•A new strategy has been introduced for the fabrication of electrochemical biosensor.•The strategy is based on the covalent capturing of molecules on electrode interface through oxime chemistry.•Guanidinium recognization contributes to the excellent performance of the electrochemical biosensor.•The strategy has been applied for the detection of aldolase activity.•The established biosensor may be extended to other substances with chemoselective groups.A new strategy to fabricate electrochemical biosensor is proposed based on the covalent capturing of molecules on electrode interface through oxime chemistry and the loading of signal probes via guanidinium-phosphate electronic interaction with a “covalent-like” stability. Taking aldolase as an example, enzyme analysis can be achieved through the covalent loading of the catalyzed products on the aminooxy modified gold electrode surface and subsequent immobilization of guanidinium functionalized sliver nanoparticles. Different from adolase substrate, the hydrolyzed products contain both carbonyl groups and phosphate acid groups in their structures. The carbonyl groups can chemoselectively react with aminoxy groups on the electrode surface to form oxime, resulting in the exposure of phosphate groups. Subsequently, signal probe can be loaded onto electrode surface through guanidinium recognition, giving a electrochemical current value. So the number of enzyme catalyzed products determines the amount of signal probes on the electrode surface, and aldolase activity can be analyzed. For the proposed method, the chemoselective oxime ligation and highly stable guanidinium recognition improve the accuracy, selectivity and stability of enzyme analysis. The established method may be extended to the analysis of other related substances containing carbonyl groups.

In this study, a colorimetric biosensor was established for the detection of protein tyrosine phosphatase 1B (PTP1B) and its inhibitor based on the guanidinium recognition assisted coordination of arginine-glycine-cysteine (RGC) modified gold nanoparticles (RGC/AuNPs) with 4-aminophenyl phosphate-functionalized Fe3O4 magnetic nanoparticles (MNPs/APP). PTP1B can catalyze the cleavage of the phosphate ester bond and the departure of the phosphate acid group from the surface of MNPs/APP, resulting in the loss of the corresponding coordination reactivity. Upon the addition of a solution of RGC/AuNPs, RGC/AuNPs remained in the supernatant solution after magnetic separation and a high absorbance value was observed. Thus, a simple colorimetric biosensor for PTP1B assay was developed. Under the optimized experimental conditions, PTP1B was detected within a linear range of 0.002 U mL−1 to 0.08 U mL−1 with the lowest detection limit of 0.0013 U mL−1. Moreover, using this proposed biosensor, the inhibition effect of betulinic acid and 6-chloro-3-formyl-7-methylchromone on PTP1B is determined with IC50 values of 9 μM and 15 μM, respectively. Therefore, this new biosensor not only has great potential for PTP1B analysis but also for the detection of its inhibitors.

•A new strategy for lipopolysaccharides (LPS) colorimetric analysis is reported.•LPS can specially bind with boronic acid under acidic condition.•LPS can spontaneously assemble to form lipid bilayer to inhibit ion transport.•The method has been applied to detect LPS contents in the drinking beverages.A new strategy is proposed based on inhibition of ion transport by lipid bilayer derived from spontaneous assembly of lipopolysaccharides (LPS), thereby a colorimetric method is established for analysis of LPS. At acidic pH values, LPS can specially bind with aminophenylboronic acid modified assembled magnetic nanospheres (APBA/AMNSs), resulting in formation of lipid bilayer around APBA/AMNSs. Under acidic condition, the lipid bilayer can inhibit the release of iron ions from AMNSs into the solution so as to decrease the oxidized extent of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt mediated by hydrogen peroxide. Using the established method, LPS can be detected over the wide linear detection range with the low detection limit. With good selectivity, reproductivity, and simplicity, the method is accurate in LPS tests of real drinking samples.Download high-res image (173KB)Download full-size image

A colorimetric method is developed for the determination of the activity of β-lactamase (β-Lac) and the screening of its inhibitors based on cysteine-induced gold nanoparticle (AuNP) aggregation. The widely used penicillin is served as a β-Lac substrate, and the strong reduction capability of its corresponding product, which can react with Cu(II) to form Cu(I) conjugates, is utilized in the method. The double catalyzed signal amplification is accomplished via the addition of both β-Lac and Cu(II) which can catalyze the oxidization of cysteine into cystine. The activity of β-Lac is determined at levels as low as 2.36 U mL−1. The inhibitory effects of clavulanic acid and sulbactam are tested and give 0.92 and 0.06 μM, respectively. The assay is simple, rapid, easy-operated, and selective, and the proposed method has a great potential not only for the detection of β-Lac activity but also for the screening of the inhibitors.

•A new strategy has been introduced for the fabrication of electrochemical biosensor.•The strategy is based on enzyme substrate as a linker.•The strategy has been applied for the detection of aldolase activity.•The established biosensor may be extended to other proteins with reversible catalyzed ability.•Pectin-thionine complex is prepared as recognization element and signal amplification probe.A new strategy to fabricate electrochemical biosensor is reported based on the linkage of enzyme substrate, thereby an electrochemical method to detect aldolase activity is established using pectin-thionine complex (PTC) as recognization element and signal probe. The linkage effect of fructose-1,6-bisphosphate (FBP), the substrate of aldolase, can be achieved via its strong binding to magnetic nanoparticles (MNPs)/aminophenylboronic acid (APBA) and the formation of phosphoramidate bond derived from its reaction with p-phenylenediamine (PDA) on the surface of electrode. Aldolase can reversibly catalyze the substrates into the products which have no binding capacity with MNPs/APBA, resulting in the exposure of the corresponding binding sites and its subsequent recognization on signal probe. Meanwhile, signal amplification can be accomplished by using the firstly prepared PTC which can bind with MNPs/APBA, and accuracy can be strengthened through magnetic separation. With good precision and accuracy, the established sensor may be extended to other proteins with reversible catalyzed ability.

In this paper, we find firstly that lignin is an effective inhibitor against α-glucosidase, with minimized IC50 value of 0.076 μM which is much lower than that of acarbose (0.66 mM), a market diabetes healer, and it can competitively inhibit enzymatic activity with Ki value of 0.3 × 10−5 M. Meanwhile, lignin can interact with α-glucosidase to form 1:1 complex with the binding constant of 1.39 × 106 M−1 at 293 K. The binding of lignin to α-glucosidase is mainly driven by hydrophobic interaction and hydrogen bond, with binding distance of 3.54 nm. The formation of lignin-α-glucosidase complex results in the alteration of α-helix structure and aromatic amino sides and the increase of protein granule volume. Furthermore, the lignin binds to α-glucosidase in the form of the first order exponential decay function. This work would be significant for the exploration of lignin as food functional factor.

A lipase-based electrochemical biosensor has been fabricated for the quantitative determination of target DNA. It is based on a stem-loop nucleic acid probe labeled with ferrocene containing a butanoate ester that is hydrolyzed by lipase. The other end of the probe DNA is linked, via carboxy groups, to magnetic nanoparticles. The binding of target DNA transforms the hairpin structure of the probe DNA and causes the exposure of ester bonds. This results in the release of electro-active ferrocene after hydrolysis of the ester bonds, and in an observable electrochemical response. The quantity of target DNA in the concentration range between 1 × 10−12 mol·L−1 and 1 × 10−8 mol·L−1 can be determined by measuring the electrochemical current. The method can detect target DNA with rapid response (30 min) and low interference.

Using Canna edulis Ker by-product as raw materials, soluble dietary fiber (SDF) was prepared using six different methods, including chemical, physical–chemical, enzymatic, physical–enzymatic, chemical–enzymatic and physical–chemical–enzymatic methods. As main component in the C. edulis by-product composed of cellulose, glucose converts to other single sugars, which form a series of compounds in the SDF. The treated methods have impact effects on single sugar composition, metal ion content, molecular size distribution, chemical bonds and groups in the structure, thermal property and color of the final product. In view of security, high yield and homogeneity as well as good thermal stability of final product, physical–enzymatic method will be a best choice for the production of SDF from C. edulis by-product. The SDF obtained can be used as dietary supplement and additive in the food industry.Highlights► Physical–enzymatic method can be well used for the production of SDF from Canna edulis by-product. ► C. edulis SDF has high yield, good homogeneity and thermal stability. ► C. edulis SDF can be used as dietary supplement and additive in the food industry.

In view of synergistic effect of resveratrol and insulin in the prevention and treatment of many chronic diseases, the interaction between them was studied and its biological implication was further discussed. Insulin could interact with resveratrol to form 1:1 complex with the binding constant of 1.03 × 103 M−1 at 298 K. The binding was spontaneous and insulin/resveratrol complex formation was an exothermal reaction. Hydrogen bond and van der Waals force played key roles in the binding process. Kinetic study indicates that resveratrol binding to insulin conformed to the first-order exponential decay function. The interaction decreased the polarity around tyrosine residue and α-helical content, destroyed the disulfide bridges, depolymerized insulin dimers to monomer, and altered the orientation of aromatic side chains in the insulin. Additionally, insulin increased resveratrol stability. These results well confirm synergistic effect of resveratrol and insulin in vitro. It would give a deeper insight into resveratrol as a kind of food functional factor.

Water-soluble extract (WSE), chelated-soluble extract (CSE) and acid-soluble extract (ASE) were obtained from Canna edulis Ker by-product, and their thermal characteristics and physiological behavior were studied. Thermal properties of WSE and ASE demonstrated the exiting of cellulose, as main constituents in the extracts. Different from those of WSE and ASE, the thermal characteristics of CSE demonstrated that it was chiefly composed of cellulose and pectin. The three extracts inhibited both gastric pepsin and lipase enzymatic activities to some extent, and tryptic digestion of β-lactoglobulin as well as lipase hydrolysis of tributyrin in vitro. Therefore, the three extracts could be used as additives in the food industry, in view of safety of C. edulis by-product confirmed by animal experiment.Highlights► Three cellulose/pectin complexes were obtained from Canna by-product. ► Thermal characteristics of the three complexes were studied. ► The three complexes inhibited gastric pepsin and lipase enzymatic activities. ► The three complexes inhibited the hydrolysis of β-lactoglobulin and tributyrin. ► The three complexes could be used as additives in the food industry.

Considering important implication of collagen and resveratrol in platelet aggregation and cancer metastasis, interaction between them and its biological significance were studied. Resveratrol could interact with collagen to form a 1:1 complex with a binding constant at about 105 M−1. It decreased fluorescence emission intensities of tyrosine, improved the formation of excimer-like species and dityrosine, and had no effect on post-translational, chemical, age-related modifications in the resveratrol/collagen solution. The binding process was spontaneous and the formation was an exothermic reaction. Thermodynamic analysis suggests that both hydrophobic interaction and hydrogen bonding played key roles in the course of resveratrol–collagen binding. Moreover, synchronous fluorescence and FT-IR results indicate that the interaction caused decrease of the polarity around tyrosine residues resulting in collagen conformation alteration. Additionally, the isomerisation of resveratrol was not prevented but its stability was improved with the addition of collagen in the solution. This work might provide a more comprehensive understanding about the anticancer and antiplatelet activities of resveratrol as a functional food factor.Highlights► Resveratrol could interact with collagen to form a 1:1 complex. ► The binding process was spontaneous. ► Hydrophobic interaction played a key role in the process of the binding. ► The interaction effect caused collagen conformation alteration. ► The stability of resveratrol was improved with the addition of collagen.

Arabinoxylan (AX) was extracted and purified from Canna edulis Ker by-product. Through column chromatography, AX was further separated, leading to the isolation of two single compounds, namely, AXI and AXII. Moreover, the structures of AXI and AXII were characterized by GC, GC–MS and NMR. The result indicated that arabinose and glucuronic acid occurred at 1,4-linked xylose units as backbone at positions 3 and 2 in both AXI and AXII with varying ratios, respectively. Furthermore, the effects of AX on enzymatic digestibility of β-lactoglobulin and tributyrin hydrolysis by lipase were evaluated. The results showed that AX had obvious inhibition effects on pepsin and lipase activities, and decreased β-lactoglobulin digestibility and tributyrin hydrolysis as well. It indicates that C. edulis AX could be used as a functional food ingredient.