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AbstractThis article is based on the MRS Medal presentation given by Delia J. Milliron at the 2023 MRS Fall Meeting & Exhibit in Boston, Mass. Milliron is cited “for the development of optically tunable metal oxide nanomaterials for applications such as energy-saving electrochromic windows.”Doped metal oxide nanocrystals (NCs) provide a highly tunable platform for localized surface plasmon resonance (LSPR) in the near- to mid-IR. This tunability can be achieved synthetically, through the size, shape, and composition of the NCs, or post-synthetically through reversible redox reactions, enabling a host of emerging applications. While the broad strokes of this tunability have been understood for a decade, over the last few years, there has been tremendous progress in understanding the relationships between the electronic structure, defect chemistry, and synthetic and post-synthetic tunability of metal oxide NCs. This article aims to provide an up-to-date picture of the optical tunability of metal oxide NC LSPR, in particular focusing on recent insights into how the NC electronic structure plays a role in LSPR tunability. Graphical abstract 

Abstract Extracellular electron transfer (EET) is a critical form of microbial metabolism that enables respiration on a variety of inorganic substrates, including metal oxides. However, quantifying current generated by electroactive bacteria has been predominately limited to biofilms formed on electrodes. To address this, we developed a platform for quantifying EET flux from cell suspensions using aqueous dispersions of infrared plasmonic tin‐doped indium oxide nanocrystals. Tracking the change in optical extinction during electron transfer enabled quantification of current generated by planktonicShewanella oneidensiscultures. Using this method, we differentiated between starved and actively respiring cells, cells of varying genotype, and cells engineered to differentially express a key EET gene using an inducible genetic circuit. Overall, our results validate the utility of colloidally stable plasmonic metal oxide nanocrystals as quantitative biosensors in aqueous environments and contribute to a fundamental understanding of planktonicS. oneidensiselectrophysiology using simplein situspectroscopy.