A new immobilized glucose oxidase using SiO2 nanoparticles as carrier

Using SiO₂ nanoparticles as a carrier, a novel immobilized glucose oxidase (GOD) (EC1.1.3.4) was prepared via crosslinking with glutaraldehyde (GA). The optimal immobilization condition was achieved with 1% (v/v) GA, 2% (v/v) 3-aminopropiltrietoxysilane (APTS), 2.5 mg GOD (in 34 mg carrier) and solution pH of 6.5. The immobilized GOD showed maximal catalytic activity at pH 7.0 and 60 °C, and more than 85% of initial activity at the temperature from 20 °C to 80 °C. After immobilization, the enzyme exhibited improved thermal, storage and operation stability. The immobilized GOD still maintained 85% of its initial activity after the incubation at 45 °C for 360 min, whereas free enzyme had only 23% of initial activity after the same incubation. After kept at 4 °C for 30 days, the immobilized and free enzyme retained 84% and 60% of initial activity, respectively. The immobilized GOD also preserved 87% of its initial activity after six consecutive operations.     

Chitin hydrolysis assisted by cell wall degrading enzymes immobilized of Thichoderma asperellum on totally cinnamoylated D-sorbitol beads

In this study, cell wall degrading enzymes produced by Thrichoderma asperellum (TCWDE) were immobilized on totally cinnamoylated D-sorbitol (TCNSO) beads and used for chitin hydrolysis. In order to optimize immobilization efficiency, the reaction time was varied from 2 to 12 h and reactions were conducted in the presence or absence of Na₂SO₄. Immobilized enzymes were analysed concerning to thermal and operational stability. Immobilization in presence of Na₂SO₄ was 54% more efficient than immobilization in absence of salt. After optimization, 32% of the total enzyme offered was immobilized, with 100% of bounding efficiency, measured as the relation between protein and enzyme immobilized. Free and TCNSO–TCWDE presented very similar kinetics with maximum hydrolysis reached at 90 min of reaction. Thermal stability of both free and TCNSO–TCWDE was similar, with losses in activity after 55 °C. Moreover, free and TCNSO–TCWDE retained 100% activity after 3 h incubation at 55 °C. TCNSO–TCWDE were used in a bath-wise reactor during 14 cycles, producing 1825 μg of N-acetylglucosamine (NAG) maintaining 83% of initial activity.     

Facile preparation of a DNA sensor for rapid herpes virus detection

In this paper, a simple DNA sensor platform was developed for rapid herpes virus detection in real samples. The deoxyribonucleic acid (DNA) sequences of the herpes simplex virus (DNA probe) were directly immobilized on the surface of interdigitated electrodes by electrochemical polymerization along with pyrrole monomers. The potential was scanned from ? 0.7 to + 0.6 V, and the scanning rate was 100 mV/s. Fourier transform infrared spectroscopy was employed to verify specific DNA sequence binding and the conducting polymer. The morphology of the conducting polymer doped with DNA strands was characterized using a field emission scanning electron microscope. As-obtained DNA sensor was used to detect the herpes virus DNA in the real samples. The results show that the current DNA sensors detected the lowest DNA concentration of 2 nM. This sensitivity appears to be better than that of the DNA sensors prepared by immobilization of the DNA probe on the 3-aminopropyl-triethoxy-silance (APTS) membrane.     

Gas sensitive vapor grown carbon nanofiber/polystyrene sensors

A new class of conductive composites with good gas sensitivity was fabricated by filling polystyrene with vapor grown carbon nanofibers (VGCNF). A solution mixing/solvent removal procedure was used. VGCNFs form conductive networks at fiber loadings above the percolation limit within the matrix. Greatly improved conductivity is achieved relative to the same volume fraction of carbon black addition when these fibers are distributed to give reasonably uniform dispersions in the matrix. The high aspect ratios of these fibers (∼70–250 nm diameters and 5–75 μm lengths) assist in forming low wt.% percolation thresholds (below 1 wt.% fiber). Excellent gas sensitivity with 10⁴–10⁵ times higher than the original resistance value in many saturated organic vapors and a maximum resistance response of about 1.1 × 10⁵ times exposure to saturated THF vapor at 6.25 wt.% of VGCNF in the polystyrene matrix was observed. The maximum resistance response declined from about 2.0 × 10⁵ times at 15 °C to about 3.4 × 10⁴ times at 55 °C. These composites exhibited stable and reusable gas sensitivity to THF vapor. Carbon black/polystyrene composites exhibit a negative vapor coefficient (NVC) upon swelling caused by filler redistribution. In contrast, VGCNF/polystyrene composites are more stable, with much smaller NVC values due to their high aspect ratios and reinforcing effects which stabilize electrical percolation pathways. Thus, VGCNF/organic polymer composites are good gas sensor candidates for detecting organic vapors.     

Trypsin immobilization on discs of polyvinyl alcohol glutaraldehyde/polyaniline composite

Discs of polyvinyl alcohol cross-linked with glutaraldehyde (PVAG) were synthesized and covered with polyaniline activated with glutaraldehyde (PANIG). Trypsin was covalently immobilized on this composite yielding a preparation containing 21.1 units per disc. The FT-IR spectra of the discs showed bands of PVA (3300 cm^?1, 2930 cm^?1 and 1440 cm^?1) and PANI (1594 cm^?1 and 1100 cm^?1). The best immobilization conditions were: trypsin concentration at 0.2 mg mL^?1, pH 7.6 and 60 min of incubation, similar to polyaniline–trypsin systems reported in the literature. The PVAG–PANIG–trypsin derivative showed an optimal pH and an optimal temperature of 7.0 and 35 °C, respectively. Hydrolysis of casein showed variations in the size of the products, revealing differences between the immobilized enzyme and the mechanism catalyzed by the native enzyme.     

Immobilization of Bacillus sp. in mesoporous activated carbon for degradation of sulphonated phenolic compound in wastewater

Xenobiotic compounds are used in considerable quantities in leather industries besides natural organic and inorganic compounds. These compounds resist biological degradation and thus they remain in the treated wastewater in the unaltered molecular configurations. Immobilization of organisms in carrier matrices protects them from shock load application and from the toxicity of chemicals in bulk liquid phase. Mesoporous activated carbon (MAC) has been considered in the present study as the carrier matrix for the immobilization of Bacillus sp. isolated from Effluent Treatment Plant (ETP) employed for the treatment of wastewater containing sulphonated phenolic (SP) compounds. Temperature, pH, concentration, particle size and mass of MAC were observed to influence the immobilization behavior of Bacillus sp. The percentage immobilization of Bacillus sp. was the maximum at pH 7.0, temperature 20 °C and at particle size 300 μm. Enthalpy, free energy and entropy of immobilization were ? 46.9 kJ mol^? 1, ? 1.19 kJ mol^? 1 and ? 161.36 J K^? 1 mol^? 1 respectively at pH 7.0, temperature 20 °C and particle size 300 μm. Higher values of ΔH⁰ indicate the firm bonding of the Bacillus sp. in MAC. Degradation of aqueous sulphonated phenolic compound by Bacillus sp. immobilized in MAC followed pseudo first order rate kinetics with rate constant 1.12 × 10^? 2 min^? 1.     

Enhanced stability of catalase covalently immobilized on functionalized titania submicrospheres

In this study, a novel approach combing the chelation and covalent binding was explored for facile and efficient enzyme immobilization. The unique capability of titania to chelate with catecholic derivatives at ambient conditions was utilized for titania surface functionalization. The functionalized titania was then used for enzyme immobilization. Titania submicrospheres (500–600 nm) were synthesized by a modified sol–gel method and functionalized with carboxylic acid groups through a facile chelation method by using 3-(3,4-dihydroxyphenyl) propionic acid as the chelating agent. Then, catalase (CAT) was covalently immobilized on these functionalized titania submicrospheres through 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) coupling reaction. The immobilized CAT retained 65% of its free form activity with a loading capacity of 100–150 mg/g titania. The pH stability, thermostability, recycling stability and storage stability of the immobilized CAT were evaluated. A remarkable enhancement in enzyme stability was achieved. The immobilized CAT retained 90% and 76% of its initial activity after 10 and 16 successive cycles of decomposition of hydrogen peroxide, respectively. Both the K_m and the V_max values of the immobilized CAT (27.4 mM, 13.36 mM/min) were close to those of the free CAT (25.7 mM, 13.46 mM/min).     

Structural characterization of CdS nanoparticles grown in polystyrene matrix by thermolytic synthesis

Cadmium sulfide nanoparticles embedded in a polystyrene matrix (CdS/PS) were successfully prepared by in situ thermolysis of a cadmium thiolate precursor dispersed in the polymer. The heat-induced formation of cadmium sulfide was studied by thermogravimetric analysis and differential thermal analysis, while the chemistry of the reaction forming the CdS/PS compound was investigated by nuclear magnetic resonance and X-ray photoelectron spectroscopy. The structural characterization was performed by X-ray diffraction and transmission electron microscopy. The CdS nanocrystals are single crystals of cubic phase (zincblende structure) of spherical shape. The average diameter of the nanocrystals embedded in the polystyrene matrix achieved by our synthesis process is as small as 2.5 ± 0.5 nm. Room temperature UV–VIS absorption spectra exhibit a shoulder at 412 nm that is consistent with the presence of CdS nanocrystals of ∅ ≈ 2 nm. The role of the polymer on the nanoparticle growth was also discussed.     

Controlling immunoglobulin G orientation on a protein-A terminated bilayer system

In this study, a bilayer system composed of N-[3-trimethoxysilyl propyl]-ethylene diamine (TEDA) and protein-A on silicon wafer was prepared by a simple two-step procedure. Self-assembly deposition of TEDA at optimal conditions resulted in the formation of homogeneous self-assembled monolayers (SAMs) ~ 2.3 nm thick with the surface roughness ~ 0.38 nm. The height value of protein-A overlayer was found to be ~ 3.5 nm, which is within experimental error of the diameter of a single protein-A (3 nm). Immunoglobulin G (IgG) molecules were then immobilized on the bilayer system by protein-A – IgG specific interactions. Using this very simple approach, the IgG layer was formed almost of a monomolecular layer for longer adsorption time (~ 100 min), and it was packed densely for adsorption time longer than 100 min, which resulted in the increase of the amount of IgG immobilized. The use of a bilayer system composed of TEDA and protein A on silicon wafer opens the door for a fundamental understanding of how protein A affects IgG orientation on the surface and also indicates a useful guide to designing surfaces for applications such as immunosensors and biochips.     

Immobilization of cholesterol esterase in mesoporous silica materials and its hydrolytic activity toward diethyl phthalate

Cholesterol esterase (CE, cholesteryl ester hydrolase, EC 3.1.1.13) from porcine pancreas (molecular weight 400–500 kDa) exhibits hydrolytic activity toward various toxic organic phthalate esters. CE was confined in the nanospace (diameter 3–30 nm) of five types of mesoporous silica (MPS) that differ in structural properties such as pore diameter, pore volume, and particle morphology. These structural properties were characterized by transmission electron microscopy, small-angle X-ray diffraction, N₂ adsorption–desorption experiments, solid-state ¹³C nuclear magnetic resonance (NMR), and solid-state ²⁹Si NMR. Catalytic activities of immobilized and free CE were evaluated by the hydrolysis of diethyl phthalate in phosphate buffer solutions containing an organic cosolvent. Optimal activity recovery was achieved when CE was immobilized in n-decane-functionalized MPS, which had a large pore size (22.5 nm). The immobilization also protected against effects of temperature within the range 30 °C–60 °C; CE immobilized in n-decyl-functionalized MPS exhibited better thermal stability than in non-functionalized MPS or free CE. Moreover, it retained approximately 60% of its catalytic activity even after six catalytic cycles.     

Synthesis of zinc oxide particles coated multiwalled carbon nanotubes: Dielectric properties,electromagnetic interference shielding and microwave absorption

Zinc oxide (ZnO) nanoparticles were coated on the surfaces of multiwalled carbon nanotubes (MWCNTs). High resolution transmission electron microscopy images show that the wurtzite ZnO immobilized on the MWCNTs is single-crystalline with a preferential [0 0 0 2] growth direction. A capacitor was generated by the interface of ZnO and MWCNTs, and a resistor–capacitor model could well describe the relationships between the structure and the dielectric properties, electromagnetic interference shielding and microwave-absorption of the composites in the frequency range of 2–18 GHz. The network built by ZnO-immobilized MWCNTs could contribute to the improvement of electrical properties. Resonant peaks associated with the capacitor formed by the interface were observed in the microwave absorption spectra, which suggest that reflection–loss peaks greatly broadens the absorption bandwidth.     

Modification of chloromethylated polystyrene with 2-mercabtobenzothiazole for application as a new sorbent for preconcentration and determination of Ag+ from different matrices

Chloromethylated polystyrene polymer (CMSP) modified with 2-mercabtobenzothiazole (MBT) has been developed for the selective separation and/or preconcentration of silver. The modified polymer (CMS-MBT) was characterized by elemental analysis and IR spectra. Batch and column modes were applied. The newly designed polymer quantitatively sorbed Ag⁺ at pH 2 when the flow rate is 5 ml min^?1. The maximum sorption capacity was 0.493 mmol g^?1 while the preconcentration factor was 250 for Ag⁺. The detection limit was 8 ng ml^?1. The desorption was effective with 5 ml of 2 mol l^?1 HNO₃ prior to detection using AAS. The modified polymer was highly ion-selective in nature even in the presence of large concentrations of electrolytes or organic media, with a preconcentrating ability for Ag⁺. The utility of the modified polymer to synthetic and drugs samples showed RSD values of <3% reflecting its accuracy and reproducibility.     

Affinity adsorption of human vitamin K-dependent coagulation factor IX onto heparin-like poly (styrene sodium sulfonate) adsorbent

Adsorption of proteins on polymer material plays an important role in a number of fields, particularly in separation of biomolecules by chromatographic methods. The work reports here the synthesis of modified cross-linked polystyrene gel beads as a stationary phase in liquid chromatography for the purification of factor IX. Suitable chemical groups, such as sulfonate which confer this polymer heparin-like adsorbing property, were grafted on the aromatic ring of the hydrophobic matrix. This functional group was chosen on the basis of the biospecific molecular interactions between factor IX and its ligand particularly heparin in such manner to enhance its binding ability and efficacy. Adsorption of factor IX on to this functional polymer was performed under physiological conditions according two modes: non-competitive adsorption (adsorption of factor IX alone) and competitive adsorption (adsorption of factor IX in the presence of another vitamin-K dependent coagulation factors). The adsorbed factor IX content at the interface allows to establish the chemisorption isotherm curves. The adsorption rate in both cases was found to be significantly high and the affinity constants, estimated by the Langmuir model, were: 4.7 × 10⁸ and 4.1 × 10⁸ l/M respectively. Affinity chromatography on column using this functional polymer as a stationary phase confirms its high ability to adsorb factor IX at low ionic strength. Thus, the synthesized packing material gel functionalised by sulfonate group can be used advantageously as a heparin-like adsorbent in purification of factor IX.     

Immobilization of Acidithiobacillus ferrooxidans on sulfonated microporous poly(styrene–divinylbenzene) copolymer with granulated activated carbon and its use in bio-oxidation of ferrous iron

The immobilization efficiencies of Acidithiobacillus ferrooxidans cells on different immobilization matrices were investigated for biooxidation of ferrous iron (Fe^2 +) to ferric iron (Fe^3 +). Six different matrices were used such as the polyurethane foam (PUF), granular activated carbon (GAC), raw poly(styrene–divinylbenzene) copolymer (rawSDVB), raw poly(styrene–divinylbenzene) copolymer with granular activated carbon (rawSDVB-GAC), sulfonated poly(styrene–divinylbenzene) copolymer (sulfSDVB) and sulfonated poly(styrene–divinylbenzene) copolymer with granular activated carbon (sulfSDVB-GAC). The sulfSDVB-GAC polymer showed the best performance for Fe^2 + biooxidation. It was used at packed-bed bioreactor and the kinetic parameters were obtained. The highest Fe^2 + biooxidation rate (R) was found to be 4.02 g/L h at the true dilution rate (D_t) of 2.47 1/h and hydraulic retention time (τ) of 0.4 h. The sulfSDVB-GAC polymer was used for the first time as immobilization material for A. ferrooxidans for Fe^2 + biooxidation.     

Oriented immobilized anti-LDL antibody carrying poly(hydroxyethyl methacrylate) cryogel for cholesterol removal from human plasma

Low density lipoprotein (LDL) cholesterol is a major ingredient of the plaque that collects in the coronary arteries and causes coronary heart diseases. Among the methods used for the extracorporeal elimination of LDL from intravasal volume, immunoaffinity technique using anti-LDL antibody as a ligand offers superior selectivity and specificity. Proper orientation of the immobilized antibody is the main issue in immunoaffinity techniques. In this study, anti-human β-lipoprotein antibody (anti-LDL antibody) molecules were immobilized and oriented through protein A onto poly(2-hydroxyethyl methacrylate) (PHEMA) cryogel in order to remove LDL from hypercholesterolemic human plasma. PHEMA cryogel was prepared by free radical polymerization initiated with N,N,N′,N′-tetramethylene diamine (TEMED). PHEMA cryogel with a swelling degree of 8.89 g H₂O/g and 67% macro-porosity was characterized by swelling studies, scanning electron microscope (SEM) and blood compatibility tests. All the clotting times were increased when compared with control plasma. The maximum immobilized anti-LDL antibody amount was 63.2 mg/g in the case of random antibody immobilization and 19.6 mg/g in the case of oriented antibody immobilization (protein A loading was 57.0 mg/g). Random and oriented anti-LDL antibody immobilized PHEMA cryogels adsorbed 111 and 129 mg LDL/g cryogel from hypercholesterolemic human plasma, respectively. Up to 80% of the adsorbed LDL was desorbed. The adsorption–desorption cycle was repeated 6 times using the same cryogel. There was no significant loss of LDL adsorption capacity.     

Preparation and characterization of biocompatible carbon electrodes

Electron transfer in microbial fuel cell and biosensors could be facilitated through high conductive materials with enhanced active surface area and appropriate redox potential suited to microbial metabolism. In the first strategy based on bulk doping, graphite/epoxy composite electrode (GECE) bulk was modified with six types of metal ion which were prepared through a wet impregnation procedure. In the second strategy, immobilization of redox dye on carbon cloth and graphite sheet was carried out using N,N′-dicyclohexylcarbodiimide for surface modification. Crystallinity, morphology, surface chemistry and electrochemical properties of all modified electrodes were investigated. Influence of redox behavior of electrodes suited to microbial metabolism and conducive to biofilm formation have been examined. It was observed that the Fe³⁺ doped GECE surfaces exhibited significantly high biofilm formation of 1.10(±0.18) × 10⁷ CFU/cm² as compared to other dopants. The microbial growth on the carbon cloth electrode and carbon fiber reinforced plate were found to be less (2.6(±0.97) × 10⁴, 4.8(±1.8) × 10³ CFU/cm² respectively) compared to GECEs.     

The effect of polymer spatial configuration on the microwave absorbing properties of non-covalent modified MWNTs

The polar polymer of linear and star polymethyl methacrylate (PMMA) was used to modify the surface of multi-walled carbon nanotubes (MWNTs). Raman and TGA were used to characterize structure of the functionalized MWNTs. The effect of polymer spatial configuration on the MWNTs dispersion, morphology and interfacial interaction was investigated by scanning electron microscopy and transmission electron microscopy. The aim of the work is to investigate the effect of polymer spatial configuration on the microwave absorbing properties. The results showed that the maximum reflection loss of linear PMMA/MWNTs hybrids was −37 dB in the frequency of 8.8 GHz, and the bandwidth below −10 dB was more than 2.1 GHz. While the maximum reflection loss of the S-PMMA/MWNTs hybrids reached −50 dB in the frequency of 8.4 GHz, and the bandwidth below −10 dB was 2.3 GHz. The results indicated that the microwave absorbing properties of star PMMA polymers modified MWNTs were superior to that of linear PMMA polymers.     

Immobilization of the urease on eggshell membrane and its application in biosensor

Eggshell membrane is a natural material, essentially made up of protein fibers having flexibility in the aqueous solution and possessing gas and water permeability. It is used as a biomembrane for immobilization of urease for the development of a potentiometric urea biosensor. Eggshell membrane was treated with polyethyleneimine (PEI) to impart polycation characteristics. Urease was immobilized on the PEI treated eggshell membrane through adsorption. SEM study was carried out to observe the changes in surface morphology after immobilization. FTIR study of membrane was carried out to observe the changes in IR spectra after immobilization of enzyme. Immobilized membrane was associated with ammonium ion selective electrode. Biosensor exhibited sigmoidal responses for the urea concentration range from 0.5 to 10 mM. The response time of the biosensor was 120 s. A single membrane was reused for 270 reactions without loss of activity. The urease–eggshell membranes were stable for 2 months when stored in buffer even at room temperature.     

Comparison of electrochemical performances of LiFePO4/C composite materials by two preparation routes

This study reports on the preparation of LiFePO₄/C composite materials prepared by the hydrothermal and sol–gel processes for comparison. The synthesis condition on the hydrothermal process was performed at 170 °C for 19 h. The polystyrene (PS) polymer was used as a carbon source; the PS was added at a range of 0–5 wt.%. The temperature of the post-thermal process was set at 750–850 °C. The citric acid (denoted as CA) was used as the reducing agent and the carbon source in the sol–gel process. The temperatures of the sintering process were set at a range of 650–850 °C. The optimal sintering temperature was at 850 °C for 12 h in the hydrothermal process; the optimal carbon residue content was approximately 3.20 wt.%. It was revealed that the highest discharge capacity of LiFePO₄/C composites by the hydrothermal process at 0.1 C is 163 mAh g^?1. The optimal sintering temperature was found to be at 750 °C for the sol–gel process. The highest carbon content was approximately 11.94 wt.% as the molar ratio of CA is 1.0. The highest discharge capacity of LiFePO₄/C composites by the sol–gel process at 0.1 C was approximately 130.35 mAh g^?1.     

Improvement in the morphology of micro-arc oxidised titanium surfaces: A new process to increase osteoblast response

This study describes a method for combining sandblast-acid etching and micro-arc oxidation to optimise titanium implant surfaces, and examines the effects of these surfaces on osteoblast response. Titanium discs were grouped as: micro-arc oxidised (MAO), sandblast-acid etched and micro-arc oxidised (MAO-SA), micro-arc oxidised and heated (MAO-HT), and untreated smooth surface. The combination of sandblast-acid etching and micro-arc oxidation in the MAO-SA group created an average surface roughness of 2.02 ± 0.15 μm compared to the untreated machined surface of 0.31 ± 0.06 μm. Scanning electron microscopy observations of the surface structures showed that the irregularly ordered valleys created by sandblast-acid etching remained after micro-arc oxidation and that micropores had also formed. These microstructures provided a better place for osteoblasts to spread compared with the other surfaces. In addition, our results indicated that adherent osteoblasts expressed greater alkaline phosphatase (ALP) activity and osteocalcin (OC) production on MAO-SA surfaces compared with MAO, MAO-HT, and smooth surfaces. The overall results clearly indicate that combining sandblast-acid etching and micro-arc oxidation techniques improves the titanium surface morphology and increases the roughness, which provides an optimal surface for cell differentiation and osseointegration.