Nanobiocatalysis for Bio-Based Energy and Products

Ping Wang
Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA

Jungbae Kim
Pacific Northwest National Laboratory, Richland, WA 99352, USA

Darrell Reneker
Department of Polymer Science, The University of Akron, Akron, OH 44325, USA

Xueyan Zhao
Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325, USA

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     Last modified: February 20, 2006

Abstract
The beginning of the 21st century is experiencing a new wave of technology revolution led by the blooming advances in life science and nanotechnology. Decoding of genes and proteins with respect to their structures and functions is affording us unprecedented power in understanding, manipulating and controlling biological systems; at the same time, nanoscale science and engineering, which have garnered interests of scientists and engineers across almost all the disciplines of science, are rapidly reshaping our vision and practice in areas ranging from hydrogen storage, fuel cells, various super-strong and smart materials to microchips, reactive systems, controlled drug release and biosensors.

The driving force comes from two aspects: one is the needs in advancing human society, and the other the concerns of environmental quality. The global population is rapidly approaching 10 billion. The needs in searching alternative energy and materials sources to improve our living and environmental qualities are becoming increasingly lucid and urgent. For alternative energy sources, researches for biofuel cells and bio-based fuels including biodiesel and ethanol are gaining substantial momentum. For materials, biorenewable alternatives to petroleum-based products and technologies are becoming a worldwide strategy.

Our research has been actively involved in this stream of development with unique contributions by bringing together nanotechnology, materials engineering and enzymology. Our goal is to develop enzyme-based nanostructure bioactive systems to replace living cells. Our interests in this are based on two considerations. First is the concern of environmental impacts brought up by genetically engineered microbes. The use enzyme system will avoid that concern. Second is efficiency. Enzymes systems will afford us much better efficiency in terms of speeds of reactions and flexibility in designing and composing reach pathways. This paper will particularly review our resent work in the following two areas:

1. Nanobiocatalysis for multiple-step bioconversions:

The combination of the features of nanostructures with the highly efficient and selective activities of enzymes is fostering a new phase in industrial biotechnology. We believe we are still at the infant stage in exploring the merits and potentials of nanobiotechnology for bioprocessing (Kim et al. 2006). On the fundamental side, we first noticed that the Brownian motion of nanoparticles affords particle-attached enzymes unique mobility and thus impact the reaction kinetics of enzymatic reactions (Jia et al. 2003). On the technological side, we first demonstrated that nanopores are extremely powerful in extending the lifetimes of enzymes (Wang et al. 2001) and nanofibers can make enzymes highly active while provide great easiness in materials handling (Jia et al. 2002).

One area we are working on is the construction of multi enzyme systems for bioconversion -- nano-structured artificial cells (El-Zahab et al. 2004). We particularly explore the potentials of multiscale design that combines both nanoscale and microscale mechanisms for biocatalysis involving multiple enzymes and cofactor(s). Nanoparticle-based multiple enzymes and cofactor will be encapsulated in microcapsules with membranes possessing pores that are comparable to the size of nanoparticles. While the nanoparticles are the “motors” that drive the complex reactions inside the capsules, the nano-sized pores of the microspheres allow efficient molecular diffusion for rapid reactant supply and product removal. This approach will also enable a pathway engineering by applying enzymes isolated from alternative biological sources for better efficiency or rational design of pathways, which is difficult, if not impossible, to achieve with living cells. Using such a technology, we have successfully achieved the synthesis of methanol and lactic acid from CO2.


2. Biofuel Cells:

The concept of biofuel cells has been known for almost one century since the first microbial biofuel cell was demonstrated in 1912. In the 1960s, NASA showed a keen interest in power generation from human wastes on the space shuttles. That inspired a wide range of R&D efforts for biofuel cells. Biofuel cells generating power from various substances, such as urea and methane, were built and tested during that period. The first enzyme-based biofuel cell was reported in 1964 using glucose oxidase (GOx) as the anodic catalyst and glucose as the “fuel”. Exciting advances have been made since that time; still, the performance of biofuel cells, in terms of power density, lifetime, and operational stability, falls far below that of chemical fuel cells.

Nevertheless, recent research showed a renewed interest in biofuel cells. In particular, enzyme-based biofuel cells are greatly promising in developing portable power generation devices for special applications such as implantable devices, sensors, drug delivery, micro-chips, portable computers, etc. To satisfy the needs for these special applications, the biocatalysts are being challenged for their extreme performance.

Recent advances in nanoscale science and technology provides new opportunities in achieving highly efficient biofuel cells (Kim et al. 2006). Synergizing with materials chemistry, various nanostructures have manifested their great potential in stabilizing and activating enzymes with performances well beyond the scope of traditional immobilization technologies. Especially, the large surface area, which these nanostructures provide for the attachment of enzymes, will increase the enzyme loading and possibly improve the power density of biofuel cells. In that sense, nanoscale engineering of the biocatalysts appears to be critical in the next stage advancement of biofuel cells. In this presentation, the potentials of nano-structured biocatalysts are examined to explore the opportunities for developing the next generation of biofuel cells. Focus is particularly on our recent work in developing hybrid materials of enzymes and carbon nanotubes and nanofibers for biofuel cells with improved power density and lifetime. Impact of the nanostructures on the reaction kinetics of the biocatalytic processes, and their impact on the performance of the fuel cells will be discussed.

Related References:

El-Zahab, B., H. Jia and P. Wang (2004). "Enabling Multienzyme Biocatalysis Using Nanoporous Materials." Biotechnol. Bioeng. 87(2): 178-183.
Jia, H., G. Zhu, B. Vugrinovich, W. Kataphinan, D. H. Reneker and P. Wang (2002). "Enzyme-Carrying Polymeric Nanofibers Prepared via Electrospinning for Use as Unique Biocatalysts." Biotechnol. Progr. 18(5): 1027-1032.
Jia, H., G. Zhu and P. Wang (2003). "Catalytic Behaviors of Enzymes Attached to Nanoparticles: The Effect of Particle Mobility." Biotechnol. Bioeng. 84(4): 406-414.
Kim, J., J. W. Grate and P. Wang (2006). "Nanostructures for enzymes stabilization." Chem. Eng. Sci. 61(3): 1017-1026.
Kim, J., H. Jia and P. Wang (2006). "Challenges in Biocatalysis for Biofuel Cells." Biotechnol. Adv. Publication available online.
Wang, P., S. Dai, S. D. Waezsada, A. Tsao and B. H. Davison (2001). "Enzyme stabilization by covalent binding in nanoporous sol-gel glass for nonaqueous biocatalysis." Biotechnol. Bioeng. 74(3): 249-255.