Can-Peng Li

Label-free electrochemical immunosensor based on gold–silicon carbide nanocomposites for sensitive detection of human chorionic gonadotrophin

Uniform and highly dispersed gold-silicon carbide (Au@SiC) nanocomposites were prepared via simple way and used for fabrication of label-free electrochemical immunosensor for sensitive detection of human chorionic gonadotrophin (hCG). Using Au@SiC as electrode material and using ferricyanide as mediator, the proposed immunosensor provides a simple and economic method with higher sensitivity and a wider concentration range for detection of hCG. Under the optimal condition, the approach provided a good linear response range from 0.1 to 5 IU/L and 5 to 1000 IU/L with a low detection limit of 0.042 IU/L. The immunosensor showed good selectivity, acceptable stability and reproducibility. Satisfactory results were obtained for determination of hCG in human serum samples. The proposed method provides a promising platform of clinical immunoassay for other biomolecules. In addition, the bio-functionalization of SiC combined with other nanomaterials will provide promising approach for electrochemical sensing and biosensing platform.

Bridged β-cyclodextrin-functionalized MWCNT with higher supramolecular recognition capability: The simultaneous electrochemical determination of three phenols

A rapid and sensitive electrochemical sensor based on disulfides bridged β-cyclodextrin dimer-functionalized multi-walled carbon nanotube (DBβ-CD-MWCNT) nanohybrids with higher supramolecular recognition capability was successfully constructed for the first time. Simultaneous trace analysis of three phenols (4-aminophenol, 4-AP; 4-chlorophenol, 4-CP; 4-nitrophenol, 4-NP) in tap-water and wastewater samples was performed based on the constructed sensor. Cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy were utilized to characterize the properties of the modified electrode. The proposed DBβ-CD-MWCNT-modified electrode displayed electrochemical signal superior to those of β-CD-MWCNT and MWCNT towards 4-AP, 4-CP, and 4-NP. Under optimal conditions, differential pulse voltammetry was used to simultaneously quantify 4-AP, 4-CP, and 4-NP within the concentration range of 0.01-20, 0.1-200, and 0.1-200 µM, respectively. The detection limits (S/N=3) of the DBβ-CD-MWCNT nanohybrid electrode for 4-AP, 4-CP, and 4-NP were 0.0042, 0.028, and 0.048 µM, respectively. Satisfactory results revealed that this proposed electrochemical sensor can provide a promising candidate for the simultaneous trace analysis of 4-AP, 4-CP, and 4-NP in environmental monitoring of water and wastewater samples. The present work might broaden the channel toward the application of bridged CD in the electrochemical sensing or biosensing.

Glycation and phosphorylation of α-lactalbumin by dry heating: Effect on protein structure and physiological functions

Alpha-lactalbumin (alpha-LA) was glycated with maltopentaose (MP) through the Maillard reaction (MP-alpha-LA) and subsequently phosphorylated by dry heating in the presence of pyrophosphate to investigate its structure and physiological functions. Glycation occurred effectively, and the sugar content of alpha-LA increased by approximately 22.3% through the Maillard reaction. The phosphorylation of MP-alpha-LA was enhanced with an increase in the dry-heating time from 1 to 5 d, and the phosphorous content of MP-alpha-LA increased by approximately 1.01% by dry heating at pH 4.0 and 85 degrees C for 5 d in the presence of pyrophosphate. The electrophoretic mobility of alpha-LA increased with an increase in the phosphorylation level. The circular dichroism spectra showed that the change in the secondary structure of the alpha-LA molecule by glycation and subsequent phosphorylation was slight. However, the Trp fluorescence intensity was increased by phosphorylation after glycation. In addition, the differential scanning calorimetry thermograms of alpha-LA showed that the denaturation temperature of MP-alpha-LA was decreased by phosphorylation. These results indicated that molten (partially unfolded) conformations of alpha-LA were formed by dry heating in the presence of pyrophosphate after glycation. The anti-alpha-LA antibody response was significantly reduced by glycation and subsequent phosphorylation. The suppressive effect of alpha-LA on the production of proinflammatory cytokines such as IL-6 and tumor necrosis factor-alpha from THP-1 cells after stimulation with lipopolysaccharide was significantly enhanced by glycation with MP and was further enhanced by phosphorylation after glycation. The Ca phosphate-solubilizing ability of alpha-LA was enhanced by phosphorylation. The apoptotic activity of alpha-LA was reduced by glycation and subsequent phosphorylation. These results suggest that phosphorylation by dry heating in the presence of pyrophosphate after glycation with MP through the Maillard reaction is a useful method for improvement of the physiological functions of alpha-LA.

Phosphorylation of egg white proteins by dry-heating in the presence of phosphate.

Food proteins were phosphorylated by heating in a dry state in the presence of phosphate. When casein, whey protein isolate (WPI), and egg white proteins (EWP), which were lyophilized from their solutions in a phosphate buffer, were dry-heated at various temperatures and pH levels for 1-5 days, EWP was more highly phosphorylated than casein and WPI. Phosphorylation of EWP was promoted with a decrease of pH from 7.0 to 3.0 when the incubation temperature was raised from 55 to 100 degrees C. The phosphorus content of EWP increased from 0.08 to 0.64% by dry-heating at pH 3.0 and 85 degrees C for 5 days in the presence of phosphate. The electrophoretic mobility of EWP increased with an increase in the phosphorylation level. The heat-induced polymerization of EWP by dry-heating was not affected by the presence of phosphate. Although the solubility of EWP decreased by dry-heating at pH 3.0-5.5, the phosphorylation depressed the insolubilization at low pH. The phosphate bonds in phosphorylated EWP (P-EWP) were stable at pH 2.0-10.0 and were more acid-labile and base-stable than phosphoesters of egg riboflavin-binding protein (RfBP). (31)P NMR spectral data suggested that besides phosphoesters, phosphodiester and polyphosphate bonds were introduced in P-EWP. Heat stability of EWP was improved, and calcium phosphate-solubilizing ability of EWP was enhanced by phosphorylation.

Dual β-cyclodextrin functionalized Au@SiC nanohybrids for the electrochemical determination of tadalafil in the presence of acetonitrile

This finding described the electrochemical detection of tadalafil based on CM-β-cyclodextrin and SH-β-cyclodextrin functionalized Au@SiC nanohybrids film. The tadalafil electrochemical signal could be dramatically amplified by introducing 40% of acetonitrile in buffer medium and further enhanced by the host-guest molecular recognition capacity of β-cyclodextrin. Uniform and monodispersed ~5.0 nm Au NPs were anchored on the SiC-NH2 surface via a chemical reduction process by using polyethylene glycol and sodium citrate as dispersant and stabilizing agent. CM-β-CD was covalently bound on Au@SiC by combining the amine group of SiC-NH2 with the carboxyl group of CM-β-CD with the aid of EDC/NHS coupling agent. SH-β-CD could tightly attach to the surface of Au@SiC by the strong coordinating capability between Au and thiol. Differential pulse voltammetry was successfully used to quantify tadalafil within the concentration range of 0.01-100 µM under optimal conditions with a detection limit (S/N = 3) of 2.5 nM. In addition, the β-CD-Au@SiC nanohybrid electrochemical sensor showed high selectivity to two other erectile dysfunction drugs sildenafil and vardenafil. The proposed electrochemical sensing platform was successfully used to determine tadalafil in raw materials, herbal sexual health products, and spiked human serum samples.

A comparison study of macrocyclic hosts functionalized reduced graphene oxide for electrochemical recognition of tadalafil

The present work described the comparison of β-cyclodextrin (β-CD) and p-sulfonated calix[6]arene (SCX6) functionalized reduced graphene oxide (RGO) for recognition of tadalafil. In this study, tadalafil and two macrocycles (β-CD and SCX6) were selected as the guest and host molecules, respectively. The inclusion complexes of β-CD/tadalafil and SCX6/tadalafil were studied by UV spectroscopy and molecular simulation calculations, proving the higher supermolecular recognition capability of SCX6 than β-CD towards tadalafil. The β-CD@RGO and SCX6@RGO composites were prepared by a wet-chemical route. The obtained composites were characterized by Fourier transform infrared spectrometry, thermogravimetric analysis, atomic force microscopy, and zeta potential. The SCX6@RGO showed a higher electrochemical response than β-CD@RGO, which was caused by the higher recognition capability of SCX6 than β-CD. By combining the merits of SCX6 and the RGO, a sensitive electrochemical sensing platform was developed based on the SCX6@RGO nanohybrids. A linear response range of 0.1-50 μM and 50-1000 μM for tadalafil with a low detection limit of 0.045 μM (S/N=3) was obtained by using this method. The constructed sensing platform was successfully used to determine tadalafil in herbal sexual health products and spiked human serum samples, suggesting its promising analytical applications for the trace level determination of tadalafil.

Improvement of foaming property of egg white protein by phosphorylation through dry-heating in the presence of pyrophosphate.

Egg white protein (EWP) was phosphorylated by dry-heating in the presence of pyrophosphate at pH 4 and 85 degrees C for 1 d, and the foaming properties of phosphorylated EWP (PP-EWP) were investigated. The phosphorus content of EWP increased to 0.71% as a result of phosphorylation. To estimate the foaming properties of EWP, the foams were prepared by 2 methods: bubbling of the 0.1% (w/v) protein solution and whipping of the 10% (w/w) protein solution with an electric mixer. The foaming power, which was defined as an initial conductivity of foam from 0.1% (w/v) protein solution, was a little higher in PP-EWP than in native EWP (N-EWP), and the foaming stability of PP-EWP was much higher than that of dry-heated EWP (DH-EWP) and N-EWP. The microscopic observation of foams from the 10% (w/w) solution showed that the foams of PP-EWP were finer and more uniform than those of N- and DH-EWP. Although there were no significant differences in the specific gravity and overrun of the foams between PP- and DH-EWP (P < 0.05), the specific gravity and overrun of the foams from PP-EWP were smaller and higher, respectively, than that of the foams from N-EWP. The drainage volume was smaller in the foams from PP-EWP than in those from N- and DH-EWP. These results demonstrated that phosphorylation of EWP by dry-heating in the presence of pyrophosphate improved the foaming properties, and that it was more effective for the foam stability than for the foam formation.

The synthesis of amphiphilic pillar[5]arene functionalized reduced graphene oxide and its application as novel fluorescence sensing platform for the determination of acetaminophen

A sensitive and selective fluorescence approach based on a competitive host-guest interaction between amphiphilic pillar[5]arene (amPA5) and signal probe (acridine orange, AO)/target molecule (acetaminophen, AP) was developed by using amPA5 functionalized reduced graphene oxide (amPA5-RGO) as a receptor. Due to the host-guest interaction, AO and AP molecules both can enter into the hydrophobic inner cavity of amPA5 that could form a complex of 1:1 guest-host with amPA5 according to the size of molecules and the cavity of amPA5, but the AP interacts more strongly with amPA5 than with AO, so it can detect AP by the host-guest competition. The low detection limit of 0.05μM (S/N=3) and a linear response range of 0.1-4.0μM and 4.0-32μM for AP was obtained by using this method. It had lower detection limit and wider linear range than other methods, therefore, it was successfully utilized to detect AP in serum samples, and exhibited a promising application in practice. The molecular docking studies indicated that the major driving forces for the formation of the inclusion complex of AP and amPA5 are hydrogen bonding, π-π interactions, and hydrophobic interactions.

Selenization of ovalbumin by dry-heating in the presence of selenite: effect on protein structure and antioxidant activity.

Ovalbumin (OVA) was selenized by dry-heating in the presence of selenite, and the structural characteristics and improved antioxidant activity of selenized OVA (Se-OVA) were investigated. Although the change of the secondary structure in the OVA molecule by selenization was small, the enthalpy change for denaturation and tryptophan fluorescence intensity of OVA decreased greatly by selenization. The digestibility of OVA was significantly improved by selenization. The results all together demonstrated that molten globule conformation of OVA was formed by selenization. Some selenized tryptic peptides from Se-OVA were identified by MALDI-TOF-MS. Remarkably, the antioxidant activity of OVA was improved when selenite was conjugated compared with free selenite. These results indicate that the enhanced antioxidant activity of Se-OVA is ascribed to the conjugated Se and the formation of a molten globule conformation of protein.

Simultaneous determination of two flavonoids based on disulfide linked β-cyclodextrin dimer and Pd cluster functionalized graphene-modified electrode

In the present work, ultrafine Pd clusters with a uniform size of ∼2.0 nm were monodispersed on the surface of reduced graphene oxide (RGO) using a clean and green approach in the absence of additional reductants and surfactants. Disulfide linked β-cyclodextrin dimer (SS-β-CD) was non-covalently bonded to the surface of Pd@RGO. By combining the merits of Pd@RGO and the SS-β-CD, a highly sensitive electrochemical sensing platform was developed based on the SS-β-CD–Pd@RGO nanohybrids. Simultaneous electrochemical detection of baicalin and luteolin using a SS-β-CD–Pd@RGO nanohybrid-modified electrode is described for the first time. The SS-β-CD showed a higher supramolecular recognition capability than the native β-CD, which may be caused by the cooperative binding abilities of two adjacent CD units. Due to the synergistic effects from the Pd@RGO (e.g. good electrochemical properties and large surface area) and SS-β-CD (e.g. hydrophilic external surface, high supramolecular recognition, and good enrichment capability), the SS-β-CD–Pd@RGO modified electrode was found to have linear response ranges of 0.02–20.00 μM for baicalin and 0.01–10.00 μM for luteolin with relatively low detection limits of 0.0052 μM for baicalin and 0.0070 μM for luteolin. The results indicated that SS-β-CD–Pd@RGO nanohybrids are excellent sensing materials for the electrochemical determination of flavonoids. The proposed method could be successfully utilized to detect baicalin and luteolin in serum samples, and has a promising application in practice.