Optical and Microcantilever-Based Sensors for Real-Time In Situ Characterization of High-Level Waste

Fundamental research is being conducted to develop sensors for cesium and strontium that can be used in real-time to characterize highlevel waste (HLW) process streams. Two fundamentally different approaches are being pursued, having in common the dependence on highly selective molecular recognition agents. In one approach, an array of chemically selective sensors with sensitive fluorescent probes to signal the presence of the constituent of interest will be coupled to fiber optics for remote analytical applications. The second approach employs sensitive microcantilever sensors that have been demonstrated to have unprecedented sensitivity in solution for Cs and CrO4. Selectivity in microcantilever-based sensors is achieved by modifying the surface of a gold-coated cantilever with a monolayer coating of an alkanethiol derivative of the molecular recognition agent. The approaches are complementary since fiber optic sensors can be deployed in the highly alkaline environment of HLW, but a method of immobilizing a fluorescent molecular recognition agent in a polymer film or bead on the surface of the optical fiber has yet to be demonstrated. The microcantilever-based sensors function by converting molecular complexation into surface stress, and they have been demonstrated to have the requisite sensitivity. However, a method of protecting Si or SiN microcantilever sensors in the highly alkaline environment of HLW while maintaining high selectivity remains to be demonstrated. The fundamental technology for fiber optic and cantilever sensors has been developed by our collaborators David Walt and Thomas Thundat, respectively, and the goal of this project is to adapt molecular recognition chemistry to the methods already being employed. To develop molecular recognition agents for Cs and Sr(II) with rapidly established equilibria needed for real-time analysis, we will focus on calixarene-crown ethers as a platform. Sensors for alkali metal ions, hydroxide, and temperature will be part of the array of sensor elements that will be demonstrated in this program for both the cantilever and fiber optic sensor approaches.