(Invited) Detection of Uranium Using Plasmonic and SERS Sensors

Abstract

Uranium, a radioactive material with a long half-life, accumulates in the environment in its oxidative form uranyl, which can contaminate soil and water. Importantly, uranyl forms complexes with anions and cations thereby influencing solubility, toxicity, and fate of these heavy metal species. Furthermore, uranyl speciation varies with pH. The resulting complex speciation complicates detection and/or requires significant sample pretreatment. As such, methods that are capable of identifying trace uranyl species in complex samples are needed. Herein, localized surface plasmon resonance spectroscopy (LSPR), Raman spectroscopy, and surface enhanced Raman scattering (SERS) serve as label-free and near real-time methods for identifying uranium species in complex aqueous solutions. A straight-forward protocol for spectral analysis will be shown using Raman spectroscopy and aqueous uranium samples. Raman excitation wavelength, pH, and coordinating ions are systematically varied. The spectral analysis results are rigorously validated using uranyl speciation models. Next, plasmonic nanomaterials are used to enhance the Raman signals for trace detection of low (and high) abundant species. Finally, an approach that promotes the reproducible detection of uranyl using SERS will be shown. All in all, the developed protocol provides an accurate and routine analysis of Raman spectra for uranyl species identification and relative abundance elucidation. These advances are expected to provide a straight-forward approach for uranium species identified using LSPR spectroscopy, Raman spectroscopy, and SERS.