A visual ratiometric fluorescence sensor for glutathione response based on MnO2 nanowires as an oxidant, quencher and recognition unit.

As the "mother of antioxidants", glutathione (GSH) plays an important role in physiological functions. Rapid and accurate monitoring of GSH is of great significance for medicinal chemistry, food chemistry, and clinical medicine. We herein report a visual ratiometric fluorescence sensor based on MnO2 nanowires (MnO2 NWs) as an oxidant, quencher and recognition unit for the determination of GSH. The powerful ratiometric fluorescent probe was constructed by mixing thiamine (VB1) and rhodamine B (RhB) with the help of MnO2 NWs. MnO2 NWs could not only effectively quench the fluorescence of RhB due to the inner filter effect (IFE), but also oxidized non-fluorescent VB1 to blue fluorescent thiochrome (oxVB1). Upon interaction with GSH, the quenched RhB fluorescence could be rapidly restored through decomposition of MnO2 NWs into Mn2+, while the oxVB1 fluorescence decreased, showing an apparent color change from blue to red. The concentration of GSH was proportional to the ratio of fluorescence intensities of RhB and oxVB1, and the detection linear range was 1 to 10 000 µM with comparable selectivity. This ratio fluorescence sensor was successfully applied to GSH determination in whitening capsules and glutathione tablets with satisfactory results, and the sensor may be a potentially powerful tool for the detection of GSH.

The Biological Activity Mechanism of Chlorogenic Acid and Its Applications in Food Industry: A Review.

Chlorogenic acid (CGA), also known as coffee tannic acid and 3-caffeoylquinic acid, is a water-soluble polyphenolic phenylacrylate compound produced by plants through the shikimic acid pathway during aerobic respiration. CGA is widely found in higher dicotyledonous plants, ferns, and many Chinese medicine plants, which enjoy the reputation of "plant gold." We have summarized the biological activities of CGA, which are mainly shown as anti-oxidant, liver and kidney protection, anti-bacterial, anti-tumor, regulation of glucose metabolism and lipid metabolism, anti-inflammatory, protection of the nervous system, and action on blood vessels. We further determined the main applications of CGA in the food industry, including food additives, food storage, food composition modification, food packaging materials, functional food materials, and prebiotics. With a view to the theoretical improvement of CGA, biological activity mechanism, and subsequent development and utilization provide reference and scientific basis.

Amphiphilic copolymers grafted on monodisperse magnetic microspheres as an efficient adsorbent for the extraction of safrole in the plasma.

Polystyrene (PS) microsphere is a kind of attractive extracting medium due to its high stability in different matrices and its particle size can be controlled. The attachment of amphiphilic copolymers to the PS microsphere surface can overcome the drawback of PS relevant to its hydrophobic nature and low wettability. In our previous work, the magnetic composite based on PS microsphere (5 µm) and poly (divinylbenzene-co-N-vinylpyrrolidone, DVB-co-NVP) shell was successfully fabricated and applied for the extraction of safrole in cola drinks. However, the large size and ease of sedimentation limited its application in the enrichment of safrole from blood samples. Considering the adjustability of PS microsphere size, we synthesized the porous PS microspheres with the uniform size of 3 µm and then functionalized with Fe3O4 nanoparticles and poly (DVB-co-NVP) layer in this work. Using the proposed material as extraction sorbent, a simple and fast magnetic solid phase extraction (MSPE) method coupled with HPLC was developed for quantification of safrole in the plasma. Under the optimized conditions, the response to safrole was linear in the range of 0.02-12 µg mL-1, and the limit of detection (LOD) was 0.006 µg mL-1. Satisfactory recoveries were obtained between 85.67% and 97.74% (spiked at 0.05, 0.2, 2 µg mL-1) and the relative standard deviations (RSDs) for the above spiked levels of the analyte were below 3.9% (n = 6). The adsorbent can be reused for 6 cycles without a significant loss of extraction capability.

Fluorescence and magnetic nanocomposite Fe3O4@SiO2@Au MNPs as peroxidase mimetics for glucose detection.

In this paper, multifunction nanoparticles (MNPs), Fe3O4@SiO2@Au MNPs, with properties of superparamagnetism, fluorescence and peroxidase-like catalytic activity were synthesized in the aqueous phase. The synthesized composites were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier translation infrared spectrum (FT-IR) and fluorometer. The results show that the multifunctional nanomaterials have good magnetic and fluorescence properties. Then, the mimetic properties of this material were investigated. The as-synthesized Fe3O4@SiO2@Au MNPs exhibited the best catalytic activity for peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) at the reaction temperature of 70 °C and pH of 3. Compared with free Fe3O4 MNPs and BSA-Au nanoclusters (NCs), the composites have better catalytic activity at higher temperature and lower pH, indicating that Fe3O4@SiO2@Au MNPs can work in more severe environment. In practical application, we have successfully established the colorimetric method for the detection of H2O2 and glucose with the detection range of 1 × 10-6 ∼ 4 × 10-5 M and 5 × 10-6 ∼ 3.5 × 10-4 M, and the detection limit of 6 × 10-7 M and 3.5 × 10-6 M, respectively. The method was also successfully applied in the detection of real samples. Furthermore, since the fluorescence of Fe3O4@SiO2@Au MNPs was quenched by H2O2, a method for the visual detection of glucose was established.