Hongfei Jia

Enzyme-carrying polymeric nanofibers prepared via electrospinning for use as unique biocatalysts.

Improvement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive polystyrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, α‐chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4% (wt/wt), corresponding to over 27.4% monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65% of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous α‐chymotrypsin exhibited a much‐improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart suspended in organic solvents including hexane and isooctane. It appeared that the covalent binding also improved the enzymes stability against structural denaturation, such that the half‐life of the nanofibrous enzyme in methanol was 18‐fold longer than that of the native enzyme.

Highly stable enzyme precipitate coatings and their electrochemical applications.

This paper describes highly stable enzyme precipitate coatings (EPCs) on electrospun polymer nanofibers and carbon nanotubes (CNTs), and their potential applications in the development of highly sensitive biosensors and high-powered biofuel cells. EPCs of glucose oxidase (GOx) were prepared by precipitating GOx molecules in the presence of ammonium sulfate, then cross-linking the precipitated GOx aggregates on covalently attached enzyme molecules on the surface of nanomaterials. EPCs-GOx not only improved enzyme loading, but also retained high enzyme stability. For example, EPC-GOx on CNTs showed a 50 times higher activity per unit weight of CNTs than the conventional approach of covalent attachment, and its initial activity was maintained with negligible loss for 200 days. EPC-GOx on CNTs was entrapped by Nafion to prepare enzyme electrodes for glucose sensors and biofuel cells. The EPC-GOx electrode showed a higher sensitivity and a lower detection limit than an electrode prepared with covalently attached GOx (CA-GOx). The CA-GOx electrode showed an 80% drop in sensitivity after thermal treatment at 50°C for 4 h, while the EPC-GOx electrode maintained its high sensitivity with negligible decrease under the same conditions. The use of EPC-GOx as the anode of a biofuel cell improved the power density, which was also stable even after thermal treatment of the enzyme anode at 50°C. The excellent stability of the EPC-GOx electrode together with its high current output create new potential for the practical applications of enzyme-based glucose sensors and biofuel cells.

Kinetic Limitations of a Bioelectrochemical Electrode Using Carbon Nanotube-Attached Glucose Oxidase for Biofuel Cells

Carbon nanotubes (CNTs) have been used for various bioelectrochemical applications, presumably for substantial improvement in performance. However, often only moderate results observed, with many governing factors have been considered and suggested yet without much systematic evaluation and verification. In this study, CNT‐supported glucose oxidase (CNT–GOx) was examined in the presence of 1,4‐benzoquinone (BQ). The intrinsic Michaelis parameters of the reaction catalyzed by CNT–GOx were found very close to those of native GOx. However, the Nafion entrapment of CNT–GOx for an electrode resulted in a much lower activity due to the limited availability of the embedded enzyme. Interestingly, kinetic studies revealed that the biofuel cell employing such an enzyme electrode only generated a power density equivalent to <40% of the reaction capability of the enzyme on electrode. It appeared to us that factors such as electron and proton transfer resistances can be more overwhelming than the heterogeneous reaction kinetics in limiting the power generation of such biofuel cells. Biotechnol. Bioeng. 2009; 104: 1068–1074.

Enzyme‐enabled responsive surfaces for anti‐contamination materials

Many real-life stains have origins from biological matters including proteins, lipids, and carbohydrates that act as gluing agents binding along with other particulates or microbes to exposed surfaces of automobiles, furniture, and fabrics. Mimicking naturally occurring self-defensive processes, we demonstrate in this work that a solid surface carrying partially exposed enzyme granules protected the surface in situ from contamination by biological stains and fingerprints. Attributed to the activities of enzymes which can be made compatible with a wide range of materials, such anti-contamination and self-cleaning functionalities are highly selective and efficient toward sticky chemicals. This observation promises a new mechanism in developing smart materials with desired anti-microbial, self-reporting, self-cleaning, or self-healing functions.

Poly(ethylene glycol) conjugated enzyme with enhanced hydrophobic compatibility for self-cleaning coatings

Enzyme-based smart materials constitute a rapidly growing group of functional materials. Often the natively evolved enzymes are not compatible with hydrophobic synthetic materials, thus significantly limiting the performance of enzymes. This work investigates the use of a polyethylene glycol (PEG)-conjugated detergent enzyme for self-cleaning coatings. As a result, PEG conjugated α-amylase demonstrated a much more homogeneous distribution in polyurethane coatings than the parent native enzyme as detected by both fluorescent microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (SEM-EDX). Additionally, the conjugated enzyme showed enhanced retention in the coating and much improved thermal stability with a halflife of 20 days detected at 80 °C and over 350 days under room temperature. Such coating-incorporated enzyme afforded interesting self-cleaning functionality against starch-based stains as examined through a slipping drop test.

Enzymic Thin Film Coatings for Bioactive Materials

Bioactive materials have been explored for a broad range of applications including biocatalysts, biosensors, antifouling membranes and other functional and smart materials. We report herein a unique method for preparation of bioactive materials through a spin coating process. Specifically, we investigated the preparation of protease Subtilisin Carlsberg‐coated plastic films and examined their activities for hydrolysis of chicken egg albumin (CEA). The process generated enzymic coatings with a typical loading of 13 μg/cm2, retaining 46% of the enzyme activity for hydrolysis of CEA in aqueous solutions. Interestingly, the surface‐coated protease thin film not only catalyzed the hydrolysis of CEA in aqueous solutions, but also showed good activity for solid‐state CEA that was coated on top of the enzyme thin film.

Biocatalytic generation of power from biofuels: biofuel cells.

Biofuel cells refer to a class of fuel cells that apply biocatalysts to power generation. Early observations of electricity generation from glucose and other organic compounds in the presence of microbes dates back to the early 1900s, while the growing interest in searching for bio-based alternative energy resources has spurred a new wave of biofuel cell development in recent years. Compared with metal catalyst-based traditional fuel cells, biofuel cells involve very different reaction routes with water as an essential reaction medium, therefore affording a mild operation condition, the use of biofuels and the application of newly emerged materials such as carbon nanotubes. Current research in this area has mostly focused on realizing the best potential of such advantages, and the overall performance of biofuel cells are steadily improving. This paper reviews the evolution and development of biofuels and biocatalysts for biofuel cells gleaned from recent publications, and presents an overview and discussion on factors limiting the power-generation efficiency of biofuel cells.

Power-Generation from Biorenewable Resources: Biocatalysis in Biofuel Cells

Publisher Summary This chapter examines the function of and challenges for biocatalysis in biofuel cells. Compared with chemical fuel cells, biofuel cells afford more fuel options, bio-compatibility, and mild operation conditions. Although the power density of biofuel cells is usually 2−3 orders of magnitude lower than that of chemical fuel cells, they are attractive for special applications such as implantable devices, sensors, drug delivery, microchips, and portable power supplies. Microbial biofuel cells also have great potential in digesting organic wastes and biomass for power generation. Exciting technical advances in the field of biofuel cells have recently emerged. Compared to noble metal-catalyzed fuel cells, biofuel cells offer ambient operation conditions and can eventually be cheaper as the production cost of the key biocatalysts continues to drop as a result of developments in genetic engineering. Biocatalysts are capable of catalyzing the oxidation of most of the conventional fuels. They are also efficient in oxidizing more complicated chemicals such as carbohydrates and various organic wastes for electricity generation. Biofuel cells afford a much broader range of fuel options. Hydrogen and methanol are the most popular fuels examined for general-purpose fuel cells. Other chemicals such as ammonia, hydrocarbons, ethanol, propanol, ethylene glycol, glycerol, cyclic alcohols, formic acid, and formate have also been investigated.