•The MIP/PSS-rGO/GCE was prepared by electropolymerization of o-PD and daidzein.•The MIP/PSS-rGO/GCE showed high selectivity of daidzein compared with other analogues.•The sensor was successfully applied for determination of daidzein in serum sample.A high sensitive and selective electrochemical sensor for detection of daidzein based on molecular imprinted polymer (MIP) modified electrode was established. The sensitive layer was prepared by electropolymerization of o-phenylenediamine (o-PD) on the surface of Poly (sodium 4-styrenesulfonate)-reduced graphene oxide (PSS-rGO) modified glassy carbon electrode (PSS-rGO/GCE) in the presence of daidzein as a template molecule. The negatively charged poly(sodium 4-styrenesulfonate) units and benzene rings of PSS-rGO can attract positive charged o-PD and provide π-π stacking effect of o-PD and daidzein, which makes the compact imprinted film and more imprinted points. The MIP/PSS-rGO composite could specifically recognize daidzein in aqueous solutions which result in the decrease of peak current of K3[Fe(CN)6]/K4[Fe(CN)6] at the MIP/PSS-rGO/GCE. Under the optimized conditions, the decrease of the peak current was linear with the concentration of daidzein in the range of 1.0-20.0 nM. The detection limit was calculated as 0.5 nM (S/N = 3). Relative to the other structurally similar substances, the current response of the MIP/PSS-rGO/GCE toward daidzein was about 6.0, 3.1, 6.9 and 5.2 times higher than those of puerarin, quercetin, genistein and chrysin which suggesting the high selectivity of MIP/PSS-rGO/GCE. The modified electrode was successfully applied to determine daidzein in human serum and pueraria extraction with satisfied recovery suggesting the potential applications in the daidzein determination of clinical samples and nature products.

AbstractIn this study, the fibrillation of hen egg-white lysozyme (HEWL) in the absence and presence of different concentrations of silybin was studied by thioflavin T spectroscopy, Congo red binding assays, 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence assay, circular dichroism, and transmission electron microscopy. The experimental results indicated that not only the fibrillation of HEWL at high temperature (65°C) and low pH (pH = 2.0) could be inhibited effectively by silybin but also the inhibition of HEWL by silybin followed a dose-dependent manner. Molecular docking studies indicated that 2 possible binding modes could be found in the interaction between silybin and HEWL via van der Waals forces and electrostatic forces as well as hydrogen bonding. One of these 2 conformations was directly entered into the cavity of HEWL (binding site I); the other was bound to the surface of HEWL (binding site II). In this way, silybin could not only increase the hydrophobicity of the cavity or the surface of HEWL but also influence the microenvironment of the binding site, which was able to stabilize the structure of HEWL and delay the process of HEWL fibrosis.

•Highly photoluminescence GLY-GQDs were synthesized and characterized.•The obtained GLY-GQDs were noted as a fluorescence probe for the determination of AA.•Relative to the reported methods, the proposed method is more sensitive and selective for the determination of AA.•The proposed method is much simpler and faster, a whole detection just needs 8 min.In this work, highly photoluminescent glycine (GLY) functionalized graphene quantum dots (GQDs) (GLY-GQDs) were synthesized by a simple and green pyrolysis method employing ethylene glycol as carbon source, GLY as functional molecule. The as-synthesized GLY-GQDs exhibited excellent water solubility with a fluorescence quantum yield of 21.7%. The fluorescence of GLY-GQDs was intensively quenched by Ce4+ via forming non luminescent complexes of GLY-GQDs-Ce4+. When ascorbic acid (AA) was in presence, Ce4+ was reduced to Ce3+ and the fluorescence of GLY-GQDs regained. In the light of this theory, a simple AA sensor was fabricated without complicated, costly and time-consuming operations. Under the optimal conditions, the fluorescence recovery ratio and the concentration of AA has a linear relationship in the range of 0.03–17.0 μM and with a detection limit of 25 nM which was one order higher sensitive than the reported methods Furthermore, this established sensor system also shows a high selectivity toward AA over a wide range of common biological molecules such as uric acid, dopamine and glutathione and so on. The proposed method was successfully applied for the AA detection in serum samples. All these suggested the potential of this GLY-GQDs based sensor in the clinical analysis.

Poly(diallyl dimethyl ammonium)chloride (PDDA) functionalized CdTe quantum dots (QDs) (PDDA–CdTe QDs) were synthesized through electrostatic self-assembly and used as fluorescence sensors. Mercury(II) ion (Hg2+) has a dramatic fluorescence quenching effect on the PDDA–CdTe QDs. Based on this quenching effect, a very sensitive fluorescence sensor for Hg2+ detection was established. Under the optimum conditions, the fluorescence quenching effect of PDDA–CdTe QDs was linear with the concentration of Hg2+ in the range from 0.006 μmol L−1 to 1.0 μmol L−1. The detection limit was calculated as 5.0 nmol L−1 according to the 3σ IUPAC criteria. This PDDA–CdTe QDs sensor system represents a new feasible method to improve the spectroscopic characterization of QDs used as Hg2+ sensors.

•The Au–PVP–graphene (GR) nanocomposite was synthesized via a simple approach.•The enlarged surface area and the enhanced electron rate of composite were discussed.•A sensitive electrochemical sensor of butylated hydroxyanisole (BHA) was built.•The electrochemical reaction mechanism of BHA was proposed.•The saturating absorption capacity at Au–PVP–graphene/GCE was calculated.Gold nanoparticles (AuNPs) and reduced graphene oxide (graphene) composites were synthesized via a simple one-pot approach in the presence of polyvinylpyrrolidone (PVP). Further, the Au–PVP–graphene nanocomposite was used as a new sensing material for the electrochemical detection of butylated hydroxyanisole (BHA). Because of the greatly enlarged surface area, the enhanced electron transfer rate, and a stronger enrichment of BHA, the sensor based on Au–PVP–graphene modified glassy carbon electrode (GCE) displayed highly sensitive electrochemical responses to BHA. Applying linear sweep voltammetry, a good linear relationship of the oxidation peak current with respect to concentrations of BHA across the range of 0.2–100.0 µM and a detection limit of 0.04 µM was achieved. The practical analytical performance of the Au–PVP–graphene/GCE was examined by evaluating detection of BHA in soybean oil and the flour samples. Satisfactory results revealed that this work offered a new way for the sensitive and simple determination of BHA in complex samples.A sensitive and selective electrochemical sensor for the fast determination of butylated hydroxyanisole (BHA) based on Au–PVP–graphene nanocomposite was fabricated. The sensor has superior electrocatalytic activity for the redox of BHA due to its large surface, fast electron transfer character and strong enrichment effect on BHA.

•The inhibitory effects of 10 flavonoids on pepsin were measured in vitro.•Binding mechanisms were investigated by spectroscopic and docking methods.•Pepsin fluorescence was quenched via static quenching with r less than 7 nm.•The interaction of Pepsin with flavonoids occurred in the hydrophobic cavity.•The common residues lining the flavonoids in the catalytic site were investigated.In the work described on this paper, the inhibitory effect of 10 flavonoids on pepsin and the interactions between them were investigated by a combination of spectroscopic and molecular docking methods. The results indicated that all flavonoids could bind with pepsin to form flavonoid–pepsin complexes. The binding parameters obtained from the data at different temperatures revealed that flavonoids could spontaneously interact with pepsin mainly through electrostatic forces and hydrophobic interactions with one binding site. According to synchronous and three-dimensional fluorescence spectra and molecular docking results, all flavonoids bound directly into the enzyme cavity site and the binding influenced the microenvironment and conformation of the pepsin activity site which resulted in the reduced enzyme activity. The present study provides direct evidence at a molecular level to understand the mechanism of digestion caused by flavonoids.Graphical abstractThe complex was formed by non-covalent reactions between flavonoids (baicalein here) and pepsin, which resulted in the significant decrease in the fluorescence intensity of pepsin. The molecular docking study shows that flavonoids are located in the hydrophobic cavity of pepsin. Since the binding of flavonoids affected the microenvironment of the pepsin activity site, flavonoids caused the inhibition of pepsin activity.

In the work described on this paper, the interactions between eight flavonoids and hyaluronidase (HAase), an important enzyme involved in a promoting inflammation pathway, were investigated by spectroscopic and molecular modeling methods. The results revealed that all flavonoids could interact with HAase to form flavonoid-HAase complexes. The binding parameters obtained from the data at different temperatures indicated that flavonoids could spontaneously bind with HAase mainly through electrostatic forces and hydrophobic interactions with one binding site. According to synchronous and three-dimensional fluorescence spectra and the molecular docking results, all flavonoids bound directly into the enzyme cavity site and the binding of flavonoid into the enzyme cavity influenced the microenvironment of the HAase activity site which led to the reduced enzyme activity. The present study provides direct evidence at a molecular level to understand the mechanism of inhibitory effect of flavonoid against HAase and explain the anti-inflammatory mechanism of the Traditional Chinese Medicines as anti-inflammatory drugs.

In this work, a very sensitive electrochemical sensor for the determination of pentachlorophenol (PCP) was constructed based on the electrocatalytic activity of the composite of ZnSe quantum dots (ZnSe QDs) decorated multiwall carbon nanotubes (MWCNTs) (ZnSe QDs-MWCNTs). The behaviors of PCP on the surface of ZnSe QDs-MWCNT modified electrode showed that the composite of ZnSe QDs-MWCNTs introduced a favorable access for the electron transfer and make an obvious electrocatalytic activity toward the oxidation of PCP. Differential pulse voltammetry (DPV) was used for the quantitative determination of PCP. Under the optimum conditions, the peak current of PCP was proportional to its concentration at the range of 8.0 × 10−8 to 4.0 × 10−6 mol L−1 with a detection limit 2.0 × 10−9 mol L−1 (S/N = 3). Compared with the reported papers, the proposed method was more sensitive and simple. The developed method was successfully applied for the determination of PCP in fish meat with satisfactory recoveries.

Poly(sodium 4-styrenesulfonate) (PSS) intercalated graphene (PSS-GN) was prepared via in situ reduction of exfoliated graphite oxides in the presence of PSS, and then mixed with CTAB to form a stable PSS-GN-CTAB nanocomposite through electrostatic self-assembly. The prepared composites were characterized by Fourier transform infrared spectrometry (FT-IR), ultraviolet and visible spectrometry (UV–vis) and X-ray diffraction (XRD). A novel 2,4-dichlorophenol (2,4-DCP) electrochemical sensor was fabricated based on a PSS-GN-CTAB modified glassy carbon electrode. It was found that the composite of PSS-GN-CTAB exhibited excellent electrocatalytic activity towards the oxidation of 2,4-DCP. Linear sweep voltammetry (LSV) was used for the quantitative determination of 2,4-DCP. Under the optimum conditions, the peak current of 2,4-DCP was proportional to its concentration at the range of 1.0 × 10−8 to 2.0 × 10−6 mol L−1 with a detection limit 2.0 × 10−9 mol L−1. The newly developed method was successfully applied for the determination of 2,4-DCP in the waste water with good recoveries. The proposed electrode system represents a new platform for designing excellent electrochemical sensors with water-dispersed graphene.

•PSS functionalized graphene (GR) was synthesized via one-step chemical reduction.•PSS–GR exhibited high electrocatalytic activity towards the oxidation of clenbuterol.•A novel sensitive electrochemical sensor of clenbuterol was established.In the present study, poly(sodium 4-styrenesulfonate) (PSS) functionalized graphene (GR) was synthesised via a simple one-step chemical reduction of exfoliated graphite oxides in the presence of PSS. Characterisation of as-made nanocomposite using Fourier transform infrared spectroscopy (FT-IR) and ultraviolet and visible spectroscopy (UV–vis) clearly demonstrate the successful attachment of PSS to graphene sheets. A novel clenbuterol (CLB) electrochemical sensor was fabricated based on isopropanol–Nafion–PSS–GR composite film modified glassy carbon electrode. In the Britton–Robinson buffer (pH 1.2), the sensor exhibited superior electrocatalytic activity towards the oxidation of CLB. Applying linear sweep voltammetry, a good linear relationship of the oxidation peak current with respect to concentrations of CLB cross the range of 7.5 × 10−8–2.5 × 10−5 mol L−1 and a detection limit of 2.2 × 10−8 mol L−1 were achieved. The proposed method was successfully applied for the determination of CLB in pork.

•PDDA-Gr was prepared via in situ reduction of exfoliated graphite oxides in the presence of PDDA.•PDDA-Gr is used to build a supersensitive sensor for determination of rutin.•The electrochemical reaction mechanism of rutin was discussed in detail.•The method was applied to the determination of rutin in complex biological samples.In this work, poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-Gr) was prepared via in situ reduction of exfoliated graphite oxides in the presence of PDDA. The obtained nanostructure was used as a novel immobilization platform for the electrochemical sensor of rutin. PDDA-Gr has superior electrocatalytic activity for the redox of rutin due to its large surface, fast electron transfer character and strong adsorption effect on rutin. The electron transfer rate constant (ks) and the electroactive surface area were calculated as 1.59 s−1 and 0.3324 cm2 respectively. The saturating absorption capacity (Γ) value of rutin on modified electrode was calculated to be 2.23 × 10−9 mol cm−2. Applying differential pulse voltammetry (DPV), a good linear relationship of the reduction peak current and the concentrations of rutin in the range of 0.0004–1.0 μM was achieved. The detection limit was 0.04 nM (S/N of 3). Under the optimum conditions, the metabolite of rutin, quercetin can be effectively separated from rutin, which suggested the great potential of the proposed method for the practical application in pharmacokinetic and clinical analyses. The method was successfully applied to the fast determination of rutin in medicine tablets and human plasma with satisfactory recoveries.

Hybrid materials formed from acid functionalized multi-walled carbon nanotubes (MWCNTs) and glutathione (GSH)-capped ZnSe quantum dots (ZnSe QDs) were prepared by a non-covalent self-assembly method. Black spots decorated on the surface of MWCNTs under transmission electron microscopy (TEM) demonstrate successful attachment of ZnSe QDs on the surface of MWCNTs. The obtained ZnSe QD–MWCNTs can accelerate greatly the transfer rate of electrons and showed an obvious synergistic electrocatalytic effect for the oxidation of paeonol (PN). Based on this electrocatalytic activity, a novel electrochemical sensor was established. Under the optimum conditions, the peak currents had a good linear relationship with the concentration of PN in the ranges of 0.06 to 10.0 μM and 10.0 to 50.0 μM. The detection limit was reduced at 0.04 μM. The established sensing platform was applied to the determination of PN in pharmaceutical and clinical analyses with satisfactory recoveries.

In this study, the binding mode of nobiletin (NOB) with pepsin was investigated by spectroscopic and molecular docking methods. NOB can interact with pepsin to form a NOB-pepsin complex. The binding constant, number of binding sites and thermodynamic parameters were measured, which indicated that NOB could spontaneously bind with pepsin through hydrophobic and electrostatic forces with one binding site. Molecular docking results revealed that NOB bound into the pepsin cavity. Synchronous and three-dimensional fluorescence spectra results provide data concerning conformational and some micro-environmental changes of pepsin. Furthermore, the binding of NOB can inhibit pepsin activity in vitro. The present study provides direct evidence at a molecular level to show that NOB could induce changes in the enzyme pepsin structure and function.

•Nanocomposite based ZnSe QDs and CTAB was prepared and characterized.•A novel electrochemical sensor for the determination of CPs was built.•The proposed sensor was more sensitive, simple and environment-friendly.In this work, a very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on a nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The composite of ZnSe–CTAB introduced a favorable access for the electron transfer and gave superior electrocatalytic activity for the oxidation of CPs than ZnSe QDs and CTAB alone. Differential pulse voltammetry (DPV) was used for the quantitative determination of the CPs including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). Under the optimum conditions, the peak currents of the CPs were proportional to their concentrations in the range from 0.02 to 10.0 μM for 2-CP, 0.006 to 9.0 μM for 2,4-DCP, and 0.06 to 8.0 for PCP. The detection limits were 0.008 μM for 2-CP, 0.002 μM for 2,4-DCP, and 0.01 μM for PCP, respectively. The method was successfully applied for the determination of CPs in waste water with satisfactory recoveries. This ZnSe–CTAB electrode system provides operational access to design environment-friendly CPs sensors.A very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The nanocomposite of ZnSe–CTAB introduced a favorable access for the electron transfer and showed excellent electrocatalytic activity for the oxidation of CPs.

In the work described on this paper, a gold nanoparticles (GNP)/l-cysteine (l-cys)/Graphene (Gr)/Nafion composite film modified glass carbon electrode (GCE) was fabricated and characterized. The modified electrode showed excellent electrocatalytic activity towards the oxidation of theophylline (TP) in 0.1 mol L−1 H2SO4 medium. Differential pulse voltammetry (DPV) was used for the determination of TP. Under the optimum conditions, the peak current of TP was proportional to its concentration at the range of 4.0 × 10−9 to 6.0 × 10−5 mol L−1 with a detection limit 4.0 × 10−10 mol L−1. The newly developed method was successfully applied for the determination of TP in tea samples and pharmaceutical tablets with good percentage of recoveries.

In this work, the inhibitory effect of two isoflavonoids including daidzein and genistein on trypsin and their binding mechanism were determined by spectroscopic and molecular docking approaches. The results indicated that both daidzein and genistein reversibly inhibited trypsin in a competitive manner with IC50 values of 68.01 × 10−6 mol L−1 and 64.70 × 10−6 mol L−1 and Ki values of 62.12 × 10−6 mol L−1 and 59.83 × 10−6 mol L−1, respectively. They could spontaneously bind with trypsin mainly through hydrophobic force and electrostatic interactions with a single binding site. Analysis of circular dichrosim spectra and molecular docking revealed that both isoflavonoids bound directly into the catalytic cavity and the microenvironment and secondary structure of trypsin were changed in this process, which caused the inhibition of trypsin activity. All these experimental results and theoretical data in this work would be help in understanding the mechanism of inhibitory effects of daidzein and genistein against trypsin and the potential of isoflavonoid to relieve symptoms of pancreatitis.

Hybrid materials formed from acid functionalized multi-walled carbon nanotubes (MWCNTs) and glutathione (GSH)-capped ZnSe quantum dots (ZnSe QDs) were prepared by a non-covalent self-assembly method. Black spots decorated on the surface of MWCNTs under transmission electron microscopy (TEM) demonstrate successful attachment of ZnSe QDs on the surface of MWCNTs. The obtained ZnSe QD–MWCNTs can accelerate greatly the transfer rate of electrons and showed an obvious synergistic electrocatalytic effect for the oxidation of paeonol (PN). Based on this electrocatalytic activity, a novel electrochemical sensor was established. Under the optimum conditions, the peak currents had a good linear relationship with the concentration of PN in the ranges of 0.06 to 10.0 μM and 10.0 to 50.0 μM. The detection limit was reduced at 0.04 μM. The established sensing platform was applied to the determination of PN in pharmaceutical and clinical analyses with satisfactory recoveries.