A HPLC with fluorescence detection method for the determination of tetracyclines residues and evaluation of their stability in honey

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.

Utilizing two different sustainable and green spectrophotometric approaches using derivative ratio spectra for the determination of a ternary severely overlapped mixture: application to veterinary formulation

Mathematical manipulation technique has proven to be a very powerful tool for efficient processing and handling of highly overlapped spectra. This work introduced two green and sustainable approaches for the successful recovery of the ternary mixture, Tylosin tartarate (TYL), Sulfadimdine (SLD), and Trimethoprim (TRI). The approaches were constructed using three different methods, derivative ratio spectrum zero-crossing method (DRSZ), double divisor ratio spectra derivative method (DDRD), and factorized derivative ratio method coupled with spectrum subtraction (FDRM-SS). The two approaches succeeded in recovering the three drugs (Linearity range achieved were 0.5-5 µg/mL for TYL, 0.3-1.3 µg/mL for SLD, and 0.3-5 µg/mL for TRI), giving convenient standard deviations and satisfactory recovery percentages. The recommended methods have been verified in accordance with (ICH) guidelines. When the results were statistically compared to the official methods, no significant difference was found. Both AGREE-Analytical GREEnness Metric Approach and Software, and White Analytical Chemistry (WAC) RGB model gave scores of 0.93 and 97.2%, respectively, which proved that the approaches were eco-friendly and abiding by the sustainability principles.

Yb-TCPP metal-organic framework as fluorescence sensor for detecting tetracycline in milk

Developing effective means for detecting contamination in milk during production, processing, and storage is both important and challenging. Tetracycline (TC), due to its use in treating animal infections, is among the most prevalent organic pollutants in milk, posing potential and significant threats to human health. However, efficient and in situ monitoring of TC remains lacking. Nevertheless, we have successfully developed a highly sensitive and selective fluorescence method for detecting TC in milk using a metal-organic framework material made from Yb-TCPP (ytterbium-tetra(4-carboxyphenyl)porphyrin). The calculated Stern-Volmer constant (KSV) was 12,310.88 M-1, and the detection limit was 2.44 × 10-6 M, surpassing previous reports. Crucially, Yb-TCPP fluoresces in the near-infrared region, promising its development into a specific fluorescence detection product for practical TC detection in milk, offering potential application value.

In Situ Fabrication of Photoluminescent Hydrogen-Bonded Organic Framework-Functionalized Ca (II) Hydrogel Film for the Tetracyclines Visual Sensor and Information Security

A facilely in situ fabricated hydrogen-bonded organic framework (HOF) hydrogel film with perfect photoluminescent performance was designed for visual sensing of tetracycline antibiotics (TCs) and information security. Luminescent HOF (MA-IPA) was combined with sodium alginate (SA) through hydrogen bonding actions and electrostatic interactions, then cross-linked with Ca2+ ions to form HOF hydrogel film (Ca@MA-IPA@SA). The HOF hydrogel film exhibited exceptional mechanical robustness along with stable blue fluorescence and ultralong green phosphorescence. After exposure to TCs, Ca2+ was combined with TCs to generate a new green fluorescence exciplex (TC-Ca2+) in hydrogel films. Due to fluorescence resonance energy transfer, the fluorescence of MA-IPA was quenched, and the fluorescent color of the HOF hydrogel film was changed from blue to green. This dichromatic fluorescent response is convenient for the visual and rapid detection of TCs. The detection limits of tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) were 5.1, 7.7, and 32.7 ng mL-1, respectively. Importantly, this hydrogel sensing platform was free of tedious operation and enabled the ultrasensitive and selective detection of TCs within 6 min. It has been successfully applied to TC detection in pork and milk samples. Based on the stable photoluminescence performance of HOF hydrogel films and fluorescent-responsive properties to TCs, two types of anticounterfeiting arrays were fabricated for information encryption and decryption. This work provides a novel approach for on-site detection of TCs and offers valuable insights into information security.

Detection of Multiple Antibiotic Residues in Turkish Pine and Blossom Honeys Using LC-MS/MS Method

Due to the high demand for honey, beekeepers often feed the bees with antibiotics to protect honeybees against illnesses; the determination of veterinary drugs and their residues in bee products especially in honey is gaining importance. In this study, commercially available 15 different brands, a total of 22 honey (14 blossoms and 8 pines) samples obtained from 5 chain supermarkets in the city of Bingöl and Diyarbakır, Turkey were analysed for 29 antibiotic residues. These antibiotics belong to 10 different categories, including tetracyclines, aminoglycosides, macrolides, sulfonamides, fluoroquinolones, benzimidazoles, anthelmintic, amphenicols, quinolines, and oxazolidines. For the qualitative and quantitative determination of the antibiotics, a triple quadrupole liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used. A total of 10 out of 22 honey (8 blossom, 57.14 % and 2 pine, 25 %) samples were found to be positive for antibiotics. Among the tested antibiotics, tetracycline, dihydrostreptomycin, streptomycin, erythromycin, and sulfadimidine were detected in the honey samples. Dihydrostreptomycin and sulfadimidine were detected in 6 samples, erythromycin was determined in 4 samples, streptomycin was found in 2 samples, and lastly, tetracycline was detected only in one sample. The highest and the lowest concentrations of antibiotics detected in the samples were dihydrostreptomycin and erythromycin found at the amount of 992.58 μg/kg and 0.77 μg/kg respectively. The proposed method was validated with a limit of quantification (LOQ) and limit of detection (LOD) ranging between 0.42 and 3.22 μg /kg and 0.13-0.97 μg /kg respectively. Good linearities were also achieved ranging between R2 =0.987 and 0.999.

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.

In-situ SERS detection of quinolone antibiotic residues in aquaculture water by multifunctional Fe3O4@mTiO2@Ag nanoparticles

Antibiotic residues in aquaculture environments disrupt the ecosystem balance and pose a potential hazard to human health when entering the food chain. Therefore, ultra-sensitive detection of antibiotics is necessary. In this study, a multifunctional Fe3O4@mTiO2@Ag core-shell nanoparticle (NP), synthesized using a layer-by-layer method, was demonstrated to be useful as an enhanced substrate for in-situ surface-enhanced Raman spectroscopy (SERS) detection of various quinolone antibiotics in aqueous environments. The results showed that the minimum detectable concentrations of the six investigated antibiotics were 1 × 10-9 mol/L (ciprofloxacin, danofloxacin, enoxacin, enrofloxacin, and norfloxacin) and 1 × 10-8 mol/L (difloxacin hydrochloride) under the enrichment and enhancement of Fe3O4@mTiO2@Ag NPs. Additionally, there was a good quantitative relationship between the antibiotics concentrations and SERS peak intensities within a certain detection range. The results of the spiked assay of actual aquaculture water samples showed that the recoveries of the six antibiotics ranged from 82.9% to 113.5%, with relative standard deviations ranging from 1.71% to 7.24%. In addition, Fe3O4@mTiO2@Ag NPs achieved satisfactory results in assisting the photocatalytic degradation of antibiotics in aqueous environments. This provides a multifunctional solution for low concentration detection and efficient degradation of antibiotics in aquaculture water.

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.

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.

The preparation of hybrid silicon quantum dots by one-step synthesis for tetracycline detection and antibacterial applications

In this study, we prepared three different silicon quantum dots (SiQDs-1, SiQDs-2 and SiQDs-3) by hydrothermal synthesis with rose Bengal as the reducing agent and triacetoxy(methyl)silane and allyloxytrimethylsilane as silicon sources. The as-prepared SiQDs not only exhibited potent antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) but also showed specific responses to tetracycline (TC). The minimum inhibitory concentrations (MICs) of SiQDs-1, SiQDs-2 and SiQDs-3 were 0.55 mg mL^-1, 0.47 mg mL^-1 and 0.39 mg mL^-1 against E. coli, respectively, and 0.45 mg mL^-1, 0.34 mg mL^-1 and 0.34 mg mL^-1 against S. aureus, respectively. By examining the morphologies of bacteria and generation of reactive oxygen species (ROS), we speculated that these SiQDs shrink the bacteria and even directly destroy the bacterial structural integrity through the production of singlet oxygen. In addition, the fluorescence quenching effectiveness of SiQDs-3 also showed a strong linear relationship with TC concentration in the range of 0-1.2 μM with a detection limit of 0.318 μM, as a result of the internal filtering effect. Together, SiQDs not only can be a candidate to treat resistant bacterial infections, but also may be applied in practical detection of TC.

Ultra-small highly fluorescent zinc-based metal organic framework nanodots for ratiometric visual sensing of tetracycline based on aggregation induced emission

Color tonality by intrinsic fluorescent metal-organic frameworks (MOFs) is highly desirable in bioanalytical applications due to its stability, low-cost and robustness with no need for functionalization and/or encapsulation of fluorophores. In the present work, ultra-small and higly fluorescent zinc-based MOFs (FMOF-5) were synthesized. The prepared FMOFs were around 5 nm in size, and gave strong blue emission at 440 nm when excited at 350 nm. Interestingly, tetracycline (TC) selectively tuned the blue emission of FMOF-5 to greenish-yellow emission (520 nm) with dramatic enhancement through aggregation induced emission (AIE). The fluorimetric analysis of TC was carried out through the ratiometric peak intensities of F520/F440, with detection limit (LOD) of 5 nM. To realize quantitative point-of-care based on color tonality, a smartphone integrated with the ratiometric visual platform was thereby design. Hence, TC was visually detected with LOD of 10 nM. The prepared FMOF-5-based probe showed high stability (3 months) and reusability (∼10 times). The developed visual-based platform presents great promise for practical point of care testing due to its low-cost, robustness, ruggedness, simple operation, and excellent selectivity and repeatability.

Study of microplastics as sorbents for rapid detection of multiple antibiotics in water based on SERS technology

Online monitoring of antibiotics in the environment attracts more and more attention. Surface-enhanced Raman scattering (SERS) is a promising technique for the detection of trace amounts of antibiotics in the environment, which is fast, non-invasive and sensitive. To investigate the enrichment of trace amounts of antibiotics in water, polyethylene microplastics (PE MPs) were prepared as sorbents to simply concentrate enrofloxacin, ciprofloxacin hydrochloride monohydrate and triclosan in water, followed by the SERS measurement of antibiotics extract washed from MPs on an AgNPs@Si SERS substrate. Limit of detection of Rhodamine 6G is 2.1 × 10^-12 M achieved from the AgNPs@Si SERS, indicating a high enhancement. The detection results show that SERS peaks of the antibiotics could be observed from the spectra of the extracts eluted from MPs, indicating MPs could adsorb and desorb antibiotics from water. Besides, for enrofloxacin and triclosan, the intensity of SERS measured from the MPs extracts are higher than that of directly from the spiked water, demonstrating the proposed method could lower the detectable concentration of hydrophobic antibiotics in water. Moreover, the proposed MPs sorbents combined with SERS method was applied to detect the antibiotics in real river water, with minimal detection of 10^-10 M, 10^-8 M, and 10^-8 M achieved for enrofloxacin, ciprofloxacin hydrochloride monohydrate and triclosan, respectively. The proposed method provides a promising simple, rapid and low reagent consuming means for monitoring antibiotics in water.

Electrochemical Biosensor Designed to Distinguish Tetracyclines Derivatives by ssDNA Aptamer Labelled with Ferrocene

Controlling food safety and preventing the growing spread of antibiotics into food products have been challenging problems for the protection of human health. Hence, the development of easy-to-use, fast, and sensitive analytical methods for the detection of antibiotics in food products has become one of the priorities in the food industry. In this paper, an electrochemical platform based on the ssDNA aptamer for the selective detection of tetracycline has been proposed. The aptasensor is based on a thiolated aptamer, labelled with ferrocene, which has been covalently co-immobilized onto a gold electrode surface with 6-mercaptohexan-1-ol. The changes in the redox activity of ferrocene observed on the aptamer-antibiotics interactions have been the basis of analytical signal generation registered by square-wave voltammetry. Furthermore, the detection of tetracycline-spiked cow milk samples has been successfully demonstrated. The limits of detection (LODs) have been obtained of 0.16 nM and 0.20 nM in the buffer and spiked cow milk, respectively, which exceed the maximum residue level (225 nM) more than 1000 times. The proposed aptasensor offers high selectivity for tetracycline against other structurally related tetracycline derivatives. The developed biosensor characterized by simplicity, a low detection limit, and high reliability shows practical potential for the detection of tetracycline in animal-origin milk.

Ultrasensitive Antibiotic Perceiving Based on Aptamer-Functionalized Ultraclean Graphene Field-Effect Transistor Biosensor

Antibiotics are powerful tools to treat bacterial infections, but antibiotic pollution is becoming a severe threat to the effective treatment of human bacterial infections. The detection of antibiotics in water has been a crucial research area for bioassays in recent years. There is still an urgent need for a simple ultrasensitive detection approach to achieve accurate antibiotic detection at low concentrations. Herein, a field-effect transistor (FET)-based biosensor was developed using ultraclean graphene and an aptamer for ultrasensitive tetracycline detection. Using a newly designed camphor-rosin clean transfer (CRCT) scheme to prepare ultraclean graphene, the carrier mobility of the FET is found to be improved by more than 10 times compared with the FET prepared by the conventional PMMA transfer (CPT) method. Based on the FET, aptamer-functionalized transistor antibiotic biosensors were constructed and characterized. A dynamic detection range of 5 orders of magnitude, a sensitivity of 21.7 mV/decade, and a low detection limit of 100 fM are achieved for the CRCT-FET biosensors with good stability, which are much improved compared with the biosensor prepared by the CPT method. The antibiotic sensing and sensing performance enhancement mechanisms for the CRCT-FET biosensor were studied and analyzed based on experimental results and a biosensing model. Finally, the CRCT-FET biosensor was verified by detecting antibiotics in actual samples obtained from the entrances of Bohai Bay.

Kill two birds with one stone: Selective and fast removal and sensitive determination of oxytetracycline using surface molecularly imprinted polymer based on ionic liquid and ATRP polymerization

Oxytetracycline (OTC) residue in food and environment has potential threats to ecosystem and human health, thus its sensitive monitoring and effective elimination are very important. In this work, a new molecularly imprinted polymer (MIP) composite was prepared through atom transfer radical polymerization by using OTC as template, gold nanoparticles modified carbon nanospheres (Au-CNS) as supporter, ionic liquids (IL) as functional monomer and cross-linking agent. The obtained MIP-IL@Au-CNS composite was characterized by Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. It displayed high imprinting factor (5.50) and adsorption capacity (56.7 mg g^-1), and could achieved the adsorption equilibrium in short time (about 15 min). Results also illustrated that the adsorption process basically conformed to the quasi-second-order kinetic model and Freundlich model, and MIP-IL@Au-CNS could be recycled at least 5 times. Furthermore, a sensitive OTC electrochemical sensor was developed by combining MIP-IL@Au-CNS with IL-modified carbon nanocomposites (IL@N-rGO-MWCNT). The resulting sensor demonstrated a linear response to OTC in the wide range of 0.02-20 μM, and the detection limit was down to 5 nM. It also had the advantages of high selectivity, fast elution/regeneration and simple construction procedure. The sensor had been applied to the detection of real samples, and acceptable recovery (96.4%-106%) and RSD (3.2%-6.2%) were obtained. This work expands the application of IL-based MIP in pollutant monitoring and enriching.

Highly selective and sensitive fluorescence detection of tetracyclines based on novel tungsten oxide quantum dots

Tetracyclines (TCs) residues in animal products have attracted extensive concern due to their potential toxic to human health. Accordingly, it is urgent to develop an efficient method to determine TCs for providing consumers with risk pre-warning. Herein, a novel tungsten oxide quantum dots (W_xO_y QDs) fluorescence probe for tetracycline (TET) detection was constructed through ethanol-thermal method, which exhibited intense blue fluorescence under 365 nm UV light. Interestingly, blue-emitting W_xO_y QDs could be quenched obviously after the addition of TET, which may be attributed to the synergism of inner filter effect (IFE), fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET). Thereby, the fluorescence method was established for TET detection based on W_xO_y QDs. Additionally, the presented method was demonstrated by monitoring TET in milk and milk powder with satisfactory recoveries. More importantly, this work offered good demonstration for the detection of food hazard factors.

Simultaneous Determination of Tetracyclines and Fluoroquinolones in Poultry Eggs by UPLC Integrated with Dual-Channel-Fluorescence Detection Method

An innovative, rapid and stable method for simultaneous determination of three tetracycline (oxytetracycline, tetracycline and doxycycline) and two fluoroquinolone (ciprofloxacin and enrofloxacin) residues in poultry eggs by ultra-high performance liquid chromatography-fluorescence detection (UPLC-FLD) was established and optimized. The samples were homogenized and extracted with acetonitrile/ultrapure water (90:10, v/v) and then purified by solid-phase extraction (SPE). LC separation was achieved on an ACQUITY UPLC BEH C18 column (1.7 µm, 2.1 mm × 100 mm), and the mobile phase was composed of acetonitrile and a 0.1 mol/L malonic acid solution containing 50 mmol/L magnesium chloride (the pH was adjusted to 5.5 with ammonia). When the five target drugs were spiked at the limit of quantification, 0.5 times the maximum residue limit (MRL), 1.0 MRL and 2.0 MRL, the recoveries were above 83.5% and the precision ranged from 1.99% to 6.24%. These figures of merit complied with the parameter validation regulations of the EU and U.S. FDA. The limits of detection and quantifications of the targets were 0.1-13.4 µg/kg and 0.3-40.1 µg/kg, respectively. The proposed method was easily extended to quantitative analyses of target drug residues in 85 egg samples, thus demonstrating its reliability and applicability.

Green-tea-synthesized silver nanoparticles as a sensing platform for determination of tetracycline in honey samples

BACKGROUND

Silver nanoparticles (AgNPs) can be easily obtained in aqueous solution by chemical reduction using appropriate reducing agents and stabilizers. The development of environmentally friendly methods using non-toxic solvents and reagents has become an alternative for the synthesis of these particles and their future application as sensor probes for agricultural products. In this work, a straightforward method based on green tea extracts as reducing and capping agent is proposed for the synthesis of AgNPs, followed by their evaluation as a sensing platform for determination of tetracycline in honey samples.

RESULTS

Highly stable nanoparticles were easily obtained by combining green tea aqueous extracts and ultrasound irradiation for 2 min. The as-synthesized AgNPs, spherical in shape and with average size of 8.5 nm, were evaluated for determination of tetracycline by following the changes on the localized surface plasmon resonance band at 450 nm induced by the presence of this antibiotic at pH 5.8. The method was successfully applied in the concentration range between 200 and 800 μg L^-1 with R²  > 0.996 and limit of detection of 52.7 μg L^-1 . Multiple honey samples were analyzed, and the recovery values obtained ranged between 82.8% and 116%, with relative standard deviation values lower than 6.69%.

CONCLUSION

The results obtained demonstrate that the AgNPs synthesized using just green tea extracts represent a promising and sustainable alternative tool for the cost-effective determination of tetracycline antibiotics in honey. © 2021 Society of Chemical Industry.

Quality, composition and health-protective properties of citrus honey: A review

Citrus honey is one of the most important monofloral honeys produced and consumed worldwide. This honey has pleasant sensorial characteristics, which include light color and typical aroma and flavor. Besides that, several constituents such as minerals, phenolic and volatile compounds, amino acids, sugars, enzymes, vitamins, methylglyoxal and organic acids are found in citrus honey. Moreover, potential biological properties have been associated with citrus honey. All these factors make it highly desired by consumers, increasing its market value, which can stimulates the practice of fraud. Also, citrus honey is susceptible to contamination and to inadequate processing. All these factors can compromise the quality, safety and authenticity of citrus honey. In this sense, this review aims to update and to discuss, for the first time, the data available in the literature about the physicochemical and the sensorial characteristics, composition, health properties, contamination, authenticity and adulteration of citrus honey. With this background, we aim to provide data that can guide future researches related to this honey.

A novel fluorescence probe for rapid and sensitive detection of tetracyclines residues based on silicon quantum dots

A novel rapid and sensitive fluorescence probe based on silicon quantum dots (Si QDs) fluorescence was fabricated for selective detection of tetracyclines (TCs) residues. Si QDs were innovatively prepared via facile One-Pot Solvent-Free Method and characterized by TEM, FT-IR, UV absorption, fluorescence, XPS and XRD. In aqueous solution, Cu²⁺ and Si QDs complexed together and the fluorescence of Si QDs quenched (static quenching) to a certain extent. TCs can be early in binding to Cu²⁺ and prevent Si QDs fluorescence quenching. As a consequence, quantitative screening of TCs can be achieved. The assay is highly selective for TCs. Represented by chlortetracycline (CTC), a member of TCs, under optimized conditions, good linear relationship in the range of 11.32-1086.72 nM was obtained, and the detection limit (LOD; S/N ratio = 3) of this assay for CTC is 0.92 nM. It was successfully applied to the determination of CTC in spiked bee honey and total TCs in actual honey samples. And the evaluation of selectivity, reproducibility and stability of the probe were favorable. These results demonstrated that the presented fluorescent probe can be a promising sensing platform for TCs analysis.

New application of Mn-doped ZnS quantum dots: phosphorescent sensor for the rapid screening of chloramphenicol and tetracycline residues

In this work, a new application of Mn-doped ZnS quantum dots (Mn-ZnS QDs) was developed to screen chloramphenicol (CAP) and tetracycline (TC) residues simply and rapidly. Mn-ZnS QDs synthesized by a hydration method and modified by l-cysteine for better stability emit phosphorescence at 583 nm with the excitation wavelength at 289 nm. Based on the overlap of the Mn-ZnS QDs excitation spectra and CAP or TCs ultraviolet spectra, the excited light of the Mn-ZnS QDs was partially absorbed by CAP or TCs owing to the inner-filter effect (IFE), leading to a decrease in the phosphorescence intensity. The phosphorescence intensities of the samples prepared by mixing different TCs and CAP were in good agreement with the expected results from adding a single antibiotic sample. Therefore, the total molar concentrations of CAP and TCs could be screened based on the linear equation of a single standard substance. Represented by tetracycline (TC), as a member of the tetracycline family, under optimized conditions, showed a good linear relational concentration range over 4 orders of magnitude from 50 to 1.5 × 105 nM with a limit of detection (LOD; S/N ratio = 3) down to 8.6 nM. The phosphorescent sensor was also used to detect total TCs in actual samples successfully. The evaluations of the recovery rate and selectivity were good. These results demonstrated that the presented phosphorescent sensor can be a simple and rapid screening platform for CAP and TCs.

In Situ Recyclable Surface-Enhanced Raman Scattering-Based Detection of Multicomponent Pesticide Residues on Fruits and Vegetables by the Flower-like MoS2@Ag Hybrid Substrate

Pesticides, extensively used in agriculture production, have received enormous attention because of their potential threats to the environment and human health. Hence, in this study, a kind of highly sensitive and stable hybrid surface-enhanced Raman scattering (SERS)-active substrates constructed with flower-like two-dimensional molybdenum sulfide and Ag (MoS₂@Ag) has been developed, and then the above substrate was sequentially utilized in the recyclable detection of pesticide residues on several kinds of fruits and vegetables. In the first place, the excellent photocatalytic performance of the MoS₂@Ag hybrid substrate was demonstrated, which was attributed to the inhibition of electron-hole combination after the formation of Schottky barrier between the Ag NPs and MoS₂ matrix. Thereafter, two calibration curves with ultra-low limits of detection (LOD) as 6.4 × 10^-7 and 9.8 × 10^-7 mg/mL were established for the standard solutions of thiram (tetramethylthiuram disulfide, TMTD) and methyl parathion (MP), and then the recyclable assay of their single and mixed residues on eggplant, Chinese cabbage, grape, and strawberry was successfully realized. It is interesting to note that the detection recoveries from 95.5 to 63.1% for TMTD and 92.3 to 62.6% for MP are greatly dependent on the size and surface roughness of these foods. In a word, the MoS₂@Ag composite matrix shows attractive SERS and photocatalysis performance, and it is expected to have the potential application on food safety monitoring.

Selective detection for seven kinds of antibiotics with blue emitting carbon dots and Al3+ ions

In this work, we presented a facile microwave method to prepare blue emitting carbon dots (CDs) using lysine as carbon source and realized the specific detection of seven types of antibiotics by CDs and Al³⁺ ions via a two-step method. The CDs have good solubility in water and their excitation spectra are exactly coincided with the absorption of some typical antibiotics, which leads to the fluorescence quenching of CDs (OFF state). The inhibition mechanism of fluorescence is induced by the combination of inner filtering effect (IFE) and static quenching effect (SQE). In addition, the quenched fluorescence can be recovered by adding Al³⁺ ions (On state), and seven types of antibiotics can be distinguished exactly according to the emission peak position and intensity. It not only provides a new and convenient method for the detection of antibiotics, but also provides a new idea for the further application of CDs in optical sensing.

A system composed of vanadium(IV) disulfide quantum dots and molybdenum(IV) disulfide nanosheets for use in an aptamer-based fluorometric tetracycline assay

A system composed of vanadium(IV) disulfide quantum dots (VS₂ QDs) and molybdenum(IV) disulfide (MoS₂) nanosheets for use in an aptamer-based fluorometric tetracycline assay was developed. The tetracycline (TET) aptamer was first immobilzed on the VS₂ QDs with a typical size of 3 nm. The blue fluorescence of the VS₂ QDs (labeled with aptamer) with emission maxima at 448 nm (under excitation at 360 nm) was subsequently quenched by MoS₂ nanosheets. If TET is recognized by the aptamer, the VS₂ QDs drift away from the basal plane of the MoS₂ nanosheets. This generated "turn-on" fluorescence of the VS₂ QDs. A VS₂ QD/MoS₂ nanosheet-based fluorometric TET aptasensor was thus constructed. Selective and sensitive TET bioanalysis was realized in a linear range of 1 to 250 ng mL^-1. The detection limit was 0.06 ng mL^-1. Its applicability of determination of TET in milk samples has been demonstrated. Graphical abstractSchematic representation of the aptamer-based fluorometric tetracycline assay.

Monitoring and risk assessment of tetracycline residues in foods of animal origin

A total of 450 samples consisting of red meat, poultry meat, aquatic product and raw milk were collected during winter 2016 and summer 2017. 22.2% (100/450) of collected meat and raw milk samples were found to be contaminated with antibiotic residues in the initial screening using Premi^®test. According to the enzyme linked immunosorbent assay (ELISA) results, the mean tetracyclines (TCs) concentration of meat samples determined as follows: chicken (155.41 µg/kg) > turkey (138.68 µg/kg) > quail (130.7 µg/kg) > cow (108.92 µg/kg) > calf (105.18 µg/kg) > goat (99.4 µg/kg) > sheep (95.22 µg/kg) > rainbow trout (35.62 µg/kg) > shrimp (31.80 µg/kg). The content of TCs in cow, goat and sheep milk samples were found to be ranged 45.6-163.5 µg/L, 72.4-101.1 µg/L and 65.5-98.9 µg/L, respectively. 5.7% (26/450) of samples had TCs confirmed the ELISA results using high performance liquid chromatography coupled with ultra-violet detection, although the concentration of TCs residues in samples was higher than that of ELISA.

A label-free aptasensor for the detection of tetracycline based on the luminescence of SYBR Green I

A novel fluorescent method based on tetracycline-binding aptamers and the luminescence of SYBR Green I (SGI) was established for the sensitive and selective detection of tetracycline. Under natural conditions, the aptamers of tetracycline show the G-quadruplex spatial structures while SGI is nearly nonfluorescent in aqueous solution. After mixture with the G-quadruplex structured aptamers, SGI can recognize and intercalate into the aptamers, resulting in a strong fluorescence emission. When the target tetracycline was added into the solution, the specific recognition and high-affinity binding of aptamers with tetracycline will induce the conformational changes of aptamers from G-quadruplex structures to hairpin structures. Thereafter, SGI will be released from the aptamer molecules, leading to the fluorescence decline. The quantitative detection of tetracycline can be achieved by measuring the fluorescence change of the system. Under the optimum conditions, the linear range of tetracycline in the milk was from 5 to 25 μg/mL, and the detection limit was as low as 0.10 μg/mL. The recoveries of the spiked milk samples were in the range of 98.98%-104.67% with the relative standard deviations (RSDs) of 0.16%-0.67%, and the results were in agreement with those from HPLC. Therefore, the biosensor based on the specific recognition of aptamers and the fluorescence properties of SGI can detect the tetracycline in milk accurately, rapidly and specifically.

One-pot carbonization synthesis of europium-doped carbon quantum dots for highly selective detection of tetracycline

The detection of tetracycline is of great significance because of its damaging effects on human health, such as renal toxicity and hemolytic anemia. Any release of tetracycline into the surrounding environment can produce bacterial drug resistance. We develop a new sensitive and selective detection approach for tetracycline in complex water samples by preparing europium-doped carbon quantum dots (Eu-CQDs) through a simple and rapid carbonization method operating at 200 °C for 5 min. The Eu-CQDs are characterized by blue photoluminescence, excitation-wavelength-dependent emission and excellent stability. Importantly, the fluorescence of the Eu-CQDs can be quenched efficiently by tetracycline, based on the strong inner filter effect mechanism between Eu-CQDs and tetracycline, making the fluorescence intensity ratio (I ₀/I) of the Eu-CQDs at 465 nm correlate linearly with the concentration of tetracycline in the range of 0.5-200 μM, with a limit of detection of 0.3 μM. This shows the broad applicability of the Eu-CQDs in pursuing the concepts of simplicity and specificity for analytical purposes.

Magnetic solid phase extraction based on graphene oxide/nanoscale zero-valent iron for the determination of tetracyclines in water and milk by using HPLC-MS/MS

A magnetic solid-phase extraction (MSPE) based on graphene oxide/nanoscale zero-valent iron (GO/nZVI) coupled with HPLC-MS/MS was proposed for the determination of trace tetracycline antibiotics (TCs) in water and milk.

An inner filter effect based sensor of tetracycline hydrochloride as developed by loading photoluminescent carbon nanodots in the electrospun nanofibers

The inner filter effect (IFE), which results from the absorption of the excitation or emission light by absorbers, has been employed as an alternative approach in sensing systems due to its flexibility and simplicity. In this work, highly photoluminescent carbon nanodots (CDs), which were simply prepared through a new one-step microwave synthesis route, were loaded in electrospun nanofibers, and the obtained nanofibers were then successfully applied to develop a fluorescent IFE-based visual sensor for tetracycline hydrochloride (Tc) sensing in milk. This developed visual sensor has high selectivity owing to the requirements of the spectral overlap between the CDs and Tc, showing high promise in sensing chemistry with an efficient response and economic effect.