PI: S. Scott Saavedra Institution: University of Arizona Proposal Number: 0428885
Intellectual Merit: This project focuses on the development of new optical/electrochemical, channel waveguide-based sensing platforms which respond to analytes that interact with chemically-gated ion channel receptors (KATP channels in the first phases of this research) reconstituted into a planar supported (poly)lipid bilayer (PSLB). The proteo-lipid membrane transducer will be tethered to a self-assembled, conducting polymer (SA-CP) film, co-polymerized with low concentrations of ion-sensitive fluorescent dyes, supported on a electroactive channel integrated optical waveguide (EA-CH-IOW). The sensor platform will transduce the binding of analytes into both electrochemical (potentiometric/impedance) and optical (absorbance/fluorescence) responses to provide a mechanistic understanding of sensor responses and allow optimization of the transducer layers. Backcoupled (near-field) waveguide detection of the fluorescence response is one of the unique features of this proposed sensor, and its development will enable a significant new chip-like sensor technology, with integrated, in-plane excitation and detection. Specific challenges and milestones for include: a) Multilayer channel waveguides must be developed with dual optical confinement geometries that provide both strong evanescent fields for excitation of ion-sensitive chromophores and a mode structure that enhances waveguide back-coupling of their luminescence response. This should lead to sensors with optical components seamlessly integrated with biomimetic sensing materials, which are easy to make, deploy, and integrate into optical communications systems. b) The upper layer of the waveguide will be electroactive, an essential feature of our mechanistic studies, where absorbance and luminescence responses are tracked simultaneously with potentiometric/impedance responses. The creation of the EA-CH-IOW requires optimizing deposition technologies, and solving material compatibility issues to integrate them with "soft" transducer layers. c) An ultrathin, hydrophilic CP film, composed of a functionalized (poly)thiophene and a (poly)counter-ion, will be self-assembled on the waveguide surface. The SA-CP layer will function as a water-swollen "cushion" for the PSLB with embedded ion channels, to create the proper environment for electrochemical transduction of changes in transmembrane ion flux. Ultra-sensitive spectral detection modalities will be facilitated by co-polymerization of the (poly)thiophene layer with crown-ether-modified dyes that exhibit significant changes in their luminescence properties upon metal ion binding. Self-assembly will be used to confine these dyes near the waveguide/CP interface, which is critical to the realization of back-coupled fluorescence detection modalities. d) New polymerizable lipid technologies, which produce stable, conformal lipid bilayers, will be used to reconstitute transmembrane K+-channels (prototypes for more complex ligand-gated channels), creating bioactive transducer layers that combine the stability of a cross-linked polymer with the biocompatibility of a lipid membrane. Demonstration of ligand-gated, ion transport through ITO/CP-supported PSLBs will open the way for broad implementation of sensors based on biomimetic poly(lipid) membrane chemistries. Broader Impact: In addition to the cross-disciplinary training provided for graduate and undergraduate students and postdoctoral fellows at the University of Arizona, many of whom are members of groups under-represented in science, several Education and Outreach activities are envisioned for this effort, including: i) Development of a new interaction with Yavapai College (Prescott, Arizona), providing research opportunities for some of their second year students, in addition to research opportunities for undergraduate students at Arizona; ii) Development of a new web-based curricular module on ATR waveguide technologies, integrated into the EHRDO activities of our NSF Science and Technology Center - Materials and Devices for Information Technology (University of Washington, lead institution).
