(H₂O)]·4H₂O}_n (Eu-MOF, H₄DTTP-2OH = 2',5'-dihydroxy-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid) has been assembled through solvothermal method. The Eu-MOF is a three-dimensional (3D) (4,4,8)-connected topological framework with binuclear Eu(III) clusters as secondary building units, in which a richly ordered hydrogen bonding network formed among the free H₂O molecules, dimethylamine cations, and phenolic hydroxyl groups provides a potential pathway for proton conduction. The proton conductivity reaches the category of superionic conductors (σ > 10^-4 S cm^-1) at room temperature with a maximum conductivity of 1.91 × 10^-3 S cm^-1 at 60 °C and 98% RH. Moreover, it also can be used as a fluorescence sensor in aqueous solution with detection limits of 0.14 μM for tetracycline, 0.13 μM for oxytetracycline and 0.11 μM for doxycycline. These results pave new methods for constructing MOFs with high proton conductivity and responsive fluorescence.

Metal-organic frameworks (MOFs) based luminescent and electrochemical sensors for food contaminant detection

With the increasing population, food toxicity has become a prevalent concern due to the growing contaminants of food products. Therefore, the need for new materials for toxicant detection and food quality monitoring will always be in demand. Metal-organic frameworks (MOFs) based on luminescence and electrochemical sensors with tunable porosity and active surface area are promising materials for food contaminants monitoring. This review summarizes and studies the most recent progress on MOF sensors for detecting food contaminants such as pesticides, antibiotics, toxins, biomolecules, and ionic species. First, with the introduction of MOFs, food contaminants and materials for toxicants detection are discussed. Then the insights into the MOFs as emerging materials for sensing applications with luminescent and electrochemical properties, signal changes, and sensing mechanisms are discussed. Next, recent advances in luminescent and electrochemical MOFs food sensors and their sensitivity, selectivity, and capacities for common food toxicants are summarized. Further, the challenges and outlooks are discussed for providing a new pathway for MOF food contaminant detection tools. Overall, a timely source of information on advanced MOF materials provides materials for next-generation food sensors.

Recent advances in luminescence and aptamer sensors based analytical determination, adsorptive removal, degradation of the tetracycline antibiotics, an overview and outlook

Tetracycline antibiotics (TCs), one of the important antibiotic groups, have been widely used in human and veterinary medicines. Their residues in foodstuff, soil and sewage have caused serious threats to food safety, ecological environment and human health. Here, we reviewed the potential harms of TCs residues to foodstuff, environment and human beings, discussed the luminescence and aptamer sensors based analytical determination, adsorptive removal, and degradation strategies of TCs residues from a recent 5-year period. The advantages and intrinsic limitations of these strategies have been compared and discussed, the potential challenges and opportunities in TCs residues degradation have also been deliberated and explored.

Nanomaterial-based fluorescent biosensors for the detection of antibiotics in foodstuffs: A review

Antibiotics are widely used as bacteriostatic or bactericidal agents against various microbial infections in humans and animals. The excessive use of antibiotics has led to an accumulation of their residues in food products, which ultimately poses a threat to human health. In light of the shortcomings of conventional methods for antibiotic detection (primarily cost, proficiency, and time-consuming procedures), the development of robust, accurate, on-site, and sensitive technologies for antibiotic detection in foodstuffs is important. Nanomaterials with amazing optical properties are promising materials for developing the next generation of fluorescent sensors. In this article, advances in detecting antibiotics in food products are discussed with respect to their sensing applications, with a focus on fluorescent nanomaterials such as metallic nanoparticles, upconversion nanoparticles, quantum dots, carbon-based nanomaterials, and metal-organic frameworks. Furthermore, their performance is evaluated to promote the continuation of technical advances.

Lanthanide bimetallic MOF-based fluorescent sensor for sensitive and visual detection of sulfamerazine and malachite

A lanthanide terbium/europium metal-organic framework (Tb_0.6Eu_0.4-MOF) was prepared by one-step solvothermal method at room temperature. A series of characterizations including scanning electron microscopy, powder X-ray diffraction spectra, Fourier transform infrared spectra and X-ray photoelectron spectroscopy were carried out to clarify the physical characteristics of the synthesized material. The data clarified that the prepared Tb_0.6Eu_0.4-MOF possessed rod-like morphology with a width of 1-2 μm, and had good crystal structure, good stability, response speed and excitation-independent emission feature. The bunchy Tb_0.6Eu_0.4-MOF was then used to construct fluorescent sensors for rapid identification of malachite green and sulfamerazine. It was revealed that the detection mechanism was inner filter effect. The effects of different parameters such as excitation wavelength and incubation times were investigated on the fluorescence analysis performance. The data clarified that the optimal excitation wavelength and incubation time was 240 nm and 3 min, respectively. The detection platform exhibited the high sensitivity and selectivity toward malachite green in the linear range of 2-180 μM and determined limit of detection was 1.12 μM. Besides, the proposed sensor allowed sensitive detection of sulfamerazine in the linear range of 2-140 μM with a low detection limit of 0.1 μM. Meaningfully, a smartphone application was designed to assist the proposed sensor to realize visual, intelligent and rapid detection of malachite green and sulfamerazine. Furthermore, the practical application of the proposed sensor has been also verified by high performance liquid chromatography, showing good accuracy, sensitivity and satisfactory recoveries. The results suggested that the Tb_0.6Eu_0.4-MOF-based ratiometric fluorescent sensor had the potential to become a promising technique for rapid detection of malachite green or sulfamerazine with smartphone application. Therefore, the prepared Tb_0.6Eu_0.4-MOF is one kind of efficient and cost-effective potential materials for developing fluorescent sensor for rapid, sensitive and selective detection of sulfamerazine and malachite.

Bimetallic metal-organic frameworks-based ratiometric fluorescence sensor for the quantitative detection of thiram in fruits samples

The identification of residual thiram (Tr) in foods is vital in view of its harmful effects on human health. Herein, a ratiometric fluorescence sensor (I₄₃₅/I₅₉₀) based on rhodamine B/NH₂-MIL-53(Al_0.75Fe_0.25) was constructed for the detection of Tr. Interestingly, the probe RhB/NH₂-MIL-53(Bim) assisted by Cu²⁺ could rapidly and sensitively recognize Tr with a low detection limit of 0.11 μg/mL in 10 min. The fluorescence sensing mechanism was investigated using fluorescence spectra, UV-Vis absorption spectra, the fluorescence lifetime and quantum yield. The results showed that the excellent sensing performance was attributed to fluorescence resonance energy transfer, electrostatic interaction, and photoinduced electron transfer. In addition, the practical application of this platform showed acceptable relative recoveries for Tr (84.03-107.81 %), and precisions were also achieved (relative standard deviation ≤ 8.69 %, n = 3). These results show that the presented herein can be applied to monitor the Tr content in real fruit samples.

3D rhombohedral microcrystals metal-organic frameworks for electrochemical and fluorescence sensing of tetracycline

Zirconium-based metal-organic frameworks (MOF) exhibiting 3D rhombohedral microcrystals were synthesized by the solvothermal method. The structure, morphology, composition, and optical properties of the synthesized MOF were carried out using different spectroscopic, microscopic, and diffraction techniques. Synthesized MOF was rhombohedral in shape and the cage structure of these crystalline molecules was the active binding site of the analyte, tetracycline (TET). The electronic property and size of the cages are chosen such that a specific interaction with TET was observed. Sensing of the analyte was demonstrated by both the electrochemical and fluorescent techniques. The MOF had significant luminescent properties and exhibited excellent electro-catalytic activity due to embedded zirconium metal ions. An electrochemical and fluorescence sensor was fabricated towards TET where TET binds via hydrogen bond to MOF, and causes fluorescence quenching due to the transfer of electrons. Both approaches exhibited high selectivity and good stability in the presence of interfering molecules such as antibiotics, biomolecules, and ions; and showed excellent reliability in tap water and wastewater sample analysis.

Green-derived carbon dots: A potent tool for biosensing in food safety

The impact of food contaminants on ecosystems and human health has attracted widespread global attention, and there is an urgent need to develop reliable food safety detection methods. Recently, carbon dots (CDs) have been considered as a powerful material to construct sensors for chemical analysis. Based on the concept of resource conversion and sustainable development, the use of natural, harmless, and renewable materials for the preparation of CDs without the involvement of chemical hazards is a current hot topic. This paper reviews the research progress of green-derived CDs and their application in food safety biosensing. The fabrications of green-derived CDs using various biomasses are described in detail, and the application of CDs especially the sensing mechanisms of photoluminescence, colorimetric, electrochemiluminescence and other sensors are provided. Finally, existing shortcomings and current challenges as well as prospects for food safety monitoring are discussed. We believe that this work provides strong insight into the application of CDs in the sensing of various contaminants.

Dual-responsive ratiometric fluorescent sensor for tetracyclines detection based on europium-decorated copper nanoclusters

Development of accurate and efficient TCs residue analysis methods is of great significance for the protection of environment, food safety and public health. Herein, a dual-responsive ratiometric fluorescence sensor being capable of simple and sensitive detection of tetracycline (TC) was presented, which was constructed by immobilizing europium ions (Eu³⁺) onto the mercaptopropionic acid stabilized copper nanoclusters (MPA-Cu NCs). In the presence of TC, the red fluorescence of Eu³⁺ was enhanced through antenna effect (AE), while the green fluorescence of MPA-Cu NCs was quenched through internal filter effect (IFE), leading to an obvious fluorescence color evolution from green to red for the probe solution. In addition to successful design of a smartphone-assisted colorimetric analysis platform for portable detection, a logic gate device capable of intelligently monitoring TC concentration is also designed.

A smartphone-assisted optosensing platform based on chromium-based metal-organic framework signal amplification for ultrasensitive and real-time determination of oxytetracycline

Ultrasensitive and onsite detection of oxytetracycline (OTC) is of vital significance for ensuring public health. Herein, a novel and versatile fluorescence biomimetic nanosensor, Mg,N-CDs@MIL-101@MIP, was elaborately tailored for the assay of OTC. MIL-101 with extraordinarily high surface area and porosity, as a favorable supporter, suppressed self-quenching of Mg,N-CDs and boosted mass transfer rate, realizing signal amplification. As an ultrasensitive signal transducer, high luminescent Mg,N-CDs yielded conspicuous fluorescence responses for OTC, enhancing the sensitivity of Mg,N-CDs@MIL-101@MIP. High-affinity imprinting sites further endowed Mg,N-CDs@MIL-101@MIP with superior anti-interference ability and reusability. Given prominent merits, Mg,N-CDs@MIL-101@MIP demonstrated a good linear range (0.05-40 μg mL^-1) with a lower limit of detection (16.8 ng mL^-1), supplying high accessibility to realize ultrasensitive and highly selective measurement of OTC in samples. Additionally, to attain precise onsite profiling of OTC, an intelligent sensing platform was developed by integrating Mg,N-CDs@MIL-101@MIP with a portable smartphone-assisted optical device. As both signal reader and analyzer, smartphone can instantly capture concentration-dependent fluorescent images and accurately digitize them, accomplishing quantitative analysis of OTC. More delightfully, the portable platform was utilized for visual determination of OTC in milk samples with satisfactory results, offering a promising tool for the high-performance onsite evaluation of food safety and environmental health.

A Zn(II)-Metal-Organic Framework Based on 4-(4-Carboxy phenoxy) Phthalate Acid as Luminescent Sensor for Detection of Acetone and Tetracycline

As hazardous environmental pollutants, residual tetracycline (TC) and acetone are harmful to the ecosystem. Therefore, it is necessary to detect the presence of these pollutants in the environment. In this work, using Zn (II) salt, 4-(4-carboxy phenoxy) phthalic acid (H₃L), and 3,5-bis(1-imidazolyl) pyridine (BMP), a new metal-organic framework (Zn-MOF) known as [Zn₃(BMP)₂L₂(H₂O)₄]·2H₂O was synthesized using a one-pot hydrothermal method. The Zn-MOF has a three-dimensional framework based on the [Zn1N₂O₂] and [Zn2N₂O₄] nodes linked by a tridentate bridge BMP ligand and an L ligand with the μ₁:η¹η⁰/μ₁:η¹η⁰/μ₀:η⁰η⁰ coordination mode. There were two kinds of left- and right-handed helix chains, Zn1-BMP and Zn1-BMP-Zn1-L. The complex was stable in aqueous solutions with pH values of 4-10. The Zn-MOF exhibited a strong emission band centered at 385 nm owing to the π*→π electron transition of the ligand. It showed high luminescence in some common organic solvents as well as in the aqueous solutions of pH 4-10. Interestingly, TC and acetone effectively quenched the luminescence of the Zn-MOF in aqueous solution and enabled the Zn-MOF to be used as a sensor to detect TC and acetone. The detection limits of TC and acetone were observed to be 3.34 µM and 0.1597%, respectively. Even in acidic (pH = 4) and alkaline (pH = 10) conditions, the Zn-MOF showed a stable luminescence sensing capability to detect TC. Luminescence sensing of the Zn-MOF for TC in urine and aquaculture wastewater systems was not affected by the interfering agent. Furthermore, the mechanism of sensing TC was investigated in this study. Fluorescence resonance energy transfer and photoinduced electron transfer were found to be the possible quenching mechanisms via UV-Vis absorption spectra/the excitation spectra measurements and DFT calculations.