Guiyin Li

Immobilization of Saccharomyces cerevisiae alcohol dehydrogenase on hybrid alginate–chitosan beads

Saccharomyces cerevisiae alcohol dehydrogenase (SCAD) was effectively immobilized on hybrid alginate-chitosan beads which are hardened with glutaraldehyde. Immobilization conditions and characterization of the immobilized enzyme were investigated. Orthogonal test design and intuitive analysis method were employed to evaluate the effects of immobilization parameters such as Na-alginate concentration, glutaraldehyde concentration, CaCl(2) concentration and immobilization time. Under optimized working conditions (3.0% Na-alginate, 0.5% chitosan, 2.0% CaCl(2), 0.5% glutaraldehyde and 6h), the SCAD activity was 339.25 U/mL. For the reduction of phenylglyoxylic acid, the immobilization process changed the enzymes optimum temperature from 30 to 40 degrees C, the enzymes optimum pH from 6.8 to 6.0, and the immobilized SCAD retained 62.76% of its original activity. The maximum reaction rate (V(max)) was 358.63 nmol min(-1) and the Michaelis-Menten constant (K(m)) was 37.33 mmol L(-1). Compared to the free SCAD, the immobilization of the enzyme showed higher thermal stability and operational stability.

Non-enzymatic electrochemical biosensor based on Pt NPs/RGO-CS-Fc nano-hybrids for the detection of hydrogen peroxide in living cells.

A highly sensitive non-enzymatic electrochemical sensor based on platinum nanoparticles/reduced graphene oxide-chitosan-ferrocene carboxylic acid nano-hybrids (Pt NPs/RGO-CS-Fc biosensor) was developed for the measurement of hydrogen peroxide (H2O2). The RGO-CS-Fc nano-hybrids was prepared and characterized by UV-vis spectrum, Fourier transform infrared spectroscopy, transmission electron microscopy, Raman spectrometer and electrochemical impedance spectroscopy. Under optimal experimental conditions, the Pt NPs/RGO-CS-Fc biosensor showed outstanding catalytic activity toward H2O2 reduction. The current response of the biosensor presented a linear relationship with H2O2 concentration from 2.0×10(-8)M to 3.0×10(-6)M with a correlation coefficient of R(2)=0.9968 and with logarithm of H2O2 concentration from 6.0×10(-6)M to 1.0×10(-2)M with a correlation coefficient of R(2)=0.9887, the low detection limit of 20nM was obtained at the signal/noise (S/N) ratio of 3. Moreover, the Pt NPs/RGO-CS-Fc biosensor exhibited excellent anti-interference capability and reproducibility for the detection of H2O2. The biosensor was also successfully applied for the detection of H2O2 from living cells containing normal and cancer cells. All these results prove that the Pt NPs/RGO-CS-Fc biosensor has the potential application in clinical diagnostics to evaluate oxidative stress of different living cells.

Formulation optimization of chelerythrine loaded O-carboxymethylchitosan microspheres using response surface methodology

The aims of this investigation were to develop a procedure to prepare chelerythrine (CHE) loaded O-carboxymethylchitosan (O-CMCS) microspheres by emulsion cross-linking method and optimize the process and formulation variables using response surface methodology (RSM) with a three-level, three-factor Box-Behnken design (BBD). The independent variables studied were O-CMCS/CHE ratio, O/W phase ratio, and O-CMCS concentration, dependent variables (responses) were drug loading content and encapsulation efficiency. Mathematical equations and response surface plots were used to relate the dependent and independent variables. The process and formulation variables were optimized to achieve maximum drug loading content and entrapment efficiency by the desirability function. The optimized microsphere formulation was characterized for particle size, shape, morphology and in vitro drug release. Results for mean particle size, drug loading content, entrapment efficiency, and in vitro drug release of CHE-loaded O-CMCS microspheres were found to be of 12.18 μm, 4.16 ± 3.36%, 57.40 ± 2.30%, and 54.5% at pH 7.4 after 70 h, respectively. The combination use of RSM, BBD and desirability function could provide a promising application for O-CMCS as controlled drug delivery carrier and help to develop procedures for a lab-scale microemulsion process.

Biosorption of palladium(II) from aqueous solution by grafting chitosan on persimmon tannin extract.

A low-cost and environmentally green biosorbent (PTCS) was prepared by grafting chitosan onto persimmon tannin extract and its potentiality for efficient adsorption of palladium ion (Pd(II)) from aqueous solution was evaluated. Various adsorption parameters such as pH, the initial Pd(II) concentration and temperature were investigated. The maximum adsorption capacity reached 330mg/g at 323K and pH 5.0 when the initial Pd(II) concentration was 100mg/L. The equilibrium adsorption data were satisfactorily fitted with Freundlich isotherm model and biosorption kinetics was found to be in good agreement with pseudo-second-order kinetics model. Thermodynamic calculations indicated that the adsorption process was endothermic and spontaneous in nature because of the negative value of free energy change (ΔG) and positive value of enthalpy change (ΔH). The positive value of entropy change (ΔS) revealed the increased randomness at the solid-liquid interface. FT-IR and XRD analysis verified that Pd(II) adsorption on PTCS was electrostatic interaction and redox reaction. Moreover, selective adsorption study revealed that the adsorbent exhibited good adsorption ability to Pd(II) in the mixture metal ions solutions. All these results indicated that the PTCS biosorbent could be used as a low-cost alternative for the adsorption of Pd(II) in waste-water treatment.

Rapamycin loaded magnetic Fe3O4/carboxymethylchitosan nanoparticles as tumor-targeted drug delivery system: Synthesis and in vitro characterization.

A novel tumor-targeted drug delivery system (Fe3O4/CMCS-Rapa NPs) was prepared using magnetic Fe3O4/carboxymethylchitosan nanoparticles (Fe3O4/CMCS NPs) as carrier and rapamycin (Rapa) as the model anti-tumor drug. The morphology, composition, and properties of the Fe3O4/CMCS-Rapa NPs were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal analysis (TG/DSC), vibration sample magnetometer (VSM), and drug release kinetics, cytotoxicity, cellular uptake, apoptosis studies in vitro. The results showed that the synthesized Fe3O4/CMCS-Rapa NPs were spherical in shape with an average size of 30±2 nm, the saturated magnetization reached 67.1 emu/g, and the loading efficiency of Rapa was approximately 6.32±0.34%. In addition, the in vitro drug release behavior displayed that the Fe3O4/CMCS NPs exhibited a biphasic drug release pattern with initial burst release and consequently sustained release. Furthermore, the Fe3O4/CMCS-Rapa NPs showed lower cytotoxicity to liver cell line (LO2) and comparatively higher cytotoxicity to human hepatocarcinoma cell line (HepG2) than native Rapa. Fe3O4/CMCS-Rapa NPs could enhance cellular uptake and reduce Rapa drug damage to the normal cells so as to improve the curative effect of drug to tumor cells. All these results demonstrated that the Fe3O4/CMCS-Rapa NPs may be useful as a promising candidate for targeted cancer diagnostic and therapy.

Equilibrium, kinetics and mechanism of Au3 +, Pd2 + and Ag+ ions adsorption from aqueous solutions by graphene oxide functionalized persimmon tannin

In this study, a novel bio-adsorbent (PT-GO) was prepared by functionalization persimmon tannin (PT) with graphene oxide (GO) and the effective adsorption behaviors of Au3+, Pd2+ and Ag+ ions from aqueous solution was investigated. The PT-GO was characterized by Fourier transform infrared spectrometer (FTIR), scanning electronic microscope (SEM), thermogravimetric analysis (TGA) and Zeta potential. Many influence factors such as pH value, bio-adsorbent dosage, initial concentration of metal ions and contact time were optimized. The maximum adsorption capacity for Au3+, Pd2+ and Ag+ was 1325.09mg/g, 797.66mg/g and 421.01mg/g, respectively. The equilibrium isotherm for the adsorption of Au3+ and Ag+ on PT-GO were found to obey the Langmuir model, while the Freundlich model fitted better for Pd2+. The adsorption process of Au3+, Pd2+ presented relatively fast adsorption kinetics with pseudo-second-order equation as the best fitting model, while the pseudo-first-order kinetic model was suitable for describing the adsorption of Ag+. Combination of ion exchange, electrostatic interaction and physical adsorption was the mechanism for adsorption of Au3+, Pd2+ and Ag+ onto PT-GO bio-adsorbent. Therefore, the PT-GO bio-adsorbent would be an ideal adsorbent for removal of precious metal ions and broaden the potential applications of persimmon tannin in environmental research.

Ultrasensitive cholesterol biosensor based on enzymatic silver deposition on gold nanoparticles modified screen-printed carbon electrode

Cholesterol is one of the essential structural constituents of cell membranes. Determination of cholesterol is of great importance in clinical analysis because the level of cholesterol in serum is an indicator in the diagnosis and prevention of heart diseases. In this work, a simple and ultrasensitive cholesterol biosensor based on enzymatic silver deposition was designed by immobilizing cholesterol oxidase (CHOD) and cholesterol esterase (CHER) onto the surface of gold nanoparticles (Au NPs) modified screen-printed carbon electrode (SPE). By the catalytic action of CHER and CHOD, the cholesterol was hydrolyzed to generate hydrogen peroxide (H2O2) which can reduced the silver (Ag) ions in the solution for the deposition of metallic Ag on the surface of Au NPs modified SPE. The ultrasensitive detection of cholesterol was achieved by anodic stripping voltammetry (ASV) measurement of the enzymatically deposited Ag. The influence of relevant experimental variables was optimized. The anodic stripping peak current of Ag depended linearly on the concentration of cholesterol in the range of 5-5000μg/mL with the regression correlation coefficient of 0.9983. A detection limit of 3.0μg/mL was attained by 3 sigma-rule. In addition, the ultrasensitive cholesterol biosensor exhibited higher specificity, acceptable reproducibility and excellent recoveries for cholesterol detection.

Highly sensitive covalently functionalized light-addressable potentiometric sensor for determination of biomarker.

A biomarker is related to the biological status of a living organism and shows great promise for the early prediction of a related disease. Herein we presented a novel structured light-addressable potentiometric sensor (LAPS) for the determination of a model biomarker, human immunoglobulin G (hIgG). In this system, the goat anti-human immunoglobulin G antibody was used as recognition element and covalently immobilized on the surface of light-addressable potentiometric sensor chip to capture human immunoglobulin G. Due to the light addressable capability of light-addressable potentiometric sensor, human immunoglobulin G dissolved in the supporting electrolyte solution can be detected by monitoring the potential shifts of the sensor. In order to produce a stable photocurrent, the laser diode controlled by field-programmable gate array was used as the light emitter to drive the light-addressable potentiometric sensor. A linear correlation between the potential shift response and the concentration of human immunoglobulin G was achieved and the corresponding regression equation was ΔV (V)=0.00714ChIgG (μg/mL)-0.0147 with a correlation coefficient of 0.9968 over a range 0-150 μg/mL. Moreover, the light-addressable potentiometric sensor system also showed acceptable stability and reproducibility. All the results demonstrated that the system was more applicable to detection of disease biomarkers with simple operation, multiple-sample format and might hold great promise in various environmental, food, and clinical applications.

Graphene and Au NPs co-mediated enzymatic silver deposition for the ultrasensitive electrochemical detection of cholesterol

Cholesterol is an essential ingredient in mammals, and serum cholesterol is a major component of atherosclerotic plaques. The level of cholesterol in human serum has become an important index for clinical diagnosis and prevention of cardiovascular disease. In this paper, a simple and ultrasensitive cholesterol biosensor based on graphene oxide (GO) and gold nanoparticles (Au NPs) co-mediated enzymatic silver deposition was designed by immobilizing cholesterol oxidase (CHOD), cholesterol esterase (CHER) and GO onto the surface of Au NPs modified screen-printed carbon electrode (SPE). Under the synergistic effect of CHER, CHOD and GO, the cholesterol was hydrolyzed to generate hydrogen peroxide, which can reduce the silver (Ag) ions in the solution to metallic Ag which deposited on the surface of Au NPs modified SPE. The ultrasensitive detection of cholesterol was achieved by anodic stripping voltammetry measurement of the enzymatically deposited Ag. Under optimal conditions, the anodic stripping peak current of Ag increased with the increasing cholesterol concentration in the range from 0.01μg/mL to 5000μg/mL with a limit of detection of 0.001μg/mL (S/N = 3). In addition, the ultrasensitive cholesterol biosensor exhibited higher specificity, acceptable reproducibility and excellent recoveries for cholesterol detection.

Novel Carboxymethyl Chitosan Microspheres for Controlled Delivery of Chelerythrine

Novel carboxymethyl chitosan (O-CMCS) microspheres containing an anti-tumor drug chelerythrine (CHE) have been successfully prepared by an emulsion crosslinking method using glutaraldehyde. The optimized microsphere formulation was characterized for particle size, shape, morphology, crystallinity and in vitro drug release. Results for mean particle size, drug loading content, entrapment efficiency and in vitro drug release of chelerythrine loaded microspheres were found to be 12.18 μm, 4.08%, 54.78% and 35.30% at pH 7.4 in 20 h, respectively. The optimized microspheres had an imperfect crystalline lattice and a spherical, rough morphology and the CHE release from O-CMCS microspheres followed the Higuchi matrix model. All these results suggested that O-CMCS microspheres are a promising carrier system for controlled drug delivery.