The fabrication of a thiol-modified chitosan magnetic graphene oxide nanocomposite and its adsorption performance towards the illegal drug clenbuterol in pork samples

Ultrasensitive Eu-Based MOF Luminescence Sensor for Clenbuterol Visible Recognition

Clenbuterol (CLB) as an illegal feed additive may cause a great security risk to food safety. However, convenient and efficient detection means for CLB in practical application remain a formidable challenge. Herein, a stable Eu-based organic framework {[H2N(CH3)2]2[Eu2(ttca)2]·H2O}n (compound 1) (H4ttca = [1,1':2',1″-terphenyl]-4,4',4″,5'-tetracarboxylic acid) has been harvested, exhibiting excellent chemical stability and thermal stability. Luminescence investigation reveals that compound 1 can sensitively and selectively detect CLB without being affected by different components from simulated serum and urine (limit detection: 22.7 nM). Furthermore, sensor 1 can also be applicable to CLB recognition in real swine feeds, presenting excellent anti-interference performance. The good cyclicity of compound 1 endows CLB determination with many advantages: low cost, high stability, and simplicity. Importantly, in view of the indication of the luminescence color (red to blue), test membranes were fabricated and employed for convenient and fast CLB detection, providing a valuable scheme for the visual monitoring of CLB in meat products. This work enriches rare earth metal compounds and luminescence sensor portfolios and breaks the concentration record (nM) for detecting CLB compared with reported complex materials, providing an effective monitoring platform for CLB visually.

Enzyme immobilized on magnetic fluorescent bifunctional nanoparticles for α-glucosidase inhibitors virtual screening from Agrimonia pilosa Ledeb extracts accompanied with molecular modeling

Agrimonia pilosa Ledeb (APL) is a significant source of inhibitors for α-glucosidase, which is an essential target enzyme for the treatment of type 2 diabetes, cancer and acquired immune deficiency syndrome. Ligand fishing is a suitable approach for the highly selective screening of bioactive substances in complex mixtures. Yet it is unable to conduct biomedical imaging screening, which is crucial for real-time identification. In this case, a bioanalytical platform combining magnetic fluorescent ligand fishing and in-situ imaging technique was established for the screening and identification of α-glucosidase inhibitors (AGIs) from APL crude extract, utilizing α-glucosidase coated CuInS2/ZnS-Fe3O4@SiO2 (AG-CIZSFS) nanocomposites as extracting material and fluorescent tracer. The AG-CIZSFS nanocomposites prepared through solvothermal and crosslinking methods displayed fast magnetic separation, excellent fluorescence performance and high enzyme activity. The tolerance of immobilized enzyme to temperature and pH was stronger than that of free enzyme. Prior to proof-of-concept with APL crude extract, a number essential parameters (glutaraldehyde concentration, immobilized time, enzyme amount, reaction solution pH, incubation temperature, incubation time, percentage of methanol in eluen, elution times and eluent volume) were optimized using an artificial test mixture. The fished ligands were identified by UPLC-MS/MS and their biological activities were preliminarily evaluated by real-time cellular morphological imaging of human colon carcinoma (HCT-116) cells based on confocal laser scanning microscope (CLSM). Their α-glucosidase inhibitory activities were further verified and studied by classical pNPG method and molecular docking. The isolated compounds exhibited significant α-glucosidase inhibitory activities with a IC50 value of 11.57 µg·mL-1. Six potential AGIs including tribuloside, ivorengenin A, tormentic acid, 1β, 2β, 3β, 19α-Tetra hydroxyurs-12-en-28-oic acid, corosolic acid and pomolic acid were ultimately screened out and identified from APL crude extracts. The proposed approach, which combined highly specific screening with in-situ visual imaging, provided a powerful platform for discovering bioactive components from multi-component and multi-target traditional Chinese medicine (TCM).

A Bifunctional Fluorescence Probe Based on AIE-ICT Strategy for Visual Detection of Cu2+/Co2+ in Complex Matrix

A novel fluorescence chemical sensor-based probe 1-{[(E)-(2-aminophenyl)azanylidene]methyl}naphthalen-2-ol (AMN) was designed and synthesized, which performed a "naked eye" detection ability toward Cu²⁺ and Co²⁺ based on aggregation-induced emission (AIE) fluorescence strategy. It has sensitive detection ability for Cu²⁺ and Co²⁺. In addition, the color changed from yellow-green to orange under the sunlight, realizing the rapid identification of Cu²⁺/Co²⁺, which has the potential of on-site visual detection under the "naked eye". Moreover, different "on" and "off" fluorescence expressions were exhibited under excessive glutathione (GSH) in AMN-Cu²⁺ and AMN-Co²⁺ systems, which could be employed to distinguish Cu²⁺ from Co²⁺. The detection limits for Cu²⁺ and Co²⁺ were measured to be 8.29 × 10^-8 M and 9.13 × 10^-8 M, respectively. The binding mode of AMN was calculated to be 2:1 by Jobs' plot method analysis. Ultimately, the new fluorescence sensor was applied to detect Cu²⁺ and Co²⁺ in real samples (tap water, river water, and yellow croaker), and the results were satisfying. Therefore, this high-efficiency bifunctional chemical sensor platform based on "on-off" fluorescence detection will provide significant guidance for the advance development of single-molecule sensors for multi-ion detection.

Influence of magnetite incorporation into chitosan on the adsorption of the methotrexate and in vitro cytotoxicity

Emerging pollutants are a group of substances involved in environmental contamination resulting mostly from incomplete drug metabolism, associated with inadequate disposal and ineffective effluent treatment techniques. Methotrexate (MTX), for instance, is excreted at high concentrations in unchanged form through the urine. Although the MTX is still effective in cancer and autoimmune disease treatment, this drug shows the ability of bioaccumulation and toxicity to the organism. Thus, the present work aimed to evaluate the adsorption of the MTX drug onto magnetic nanocomposites containing different amounts of incorporated magnetite (1:1, 1:5, and 1:10 wt%), combining the theoretical-experimental study as well as the in vitro cytotoxicity. Moreover, equilibrium studies (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Hill, Redlich-Peterson, and Sips), kinetic (PFO, PSO, and IPD), and thermodynamic (ΔG°, ΔH°, and ΔS°) were used to describe the experimental data, and ab initio simulations were employed in the theoretical study. Magnetic nanocomposites were synthesized by the co-precipitation method using only FeCl₂ as the iron precursor. Adsorbents were characterized by FTIR, XRD, Raman, SEM-EDS, BET, and VSM analysis. Meanwhile, cytotoxic effects on L929 and A375 cell lines were evaluated through MTT, NR, and LDH assays. The adsorption of the MTX was carried out in a typical batch system, exploring the different experimental conditions. The theoretical study suggests the occurrence of chemisorption between CS·Fe₃O₄-MTX. The maximum adsorption capacity of MTX was 285.92 mg g^-1, using 0.125 g L^-1 of CS·Fe₃O₄ 1:1, with an initial concentration of the MTX (50 mg L^-1), pH 4.0 at 293 ± 1.00 K. The best adjustment of equilibrium and kinetic data were the Sips (low values for statistical errors) and PSO (q_e = 96.73 mg g^-1) models, respectively. Thermodynamic study shows that the adsorption occurred spontaneously (ΔG° < 0), with exothermic (ΔH° =  - 4698.89 kJ mol^-1) and random at the solid-solution interface (ΔS° = 1,476,022.00 kJ mol^-1 k^-1) behavior. Finally, the in vitro study shows that magnetic nanomaterials exhibit higher cytotoxicity in melanoma cells. Therefore, the magnetic nanocomposite reveals to be not only an excellent tool for water remediation studies but also a promising platform for drug delivery.

Sensitive and Selective Detection of Clenbuterol in Meat Samples by a Graphene Quantum Dot Fluorescent Probe Based on Cationic-Etherified Starch

The use of clenbuterol (CLB) in large quantities in feedstuffs worldwide is illegal and potentially dangerous for human health. In this study, we directly prepared nitrogen-doped graphene quantum dots (N-GQDs) by a one-step method using cationic-etherified starch as raw material without pollution, which has the advantages of simple, green, and rapid synthesis of N-GQDs and high doping efficiency of nitrogen elements, compared with the traditional nitrogen doping method of reacting nitrogen source raw material with quantum dots. The N-GQDs synthesized by cationic etherification starch with different substitution degrees (DSs) exhibit good blue-green photoluminescence, good fluorescence stability, and water solubility. By comparing the fluorescence emission intensity of the two methods, the N-GQDs prepared by this method have higher fluorescence emission intensity and good fluorescence stability. Based on the static quenching mechanism between CLB and N-GQDs, a fluorescent probe was designed to detect CLB, which exhibited a wide linear range in the concentration range of 5 × 10⁻¹⁰~5 × 10⁻⁷ M (R² = 0.9879) with a limit of detection (LOD) of 2.083 × 10⁻¹³ M. More excitingly, the N-GQDs fluorescent probe exhibited a satisfactory high selectivity. Meanwhile, it can be used for the detection of CLB in chicken and beef, and good recoveries were obtained. In summary, the strategic approach in this paper has potential applications in the detection of risky substances in the field of food safety.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

Ratiometric Fluorescent Probe Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

In view of the potential harm caused by illegal feeding of clenbuterol (CLB) in the livestock industry, herein, a novel ratiometric fluorescent probe based on graphene quantum dots (GQDs)@[Ru(bpy)₃]²⁺ was elaborately constructed for CLB detection. In this probe, GQDs acted as response signals, and their fluorescence was remarkably quenched by CLB through the diazotization-coupling reaction. As for [Ru(bpy)₃]²⁺ as a reference signal, its fluorescence was hardly affected. The intensity ratio of two fluorophores showed good linearity with CLB concentration in the range of 0.05-40 μM, accompanied by visualization of fluorescence variation from yellow to red. The detection limit was as low as 0.029 μM. Particularly, the probe was successfully used to detect CLB in pork and beef samples with satisfactory recoveries. To our knowledge, this is the first report on a ratiometric fluorescent probe for the detection of CLB, which possesses broad application prospects in food safety risk monitoring.