Covalent immobilization of glucose oxidase on the surface of polyaniline films graft copolymerized with acrylic acid

Direct Electron Transfer of Glucose Oxidase on Pre-Anodized Paper/Carbon Electrodes Modified through Zero-Length Cross-Linkers for Glucose Biosensors

A disposable paper-based glucose biosensor with direct electron transfer (DET) of glucose oxidase (GOX) was developed through simple covalent immobilization of GOX on a carbon electrode surface using zero-length cross-linkers. This glucose biosensor exhibited a high electron transfer rate (ks, 3.363 s-1) as well as good affinity (km, 0.03 mM) for GOX while keeping innate enzymatic activities. Furthermore, the DET-based glucose detection was accomplished by employing both square wave voltammetry and chronoamperometric techniques, and it achieved a glucose detection range from 5.4 mg/dL to 900 mg/dL, which is wider than most commercially available glucometers. This low-cost DET glucose biosensor showed remarkable selectivity, and the use of the negative operating potential avoided interference from other common electroactive compounds. It has great potential to monitor different stages of diabetes from hypoglycemic to hyperglycemic states, especially for self-monitoring of blood glucose.

Novel Nanozeolitic Imidazolate Framework (ZIF-8)-Luciferase Biocomposite for Nanosensing Applications

The identification of new strategies to improve the stability of proteins is of utmost importance for a number of applications, from biosensing to biocatalysis. Metal-organic frameworks (MOFs) have been shown as a versatile host platform for the immobilization of proteins, with the potential to protect proteins in harsh conditions. In this work, a new thermostable luciferase mutant has been selected as a bioluminescent protein model to investigate the suitability of MOFs to improve its stability and prompt its applications in real-world applications, for example, ATP detection in portable systems. The luciferase has been immobilized onto zeolitic imidazolate framework-8 (ZIF-8) to obtain a bioluminescent biocomposite with enhanced performance. The biocomposite ZIF-8@luc has been characterized in harsh conditions (e.g., high temperature, non-native pH, etc.). Bioluminescence properties confirmed that MOF enhanced the luciferase stability at acidic pH, in the presence of organic solvents, and at -20 °C. To assess the feasibility of this approach, the recyclability, storage stability, precision, and Michaelis-Menten constants (K_m) for ATP and d-luciferin have been also evaluated. As a proof of principle, the suitability for ATP detection was investigated and the biocomposite outperformed the free enzyme in the same experimental conditions, achieving a limit of detection for ATP down to 0.2 fmol.

A biocompatible PAA-Cu-MOP hydrogel for wound healing

Wounds infected by bacteria are dangerous for human beings. However, along with the emergence of new strains and strong bacterial resistance, traditional antibiotics are unable to meet the medical needs for treating bacterial infections. Thus, new antibacterial substances with superior antimicrobial properties are urgently needed. Herein, a hydrogel containing poly acrylic acid (PAA), glycerol and Cu-MOP (named PAA-Cu-MOP hydrogel) is obtained by a facile mixing and ultrasonic procedure for wound healing treatment. This PAA-Cu-MOP hydrogel with high biocompatibility exhibits excellent wound healing behavior and is even better than the one of recombinant human epidermal growth factor. Tissue experiment results reveal that the PAA-Cu-MOP hydrogel accelerates the wound healing process by promoting angiogenesis, stimulating cell proliferation, and up-regulating cell factors.

Development of a rapid and simple glycine analysis method using a stable glycine oxidase mutant

Glycine analysis is important in research fields such as physiology and healthcare because the concentration of glycine in human plasma has been reported to change with various disorders. Glycine oxidase from Bacillus subtilis (GlyOX) is useful for quantitative analysis of glycine. However, GlyOX is not sufficiently stable for use in physiology-based research or clinical settings. In this report, site-directed mutagenesis was used to engineer a GlyOX mutant suitable for glycine analysis. The GlyOX triple-mutant (T42 A/C245 S/L301V) retained most of its enzymatic activity during storage for over a year at 4 °C. A colorimetric enzyme analysis protocol was established using the GlyOX triple-mutant to determine glycine concentrations in human plasma. The analysis showed high accuracy (-5.4 to 3.5% relative errors when compared with the results from an amino acid analyzer, and 96.0-98.7% recoveries) and high precision (<4% between-run variation). Sample pretreatments of deproteinization and derivatization were not required. Therefore, this novel enzymatic analysis offers an effective and useful method for determining glycine concentrations in physiology related research and the healthcare field.

Improved biotribological properties of PEEK by photo-induced graft polymerization of acrylic acid

The keys of biomaterials application in artificial joints are good hydrophilicity and wear resistance. One kind of the potential bio-implant materials is polyetheretherketone (PEEK), which has some excellent properties such as non-toxic and good biocompatibility. However, its bioinert surface and inherent chemical inertness hinder its application. In this study, we reported an efficient method for improving the surface wettability and wear resistance for PEEK, a layer of acrylic acid (AA) polymer brushes on PEEK surface was prepared by UV-initiated graft polymerization. The effects of different grafting parameters (UV-irradiation time/AA monomer solution concentration) on surface characteristics were clearly investigated, and the AA-g-PEEK specimens were examined by ATR-FTIR, static water contact angle measurements and friction tests. Our results reveal that AA can be successfully grafted onto the PEEK surface after UV irradiation, the water wettability and tribological properties of AA-g-PEEK are much better than untreated PEEK because that AA is a hydrophilic monomer, the AA layer on PEEK surface can improve its bearing capacity and reduce abrasion. This detailed understanding of the grafting parameters allows us to accurately control the experimental products, and this method of surface modification broadens the use of PEEK in orthopedic implants.

Square-wave voltammetry assays for glycoproteins on nanoporous gold

Electrochemical enzyme-linked lectinsorbent assays (ELLA) were developed using nanoporous gold (NPG) as a solid support for protein immobilization and as an electrode for the electrochemical determination of the product of the reaction between alkaline phosphatase (ALP) and p-aminophenyl phosphate (p-APP), which is p-aminophenol (p-AP). Glycoproteins or concanavalin A (Con A) and ALP conjugates were covalently immobilized onto lipoic acid self-assembled monolayers on NPG. The binding of Con A - ALP (or soybean agglutinin - ALP) conjugate to glycoproteins covalently immobilized on NPG and subsequent incubation with p-APP substrate was found to result in square-wave voltammograms whose peak difference current varied with the identity of the glycoprotein. NPG presenting covalently bound glycoproteins was used as the basis for a competitive electrochemical assay for glycoproteins in solution (transferrin and IgG). A kinetic ELLA based on steric hindrance of the enzyme-substrate reaction and hence reduced enzymatic reaction rate after glycoprotein binding is demonstrated using immobilized Con A-ALP conjugates. Using the immobilized Con A-ALP conjugate, the binding affinity of immunoglobulin G (IgG) was found to be 105 nM, and that for transferrin was found to be 650 nM. Minimal interference was observed in the presence of 5 mg mL-1 BSA as a model serum protein in both the kinetic and competitive ELLA. Inhibition studies were performed with methyl D-mannoside for the binding of TSF and IgG to Con A-ALP; IC50 values were found to be 90 μM and 286 μM, respectively. Surface coverages of proteins were estimated using solution depletion and the BCA protein concentration assay.

Highly sensitive glucose sensor based on pt nanoparticle/polyaniline hydrogel heterostructures

Glucose enzyme biosensors have been shown useful for a range of applications from medical diagnosis, bioprocess monitoring, to beverage industry and environmental monitoring. We present here a highly sensitive glucose enzyme sensor based on Pt nanoparticles (PtNPs)-polyaniline (PAni) hydrogel heterostructures. High-density PtNPs were homogeneously loaded onto the three-dimensional (3D) nanostructured matrix of the PAni hydrogel. The PtNP/PAni hydrogel heterostructure-based glucose sensor synergizes the advantages of both the conducting hydrogel and the nanoparticle catalyst. The porous structure of the PAni hydrogel favored the high density immobilization of the enzyme and the penetration of water-soluble molecules, which helped efficiently catalyze the oxidation of glucose. In addition, the PtNPs catalyzed the decomposition of hydrogen peroxide that was generated during the enzymatic reaction. The transferred charges from these electrochemical processes were efficiently collected by the highly conducting PtNP/PAni hydrogel heterostructures. The glucose enzyme sensor based on this heterostructure exhibited unprecedented sensitivity, as high as 96.1 μA·mM(-1)·cm(-2), with a response time as fast as 3 s, a linear range of 0.01 to 8 mM, and a low detection limit of 0.7 μM.

Immobilization of glucose oxidase onto gelatin for biosensor construction

The properties of a glucose biosensor made by immobilization of glucose oxidase onto gelatin in a layer of electrochemically deposited polyaniline have been investigated. Glucose oxidase was immobilized within gelatin cross-links with chromium(III) acetate. The glucose oxidase biosensor was developed by forming a polyaniline-deposited electrode surface as support for the immobilized enzyme gel, in order to increase its durability. The polyaniline/gelatin/glucose oxidase biosensor has been characterized using chemical and electrochemical methods. Temperature, pH, cross-linking agent concentration, enzyme concentration, kinetic properties, reusability and the effect of electro-active compounds were among the parameters studied. The response time of the glucose oxidase biosensor is 90 s, the detection limit is below 1 mmol/dm3 and the sensor can be used 20 times within a 2-month period without losing its stability.

Copper selenide nanocrystals for photothermal therapy

Ligand-stabilized copper selenide (Cu(2-x)Se) nanocrystals, approximately 16 nm in diameter, were synthesized by a colloidal hot injection method and coated with amphiphilic polymer. The nanocrystals readily disperse in water and exhibit strong near-infrared (NIR) optical absorption with a high molar extinction coefficient of 7.7 × 10(7) cm(-1) M(-1) at 980 nm. When excited with 800 nm light, the Cu(2-x)Se nanocrystals produce significant photothermal heating with a photothermal transduction efficiency of 22%, comparable to nanorods and nanoshells of gold (Au). In vitro photothermal heating of Cu(2-x)Se nanocrystals in the presence of human colorectal cancer cell (HCT-116) led to cell destruction after 5 min of laser irradiation at 33 W/cm(2), demonstrating the viabilitiy of Cu(2-x)Se nanocrystals for photothermal therapy applications.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Affinity covalent immobilization of glucoamylase onto ρ-benzoquinone activated alginate beads: I. Beads preparation and characterization

ρ-Benzoquinone-activated alginate beads were presented as a new carrier for affinity covalent immobilization of glucoamylase enzyme. Evidences of alginate modification were extracted from FT-IR and thermal gravimetric analysis and supported by morphological changes recognized through SEM examination. Factors affecting the modification process such as ρ-benzoquinone (PBQ) concentration, reaction time, reaction temperature, reaction pH and finally alginate concentration, have been studied. Its influence on the amount of coupled PBQ was consequently correlated to the changes of the catalytic activity and the retained activity of immobilized enzyme, the main parameters judging the success of the immobilization process. The immobilized glucoamylase was found kept almost 80% of its native activity giving proof of non-significant substrate, starch, diffusion limitation. The proposed affinity covalent immobilizing technique would rank among the potential strategies for efficient immobilization of glucoamylase enzyme.

Alkyl passivation and amphiphilic polymer coating of silicon nanocrystals for diagnostic imaging

A method to produce biocompatible polymer-coated silicon nanocrystals for medical imaging is shown. Silica-embedded Si nanocrystals are formed by HSQ thermolysis. The nanocrystals are then liberated from the oxide and terminated with Si-H bonds by HF etching, followed by alkyl monolayer passivation by thermal hydrosilylation. The Si nanocrystals have an average diameter of 2.1 nm ± 0.6 nm and photoluminesce with a peak emission wavelength of 650 nm, which lies within the transmission window of 650-900 nm that is useful for biological imaging. The hydrophobic Si nanocrystals are then coated with an amphiphilic polymer for dispersion in aqueous media with the pH ranging between 7 and 10 and an ionic strength between 30 mM and 2 M, while maintaining a bright and stable photoluminescence and a hydrodynamic radius of only 20 nm. Fluorescence imaging of polymer-coated Si nanocrystals in biological tissue is demonstrated, showing the potential for in vivo imaging.

Lysine-based peptide-functionalized PLGA foams for controlled DNA delivery

Due to its hydrophobicity and negatively charged surfaces, PLGA-based scaffolds have encountered problems in controlled-release and tissue engineering applications. The effects of charge modification of PLGA micro-porous foams on DNA delivery and DNA transfection are investigated herein. Tailor-designed l-lysine peptides (K4 and K20) were employed to modify the surface charge of PLGA foams using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide cross linkers and the effects of charge modification of PLGA were examined in three main aspects: DNA adsorption, DNA release properties and DNA transfection. Successful conjugation of peptide and DNA adsorption were verified by X-ray photoelectron spectroscopy. A plasmid encoding bone morphogenetic protein-2 (BMP2) was used throughout the current study and the results indicate that adsorption capacity and release behavior of DNA were highly dependent on the charge properties of the foam surfaces. The release rates of DNA from the K4- and K20-functionalized foams are more sustainable as compared to the blank foam. As a result, the sustained release of DNA from modified foams led to negligible cytotoxicity and sustained expression of DNA which is favorable for DNA delivery and tissue engineering application. Furthermore, the ease of fabrication and modification of PLGA foams makes it a promising DNA delivery device.

Stimuli-responsive hydrogel membranes coupled with biocatalytic processes

A nanostructured signal-responsive thin hydrogel membrane was coupled with enzyme-based systems to yield "smart" multisignal-responsive hybrid systems with built-in "logic". The enzyme systems transduce biochemical input signals into structural changes of the membrane, thus resulting in the amplification of the biochemical signals and their transformation into the gated transport of molecules through the membrane. Coupling of the biocatalytic systems with a stimuli-responsive membrane is a promising approach for the development of materials that can regulate transport and release of chemicals/drugs by receiving and processing the biochemical information via biochemical reactions.

Functionalized Membranes by Layer-By-Layer Assembly of Polyelectrolytes and In Situ Polymerization of Acrylic Acid for Applications in Enzymatic Catalysis

This research work was directed toward the development of highly active, stable, and reusable functionalized polymeric membrane domains for enzymatic catalysis. Functionalized membranes were created by two different approaches. In the first approach, which involved alternative attachment of cationic and anionic polyelectrolytes, functionalization was performed using a layer-by-layer (LBL) assembly technique within a nylon-based microfiltration (MF) membrane. In the second approach, a hydrophobic polyvinylidene fluoride (PVDF) MF membrane was functionalized by the in situ polymerization of acrylic acid. The enzyme, glucose oxidase (GOX), was then electrostatically immobilized inside the functionalized membrane domains to study the catalytic oxidation of glucose to gluconic acid and H2O2. Characterization of the functionalized membranes, in terms of polyelectrolyte/polymer domains and permeate flux, was also conducted. The kinetics of H2O2 formation was discussed, along with the effects of residence time and pH on the activity of GOX. The stability and reusability of the electrostatically immobilized enzymatic system were also investigated.

Modified Fenton reaction for trichlorophenol dechlorination by enzymatically generated H2O2 and gluconic acid chelate

Glucose oxidase is a well-known enzyme that catalyzes the oxidation of beta-D-glucose to produce gluconic acid and hydrogen peroxide. Fenton reaction is a powerful oxidation technology used for the oxidation of groundwater pollutants. For the application of Fenton reaction in groundwater remediation, successful operation of Fenton reaction near neutral pH, and on-site generation of both H2O2 and chelate will be beneficial. The focus of this experimental study was to couple the glucose oxidation reaction with chelate-based Fenton reaction. The idea was to use the hydrogen peroxide and chelate gluconic acid generated during glucose oxidation for the dechlorination of 2,4,6-trichlorophenol (TCP) by Fenton reaction. The oxidation of glucose was achieved using the enzyme in free and immobilized forms. The rate of production of hydrogen peroxide was determined for each system, and was used to estimate the time required for complete consumption of glucose during the process, thus avoiding any traces of glucose in the Fenton reaction. In the case of free enzyme reaction, separation of the enzyme was achieved using an ultrafiltration membrane before initiating the Fenton reaction. The oxidation of TCP by Fenton reaction was performed at varying ratios of gluconic acid/Fe, and its effect on the decomposition of TCP and H2O2 was studied. TCP degradation was studied both in terms of parent compound degradation and free chloride generation.

Photoreactive cellulose membrane—A novel matrix for covalent immobilization of biomolecules

We report a simple and mild procedure for the preparation of a photoreactive cellulose membrane capable of forming a covalent bond with a biomolecule in presence of 365 nm UV light. Photoreactive cellulose membrane was prepared by the reaction of fluoro group of 1-fluoro-2-nitro-4-azidobenzene (FNAB) and hydroxyl group of the cellulose in an alkaline medium. X-ray photoelectron spectroscopy (XPS) of the photoreactive cellulose confirmed the incorporation of FNAB moiety. Azido group of the photoreactive membrane on exposure to UV light transforms into highly reactive nitrene which binds with a protein. The efficacy of the activated membrane was checked by immobilizing glucose oxidase (GOD) onto it in presence of light. Immobilized GOD was found to have improved thermal, pH and storage stability. Photoreactive cellulose membrane was successfully used in enzyme-linked immunosorbent assay (ELISA) technique. The antibody immobilized onto such support by UV irradiation in 30 min showed similar ELISA value than the antibody immobilized onto a polystyrene ELISA plate in 12h incubation at 4 degrees C by conventional method.

A fluorescent glucose biosensor based on immobilized glucose oxidase on bamboo inner shell membrane

A fluorescent glucose biosensor was constructed by immobilizing glucose oxidase on a bamboo inner shell membrane with glutaraldehyde as a cross-linker. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution with a concomitant increase in the fluorescence intensity of an oxygen transducer, tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(Pi) ditetrakis(4-chlorophenyl)borate. The enzyme immobilization, effect of pH, temperature and ionic strength have been studied in detail. The biosensor exhibited repeatable response to a 2.0 mM glucose solution with a relative standard deviation of 3.0% (n = 10). It showed good storage stability and maintained 95% of its initial response after it had been kept at 4 degrees C for 8 months. The biosensor has a linear response range of 0.0-0.6 mM glucose with a detection limit of 58 microM (S/N = 3). Common potential interferants in samples do not pose any significant interference on the response of the glucose biosensor. It was successfully applied to the determination of glucose content in some commercial wines and medical glucose injections.

Enzyme immobilization on poly(ethylene-co-acrylic acid) films studied by quartz crystal microbalance with dissipation monitoring

In this study, we use the quartz crystal microbalance with dissipation monitoring (QCM-D) to study the immobilization of the enzyme horseradish peroxidase (HRP) on poly(ethylene-co-acrylic acid) (PEAA) films. The surface polarity of spin-coated PEAA films was varied by heat treatments in air or in a 30% NaOH aqueous solution leading to COOH-depleted or COOH-enriched surfaces, respectively. Two reaction schemes, direct adsorption and amine coupling, were employed for HRP immobilization on the two surfaces. The shifts in frequency and dissipation, Deltaf and DeltaD, measured by QCM-D and the ratio DeltaD/Deltaf were used to evaluate the binding amount and the conformation of the adsorbed enzyme. It is found that HRP immobilized via covalent linkages forms rigid and little dissipative films. In contrast, directly adsorbed HRP films exhibit a highly dissipative structure. HRP-catalyzed oxidation of the 4-chloro-1-naphthol in the presence of H(2)O(2) was used to characterize the catalytic activity of the HRP films. The results show that the enzymatic activity of the covalently immobilized HRP tends to be higher.

Surface modification and functionalization through the self-assembled monolayer and graft polymerization

The modification of a surface at the molecular level with precise control of the building blocks generates an integrated molecular system. This field has progressed rapidly in recent years through the use of self-assembled monolayer (SAM) interfaces. Recent developments on surface-initiated chemical reactions, functionalization, and graft polymerization on SAM interfaces are emphasized in the present review. A number of surface modifications by grafting are reviewed. The grafting of polyaniline on a glass surface, previously modified with a silane self-assembled monolayer (SAM), is examined in detail for both planar and 3-D systems, such as fibers, nanoparticles, and even polymer patterned surfaces. We also discuss the graft polymerization of water-soluble polymers on the surface of silicon nanoparticles, which generate stable aqueous colloidal solutions and have numerous applications. Finally, we compare and review some surface-modification techniques on the surfaces of polymers, such as two-solvent entrapment, polymer blending, and chemical grafting, which improve their biocompatibility.

Glucose oxidase?magnetite nanoparticle bioconjugate for glucose sensing

Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of magnetite (Fe3O4) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase to the amino-modified nanoparticle surface. Functionalization of the magnetic nanoparticle surface with amino groups greatly increased the amount and activity of the immobilized enzyme compared with immobilization procedures involving physical adsorption. The enzymatic activity of the glucose oxidase-coated magnetic nanoparticles was investigated by monitoring oxygen consumption during the enzymatic oxidation of glucose using a ruthenium phenanthroline fluorescent complex for oxygen sensing. The glucose oxidase-coated magnetite nanoparticles could function as nanometric glucose sensors in glucose solutions of concentrations up to 20 mmol L(-1). Immobilization of glucose oxidase on the nanoparticles also increased the stability of the enzyme. When stored at 4 degrees C the nanoparticle suspensions maintained their bioactivity for up to 3 months.