Optical Bioassays Based on the Signal Amplification of Redox Cycling.

Optical bioassays are challenged by the growing requirements of sensitivity and simplicity. Recent developments in the combination of redox cycling with different optical methods for signal amplification have proven to have tremendous potential for improving analytical performances. In this review, we summarized the advances in optical bioassays based on the signal amplification of redox cycling, including colorimetry, fluorescence, surface-enhanced Raman scattering, chemiluminescence, and electrochemiluminescence. Furthermore, this review highlighted the general principles to effectively couple redox cycling with optical bioassays, and particular attention was focused on current challenges and future opportunities.

Influence of Bagging on Fruit Quality, Incidence of Peel Browning Spots, and Lignin Content of 'Huangguan' Pears.

The 'Huangguan' pear is one of the high-quality pear cultivars produced in China. However, the bagged fruit of the 'Huangguan' pear often suffers from peel browning spots after rain during their mature period. In this study, in an effort to discover the impact of bagging treatments on the occurrence of peel browning spots and fruit quality, fruits were covered by single-layer, two-layer, or triple-layer paper bags six weeks after reaching full bloom. The results showed that the bagged fruits were characterized by smooth surfaces and reduced lenticels compared with the unbagged ones. The unbagged and the two-layer bagged fruits had yellow/green peels, while the single- and triple-layer bagged ones had yellow/white peels. Compared with the unbagged fruits, the bagged fruits had higher vitamin C (Vc) contents and values of peel color indexes L and a and lower soluble solid contents (SSCs), titratable acid (TA) contents, absorbance index differences (IAD), and b values. Additionally, the triple-layer bagged group was superior to other groups in terms of fruit quality, but it also had the maximum incidence of peel browning spots. Before and after the appearance of peel browning spots, the bagged fruits had smoother and thinner cuticles compared with the unbagged ones. Furthermore, the triple-layer bagged fruits had minimum lignin contents and maximum phenolic contents in their peels, with minimum activity of lignin synthesis-related enzymes such as phenylalanine ammonia lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO), as well as minimum expressions of relevant genes such as cinnamyl alcohol dehydrogenase (CAD), cinnamoyl CoA reductase (CCR), 4-coumarate: coenzyme A ligase (4CL6), and cinnamate 4-hydroxylase (C4H1). It was deduced that POD activity and the relative expressions of CAD9, CCR3, CCR4, and CCR5 may play key roles in the occurrence of peel browning spots. In summary, lignin synthesis affected the incidence of peel browning spots in bagged 'Huangguan' pears. This study provides a theoretical basis for understanding the incidence of peel browning spots in 'Huangguan' pears.

Ligand engineering to achieve synergistic properties in a 2D bilayer supertetrahedral chalcogenide cluster-based assembled material.

Incorporating functional organic linkers into supertetrahedral chalcogenolate cluster-based materials is an effective synthetic strategy to expand structural diversity and generate tunable optical and photoelectric properties arising from synergistic effects. Herein, a mixed ligand engineering approach was adopted to design a supertetrahedral cluster-based assembled material [(Cd6Ag4(SPh)16(TPPA)(BPE)0.5)·2DMF]n (denoted as SCCAM-3) with a 2D bilayer architecture and broader visible-light absorption. Interestingly, SCCAM-3 demonstrates a long-lived afterglow at 83 K and efficient photocatalytic activity for degrading tetracycline in water.

Time-Series Transcriptome Analysis Reveals the Molecular Mechanism of Ethylene Reducing Cold Sensitivity of Postharvest 'Huangguan' Pear.

'Huangguan' pear (Pyrus bretschneideri Rehd) fruit is susceptible to cold, characterized by developing peel browning spots (PBS) during cold storage. Additionally, ethylene pretreatment reduces chilling injury (CI) and inhibits PBS occurrence, but the mechanism of CI remains unclear. Here, we deciphered the dynamic transcriptional changes during the PBS occurrence with and without ethylene pretreatment via time-series transcriptome. We found that ethylene suppressed the cold-signaling gene expression, thereby decreasing the cold sensitivity of the 'Huangguan' fruit. Moreover, the "Yellow" module closely correlated with PBS occurrence was identified via weighted gene co-expression network analysis (WGCNA), and this module was related to plant defense via Gene Ontology (GO) enrichment analysis. Local motif enrichment analysis suggested that the "Yellow" module genes were regulated by ERF and WRKY transcription factors. Functional studies demonstrated that PbWRKY31 has a conserved WRKY domain, lacks transactivation activity, and localizes in the nucleus. PbWRKY31-overexpressed Arabidopsis were hypersensitive to cold, with higher expression levels of cold signaling and defense genes, suggesting that PbWRKY31 participates in regulating plant cold sensitivity. Collectively, our findings provide a comprehensive transcriptional overview of PBS occurrence and elucidate the molecular mechanism by which ethylene reduces the cold sensitivity of 'Huangguan' fruit as well as the potential role of PbWRKY31 in this process.

Chinese Traditional Pear Paste: Physicochemical Properties, Antioxidant Activities and Quality Evaluation.

As a traditional folk medicine, pear paste has important nutritional and health effects. The physicochemical properties and antioxidant activities of pear pastes prepared from 23 different cultivars were investigated, including color parameters ( L*, a*, b* and h°), transmittance, pH, titratable acidity (TA), soluble sugar content, total phenolics content (TPC), total flavonoids content (TFC), DPPH and •OH radical scavenging activity (RSA), and ferric reducing antioxidant power (FRAP). It was demonstrated that the physicochemical properties and antioxidant activities of pear pastes from various cultivars differed significantly. Pear cultivars of "Mantianhong", "Xiangshui" and "Anli" possessing higher TPC and TFC exhibited excellent antioxidant activity determined by DPPH RSA, •OH RSA and FRAP, while the lowest TPC and TFC was observed for the cultivars of "Xueqing", "Nansui", "Hongxiangsu", and "Xinli No. 7", which also demonstrated the poor antioxidant activity. Multivariate analyses, including factor and cluster analysis, were used for the quality evaluation and separation of pear pastes based on their physicochemical and antioxidant properties. Factor analysis reduced the above thirteen parameters to final four effective ones, i.e. DPPH RSA, color b*, FRAP and TA, and subsequently these four parameters were used to construct the comprehensive evaluation prediction model for evaluating the quality of pear pastes. The pear pastes could be separated into three clusters and differentiated for the diverse of pear cultivars via cluster analysis. Consistently, "Mantianhong", "Xiangshui" and "Anli" pear with higher quality clustered into one group, in contrast, "Xueqing", "Nansui", "Hongxiangsu", and "Xinli No. 7" with lower quality clustered into the other group. It provided a theoretical method to evaluate the quality of pear paste and may help the fruit processing industry select the more suitable pear cultivars for pear paste making.

Changes in α-Farnesene and Phenolic Metabolism and the Expression of Associated Genes during the Development of Superficial Scald in Two Distinct Pear Cultivars.

Superficial scald is a postharvest physiological disorder that occurs in pear during and after cold storage. In this study, the superficial scald index; α-farnesene and its oxidation products, conjugated trienols (CTols); phenolic content; and the expression of its related genes were investigated in two different pear cultivars, 'Wujiuxiang' (Pyrus communis L.) and 'Yali' (Pyrus bretschneideri R.), following 115 days of cold storage at 0 °C followed by 7 days of shelf life at 20 °C. The results indicated that the superficial scald occurred after 115 days of cold storage and became more severe during the shelf life of the 'Wujiuxiang' pear, whereas no scald was observed in 'Yali'. The α-farnesene levels increased rapidly at first and then decreased, while the CTols contents increased significantly in 'Wujiuxiang' as compared to 'Yali', and the expression levels of the genes involved in α-farnesene and CTols metabolism (HMGR1, HMGR2, GSTU7, GPX5, and GPX6), as well as the phenolic synthesis (PAL1, PAL2, C4H1, 4CL2, C3H, and ANR) of the peel, were significantly up-regulated at the onset of the superficial scald. In addition, the relative conductivity and contents of catechin and epicatechin were higher, and the expression level of the laccase gene (LAC7) significantly increased with the development of superficial scald, while lower contents of chlorogenic acid, arbutin, and isorhamnetin-3-3-glucoside, as well as the lower expression levels of a phenolic-synthesis-related gene (C4H3) and polyphenol oxidase genes (PPO1 and PPO5), were noticed in 'Wujiuxiang' as compared to 'Yali'. The results indicated that the onset and progression of superficial scald were associated with the accumulation of CTols, cell membrane breakdown, and higher catechin, epicatechin, and rutin contents, as well as the expression of associated genes of the peels of pear fruit.

Bumblebees retrieve only the ordinal ranking of foraging options when comparing memories obtained in distinct settings.

Are animals' preferences determined by absolute memories for options (e.g. reward sizes) or by their remembered ranking (better/worse)? The only studies examining this question suggest humans and starlings utilise memories for both absolute and relative information. We show that bumblebees' learned preferences are based only on memories of ordinal comparisons. A series of experiments showed that after learning to discriminate pairs of different flowers by sucrose concentration, bumblebees preferred flowers (in novel pairings) with (1) higher ranking over equal absolute reward, (2) higher ranking over higher absolute reward, and (3) identical qualitative ranking but different quantitative ranking equally. Bumblebees used absolute information in order to rank different flowers. However, additional experiments revealed that, even when ranking information was absent (i.e. bees learned one flower at a time), memories for absolute information were lost or could no longer be retrieved after at most 1 hr. Our results illuminate a divergent mechanism for bees (compared to starlings and humans) of learned preferences that may have arisen from different adaptations to their natural environment.

A comprehensive insight on the main physiological biochemical and related genes expression changes during the development of superficial scald in "Yali" pear.

Superficial scald is a serious physiological disorder in "Yali" pear (Pyrus bretschneideri Rehd. cv. Yali) after long-term cold storage. Changes in superficial scald, ethylene production, α-farnesene and phenylpropane metabolism with associated gene expression in "Yali" pear treated with and without (control) 1-methylcyclopropene (1-MCP) were investigated. Compared with the control group (without 1-MCP), 1-MCP (1.0 µl L-1) significantly lowered the superficial scald index after 180 days of cold storage. During cold storage and shelf life, the contents of α-farnesene, conjugated trienols, chlorogenic acid, and epicatechin in the peel were reduced, while quercetin was enhanced in 1-MCP-treated fruit, and the expression of genes associated with ethylene synthesis (ACS1, ACO1), receptors (ETR2, ERS1) and signal transduction (ERF1), α-farnesene metabolism (AFS1, HMGR2, GST7), phenolic biosynthesis (PAL1, C4H1, C4H2, HCT3, 4CL2, C3H), and oxidases (PPO1, PPO5, and LAC7) were significantly downregulated by 1-MCP. These results suggested that the onset and development of superficial scald was closely related to the ethylene receptor, conjugated trienols, chlorogenic acid and epicatechin and related genes expression in "Yali" pear.

Fluorescent Immunoassay with a Copper Polymer as the Signal Label for Catalytic Oxidation of O-Phenylenediamine.

This work suggested that Cu2+ ion coordinated by the peptide with a histidine (His or H) residue in the first position from the free N-terminal reveals oxidase-mimicking activity. A biotinylated polymer was prepared by modifying His residues on the side chain amino groups of lysine residues (denoted as KH) to chelate multiple Cu2+ ions. The resulting biotin-poly-(KH-Cu)20 polymer with multiple catalytic sites was employed as the signal label for immunoassay. Prostate specific antigen (PSA) was determined as the model target. The captured biotin-poly-(KH-Cu)20 polymer could catalyze the oxidation of o-phenylenediamine (OPD) to produce fluorescent 2,3-diaminophenazine (OPDox). The signal was proportional to PSA concentration from 0.01 to 2 ng/mL, and the detection limit was found to be eight pg/mL. The high sensitivity of the method enabled the assays of PSA in real serum samples. The work should be valuable for the design of novel biosensors for clinical diagnosis.

A General, Label-Free and Homogeneous Electrochemical Strategy for Probing of Protease Activity and Screening of Inhibitor.

Proteases play a critical role in regulating various physiological processes from protein digestion to wound healing. Monitoring the activity of proteases and screening their inhibitors as potential drug molecules are of great importance for the early diagnosis and treatment of many diseases. In this work, we reported a general, label-free and homogeneous electrochemical method for monitoring protease activity based on the peptide-copper interaction. Cleavage of peptide substrate results in the generation of a copper-binding chelator peptide with a histidine residue in the first or third position (His1 or His3) at the N-terminal. The redox potential and current of copper coordinated with the product are different from the free copper or the copper complex with the substrate, thus allowing for the detection of protease activity. Angiotensin-converting enzyme (ACE) and thrombin were determined as the model analytes. The label-free and homogeneous electrochemical method can be used for screening protease inhibitors with high simplicity and sensitivity.

Colorimetric and Electrochemical Methods for the Detection of SARS-CoV-2 Main Protease by Peptide-Triggered Assembly of Gold Nanoparticles.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) has been regarded as one of the ideal targets for the development of antiviral drugs. The currently used methods for the probing of Mpro activity and the screening of its inhibitors require the use of a double-labeled peptide substrate. In this work, we suggested that the label-free peptide substrate could induce the aggregation of AuNPs through the electrostatic interactions, and the cleavage of the peptide by the Mpro inhibited the aggregation of AuNPs. This fact allowed for the visual analysis of Mpro activity by observing the color change of the AuNPs suspension. Furthermore, the co-assembly of AuNPs and peptide was achieved on the peptide-covered electrode surface. Cleavage of the peptide substrate by the Mpro limited the formation of AuNPs/peptide assembles, thus allowing for the development of a simple and sensitive electrochemical method for Mpro detection in serum samples. The change of the electrochemical signal was easily monitored by electrochemical impedance spectroscopy (EIS). The detection limits of the colorimetric and electrochemical methods are 10 and 0.1 pM, respectively. This work should be valuable for the development of effective antiviral drugs and the design of novel optical and electrical biosensors.

Tin-sulfur based catalysts for acetylene hydrochlorination.

In the present work, tin-sulfur based catalysts were prepared using Na2SO3 and (CH3SO3)2Sn and were tested in acetylene hydrochlorination. Based on the analysis of experiments results, the acetylene conversion of (CH3SO3)2Sn/S@AC is still over 90%after a 50 h reaction, at the reaction conditions of T = 200 oC, VHCl/VC2H2 = 1.1:1.0 and C2H2-GSHV = 15 h-1. According to the results of X-ray photoelectron spectroscopy (XPS), HCl adsorption experiments, and acetylene temperature programmed desorption (C2H2-TPD), it is reasonable to conclude that the interaction between Sn and S not only can retard the oxidation of Sn2+ in catalysts but also strengthen the reactant adsorption capacity of tin-based catalysts. Furthermore, results obtained from nitrogen adsorption/desorption and XPS proved that the CH3SO3- can effectively decrease the coke deposition of (CH3SO3)2Sn/AC and thus prolong the lifetime of (CH3SO3)2Sn/AC.

Calcium content and its correlated distribution with skin browning spot in bagged Huangguan pear.

Skin browning spot (SBS) is an important physiology disorder that often occurs in bagged fruit at the mature stage in the Huangguan (Pyrus bretschneideri × Pyrus pyrifolia) pear. Using atomic absorption spectrometry, X-ray microanalysis, and the potassium-pyroantimonate precipitation method, the water-soluble and total Ca(2+), Mg(2+), and K(+) contents, their microdistribution, and the Ca(2+) localization were investigated in bagged Huangguan pear fruit in the presence and absence of SBS. Our results show that the water-soluble and total Ca(2+) contents in both the skin and flesh tissue and the total Ca(2+) content only in the skin tissue of the fruits with SBS were significantly lower compared to those of the fruits without SBS. However, a higher K(+) content in the skin tissue was found in the fruits with SBS. There were no significant differences in the water-soluble and total Mg(2+) contents in the skin and flesh tissue between the fruits with and without SBS. In addition, the results of the X-ray microanalysis were consistent with changes in the total Ca(2+), Mg(2+), and K(+) contents in the skin and flesh tissue of the pear fruit that were affected by SBS. Compared to the skin tissue of pear fruit without SBS and the healthy part near the lesion zone of SBS, the lesion zone of SBS exhibited a high accumulation of Ca(2+) grains in the cell membrane of the epidermis cells, while fewer Ca(2+) grains were found in the vacuoles and cell walls. Altogether, these results indicate that Ca(2+) deficiency and the cellular Ca(2+) distribution in skin tissue contributed to the occurrence of SBS in bagged Huangguan pear fruit.

catena-Poly[[{2-[(2-hy-droxy-eth-yl)imino-meth-yl]-6-meth-oxy-phenolato}copper(II)]-µ-thio-cyanato].

In the title thio-cyanate-bridged polynuclear copper(II) complex, [Cu(C(10)H(12)NO(3))(NCS)](n), the Cu atom is five-coordinated in a square-pyramidal geometry, with one phenolato O, one imino N and one hy-droxy O atom of a Schiff base ligand and one thio-cyanato N atom defining the basal plane, and with one thio-cyanato S atom occupying the apical position. In the crystal structure, pairs of adjacent complex mol-ecules are linked through inter-molecular O-H⋯O hydrogen bonds into dimers. The dimers are further linked via Cu⋯S inter-actions, forming two-dimensional layers parallel to the bc plane.

The toxic function of cesium 5-sulfosalicylate based on the investigation of its trans-erythrocytes membrane behaviors and morphological properties.

In order to evaluate the cesium-induced toxic functional changes in organisms, transmembrane activities of cesium 5-sulfosalicylate (Cs(H(2)Ssal)) into human erythrocyte in vitro is presented in this paper, including kinetic characteristic of transport process and pathways involved in it. The uptake amount of Cs(H(2)Ssal) by erythrocyte was determined both by Graphite Furnace Atomic Absorption Spectrometry (GFAAS) and spectrofluorimetry. The pathways of Cs(H(2)Ssal) transporting into erythrocyte are proposed according to inhibition investigation. The influence of Cs(H(2)Ssal) on morphological properties of erythrocytes was examined using Scanning Electron Microscopy (SEM) to determined the endurable concentration extent of erythrocytes to Cs(H(2)Ssal). Results show that transmembrane of Cs(H(2)Ssal) has characteristic of first-order kinetic process during the first 2h, and four pathways were involved in its transporting activities: Ca(2+) channel, Na(+)-K(+) pump, Na(+)-Cs(+) countertransport, and anion Cl(-)/CsCO(3)(-) exchange. The transmembrane process of Cs(H(2)Ssal) can both prevent the uptake of K(+) and induces abnormal accumulation of extracellular K(+) as well as occupy some K(+)-binding sites in protein, causing some tissues losing their activities and functions. Only high concentrations of Cs(H(2)Ssal) could change morphological properties of erythrocytes greatly and cause hemolysis eventually.