Understanding the Enhanced Kinetics of Enzyme-Quantum Dot Constructs
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Understanding the Enhanced Kinetics of Enzyme-Quantum Dot Constructs Joyce Breger1,4, Scott Walper1, Mario Ancona3, Michael Stewart2, Eunkeu Oh2, Kimihiro Susumu2, and Igor Medintz1 1 Center for Bio/Molecular Science and Engineering, Code 6900, 2Optical Sciences Division, Code 5600, 3Electronic Science and Technology Division, Code 6800, U.S. Naval Research Laboratory, Washington, DC 20375, 4American Society for Engineering Education, 1818 N Street NW, Suite 600 Washington, DC 20036 ABSTRACT Bio-inspired, hybrid architectures employing quantum dots (QDs) appended with functionally active biomolecules such as enzymes have the potential to be utilized in numerous applications. Some examples include nanosensors for medical diagnostics, chemical/biological threat detection, as well as “bio-factories” in complex industrial synthetic processes. The main advantage in creating these nanofactories is increased rates in catalysis and efficiency when enzymes are associated with nanoscaffolds, as shown in numerous studies. However, the mechanism for this enhancement remains elusive. Gaining a fundamental, mechanistic understanding of enzyme-QD nanostructures is important in the development of numerous device applications. In this work, we review an array of enzymes attached to QDs and generate a hypothesis in regards to the unique architecture of the enzyme-nanoparticle (NP) construct that leads to increases in catalysis. We highlight work with phosphotiresterase (PTE) attached to two distinctly sized QDs in neutralizing a simulant nerve agent, as well as in other enzyme systems. INTRODUCTION Enzymes play an important role in a myriad of industrial and medicinal purposes. In industrial processes, enzymes can be quite costly and immobilizing them for retention can decrease their activity. Therefore, research interests have focused on ways to engineer enzyme constructs that are retainable, robust, capable of increased catalysis, and capable of performing multiple steps in synthetic pathways. NPs such as QDs have a high surface to volume ratio, can be made stable in aqueous environments across a broad pH range, and allow for the attachment of numerous unique moieties to the surface while still maintaining the QD’s superior optical properties. These optical characteristics include high quantum yield, broad absorption spectra with large molar extinction coefficients, and narrow, symmetric emission spectra which all can be exploited for rapid, optical measurement. By attaching enzymes or other biorecognition moieties to the surface of NPs, these designer nanofactories can be exploited in a number of applications including energy conversion, bioelectronics, drug delivery and theranostics.[1, 2] A number of hypothesis have been set forth to explain the enhanced kinetics of enzymes associated with a variety of NPs.[3] Here, we present two different formats for studying enzyme kinetics when associated with QDs and our resulting thoughts as to why catalysis improves in the unique configuration. EXPERIMENT Core/shell CdSe/ZnS QDs with emis
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