A Visible Light Driven Photoelectrochemical Chloramphenicol Aptasensor Based on a Gold Nanoparticle-Functionalized 3D Flower-like MoS2/TiO2 Heterostructure.

Developing a photoactive material by combining the characteristics of a wide light response range and effective separation of photogenerated electron-hole pairs remains a huge challenge for the construction of a photoelectrochemical (PEC) sensing platform. Herein, a gold nanoparticle (AuNP)/MoS2/TiO2 composite was prepared through the facile hydrothermal method coupled with an in situ photoreduction technology. Benefiting from both the compositional and structure merits, the composite not only extends the absorption range to visible light but also enhances the photoelectric conversion efficiency by transferring photogenerated electrons into the conduction band of semiconductors from the plasmonic AuNP. Meanwhile, the thiolated aptamers were attached to the surface of AuNP/MoS2/TiO2 composites through the Au-S bonding to construct a visible light driven PEC aptasensor for ultrasensitive detection chloramphenicol (CAP). In the presence of CAP, the aptamers anchored on the surface of the photoactive materials could specifically recognize CAP and interact with it to form a bioaffinity complex with a steric hindrance effect, resulting in the rapid decrease of photocurrent responses. Based on this photocurrent suppression strategy, the constructed PEC aptasensing platform exhibited a high sensitivity with a wide linear range from 5 pM to 100 nM and a low detection limit of 0.5 pM.

Monitoring Leaf Nitrogen Accumulation With Optimized Spectral Index in Winter Wheat Under Different Irrigation Regimes.

Rapid and non-destructive estimation of leaf nitrogen accumulation (LNA) is essential to field nitrogen management. Currently, many vegetation indices have been used for indicating nitrogen status. Few studies systematically analyzed the performance of vegetation indices of winter wheat in estimating LNA under different irrigation regimes. This study aimed to develop a new spectral index for LNA estimation. In this study, 2 years of field experiments with different irrigation regimes were conducted from 2015 to 2017. The original reflectance (OR) and three transformed spectra [e.g., the first derivative reflectance (FDR), logarithm of the reciprocal of the spectra (Log(1/R)), and continuum removal (CR)] were used to calculate two- and three-band spectral indices. Correlation analyses and univariate linear and non-linear regression between transformed-based spectral indices and LNA were performed. The performance of the optimal spectral index was evaluated with classical vegetation index. The results showed that FDR was the most stable transformation method, which can effectively enhance the relationships to LNA and improve prediction performance. With a linear relationship with LNA, FDR-based three-band spectral index 1 (FDR-TBI1) (451, 706, 688) generated the best performance with coefficient of determination (R 2) of 0.73 and 0.79, the root mean square error (RMSE) of 1.267 and 1.266 g/m2, and the ratio of performance to interquartile distance (RPIQ) of 2.84 and 2.71 in calibration and validation datasets, respectively. The optimized spectral index [FDR-TBI1 (451, 706, 688)] is more effective and might be recommended as an indicator for estimating winter wheat LNA under different irrigation regimes.

Laccase immobilized polyaniline/magnetic graphene composite electrode for detecting hydroquinone.

Magnetic graphene nanocomposites were prepared by hydrothermal synthesis, and aniline polymerization was initiated by magnetic graphene. These polyaniline/magnetic graphene (PANI/MG) composites were used to immobilize laccase to construct biosensors. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy (IR) were used to characterize these composites. Cyclic voltammetry and chronoamperometry technique were used to test the electrical properties of the constructed polyaniline/magnetic graphene laccase modified electrode. The results show that the polyaniline/magnetic graphene immobilizing laccase modified electrode exhibited superior electrical properties, including high sensitivity, detection limit and linear range. The hydroquinone was used as an analytical and detection probe. The selectivity was 0.03639 A/(mol/L), the linear range was 0.4-337.2 µmol/L, and the detection limit was 2.94 µM (signal/noise = 3, minimum identification value of effective signal). The biosensor can reach the conditions for detecting the actual water sample.

Assessment of plant water status in winter wheat (Triticum aestivum L.) based on canopy spectral indices.

Rapid and non-destructive estimation of plant water status is essential for adjusting field practices and irrigation schemes of winter wheat. The objective of this study was to find new combination spectral indices based on canopy reflectance for the estimation of plant water status. Two experiments with different irrigation regimes were conducted in 2015-2016 and 2016-2017. The canopy spectra were collected at different growth stages of winter wheat. The raw and derivative reflectance of canopy spectra showed obvious responses to the change of plant water status. Except for equivalent water thickness (EWT), other water metrics had good relationships with new combination spectral indices (R2>0.7). An acceptable model of canopy water content (CWC) was established with the best spectral index (RVI (1605, 1712)). Models of leaf water content (LWC) and plant water content (PWC) had better performances. Optimal spectral index of LWC was FDRVI (687, 531), having R2, RMSE and RPD of 0.77, 2.181 and 2.09; R2, RMSE and RPD of 0.87, 2.652 and 2.34 for calibration and validation, respectively. And PWC could be well estimated with FDDVI (688, 532) (R2, RMSE and RPD of 0.79, 3.136 and 2.21; R2, RMSE and RPD of 0.83, 3.702 and 2.18 for calibration and validation, respectively). Comparing the performances of estimation models, the new combination spectral indices FDRVI (687, 531) based on canopy reflectance improved the accuracy of estimation of plant water status. Besides, based on FDRVI (687, 531), LWC was the optimal water metrics for plant water status estimation.

Galactomannan with novel structure produced by the coral endophytic fungus Aspergillus ochraceus.

The homogeneous extracellular polysaccharide, AW1, was obtained from the fermented broth of the fungus Aspergillus ochraceus derived from coral Dichotella gemmacea. AW1 was a galactomannan with a molar ratio of mannose and galactose of 2.16:1.00 and a molecular weight of about 29.0kDa. The structure of AW1 was investigated by chemical and spectroscopic methods, including methylation analysis, one- and two-dimensional nuclear magnetic resonance (1D, 2D NMR) and electrospray mass spectrometry with collision-induced dissociation (ES-CID MS/MS) spectroscopic analyses. The results showed that the backbone of AW1 consisted of (1⟶2)-linked α-d-mannopyranose residues. The mannopyranose residues in the backbone were substituted at C-6 by the (1⟶)-linked α-d-mannopyranose units and (1⟶5)-linked ß-d-galactofuranose oligosaccharides with different degrees of polymerization. The investigation demonstrated that AW1 was a novel galactomannan with different structural characteristics from other fungal galactomannans, and could be a potential resource of the (1⟶5)-linked ß-d-galactofuranose oligosaccharides.

Preparation and structural elucidation of a glucomannogalactan from marine fungus Penicillium commune.

The coral-associated fungus Penicillium commune produces an extracellular polysaccharide, FP2-1, when grown in potato dextrose-agar medium. FP2-1 was isolated from the fermented broth using anion-exchange and size-exclusion chromatography, and its structure was elucidated by chemical and spectroscopic analyses, including detailed nuclear magnetic resonance spectroscopy. The results showed that FP2-1 was a glucomannogalactan with a molar ratio of galactose, mannose and glucose of 3.9:1.9:1.0. Structure of FP2-1 may be represented, at an average, as a backbone of (1→2)-linked α-mannopyranose with the every second residue substituted at position 6 by a pentasaccharide branch. The branches consist of four (1→6)-linked ß-galactofuranose residues with terminal α-glucopyranose residue attached to the last galactofuranose residue at position 2. FP2-1 was a novel galactofuranose-containing extracellular polysaccharide differing from previously described extracellular polysaccharides.

Preparation and characterization of an extracellular polysaccharide produced by the deep-sea fungus Penicillium griseofulvum.

The deep-sea fungus Penicillium griseofulvum produces an extracellular polysaccharide, Ps1-1, when grown in potato dextrose-agar medium. Ps1-1 was isolated from the fermented broth using ethanol precipitation, anion-exchange and size-exclusion chromatography. Ps1-1 is a galactomannan with a molecular weight of about 20 kDa, and a molar ratio of mannose and glucose of 1.1:1.0. On the basis of one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) and mass spectroscopic analyses, Ps1-1 is composed of a long chain of galactofuranan and a mannose core. The galactofuranan chain consists of (1→5)-linked ß-galactofuranose, with additional branches at C-6 consisting of (1→)-linked ß-galactofuranose residues and phosphate esters. The mannan core is composed of (1→6)-linked α-mannopyranose substituted at C-2 by (1→)-linked α-mannopyranose residues, disaccharide and trisaccharide units of (1→2)-linked α-mannopyranose. The investigation demonstrated that Ps1-1 was a galactofuranose-containing galactomannan differing from previously described extracellular polysaccharides.

Structural elucidation of an extracellular polysaccharide produced by the marine fungus Aspergillus versicolor.

A homogenous extracellular polysaccharide, designated AWP, was isolated from the fermented liquid of the marine fungus Aspergillus versicolor from the coral Cladiella sp. and purified by anion-exchange and size-exclusion chromatography (SEC). Chemical and spectroscopic analyses, including one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy showed that AWP consisted of glucose and mannose in a molar ratio of 8.6:1.0, and its average molecular weight was estimated to be 500kDa. AWP is a slightly branched extracellular polysaccharide. The backbone of AWP is mainly composed of (1→6)-linked α-D-glucopyranose residues, slightly branched by single α-d-mannopyranose units attached to the main chain at C-3 positions of the glucan backbone. The investigation demonstrated that AWP is a novel extracellular polysaccharide different from those of other marine microorganisms.

Structure and antioxidant activity of an extracellular polysaccharide from coral-associated fungus, Aspergillus versicolor LCJ-5-4.

An extracellular polysaccharide AVP was isolated from the fermented broth of coral-associated fungus Aspergillus versicolor LCJ-5-4. AVP was a mannoglucan with molecular weight of about 7kDa, and the molar ratio of glucose and mannose was 1.7:1.0. On the basis of detailed one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopic analyses, the backbone of AVP was characterized to be composed of (1→6)-linked α-d-glucopyranose and (1→2)-linked α-d-mannopyranose units. The mannopyranose residues in the backbone were substituted mainly at C-6 by the side chain of (1→2)-linked α-d-mannopyranose trisaccharides units. The antioxidant activity of AVP was evaluated with the scavenging abilities on 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals in vitro, and the results indicated that AVP had good antioxidant activity, especially scavenging ability on superoxide radicals. AVP was a novel extracellular polysaccharide with different structural characteristics from other extracellular polysaccharides and could be a potential source of antioxidant.

Preparation, structure and anticoagulant activity of a low molecular weight fraction produced by mild acid hydrolysis of sulfated rhamnan from Monostroma latissimum.

A low molecular weight fraction, designated LMWP, was prepared by mild acid hydrolysis of sulfated rhamnan from Monostroma latissimum and purified by anion-exchange and gel-permeation chromatography. Chemical and spectroscopic analyses showed that LMWP was mainly composed of rhamnose, and its molecular weight was about 33.6 kDa. The backbone of LMWP consists of 1,3-linked α-L-rhamnose units with partially sulfate groups at the C-2 position. Approximately 25% of 1,3-linked α-L-rhamnose units is substituted at C-2 by sulfated or non-sulfated 1,3-linked α-L-rhamnose and 1,2-linked α-L-rhamnose units. LMWP effectively prolonged clotting time as evaluated by the activated partial thromboplastin time assay and was a potent thrombin inhibitor mediated by heparin cofactor II. The investigation demonstrated that LMWP is a novel sulfated polysaccharide with anticoagulant activity.

Chemical characteristic of an anticoagulant-active sulfated polysaccharide from Enteromorpha clathrata.

A sulfated polysaccharide FEP from marine green alga Enteromorpha clathrata was extracted with hot water and further purified by ion-exchange and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that FEP was a high arabinose-containing sulfated polysaccharide with sulfate ester of 31.0%, and its average molecular weight was about 511kDa. The backbone of FEP was mainly composed of (1→4)-linked ß-L-arabinopyranose residues with partially sulfate groups at the C-3 position. In vitro anticoagulant assay indicated that FEP effectively prolonged the activated partial thromboplastin time and thrombin time. The investigation demonstrated that FEP was a novel sulfated polysaccharide with different chemical characteristics from other sulfated polysaccharides from marine algae, and could be a potential source of anticoagulant.

Sequence analysis of the sulfated rhamno-oligosaccharides derived from a sulfated rhamnan.

Three sulfated rhamno-oligosaccharides, designated O1, O2 and O3, were obtained by mild acid hydrolysis of the sulfated rhamnan and purified by gel-permeation chromatography. On the basis of one- and two-dimensional nuclear magnetic resonance (1D, 2D NMR) spectroscopic analyses, the oligosaccharide O1 was characterized to be α-L-Rhap-(2SO4)-(1→3)-α-L-Rhap. The fragmentation pattern of the homogeneous disaccharide in the product ion spectra was recognized by negative-ion electrospray tandem mass spectrometry with collision-induced dissociation (ES-CID MS/MS). With the principles established, the sequences of the oligosaccharides O2 and O3 were deduced to be α-L-Rhap-(2SO4)-(1→3)-α-L-Rhap-(1→3)-α-L-Rhap, and α-L-Rhap-(2SO4)-(1→3)-α-L-Rhap-(1→3)-α-L-Rhap-(1→3)-α-L-Rhap (2SO(4)), respectively. The investigation demonstrated that the sulfated rhamnan-derived oligosaccharides were novel sulfated oligosaccharides different from those of other polysaccharides-degraded from algae, and it could be possible to determine the sequence of the sulfated rhamno-oligosaccharides directly from the glycosidic cleavage fragmentation in the product ion spectra.

Structural characterization and antioxidant properties of an exopolysaccharide produced by the mangrove endophytic fungus Aspergillus sp. Y16.

A homogeneous exopolysaccharide, designated As1-1, was obtained from the culture medium of the mangrove endophytic fungus Aspergillus sp. Y16 and purified by anion-exchange and gel-permeation chromatography. Results of chemical and spectroscopic analyses, including one- and two-dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy showed that As1-1 was mainly composed of mannose with small amounts of galactose, and that its molecular weight was about 15 kDa. The backbone of As1-1 mainly consists of (1→2)-linked α-d-mannopyranose units, substituted at C-6 by the (1→6)-linked α-d-mannopyranose, (1→)-linked ß-d-galactofuranose and (1→)-linked ß-d-mannopyranose units. As1-1 possessed good in vitro antioxidant activity as evaluated by scavenging assays involving 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide radicals. The investigation demonstrated that As1-1 is an exopolysaccharide different from those of other marine microorganisms, and could be a potential antioxidant and food supplement.

Structural characterization of extracellular polysaccharides produced by the marine fungus Epicoccum nigrum JJY-40 and their antioxidant activities.

Two extracellular polysaccharides, ENP1 and ENP2, were isolated from the fermentation liquid of the marine fungus Epicoccum nigrum JJY-40 by anion-exchange chromatography and gel-filtration chromatography, and their structures were investigated using chemical and spectroscopic methods including methylation analysis and NMR spectroscopy. The results demonstrated that ENP1 was composed of mannose, glucose, and galactose in the molar ratio of 5.0:2.1:1.0, and the main chain of the polysaccharide consisted of (1 → 2)-linked mannose, (1 → 3)-linked mannose, terminal mannose, (1 → 6)-linked glucose, (1 → 4)-linked glucose, and (1 → 4)-linked galactose. ENP2 was composed of mannose, galactose, glucose, and glucuronic acid in a molar ratio of 12.4:11.2:8.3:1.0, and its glycosidic linkage patterns included terminal mannose, (1 → 6)-linked glucose, (1 → 4)-linked galactose, and (1 → 3)-linked mannose. The two polysaccharides had a partially branched structure with branch point located at C-3 position of (1 → 6)-linked glucose residue. The molecular weights of ENP1 and ENP2 were 19.2 kDa and 32.7 kDa, respectively. Antioxidant properties of the two polysaccharides were evaluated with hydroxyl, superoxide, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and lipid peroxidation inhibition in vitro, and results showed that ENP2 and ENP1 had good antioxidant activities, especially ENP2. ENP2 could be effective as a potential antioxidant.