Recent advances in nanofabrication have enabled construction of materials with unique photophysical properties, such as quantum dots and metal nanoparticles/nanoclusters. Such materials are particularly attractive for use as elements in biosensors, which can find application in important areas from medicine to homeland security. In particular, materials exhibiting high optical stability can enable long-term monitoring; materials with relatively long-range nanoscale energy transfer interactions are attractive for potential integration into a broad family of biosensing formats including those relying on large proteins or supramolecular assemblies. To date, however, the understanding of energy transfer between such nanomaterials is incomplete. Therefore, developing and exploiting these interactions for technological purposes such as biosensing hinges upon more thorough investigation of the underlying phenomena.
Furthermore, many biochemical assays, particularly those relying on competition or displacement, are designed simply for solution-phase analyses, functioning only as single-shot determinations. Proper encapsulation of these reagents can enable the reversible, repeatable use of these systems and make them suitable for continuous measurements as is often essential for medical and environmental monitoring. We propose to perform comprehensive studies to elucidate the distance-dependent behavior of nanoscale energy transfer between quantum dots and gold nanoparticles/nanoclusters. Our two primary objectives involve: (1) Discovering fundamental size and distance effects on the photophysics of energy transfer from semiconductor quantum dots to metal nanoparticles/nanoclusters; (2) Converting existing encapsulated energy transfer assays using organic dyes into photostable systems using nanomaterials.
These objectives will be accomplished by a series of studies progressing from investigations of fundamental interactions between different donors and acceptors at defined distances, to integration of materials into an existing assay for glucose, and finally to an encapsulated, reversible sensing system of protein-ligand reagents trapped within a semipermeable microcapsule. Successful completion of these objectives will prove the advantages of the nanomaterial donor-acceptor system via enhanced photostability and sensitivity as well as rapid reversibility of the encapsulated model assay. This work will lay the foundation for development of a new class of biosensors with enhanced sensitivity, longevity, and potential for continuous monitoring.
Intellectual Merit. Our work will establish the feasibility of using nanoscale energy transfer between quantum dots and gold nanoparticles/nanoclusters to engineer sensing elements for in vitro analysis and in vivo monitoring, using an existing glucose assay as a model system. To accomplish this goal, an integrative theoretical and experimental approach has been adopted: we will develop models for multimolecular affinity interactions with models of Förster and nanoscale energy transfer from first principles, match these with experimental observations, and extract values for relevant photophysical parameters to enable a priori design of encapsulated biosensor assays with optimized sensitivity and response range. These scientific and engineering challenges will address key issues in expanding the knowledge base available to exploit the unique properties of nanoscale materials for technologically important uses in the chemical, biotechnology, environmental, defense, and medical device industries.
Broader Impacts. The knowledge uncovered regarding nanoscale photophysics and the application of nanomaterial energy transfer to biosensing extends beyond the limited applications to be studied in the project. The ultimate goal of this work is to move previous discoveries and observations from interesting science to engineering practice, and disseminate the resulting biosensor design rules for widespread use. The comprehensive, general theory and experimental approach developed will be applicable to other nanomaterial combinations, enabling straightforward characterization of new materials, and will also be useful as a design and selection tool to establish expected performance limits for existing donor-acceptor combinations, as well as their suitability to specific assay formats. The experimental and theoretical framework of this project is also well-suited for integration with the PIs? current teaching and outreach activities, which include courses, conference workshops, and virtual labs for K-12 education. The research results will be disseminated through the typical routes of publication in scholarly journals and presentation at professional meetings, and will also form the core content of Internet-based virtual labs.
