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Tea is an important economic crop and health beverage in China. The presence of heavy metal ions in tea poses a significant threat to public health. Here, we prepared an aptamer biosensor labelled with AIEgen nanospheres to detect Pb2+ in tea. The dsDNA modified by amino and phosphoric acid was combined with the carboxylated AIEgen NPs to form AIEgen-DNA with a fluorescence group, which was then fixed to the surface of Zr-MOFs to quench the fluorescence of AIEgen NPs. At the same time, PEG was added to remove nonspecific adsorption. Then Pb2+ was added to cut the DNA sequences containing the cutting sites, and AIEgen NPs and part of the DNA sequences were separated from the Zr-MOFs surface to recover the fluorescence. By comparing the fluorescence changes before and after adding Pb2+, the detection limit of Pb2+ can reach 1.70 nM. The fluorescence sensor was applied to detect Pb2+ in tea, and the detection results showed that the tea purchased on the market did not contain the concentration of Pb2+ within the detection range. This study provides new insights into monitoring food and agriculture-related pollutants based on fluorescent biosensors. [ABSTRACT FROM AUTHOR]

Four evergreen broadleaf Rhododendron spp. (Rhododendrons), namely, Rhododendron aganniphum, R. nyingchiense, R. wardii, and R. triflorum, occur in harsh subalpine habitats in the southwest Qinghai-Tibet Plateau (QTP), China. Considering that the four Rhododendrons cannot escape their unique environment, they must evolve a set of adaptations to survive, but the information is lacking. To uncover their physiological adaptation characteristics, in the present study, we monitored their physiological characteristics by determination of their seasonal variation in antioxidant enzyme activity, osmotic adjustment substrates, and carbohydrate contents, and their pigment content and photosynthetic efficiency. The results showed that superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities and proline content of four Rhododendrons had a significant difference in autumn and were insignificant in summer. Specifically, R. aganniphum had the maximum protective enzyme activity and proline content in winter as well as chl a, b, and car contents. The values of maximal quantum yield (Fv/Fm), photochemical efficiency (ΦPSII), and non-photochemical quenching (NPQ) of four Rhododendrons were significantly higher in summer than in other seasons. The lower qP indicated the four Rhododendrons were susceptible to photoinhibition. Overall, the four Rhododendrons had similar physical characteristics in subalpine habitats. The parameters of the maximum quantum yield of photosystem II (PSII), the actual quantum yield of PSII, the non-photochemical chlorophyll fluorescence quenching, and chlorophyll a content increased in summer. Meanwhile, the protective enzyme activity and total soluble sugar content, proline content, and carotenoid content increased in spring, autumn, and winter. These results suggested that the four Rhododendrons can adapt to subalpine habitats by heat dissipation to avoid the damage of excessive radiation during the warm season while scavenging reactive oxygen and increasing the intracellular fluid concentration to avoid damage caused by chilling temperatures during the cold seasons. These findings would provide a reference for the conservation and application of these valuable ornamental evergreen broadleaf Rhododendrons, and enrich theory of plant eco-physiology in the high altitudes of the QTP. [ABSTRACT FROM AUTHOR]

A new fluorogenic bio-adsorbent was successfully synthesized for detection and adsorption of mercury ions in aqueous solution. It showed high sensitivity in removing Hg (II) at low concentration with a detection limit of 84 ppb which was below the maximum discharge standard in enterprise drain off water in China, besides, the adsorbent had good selectivity towards Hg (II) among numerous kinds of cations in water that it showed fluorescent quenching properties for Hg (II) ions due to photo-induced electron transfer. In addition, batch adsorption experiments were investigated to study the influence of initial concentration of metal ions, contact time, pH of the solution on the adsorption capacity. Equilibrium adsorption isotherms demonstrated the Hg (II) removing process fitted well with Langmuir isotherm model, and the maximum adsorption capacity for mercury was measured to be 143.88 mg/g. Furthermore, the adsorption kinetics was found to follow pseudo-second-order model. FTIR spectra and SEM-elemental mapping clearly confirmed the adsorbed heavy metal ions. • The synthesized adsorbent AMC shows selective fluorescence response exclusively for Hg (II) in water. • The adsorption efficiency of AMC reaches >96% in concentration below 50 mg/L. • The detection limit of AMC towards Hg (II) is 8.4 × 10−8 M which is below the corresponding maximum discharge standard. • The adsorbent AMC is reusable after several cycles of regeneration. [ABSTRACT FROM AUTHOR]

Huidouba is a kind of fungus plant that grows by spiders parasitizing tea trees at an altitude of 1500 m above Mount Emei. The bioactive polysaccharides extracted from Huidouba have been traditionally used in the treatment of diabetes in China. In this study, the optimal hot-water extraction condition of crude Huidouba polysaccharides was obtained using Box–Behnken design: the temperature of 93.7 °C, the time of 3.57 h, the liquid-to-solid ratio of 28.47 mL/g, and the yield was 0.46%. Three purified Huidouba polysaccharides (HDBPs, including HDBP-d, HDBP-1, and HDBP-2) were separated through deproteinization, ultrafiltration, and column chromatography. Then the inhibition mechanism and kinetics of HDBPs against α-glucosidase were investigated. The inhibitory activity of HDBPs on α-glucosidase was positively correlated with their concentration, and their mechanism of quenching fluorescence was ascertained to be the static type induced by the formation of HDBPs-α-glucosidase complex. HDBP-d and HDBP-2 inhibited the activity of α-glucosidase in a reversible competitive-type manner while HDBP-1 was a noncompetitive-type inhibitor. The inhibitory activities of HDBPs on α-glucosidase correlated inversely with temperature in most cases, and showed weaker inhibitory activity at extreme acidic or alkaline conditions. These findings highlight the efficacy, kinetics and mechanism of HDBPs inhibiting α-glucosidase in vitro. The study provided a replaceable approach for chemical inhibitors of α-glucosidase with natural fungus plant extracts, and suggested the theoretical basis that the plant-derived polysaccharides with glucosidase inhibition effects were applied in medicines. • The optimum hot-water extraction conditions of the CHDBP were obtained. • α-Glucosidase activity was inhibited due to the formation of HDBPs-enzyme complex. • HDBP-d and HDBP-2 were reversible and competitive inhibitors of α-glucosidase. • HDBP-1 was a reversible and non-competitive inhibitor of α-glucosidase. • HDBPs showed weaker inhibition activity during extreme TEMP and pH conditions. [ABSTRACT FROM AUTHOR]

The topsoil temperature in arid areas of Xinjiang, China can be up to about 80°C in summer. This may significantly affect the chemical properties of soil humic substances. However, the effects of high temperature on characteristics of soil humic substances and their complexation with toxic metals are still poorly known. In the present study, binding of Hg(II) to unheated soil humic substances and heated soil humic substances from sandy soils was comparatively investigated using three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy. Two fluorescent peaks (peak I at Ex/Em = 365-370/470-474 nm; peak II at Ex/Em = 270-275/468-472 nm) identified as humic-like fluorescence were observed in the EEM spectra of humic substances. Both peaks were clearly quenched by Hg(II), indicating the strong interaction of humic-like substances with Hg(II), and showed blue shifts after heat treatment. Heat treatment caused an increase of the fraction of accessible fluorophore ( f), binding sites number ( n) and effective quenching constants (log K), indicating that more binding sites in humic substances could bind Hg(II) and form more stable humic substances-Hg(II) complexes after heat treatment. However, a decrease of binding constants (log K) suggested that heat treatment would reduce the binding capacity of each binding site of humic substances to Hg(II). This study implies the transport of Hg(II) may be affected by high temperature in the arid zone due to the modification of the physicochemical properties of humic substances in soil. [ABSTRACT FROM AUTHOR]

It has drawn extensive research interest to integrate luminescent ligands into metal-organic frameworks as luminescent materials due to striking luminescent properties. In this work, a Co-MOF with weak fluorescence emission, [Co(OBA)(2,2′-BPY)], was synthesized by a mixed solvothermal route with Co(NO 3) 2 as the Co2+ ion source, 4,4′-Oxybis(benzoic acid) (OBA) and 2,2′-Bipyridyl (2,2′-BPY) as the ligands. Its fluorescence was obviously enhanced through integrating a small amount of luminescent ligands: 2-aminoterephthalic acid. Interestingly, the above enhanced fluorescence could be selectively quenched by the organophosphorus pesticides with p-nitrophenyl group such as p-nitrophenyl phosphate (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) in water systems. As a case, the detection limit towards PNPP was up to 352 nM (0.07 mg kg−1), which is far lower than the standards for similar pesticide residues in fruits in China (0.1–0.6 mg kg−1) [ 1 ]. At the same time, the above phenomenon of the fluorescence quenching was not interfered from some other pesticides, metallic ions, amino acids and aromatic nitrocompounds, implying the present fluorescent material has potential application as a highly selective probe for detecting PNPP pesticide residues in food and domestic water. Furthermore, a possible quenching mechanism was discussed. • 2-aminoterephthalic acid co-coordinated Co-MOF sensor is prepared by a mixed solvothermal route. • Its fluorescence is selectively quenched by organophosphorus pesticides with p-nitrophenyl. • The as-prepared Co-MOF sensor had a low detection limit of 352 nM (0.07 mg kg−1) towards PNPP. • The as-prepared fluorescent probe presents a fast response of 25 s and good cycle stability for PNPP. [ABSTRACT FROM AUTHOR]

The most abundant agricultural biomass in the Northeast of China can be directly converted into the carbon quantum dots. The obtained carbon quantum dots is able to detect iron(III) with high selectivity and good efficiency. [Display omitted] • The conversion of whole biomass wastes to CQDs using one-pot strategy. • Polar groups brought from the biomass make the CQDs with good water compatibility. • The CQDs have strong fluorescence and selective quenching effect for Fe3+. • The detection of Fe3+ is desired in environmental remediation and medical diagnosis. Eco-friendly synthesis of Carbon quantum dots (CQDs) in water is reported, exploiting various typical crop biomasses as carbon sources. The resultant CQDs exhibit strong fluorescence, good dispersion in common solvents and uniformly dispersed particle size. The synthesized CQDs are highly dispersible in water, due to the presence of surface hydroxyl and carboxyl groups. The CQDs suspension exhibits strong blue fluorescence under UV irradiation, with an optimal excitation wavelength in the range from 350 to 390 nm, which varies with the change of CQD concentration. The emission corresponds to two band transitions, which are originated from π → π* of C C bonds and n → π* of C O bonds, respectively. Due to its strong fluorescence and energy transfer, the synthesized CQDs materials can be used as a fluorescent probe for the detection of Fe3+ ions with good selectivity and sensitivity, within the Fe3+ concentration range of 0–500 μM. The research is of significance for converting crop waste to high added-value products, and the obtained CQDs with selective Fe3+ ions determination ability are attractive for the environmental monitoring and medical diagnosis. [ABSTRACT FROM AUTHOR]

• Spectral properties and Cu-binding properties of DOM collected from the upper lake and lower lake in Nansi Lake were studied. • Humic-/fulvic-like substances were the main substance of DOM collected from Nansi Lake. • Protein-like components exhibited higher Cu (II) binding abilities than humic-/fulvic-like ones. • Interactions of Cu2+ with DOM were probably affected by submerged plants and the water conservancy projects. Interaction between dissolved organic matter (DOM) and heavy metals have been widely studied, and the differences in DOM properties have a great impact on the capacity of DOM-metals binding. In this study, the samples were collected from the upper lake and lower lake in Nansi Lake, respectively. According to the ratio of the fluorescence intensity of component to the total fluorescence intensity (%F max) in the two areas, obvious differences were found in the properties of DOM. The content of humic-like substances showed a decreasing trend from the north to south in Nansi Lake. On this basis, samples from north and south ends of Nansi Lake were selected for fluorescence titration. All components were quenched with the increasing of Cu2+ addition. Combining the results of Synchronous fluorescence (SF) spectra with two-dimensional correlation spectroscopy (2D-COS), fluorescent quenching near 275 nm was quicker than the changes that occurred at the wavelength that after 275 nm, which suggested that the complexation occurred firstly for protein-like components as compared with humic-like components. The modified Stern-Volmer model suggested that protein-like components had larger effective quenching constants (log K a = 3.47 ± 0.13 for component C5 in the upper lake and log K a = 3.57 ± 0.19 for component C4 in the lower lake) than humic-like components and it is not affected by the region, indicating that protein-like substances might have a higher metal binding potential than humic-like substances in Nansi Lake. The binding constants and the binding sites suggested that humic-like components also had a nonnegligible binding potential in Nansi Lake although the protein-like components revealed a stronger binding ability in fluorescence quenching. [ABSTRACT FROM AUTHOR]

Color is considered an index to evaluate the quality of the unripe fruit of Rubus chingii Hu in China. This study compared the contents of the active polyphenolic constituents in unripe differently colored fruits. The data showed that there were significant differences between the yellow fruit (YF) and green fruit (GF) in the composition of ellagitannins (ETs) and ellagic acid (EA). Then, the structure-activity relationship of the main ellagitannins (lambertianin A, sanguiin H-6, casuarictin) and ellagic acid in unripe fruits were investigated by the antioxidant activities assay, non-enzymatic glycation inhibitory activity assay and glucose uptake assay in L6 cells. The results showed that the number of hydroxyl groups and galloyl configuration at the glucose C-1 significantly affected the activity of ellagitannins. However, ellagic acid, which had fewer hydroxyl groups, exhibited the highest bioactive properties. Moreover, the fluorescence quenching analysis and molecular docking results demonstrated that ellagitannin was a concentration-dependent antiglycation compound. This study suggested that EA and ETs had different action mode and the content of ETs was an important factor influencing the unripe fruits of Rubus chingii Hu. • Ellagitannin composition between two color of Rubus Chingii Hu have difference. • The hydroxyl group and configuration galloyl affect activity of ellagitannins. • Ellagitannin is an antiglycation compound related to the concentration. • Ellagic acid is more effective on antiglycation activity and glycose uptake. [ABSTRACT FROM AUTHOR]