Enzyme immobilization in reactive nanoparticles produced by inverse microemulsion polymerization

Porphyrin-nanosensor conjugates. New tools for the measurement of intracellular response to reactive oxygen species

Reactive oxygen species (ROS) have for some time been implicated in the onset and progression of medical conditions including cancer, ageing, heart disease and Alzheimer's disease. Recently, it has been postulated that ROS play a much more subtle role in intracellular signalling mechanisms as second messengers. Given the importance of these species in influencing cellular processes, it is surprising that tools for studying intracellular levels of ROS are extremely limited and devices for studying the cells' response to internally generated ROS are virtually non-existent. In order to study the response of cells to intracellular ROS we have designed a nano-scale device that can both generate ROS and simultaneously monitor the cells' reaction as a function of changes in the important signalling ion, calcium. Here we report the synthesis, characterisation, and calibration of a new ROS nano-probe and demonstrate its ability to detect cellular response to elevated levels of intracellular ROS.

Multi-scale features in recent development of enzymic biocatalyst systems

Functional relation among elements of different size scales in a system is probably a main challenge across the areas of the science of engineering ever since their emergence. Multi-scale time and size correlation for description and prediction of complex systems, however, has been systematically examined only recently with the aid of new computational tools. In the pursuit of efficient and sustainable chemical processing technologies, people have seen a growing emphasis on synthetic biotechnology in recent R&D efforts. In particular, industrial enzyme technologies are attracting enormous attention. Having been traditionally developed for food and detergent applications, industrial enzyme technologies are being re-examined and tested to their limits to keep abreast of the challenges in drug, biochemical, and the emerging biorenewable energy industries. Toward that, enzymes are required to function in non-conventional conditions, such as organic solvents, extreme pH, and temperatures; they also have to compete against alternative chemical technologies in terms of costs and efficiency. Accordingly, enzymic biocatalyst systems are being tackled dynamically at all size levels through efforts ranging from molecular level protein engineering and modification, nanoscale structure fabrication, and microenvironment manipulation to the construction of microchip devices and macroscopic industrial bioreactors and devices. These efforts are probably still on a case-to-case trial basis without much consideration of cross-scale correlations. Discovering, understanding, and controlling of the common features that relate functions of biocatalysts at different size scales may eventually be realized in future.

Phosphate sensing by fluorescent reporter proteins embedded in polyacrylamide nanoparticles

Phosphate sensors were developed by embedding fluorescent reporter proteins (FLIPPi) in polyacrylamide nanoparticles with diameters from 40 to 120 nm. The sensor activity and protein loading efficiency varied according to nanoparticle composition, that is, the total monomer content (% T) and the cross-linker content (% C). Nanoparticles with 28% T and 20% C were considered optimal as a result of relatively high loading efficiency (50.6%) as well as high protein activity (50%). The experimental results prove that the cross-linked polyacrylamide matrix could protect FLIPPi from degradation by soluble proteases to some extent. This nanoparticle embedding method provides a novel promising tool for in vivo metabolite studies. It also demonstrates a universal method for embedding different fragile bioactive elements, such as antibodies, genes, enzymes, and other functional proteins, in nanoparticles for, for example, sensing, biological catalysis, and gene delivery.

Lipolytic Enzymes with Improved Activity and Selectivity upon Adsorption on Polymeric Nanoparticles

Nanostructured polystyrene (PS) and polymethylmethacrylate (PMMA) were used as carriers for the preparation of bioconjugates with lipolytic enzymes, such as Candida rugosa lipase (CRL) and Pseudomonas cepacia lipase (PCL). Simple addition of the lipase solution to the polymeric nanoparticles under protein-friendly conditions (pH 7.6) led to the formation of polymer-enzyme bioconjugates. Energy filtered-transmission electron microscopy (EF-TEM) performed on immuno-gold labeled samples revealed that the enzyme preferentially binds to the polymer nanoparticles and that the binding does not affect the nanostructured features of the carriers. The studies performed on the activity of the bioconjugates pointed out that the lipases adsorbed onto polymeric nanoparticles show an improved performance in terms of activity and selectivity with respect to those shown by lipases adsorbed on the same non-nanostructured carriers. The residual activities of CRL and PCL immobilized on nanostructured PMMA and PS reached 60% and 74%, respectively. Moreover, we found that enantioselectivity and pH and thermal stability increase upon immobilization. These results highlight the fact that new protein conformers with improved enantioselectivity stabilized after adsorption on nanoparticles are obtained. On the basis of the chemical structures of the selected polymers and the slopes of the adsorption isotherms, a hydrophobic binding model for lipase/nanostructured polymers is suggested.

Nanoscale biocatalyst systems

Since the large-scale application of immobilized enzymes in the 1960s, substantial research efforts have aimed to optimize the structure of carrier materials for better catalytic efficiency. In this regard, nanoscale materials provide the upper limits in balancing the key factors that determine the efficiency of biocatalysts, including surface area, mass transfer resistance, and effective enzyme loading. Various nanomaterials, such as nanoparticles, nanofibers, nanotubes and nanoporous matrices, have shown potential for revolutionizing the preparation and use of biocatalysts. Beyond their high surface area:volume ratios, nanoscale biocatalyst systems exhibit unique behaviors that distinguish them from traditional immobilized systems. The Brownian motion of nanoparticles, confining effect of nanopores and self-assembling behaviors of discrete nanostructures are providing exciting opportunities in this field. The development of catalyst systems that are highly stable and efficient, capable of self-targeting or that function as molecular machines to catalyze multiple reactions is rapidly reshaping our vision of biocatalysts.

Unusually large acrylamide induced effect on the droplet size in AOT/Brij30 water-in-oil microemulsions

Droplet microemulsions are widely used as templates for controlled synthesis of nanometer sized polymer gel beads for use as, e.g., nanobiosensors. Here we examine water-in-oil microemulsions typically used for preparation of sensors. The cores of the microemulsion droplets are constituted by an aqueous component consisting of water, reagent monomer mixture, buffer salts, and the relevant dyes and/or enzymes. The cores are encapsulated by a mixture of the surfactants Brij30 and AOT and the resulting microemulsion droplets are suspended in a continuous hexane phase. The size of the final polymer particles may be of great importance for the applications of the sensors. Our initial working hypothesis was that the size of the droplet cores and therefore the size of the synthesized polymer gel beads could be controlled by the surfactant-to-water ratio of the template microemulsion. In the present work we have tested this hypothesis and investigated how the monomers and the ratio between the two surfactants affect the size of the microemulsion droplets and the microemulsion domain. We find that the monomers in water have a profound effect on the microemulsion domain as well as on the size of the microemulsion droplets. The relation between microemulsion composition and droplet size is in this case more complicated than assumed in standard descriptions of microemulsions [R. Strey, Colloid Polym. Sci. 272 (1994) 1005-1019; I. Danielsson, B. Lindman, Colloids Surf. 3 (1981) 391-392; Y. Chevalier, T. Zemb, Rep. Progr. Phys. 53 (1990) 279-371].

Composite Magnetic Particles as Carriers for Laccase fromTrametes versicolor

In this paper we report a study of laccase immobilisation on different kinds of carrier particles. The immobilisation of enzyme on the particle surface with respect to the immobilisation efficiency and the properties of the immobilised enzymes is discussed. The immobilisation of laccase on polystyrene particles bearing reactive beta-diketone groups is characterised by high efficiency, but grafting of the enzyme increases the stability of the colloidal system, which makes the separation/purification procedure difficult. Additionally, the extreme colloidal stability of the immobilisates hinders the application of such particles with immobilised enzymes in some applications where the recycling of the enzyme should be performed. It has been found that hybrid PS-AAEM particles equipped with maghemite show similar immobilisation efficiency to that of their analogues without maghemite and can additionally be manipulated in magnetic fields. The activity of the immobilised laccase is much higher in the pH region 5-7 and the temperature range 50-70 degrees C as compared with that of the free enzyme. Immobilised enzymes also exhibit much better storage stability.

Challenges in biocatalysis for enzyme-based biofuel cells

Enzyme-based biofuel cells are attracting attention rapidly partially due to the promising advances reported recently. However, there are issues to be addressed before biofuel cells become competitive in practical applications. Two critical issues are short lifetime and poor power density, both of which are related to enzyme stability, electron transfer rate, and enzyme loading. Recent progress in nanobiocatalysis opens the possibility to improve in these aspects. Many nano-structured materials, such as mesoporous media, nanoparticles, nanofibers, and nanotubes, have been demonstrated as efficient hosts of enzyme immobilization. It is evident that, when nanostructure of conductive materials are used, the large surface area of these nanomaterials can increase the enzyme loading and facilitate reaction kinetics, and thus improving the power density of biofuel cells. In addition, research efforts have also been made to improve the activity and stability of immobilized enzymes by using nanostructures. It appears to be reasonable to us to expect that progress in nanostuctured biocatalysts will play a critical role in overcoming the major obstacles in the development of powerful biofuel cells.

Enabling multienzyme biocatalysis using nanoporous materials

Multistep reactions catalyzed by a covalently immobilized enzyme-cofactor-enzyme system were achieved. Lactate dehydrogenase (LDH), glucose dehydrogenase (GDH), and cofactor NADH were incorporated into two porous silica glass supports. One of the glass supports had pores of 30 nm in diameter, while the other was of 100-nm pore size. Effective shuttling of the covalently bound NADH between LDH and GDH was achieved, such that regeneration cycles of NADH/NAD(+) were observed. The glass of 30-nm pore size afforded enzyme activities that were about twice those observed for the glass of 100-nm pore size, indicating the former provided better enzyme-cofactor integration. The effect of the size of spacers was also examined. The use of longer spacers increased the reaction rates by approximately 18 times as compared to those achieved with glutaraldehyde linkage. It appeared that the concave configuration of the nanopores played an important role in enabling the multistep reactions. The same multienzyme system immobilized on nonporous polystyrene particles of 500-nm diameter was only approximately 2% active as the glass-supported system. It is believed that the nanoporous structure of the glass supports enhances the molecular interactions among the immobilized enzymes and cofactor, thus improving the catalytic efficiency of the system.

Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobility

Nanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes-Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility-activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110-1000 nm were prepared. A model enzyme, alpha-chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle-attached enzyme. Compared to K(M), k(cat) appeared to be less sensitive to particle size and viscosity.

Water-swellable polyelectrolyte microgels polymerized in an inverse microemulsion using a nonionic surfactant

A series of poly(dimethylacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) microgels slightly crosslinked by methylene-bis-acrylamide (MBA) were polymerized in a novel inverse microemulsion polymerization (IMEP) system. To determine a suitable composition of the IMEP system, the phase diagram of a pseudoternary system was made. The pseudoternary polymerization system consisted of n-hexane, a nonionic surfactant (polyoxyethylene oleyl ether, C18En), and an aqueous monomer solution. Polymerization was performed in a single-phase reversed micelle solution. The reversed micelles were about 50 nm in diameter, as determined by FF-TEM. The viscometric characteristics of the polymers extracted from the IMEP system were studied in 3 mM sodium chloride aqueous solution. The intrinsic viscosity values for the noncrosslinked and crosslinked (0.1 mol% MBA was incorporated) samples were 25 and 7.4 dl/g, respectively. The overlap concentration (c*) of crosslinked polymer microgel occurred at c[eta] = 1 in the solvent. When the volume fraction (phi) of the microgel was 0.7, the value of the apparent yield stress of the microgel solution was observed. These results show that the microgel has a significant thickening effect above c* due to friction between the microgel particles. It is assumed that the microgels polymerized in a confined space retain the shape or size of the nanosized reactor with a diameter on the order of 50 nm.

Development and characterization of solid lipid nanoparticles loaded with magnetite

This paper describes the preparation of colloidal lipid particles containing magnetite from warm emulsions. A two step method was used to obtain the nanoparticles: (i) formulation of a transparent phase by heating a O/W emulsion (aqueous surfactant solution melted with a lipid phase, containing the ethyl oleate and soybean lecithin) in which modified lipophilic magnetite is incorporated, and (ii) preparation of the nanoparticles by dispersing the warm transparent phase in cold water (7 degrees C) under mechanical stirring. The latter method gives spherical nanoparticles of a mean size of 62 nm measured by Photon Correlation Spectroscopy and Transmission Electronic Microscopy. The magnetite entrapment efficiency was determined by use of a magnetophoretic sedimentation method.

Latex particles with thermo-flocculation and magnetic properties for immobilization of alpha-chymotrypsin

Core-shell-type latex particles composed of styrene, N-isopropylacrylamide (NIPAAm), and N-acryloxysuccinimide (NAS) were synthesized by surfactant-free emulsion polymerization. The latex particles show thermo-flocculation behavior due to the presence of temperature-sensitive monomer NIPAAm and could be used for immobilization of alpha-chymotrypsin through covalent bonding with the reactive ester groups of NAS. Enzyme recycle could be accomplished in this immobilized enzyme system by sedimentation of the thermo-flocculated latex particles in 20 min at 30 degrees C by raising the salt (NaCl) concentration to 0.5 M. To further enhance the sedimentation rate, ultrafine magnetite particles were prepared and included during polymerization to produce magnetic temperature-sensitive latex particles (MTLP), which could be recovered 6 times faster after thermo-flocculation by applying a low magnetic field. However, a higher salt concentration was necessary to flocculate the MTLP under the same condition as a result of its increased surface hydrophilicity, which originates from different polymerization conditions and the incorporation of magnetite. The immobilized enzyme shows high activity even against macromolecular substrates (hemoglobin and casein) owing to limited diffusion resistance, with full activity retention for nonmagnetic latex but one-half reduction in activity if the magnetic property was introduced. Optimal enzyme immobilization pH and enzyme loading were determined, and properties of the immobilized enzyme were characterized. The immobilized enzyme was used in 10 repeated batch hydrolyses of casein with successive flocculation/dispersion cycles and showed less than 15% activity decrease at the end. Overall, introducing the magnetic property to the latex could effectively enhance the solid-liquid separation rate after thermo-flocculation and maintain enzyme activity after repeated use but adversely influence the activity of the immobilized enzyme.