Amino-Functionalized Al-MOF for Fluorescent Detection of Tetracyclines in Milk

An asynchronous response fluorescence sensor combines machine learning theory to qualitatively and quantitatively detect tetracyclines

Excess use of tetracyclines poses significant health risks arising from animal-derived foods, meaning simple and sensitive methods to detect tetracyclines would be beneficial given current laboratory methods are complex and expensive. Herein, we describe an asynchronous response fluorescence sensor constructed based on Zn-based metal-organic framework and Ru(bpy)32+ (denoted as Ru@Zn-BTEC) for the qualitative and quantitative detection of tetracyclines in foods. Under excitation at 365 nm, the sensor emitted red fluorescence at 609 nm. When tetracyclines were present, these molecules aggregated in the Ru@Zn-BTEC framework, causing green fluorescence emission at 528 nm. The developed sensing system accurately distinguished the different categories of tetracyclines with a classifier accuracy of 94 %. The Ru@Zn-BTEC sensor demonstrated a detection limit of 0.012 μM and satisfactory recovery (87.81 %-113.84 %) for tetracyclines in food samples. This work provides a pathway for constructing asynchronous response fluorescence sensors for food analysis.

Oxolinic Acid Generated Green Fluorescence Based on a Terbium-Functionalized Covalent Organic Framework

Oxolinic acid (OXO), a classic environmental contaminant, has a terrible detrimental effect on human health. The exploration of efficient strategies to detect and detecting OXO has remarkable significance. Herein, we reported a novel terbium(III)-functionalized covalent organic framework (Bpy-DhBt-COF@Tb3+) by fixing Tb3+ on the bipyridine-connecting COF (Bpy-DhBt-COF) as a turn-on fluorescent switch toward OXO for the first time. In this platform, Tb3+ acts as the specific recognition units for OXO and the response signal, while Bpy-DhBt-COF acts as the safehaven for Tb3+. Once introducing OXO to Bpy-DhBt-COF@Tb3+, OXO can instead water molecules coordinate with Tb3+ and sensitize Tb3+ instantly, thereby producing a significant fluorescence signal. Profiting from the excellent porosity of Bpy-DhBt-COF@Tb3+, it can obtain optimal response toward OXO only within 10 s with an ultrasensitive detection limit of 12.5 nM. Furthermore, Bpy-DhBt-COF@Tb3+ displayed outstanding selectivity toward OXO than other general quinolones. Based on these, a Tb3+-based COF was explored for the first time for the turn-on fluorescence detection of an OXO with rapid response, high sensitivity, and outstanding selectivity. In this work, we not only exhibit the attractive performance of Tb3+-functionalized COF to detect OXO but also propose a prospect strategy for creating other fluorescent sensors for multiple targets.

A dual-response ratiometric fluorescent sensor by europium-doped silicon nanoparticles for fluorescent and smartphone imaging detection of tetracycline

Given the threat to human health posed by the abuse of tetracycline (TC), the development of a portable, on-site methods for highly sensitive and rapid TC detection is crucial. In this work, we initially synthesized europium-doped silicon nanoparticles (SiEuNPs) through a facile one-pot microwave-assisted method. Due to its blue-red dual fluorescence emission (465 nm/627 nm), which was respectively attributed to the silicon nanoparticles and Eu3+, SiEuNPs were designed as a ratiometric fluorescent sensor for TC detection. For the dual-signal reverse response mechanism: TC quenched the blue emission from silicon nanoparticles through inner filter effect (IFE), and enhanced the red emission through "antenna effect" (AE) between TC and Eu3+, the nanoprobe was able to detect TC within a range of 0.2-10 μM with a limit of detection (LOD) of 10.7 nM. Notably, the equilibrium detection time was only 1 min, achieving rapid TC detection. Furthermore, TC was also measured in real samples (tap water, milk and honey) with recoveries ranging from 95.7 % to 117.0 %. More importantly, a portable smartphone-assisted on-site detection platform was developed, enabling real-time qualitative identification and semi-quantitative analysis of TC based on fluorescence color changes. This work not only provided a novel doped silicon nanoparticles strategy, but also constructed a ratiometric sensing platform with dual-signal reverse response for intuitive and real-time TC detection.

A dual-response ratiometric fluorescent sensor for oxytetracycline determination in milk and mutton samples

Owing to the adverse effects of oxytetracycline (OTC) residues on human health, it is of great importance to construct a rapid and effective strategy for OTC detection. Herein, we developed a dual-response fluorescence sensing platform based on molybdenum sulfide quantum dots (MoS2 QDs) and europium ions (Eu3+) for ratiometric detection of OTC. The MoS2 QDs, synthesized through an uncomplicated one-step hydrothermal approach, upon OTC integration into the MoS2 QDs/Eu3+ sensing system, exhibit a significant quenching of blue fluorescence due to the inner filter effect (IFE), simultaneously enhancing the distinct red emission of Eu3+ at 624 nm, a phenomenon attributed to the antenna effect (AE). This sensor demonstrates exceptional selectivity and sensitivity towards OTC, characterized by a linear detection range of 0.2-10 μM and a notably low detection limit of 2.21 nM. Furthermore, we achieved a visual semi-quantitative assessment of OTC through the discernible fluorescence color transition from blue to red under a 365 nm ultraviolet lamp. The practical applicability of this sensor was validated through the successful detection of OTC in milk and mutton samples, underscoring its potential as a robust tool for OTC monitoring in foodstuffs to safeguard food safety.

Portable tri-color ratiometric fluorescence paper sensor for intelligent visual detection of dual-antibiotics and aluminium ion

The toxicological effect between co-existed antibiotics and metal ions was dangerous to the ecological environment and public health. However, the rapid quantification tools with convenience, accuracy and low cost for the detection of multiple targets were still challenging. Herein, a portable tri-color ratiometric fluorescence paper sensor was constructed by coupling of blue carbon dots and fluorescence imprinted polymer for down/up conversion simultaneous detection of tetracycline and sulfamethazine. Interestingly, the cascade detection of aluminum ion was also realized based on the individual detection system of tetracycline without the assistance of complex coupling reagents. The detection limits of smartphone method for the visual detection of tetracycline, sulfamethazine and aluminum ion were calculated as 0.014 μM, 0.004 μM and 0.019 μM, respectively. The portable fluorescence paper sensor was applied for the visual detection of tetracycline, sulfamethazine and aluminum ion in actual samples successfully with satisfactory recoveries. With the advantages of rapidness, low cost, and portability, the developed portable fluorescence paper sensor provided a new strategy for the visual real-time detection of multiple targets.

A combined experimental and theoretical approach for doxycycline sensing using simple fluorescent probe with distinct fluorescence change in wide range of interferences

Overuse of doxycycline (DOXY) can cause serious problems to human health, environment and food quality. So, it is essential to develop a new sensing methodology that is both sensitive and selective for the quantitative detection of DOXY. In our current research, we synthesized a simple fluorescent probe 4,4'-bis(benzyloxy)-1,1'-biphenyl (BBP) for the highly selective detection of doxycycline by through fluorescence spectroscopy. The probe BBP displayed ultra-sensitivity towards doxycycline due to Forster resonance energy transfer (FRET). Fluorescence spectroscopy, density functional theory (DFT), 1H NMR titration, UV-Vis, and Job's plot were used to confirm the sensing mechanism. The charge transfer between the probe and analyte was further examined qualitatively by electron density differences (EDD) and quantitively by natural bond orbital (NBO) analyses. Whereas the non-covalent nature of probe BBP towards DOXY was verified by theoretical non-covalent interaction (NCI) analysis as along with Bader's quantum theory of atoms in molecules (QTAIM) analysis. Furthermore, probe BBP was also practically employed for the detection of doxycycline in fish samples, pharmaceutical wastewater and blood samples.

State-of-the-art nanosensors and kits for the detection of antibiotic residues in milk and dairy products

Antibiotic resistance is increasingly seen as a future concern, but antibiotics are still commonly used in animals, leading to their accumulation in humans through the food chain and posing health risks. The development of nanomaterials has opened up possibilities for creating new sensing strategies to detect antibiotic residues, resulting in the emergence of innovative nanobiosensors with different benefits like rapidity, simplicity, accuracy, sensitivity, specificity, and precision. Therefore, this comprehensive review provides pertinent and current insights into nanomaterials-based electrochemical/optical sensors for the detection of antibitic residues (ANBr) across milk and dairy products. Here, we first discuss the commonly used ANBs in real products, the significance of ANBr, and also their binding/biological properties. Then, we provide an overview of the role of using different nanomaterials on the development of advanced nanobiosensors like fluorescence-based, colorimetric, surface-enhanced Raman scattering, surface plasmon resonance, and several important electrochemical nanobiosensors relying on different kinds of electrodes. The enhancement of ANB electrochemical behavior for detection is also outlined, along with a concise overview of the utilization of (bio)recognition units. Ultimately, this paper offers a perspective on the future concepts of this research field and commercialized nanomaterial-based sensors to help upgrade the sensing techniques for ANBr in dairy products.

Simple fluorescence "turn-off" assay for Congo red using commercial 2-aminophthalic acid

In this work, the fluorescence properties of 2-aminophthalic acid (NH2-BDC) were studied. NH2-BDC possessed excellent optical properties including bright blue emission with maximum emission at 425 nm, a high quantum yield of 38.49% and excellent photostability. And the fluorescence of NH2-BDC could be selectively quenched by Congo red, which was ascribed to the inner filter effect. Accordingly, NH2-BDC was further employed for fluorescence "turn-off" assay of Congo red with a linear range of 0.05-50 μM and a limit of detection of 1.72 μM. And the sensor was used for the detection of Congo red in real water samples with acceptable results.

Design of a dual-mode ratiometric fluorescent probe via MOF-on-MOF strategy for Al (III) and pH detection

BACKGROUND

The construction of ratiometric fluorescent MOF sensors with integrated self-calibration and dual-channel detection can efficiently overcome the deficiencies of single-signal sensing. In this regard, the rational design of structurally functionalized MOFs is paramount for enhancing their performance in ratiometric fluorescent sensors. Lately, the concept of MOF-on-MOF design has garnered notable interest as a potential strategy for regulating the structural parameters of MOFs by integrating two or more distinct MOF types. Great efforts have been dedicated to exploring new MOF-on-MOF hybrids and developing their applications in diverse fields. Even so, these materials are still in the stage of advancement in the sensing field.

RESULTS

Herein, a Zr-based metal-organic framework anchored on a rare-earth metal-organic framework (UiO-66(OH)2@Y-TCPP) was prepared for the ratiometric fluorescence detection toward Al (III) and pH. In this probe, the UiO-66(OH)2 featured hydroxyl active sites for Al (III), leading to a significant enhancement in fluorescence intensity upon the addition of Al (III), while the signal emitted by the red-emitting Y-TCPP, serving as the reference, remained constant. UiO-66(OH)2@Y-TCPP exhibited excellent selectivity for Al (III) sensing with a wider linear range of 0.1-1000 μM, and a lower detection limit of 0.06 μM. This probe has also been utilized for the quantitative determination of Al (III) in hydrotalcite chewable tablets with satisfactory results. In addition, the probe realized ratiometric pH sensing in the range of 7-13 using UiO-66(OH)2 as an interior reference. The paper-based probe strip was developed for visual pH sensing. By installing color recognition and processing software on a smartphone, real-time and convenient pH sensing could be achieved.

SIGNIFICANCE

This is the first ratiometric fluorescent sensor for Al (III) and pH detection based on a MOF-on-MOF composite probe, which yields two different response modes. The detection results of Al (III) in hydrotalcite chewable tables and smartphone imaging for pH test paper demonstrate the practicability of the probe. This work opens up a new outlook on constructing a multi-functional application platform with substantial potential for employment in environmental and biological analysis tasks.

Nanozyme-induced deep learning-assisted smartphone integrated colorimetric and fluorometric dual-mode for detection of tetracycline analogs

In this work, a colorimetric and fluorescent dual-mode probe controlled by NH2-MIL-88 B (Fe, Ni) nanozymes was developed to visually detect tetracycline antibiotics (TCs) residues quantitatively, as well as accurately distinguish the four most widely used tetracycline analogs (tetracycline (TC), chrycline (CTC), oxytetracycline (OTC), and doxycycline (DC)). Colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) may be oxidized to blue oxidized TMB by the Fe Fenton reaction, which was catalyzed by the NH2-MIL-88 B (Fe, Ni) nanozyme with POD-like activity. The colorimetric detection system allows TCs to interact with NH2-MIL-88 B (Fe, Ni). This inhibits the production of ·OH, weakens the oxidation process of TMB, and ultimately lightens the blue color in the system by blocking the electron transfer between NH2-MIL-88 B (Fe, Ni) and H2O2. Furthermore, TCs can interact with NH2-MIL-88 B (Fe, Ni) as a result of the internal filtering effect, which causes the fluorescence intensity to decrease as TCs concentration increases. Additionally, a portable instrument that combines a smartphone sensing platform with colorimetric and fluorescent signals was created for the quick, visual quantitative detection of TCs. The colorimetric and fluorescent dual-mode nano platform enables color change, with detection limits (LODs) of 0.182 μM and 0.0668 μM for the spectrometer and smartphone sensor, respectively, based on the inhibition of fluorescence and enzyme-like activities by TCs. Overall, the colorimetric and fluorescence dual-mode sensor has good stability, high specificity, and an efficient way to eliminate false-positive issues associated with a single detection mode.

Aggregation-induced emission carbon dots as Al3+-mediated nanoaggregate probe for rapid and selective detection of tetracycline

Worldwide abuse of tetracycline (TC) seriously threatens environmental safety and human health. Metal-TC complexes formed by residual TC in the environment can also contribute to the spread of antibiotic resistance. Therefore, monitoring of TC residues is still required. Here, we report novel aggregation-induced emission carbon dots (AIE-Cdots) as nanoaggregate probes for the rapid and selective detection of TC residue. Riboflavin precursors with rotational functional groups led to the development of AIE-Cdots. The aggregation of AIE-Cdots was induced selectively for Al3+, amplifying the fluorescence signals owing to the restricted rotation of the side chains on the AIE-Cdot surface. The fluorescence signal of such Al3+-mediated nanoaggregates (Al3+-NAs) was further triggered by the structural fixation of TC at the Al3+ active sites, suggesting the formation of TC-coordinated Al3+-NAs. A linear correlation was observed in the TC concentration range of 0-10 μM with a detection limit of 42 nM. In addition, the strong Al3+ binding affinity of AIE-Cdots produced similar NAs and enhanced fluorescence signals in Al3+-TC mixtures. These AIE-Cdots-based nanoplatforms have a rapid response, good selectivity, and reliable accuracy for detecting TC or aluminum complexes, meeting the requirements for hazardous substance monitoring and removal in environmental applications.

Dual-emission carbon dots for ratiometric fluorescence sensing of thiabendazole in fruits

Quantitative determination of pesticides in fruits and vegetables is essential for human healths. Herein, a new dual-emission carbon dots with high fluorescence stability at a pH range of 4-10 and a temperature range of 0-60 °C was synthesized. And a novel ratiometric fluorescence probe was proposed to detect thiabendazole (TBZ) residue with a wide linear range (0-1000 μM) and low detection limit (0.15 μM). The emission at 512 nm exhibited a special "turn-off" fluorescence sensing of TBZ due to internal filter effect, while that at 361 nm barely changed and worked as reference. Furthermore, the ratiometric fluorescence strategy was successfully applied for determining TBZ in fruits with good recoveries (96.73%-111.17 %, 93.29%-120.78 % and 96.28%-100.57 %, respectively). Notably, the constructed ratiometric fluorescence probe had comparable accuracy to HPLC in detecting unknown concentrations of TBZ in pear juice, demonstrating dual-emission carbon dots possess wide and promising applicability for fluorescence sensing pesticides in the future.

A fluorescence and SERS dual-mode sensing on tetracycline antibiotics based on Ag@NH2-MIL-101(Al) nanoprobe

Antibiotic residues are becoming more and more concern due to the increasingly serious resistance from bacteria to organism. On-site and accurate evaluation on antibiotics is necessary and urgent to effectively solve such public issue. To provide point-of-care-test (POCT) ideas for antibiotic accurate evaluation, a fluorescence (FL)-surface-enhanced Raman scattering (SERS) dual-mode detection of tetracycline antibiotic (TCs) was realized for the first time. Based on the inner filter effect in Ag@NH2-MIL-101(Al) nanoprobe, the fluorescence quenching was induced and the SERS signal was swiftly turn on through π-π interaction and hydrogen bonding in the presence of TCs. This FL-SERS dual mode sensor displayed excellent detection limits (FL in ∼10-3 ppm, SERS in ∼10-5 ppm), and achieved a reliable detection of TCs in honey with a recovery rate of 84.45%-112.08%. This method combines the advantages of FL and SERS detection, meanwhile, two techniques verified against each other to achieve highly sensitive and specific FL-SERS dual-mode sensor for TCs. We believe that such antibody-or aptamer-independent FL and SERS complementary nanoprobe can be applied to fast, direct and multiple sensing in environment and food hazards.

Boron difluoride modified zinc metal-organic framework-based "off-on" fluorescence sensor for tetracycline and Al3+ detection

A novel fluorescence "off-on" probe was developed using a boron difluoride-modified zinc metal-organic framework (Zn-MOF3) for sensitive determination of tetracycline (TC) and Al3+. The Zn-MOF3 has excellent optical property and good applicability in aqueous phase. The fluorescence recorded at 436 nm was quenched at the excitation wavelength of 336 nm. Signal-off detection of tetracycline via fluorescence quenching of Zn-MOF3 is based on the inner filter effect. Fluorescence on-off-on detection of Al3+ occurs via the specific binding between tetracycline and Al3+. The limits of detection for TC and Al3+ were 28.4 nM and 106.7 nM, respectively. This probe exhibited high selectivity which was used for the determination of TC and Al3+ with satisfied recoveries (89.8 to 105.6% for TC, 90.0 to 110.4% for Al3+) and good precision (< 5%) in milk. The developed sensor represents the first "off-on" system for fluorescence detection of TC and Al3+ based on Zn-MOF3 with a better aspect of the innovation.

Terbium doping and energy level modification of zirconium organic frameworks as probes for the improved determination of histamine and visual inspection of food freshness

Food safety is a common concern among people, and the development of high-performance food freshness detection technology is crucial, but is still highly challenging. Fluorescent sensing based on metal organic frameworks is a promising technology to tackle this issue. In this work, three UiO-66 type Zirconium organic frameworks (ZrOFs) which are functionalized with varying numbers of hydroxyl groups to alter the energy levels, and partial replacement of Zirconium(IV) by Terbium(III) ions to introduce additional emitting centers, were explored as probes for the sensing of Histamine (His). With one hydroxyl group introduced, UiO-66-OH@Tb can be developed as ratiometric fluorescent probe with improved sensing performance, showing a wide detection range of 0 to 120 mg/L, and a low detection limit of 0.13 mg/L. UiO-66-OH@Tb can also be fabricated into composite film to function as visual sensing material of His. This work can provide instructions for the development of other fluorescent sensors.

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.

Octahedral Cu2O nanomaterials as electrochemical aptasensor for sensitive detection of tetracycline in milk

In this work, A novel label-free electrochemical biosensor based on octahedral Cu2O @ Au nanocomposites was developed for the detection of tetracycline. The gold nanoparticles (AuNPs) on the surface of Cu2O nanomaterials not only improve the electrochemical performance, but also can be used as a binding site for thiol-modified tetracycline aptamers, which can specifically bind to tetracycline. Cu2O @ Au nanocomposites provide a synergistic effect of electrochemical signal amplification and tetracycline recognition strategy. Under the optimal conditions, the proposed biosensor exhibited different electrochemical reactions for different concentrations of tetracycline, with a linear range of 1 nM-1000 μM and a detection limit of 0.16 nM. This work provides a new idea for rapid and sensitive detection of tetracycline by using a simple and economical tetracycline aptamer combined with Cu2O @ Au biosensor platform.

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.

Preparation of fluorescent sensor based on Zn metal-organic framework for detection and determination of raloxifene as an anticancer drug

Breast cancer is the second leading cause of death for women worldwide. Raloxifene (RLX) is a somewhat effective drug in lowering cholesterol, preventing and treating invasive breast cancer in postmenopausal women with osteoporosis, and does not interfere with breast tissue. Nevertheless, considering the possibility of risk in biological function due to excessive use of anticancer drugs and the adverse effects of drugs in wastewater on plants, animals, and aquatic, it is useful to determine the concentration of RLX in water and human body fluids. Here, a fluorescent metal-organic framework (MOF) nanoparticle based on trinuclear zinc clusters called Zn-MOF was presented, which is a high-performance and fast-response fluorescent chemosensor that can be used to detect RLX based on the fluorescence quenching medium in water. FTIR, XRD, SEM, and EDS analyses were used to identify the functional group and determine the structure and morphology of Zn-MOF. pH range 3-10. The prepared nanoparticles showed symmetric emission with excitation at a wavelength of 310.0 nm. The performance of the proposed fluorescent nanosensor was proportional to the quenching of the fluorescent signal with increasing RLX concentration at 404.0 nm; the quenching fluorescence response was linear in RLX concentration from 0.7 to 350 ng/mL with a significant detection limit equal to 0.485 nM.

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.

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.

Concentration- and Self-Catalysis-Dominated Rapid Synthesis of Multifunctional UiO-66(Ce) for Dual-Mode Sensing of Tetracycline

Simple and rapid synthesis of multifunctional metal-organic frameworks (MOFs) at room temperature (RT) with their multifunction controllable is still appealing for further expansion of the practical applications of MOFs. Herein, in this work, rapid RT synthesis of a multifunctional UiO-66(Ce) [M-UiO-66(Ce)] with both oxidase-like activity and fluorescence emission properties was facilely achieved within 15 min through a straightforward reactant concentration modulation and self-catalytic postmodification strategy. Appropriate concentrations of cerium ammonium nitrate or 1,4-benzenedicarboxylic acid (BDC) were beneficial for the synthesis of UiO-66(Ce) with better crystallization. During the postmodification process, through regulation of the self-photocatalysis of UiO-66(Ce), a high conversion rate from BDC to BDC-OH of up to 14% can be obtained, resulting in a significantly enhanced fluorescence signal of M-UiO-66(Ce) within 2 min. Moreover, M-UiO-66(Ce) enabled the accurate and reliable detection of tetracycline (TC) in real samples. Besides, the colorimetric and fluorescence modes complemented each other, expanding the linear range of TC detection and exhibiting its great potential for practical applications. This work provides new insights for the convenient and rapid synthesis of multifunctional materials based on MOFs, which is favorable for promoting the large-scale preparation of MOFs and their practical application in on-site environmental pollutant sensing.

Sensitive fluorescent detection of phosmet and chlortetracycline in animal-derived food samples based on a water-stable Cd(II) chain-based zwitterionic metal-organic framework

The residues of pesticides and antibiotics have always been a major concern in agriculture and food safety. In order to provide a new method for the rapid detection of organophosphorus pesticides and antibiotics, a novel Cd(II) chain-based zwitterionic metal-organic framework MOF 1 with high sensitivity fluorescence sensing performance was successfully synthesized. A series of researches showed that the water- and pH-stable bifunctional MOF 1 has a great ability to detect phosmet (PSM) and chlortetracycline (CTC) in water through fluorescence quenching effect, with high detection sensitivity, low detection limits (0.0124 μM and 0.0131 μM), short response time (40 s) and reusability. Practical application results revealed that MOF 1 could detect PSM and CTC in milk, beef, chicken and egg samples, with satisfactory recoveries (95.2%-103.7%). As a novel fluorescence probe, MOF 1, is known the first case that can detect PSM in animal-derived samples, and the first dual-function material capable of detecting PSM and CTC. Mechanism studies displayed that competitive absorption and photoinduced electron transfer clearly authenticate the high quenching performance of the material.

Highly Efficient Fluorescent Detection of Vitamin B12 Based on the Inner Filter Effect of Dithiol-Functionalized Silver Nanoparticles

We report a fluorescent assay for the determination of vitamin B12 (VB12) based on the inner filter effect (IFE) of 1,3-propanedithiol-functionalized silver nanoparticles (PDT-AgNPs). PDT was simply functionalized on the surface of AgNPs through Ag-thiol interaction, which leads to significantly enhanced fluorescence, with excitation and emission at 360 and 410 nm, respectively, via their thiol-mediated aggregation. Since target VB12 has strong absorption centered at 360 nm, which is almost completely overlapping with the excitation spectra of PDT-AgNPs, the VB12 induced strong quenching of the fluorescence of PDT-AgNPs via IFE. The IFE-based mechanism for the fluorescence quenching of PDT-AgNPs in the presence of VB12 was confirmed by the analyses of Stern-Volmer plots at different temperatures and fluorescence decay curves. The fluorescence-quenching efficiency of PDT-AgNPs was linearly proportional to the concentration of VB12 in a wide range of 1 to 50 μM, with a lower detection limit of 0.5 μM, while preserving excellent selectivity toward target VB12 among possible interfering molecules. Furthermore, the PDT-AgNPs-mediated assay succeeded in quantitatively detecting VB12 in drug tablets, indicating that PDT-AgNPs can serve as an IFE-based fluorescent probe in pharmaceutical preparations by taking advantages of its ease of use, rapidity, and affordability.

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.

A Turn-Off Fluorescent Biomimetic Sensor Based on a Molecularly Imprinted Polymer-Coated Amino-Functionalized Zirconium (IV) Metal-Organic Framework for the Ultrasensitive and Selective Detection of Trace Oxytetracycline in Milk

Developing sensitive and effective methods to monitor oxytetracycline residues in food is of great significance for maintaining public health. Herein, a fluorescent sensor (NH₂-UIO-66 (Zr)@MIP) based on a molecularly imprinted polymer-coated amino-functionalized zirconium (IV) metal-organic framework was successfully constructed and first used for the ultrasensitive determination of oxytetracycline. NH₂-UIO-66 (Zr), with a maximum emission wavelength of 455 nm under 350 nm excitation, was prepared using a microwave-assisted heating method. The NH₂-UIO-66 (Zr)@MIP sensor with specific recognition sites for oxytetracycline was then acquired by modifying a molecularly imprinted polymer on the surface of NH₂-UIO-66 (Zr). The introduction of NH₂-UIO-66 (Zr) as both a signal tag and supporter can strengthen the sensitivity of the fluorescence sensor. Thanks to the combination of the unique characteristics of the molecularly imprinted polymer and NH₂-UIO-66 (Zr), the prepared sensor not only exhibited a sensitive fluorescence response, specific identification capabilities and a high selectivity for oxytetracycline, but also showed good fluorescence stability, satisfactory precision and reproducibility. The fabricated sensor displayed a fluorescent linear quenching in the OTC concentration range of 0.05-40 μg mL^-1, with a detection limit of 0.012 μg mL^-1. More importantly, the fluorescence sensor was finally applied for the detection of oxytetracycline in milk, and the results were comparable to those obtained using the HPLC approach. Hence, the NH₂-UIO-66 (Zr)@MIP sensor possesses great application potential for the accurate evaluation of trace oxytetracycline in dairy products.

Smartphone-assisted ratiometric sensing platform for on-site tetracycline determination based on europium functionalized luminescent Zr-MOF

Accurate on-site analysis of tetracycline (TC) is of great research value for ensuring food safety and estimating environmental pollution. Herein, a smartphone-based fluorescent platform for TC detectionhas been developed based on a europium functionalized metal-organic framework (Zr-MOF/Cit-Eu). Based on the inner filter and antenna effect between Zr-MOF/Cit-Eu and TC, the probe exhibited a ratiometric fluorescent response toward TC, resulting in an emission color change from blue to red. Excellent sensing performance was achieved with a detection limit of 3.9 nM, consistent with the linear operation spanning nearly four orders of magnitude. Subsequently, visual test strips based on Zr-MOF/Cit-Eu were prepared, possessing the potential for accurate testing of TC via RGB signals. Finally, the proposed platform was well applied in actual samples with satisfied recoveries (92.27 to 110.22%). This MOF-based on-site fluorescent platform holds great potential on constructing intelligent platform for visual and quantitative detection of organic contaminants.

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.

Amino-functionalized Al-MOF modulated TpTt-COF with dual-emission for fluorescent and optosmart detecting tetracycline in food samples

Tetracycline residues in animal-derived food pose serious harm to human health, making it demanded to develop simple and sensitive method for detecting tetracycline. Herein, a dual-emission synchronous response fluorescence probe is reported based on amino-functionalized Al-MOF modulated TpTt-COF (donate as NMT). NMT exhibits excellent dual-emission at 455 and 575 nm under single excitation. Tetracycline is sensitively detected through quenching the dual-emission of NMT. NMT specifically recognizes tetracycline through intermolecular hydrogen bonding between -OH/-NH₂ of tetracycline and deprotonated O^-/-NH-/CN of NMT. A calibration curve is built between the fluorescence ratio and the tetracycline concentration with a detection limit of 0.014 μmol/L. NMT is employed to detect tetracycline in milk, pork and chicken, and displays satisfactory recoveries of 94.39-105.67%, respectively. The optosmart sensor based on NMT and smartphone has been constructed for visually detecting tetracycline. This method provides routes to construct MOF-COF fluorescence probes and has good prospects in food analysis.

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.

Discrimination of Chinese green tea according to tea polyphenols using fluorescence sensor array based on Tb (III) and Eu (III) doped Zr (IV) metal-organic frameworks

A facile and rapid fluorescence sensor array based on Tb (III) and Eu (III) doped Zr (IV) metal-organic frameworks was proposed for Chinese green tea discrimination. According to large porosity of Tb@UiO-66-(COOH)₂ and Eu@UiO-66-(COOH)₂, phenolic hydroxyl groups of tea polyphenols could coordinate with free carboxylic acid groups and was captured into the pores, which led to the disturbance of electronic structure of ligand and inhibited the energy transfer efficiency from ligand to Tb (III) and Eu (III) center, causing the fluorescence quenching effect. Based on Hierarchy Cluster Analysis and Linear Discrimination Analysis, the fluorescence sensor array was employed for successful tea polyphenols classification through the analysis of different fluorescence quenching effect to tea polyphenols. Green tea samples within different categories and grades were also successfully discriminated using this assay according to tea polyphenols, providing a new method for Chinese green tea identification.

Amino-functionalized Fe(III)-Based MOF for the high-efficiency extraction and ultrasensitive colorimetric detection of tetracycline

In order to achieve the simultaneous extraction and detection of tetracycline (TC) in milk, the amino-functionalized Fe-based metal-organic frameworks (NH₂-MIL-88B) was synthesized via a solvothermal method with Fe³⁺ and 2-aminoterephthalic acid (NH₂-BDC) as precursor. Thanks to the unique structure of NH₂-MIL-88B, it could be used to highly effective extract of TC in milk. More interestedly, the introduced -NH₂ could react with -OH from TC by a hydrogen-bonding interaction to cause the electronic interactions that enhances the peroxidase-like activity of NH₂-MIL-88B, which result in the enhancement of Fenton reaction by the transfer of the electron between TC and NH₂-MIL-88B. Under the optimal testing conditions, the linear absorbance response is well correlated with the TC concentration range of 50-1000 nM, which can reach a low LOD of 46.75 nM. Besides, the sensor exhibits excellent selectivity to TC, and the proposed strategy can also be applied to milk with good recovery (83.33-107.00%). Finally, the NH₂-MIL-88B and cellulose acetate (CA) are combined to form nanozyme hybrid membranes through the non-solvent induced phase separation method, which can be used to prepare point-of-care testing (POCT) for rapid and in-situ detection of TC.

Development of europium(III) complex functionalized silica nanoprobe for luminescence detection of tetracycline

Increasing awareness of the health and environment impacts of the antibiotics misuse or overuse, such as tetracycline (TC) in treatment or prevention of infections and diseases, has driven the development of robust methods for their detection in biological, environmental and food systems. In this work, we report the development of a new europium(III) complex functionalized silica nanoprobe (SiNPs-Eu³⁺) for highly sensitive and selective detection of TC residue in aqueous solution and food samples (milk and meat). The nanoprobe is developed by immobilization of Eu³⁺ ion onto the surface of silica nanoparticles (SiNPs) as the emitter and TC recognition unit. The β-diketone configuration of TC can further coordinate with Eu³⁺ steadily on the surface of nanoprobe, facilitating the absorption of light excitation for Eu³⁺ emitter activation and luminescence "off-on" response. The dose-dependent luminescence enhancement of SiNPs-Eu³⁺ nanoprobe exhibits good linearities, allowing the quantitative detection of TC. The SiNPs-Eu³⁺ nanoprobe shows high sensitivity and selectivity for TC detection in buffer solution. Time resolved luminescence analysis enables the elimination of autofluorescence and light scattering for highly sensitive detection of TC in milk and pork mince with high accuracy and precision. The successful development of SiNPs-Eu³⁺ nanoprobe is anticipated to provide a rapid, economic, and robust approach for TC detection in real world samples.

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 dual-signal fluorescent colorimetric tetracyclines sensor based on multicolor carbon dots as probes and smartphone-assisted visual assay

The widespread presence of tetracyclines in the environment has raised concerns about the potential risks to ecosystems and human health. The ratiometric fluorescence sensor for detecting tetracyclines was developed using europium-doped carbon dots (Eu-CDs) as probes under alkaline conditions. The sensing mechanism of sensor for tetracyclines was considered as inner filter effect (IFE), antenna effect (AE), and self-quenching effect (SQE). The sensor had a wide linear detection range than the reported europium ions-based tetracyclines sensors. The linear detection ranges of oxytetracycline (OTC), tetracycline (TC), doxycycline (DC) and chlorotetracycline (CTC) were respectively 0.00-603.75 μM, 0.00-623.82 μM, 0.00-594.61 μM and 0.00-601.54 μM, and the corresponding detection limits were respectively 9.50 nM, 15.80 nM, 10.40 nM and 90.30 nM. The smartphone with RGB Color Picker was further employed to analyze the concentration of tetracyclines, which provided a new method for visual tetracyclines detection. The application of Eu-CDs test paper was also explored, and the results showed that the Eu-CDs test paper has great potential application in the visual detection of tetracyclines. In addition, the accuracy of the established tetracyclines sensor was compared with that of the China national standard method by high-performance liquid chromatography (HPLC), and the results showed that the established method in this work has similar accuracy to the China national standard method. The sensor has been employed to detect tetracyclines in the actual samples with satisfactory results, which indicated that this method has promising applications in the real-time monitoring tetracyclines of food and environment.

Zn-MOFs composites loaded with silver nanoparticles are used for fluorescence sensing pesticides, Trp, EDA and photocatalytic degradation of organic dyes

The abuse of pesticides, antibiotics, organic solvents, etc., not only deteriorates the ecological environment, but even affects the normal development of organisms, posing a serious threat to global public health.Efficient and sensitive detection of pesticides, antibiotics, organic solvents and so on are very important, but also a challenge to scientists. By depositing Ag nanoparticles on the surface of Zn-MOF (1: {[Zn₂(bta)(bpy)(H₂O)₂]·2H₂O}_n), a new type of composite material (Ag@1) was successfully synthesized and analyzed by TEM, EDS, XPS, XRD, IR and other characterization methods. Ag@1 can serve as multi-response fluorescence sensor to detect pesticides (fluazinam (FLU) and emamectin benzoate (EMB)), Tryptophan (Trp) and Ethylenediamine (EDA). In particular, Ag@1 showed "turn-off" fluorescence sensing for FLU and EDA, and "turn-on" fluorescence sensing for EMB and Trp. It is worth mentioning that we further explored its analysis of FLU and Trp in real water samples and fetal bovine serum. The recoveries are satisfactory, 97.95 % - 102.39 % and 96.69 % - 101.85 %, respectively. In addition, the photocatalytic performance of Ag@1 was found to be excellent, the degradation rate of methylene blue (MB) reached 86 %, and its degradation mechanism was discussed.

Multi-excitation wavelength of gold nanocluster-based fluorescence sensor array for sulfonamides discrimination

Sulfonamides (SAs) are widely used in many fields because of their advantages, including low price, wide antibacterial spectrum, and high stability. However, their accumulation in the human body leads to a variety of serious diseases. Therefore, it is necessary to design a convenient, effective, and sensitive method to detect SAs. Moreover, the fluorescence excitation spectrum has rich information characteristics, especially for the interaction between fluorophore and quencher via various mechanisms. However, the excitation wavelength-guided sensor array construction does not draw proper attention. To address these issues, we used BSA-AuNCs as a single probe to construct a sensor array for the detection of five SAs. The selected SAs showed different quenching effects on the fluorescence intensities of BSA-AuNCs. The changes in the fluorescence intensity at different excitation wavelengths (λ = 230, 250, and 280 nm) have been applied to construct our sensor array and address the distinguishability between the selected SAs. With helping of pattern recognition methods, five different SAs have been identified at three different concentrations. Additionally, qualitative analysis at different moral ratios and quantitative analysis at nanogram concentrations have been considered. Moreover, the proposed sensor array was successfully used to distinguish between different SAs in commercial milk with an accuracy of 100 %. This study provides a simple and powerful approach to SAs detection. Also, it shows a broad application prospect in the field of food and drug monitoring.

Fluorescence turn-off sensing strategy based on Al-based MOF for selective detection of tricresyl phosphate

Tricresyl phosphate (TCP), a notable emerging pollutant with a high bioconcentration factor and biotoxicity, is a typical representative of aryl-organophosphorus flame retardants. The electrochemical and chromatographic technologies used in conventional TCP detection have a variety of drawbacks. Hence, it is crucial to suggest an easy, accurate, and selective method for detecting TCP. In this study, we presented a brand-new method based on NH₂-MIL-53(Al) nanoprobe for the direct luminescence assay of TCP. NH₂-MIL-53(Al) possessed an excellent crystal structure and superior optical qualities. Notably, the introduction of TCP caused a considerable dampening of the photoluminescence signal of the nanoprobe. The fluorescence response based on static quenching was verified by fluorescence lifetime decay curves. The thermodynamic analysis further concluded that TCP and nanoprobe spontaneously produced non-fluorescent complexes due to hydrophobic interaction. The quenching efficiency (F₀-F)/F₀ of the nanoprobe and the TCP concentration displayed good linearity in the scope of 0.3-3.0 μM (R² = 0.996), and the LOD was 0.058 μM under the ideal detection conditions. More significantly, the technique was effectively used to identify TCP in lake and tap water (RSD ≤5.79%), which provided a fresh perspective on how to recognize OPFRs in environmental water.

Novel strategies for the formulation and processing of aluminum metal-organic framework-based sensing systems toward environmental monitoring of metal ions

Aluminum is a relatively inexpensive and abundant metal for the mass production of metal-organic frameworks (MOFs). Aluminum-based MOFs (Al-MOFs) have drawn a good deal of research interest due to their unique properties for diverse applications (e.g., excellent chemical and structural stability). This review has been organized to highlight the current progress achieved in the synthesis/functionalization of Al-MOF materials with the special emphasis on their sensing application, especially toward metal ion pollutants in the liquid phase. To learn more about the utility of Al-MOF-based sensing systems, their performances have been evaluated for diverse metallic components in reference to many other types of sensing systems (in terms of the key quality assurance (QA) criteria such as limit of detection (LOD)). Finally, the challenges and outlook for Al-MOF-based sensing systems are discussed to help expand their real-world applications.

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.

Metal-Organic Framework Fluorescence Sensors for Rapid and Accurate Detection of Melamine in Milk Powder

In this research, a simple, label-free, and ultra-sensitive fluorescent platform based on a metal-organic framework (MOF) has been developed to detect melamine in milk powder. This fluorescence sensor was fabricated from sensitized terbium (Tb)@NH₂-MIL-253 (Al) MOF using a hydrothermal method that involved combining the green emission of Tb (λ_em = 545 nm) with the blue emission of NH₂-MIL-253(Al) MOF (λ_em = 430 nm) under a single excitation wavelength (λ_ex = 335 nm). The fluorescence sensor was then used under optimized conditions (pH = 9.0; sensor concentration = 30 mg/L; response time = 30 s) to quantify melamine in milk powder. The accuracy, sensitivity, and reproducibility of this sensor were established compared to the high-performance liquid chromatography (HPLC) method. The linear range and lower limit of detection (LLOD, computed with 3σ/S) of the sensor were between 40-396.45 nM (equal to 25 µg/kg-0.25 mg/kg) and 40 nM (equal to 25 µg/kg), respectively, which is much less than the maximum residual level (MRL) for the detection of melamine in infant formula (1 mg/kg) and other foods/feeds (2.5 mg/kg). Additionally, the results had good agreement with the HPLC outcomes, suggesting that the NH₂-MIL-253(Al) MOF sensing probe has great precision and repeatability. To conclude, the new fluorescence sensor developed in this study can accurately and sensitively detect melamine in food samples, which may be useful for screening for adulteration of milk powders and other foods.

A critical review on the synthesis of NH2-MIL-53(Al) based materials for detection and removal of hazardous pollutants

Nowadays, emerging hazardous pollutants have caused many harmful effects on the environment and human health, calling for the state of the art methods for detection, qualification, and treatment. Metal-organic frameworks are porous, flexible, and versatile materials with unique structural properties, which can solve such problems. In this work, we reviewed the synthesis, activation, and characterization, and potential applications of NH₂-MIL-53(Al). This material exhibited intriguing breathing effects, and obtained very high surface areas (182.3-1934 m²/g) with diverse morphologies. More importantly, NH₂-MIL-53(Al) based materials could be used for the detection and removal of various toxic pollutants such as organic dyes, pharmaceuticals, herbicides, insecticides, phenols, heavy metals, and fluorides. We shed light on plausible adsorption mechanisms such as hydrogen bonds, π-π stacking interactions, and electrostatic interactions onto NH₂-MIL-53(Al) adsorbents. Interestingly, NH₂-MIL-53(Al) based adsorbents could be recycled for many cycles with high stability. This review also recommended that NH₂-MIL-53(Al) based materials can be a good platform for the environmental remediation fields.

Multifunctional fluorescent Eu-MOF probe for tetracycline antibiotics and dihydrogen phosphate sensing and visualizing latent fingerprints†‡

The contamination of tetracycline antibiotics and dihydrogen phosphate (H₂PO₄⁻) in food and the environment is one of the major concerns for human health. Herein, a water-stable carboxyl-functionalized europium metal–organic framework (Eu-MOF) was prepared and demonstrated, for the first time, as a dual-responsive fluorescent sensor of tetracycline antibiotics (oxytetracycline (OTC), tetracycline (TC), and doxycycline (DOX)) and H₂PO₄⁻via fluorescent turn-on and turn-off, respectively. Eu-MOF presents a sensitive and selective detection of OTC with a rapid response time (1 min) and good anti-interference ability. The limits of detection (LODs) of 78 nm, 225 nm, and 201 nM were achieved for OTC, TC, and DOX, respectively. Coordination and hydrogen bonding led to energy and electron transfer from the TC to the MOF, contributing to the fluorescent enhancement mechanism. Moreover, Eu-MOF can effectively detect H₂PO₄⁻via fluorescence turn-off with a LOD of 0.70 μM. The interactions between H₂PO₄⁻ and MOF interrupt the energy transfer from ligand to MOF, leading to fluorescence quenching. In addition, Eu-MOF was successfully applied to determine OTC and H₂PO₄⁻ in real samples, obtaining satisfactory recoveries and RSDs. More fascinating, Eu-MOF could be utilized to develop latent fingerprints on various surfaces, providing well-defined fluorescent fingerprint details in which the sweat pores can be seen with the naked eye.

Water-stable Eu-MOF as a fluorescent probe for detecting tetracycline antibiotics and dihydrogen phosphate in real samples and visualization of latent fingerprints.