NER: Exploratory Research on Developing a Nanoscale Sensing Device for Measuring the Supply of Iron to Eukaryotic Phytoplankton in Natural Seawater

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This proposal was received in response to NSE, NSF-0019.The long delay in recognizing the potentially key role of Fe in coastal marine systems has been in large part because of the complexity of microbial:Fe interactions in seawater. There still is no analytical method for determining biologically available Fe for either prokaryotic or eukaryotic phytoplankton. However, there is evidence that Fe availability to eukaryotic phytoplankton can be regulated by additions of the fungal siderophore desferrioxamine B (DFB) to coastal waters. The DFB-Fe complex not only is unavailable for uptake at significant rates, but also outcompetes the natural organic ligand classes in seawater for Fe. Measurement of DFB-Fe concentrations in a titration series should therefore provide a first order measure of the Fe supply to phytoplankton.This project will investigate the feasibility of miniaturizing a current bulk liquid membrane system that can actively isolate and concentrate 59Fe-DFB from aqueous solutions by constructing liposomes with the needed transport characteristics. The high surface area and optimal diffusional aspects of these nanodevices will enable efficient 59Fe-DFB accumulations at the extremely low dissolved Fe concentrations (1 nM) encountered in coastal waters. The transport characteristics of these nanodevices will be measured as a function of liposome compositions and fabrication conditions to optimize the active transport of 59Fe-DFB from a seawater matrix. If progress permits, the relationship between 59Fe accumulated by these nanodevices and cellular 59Fe uptake and growth of natural population cultures will be explored. The immediate goal of this exploratory project is to demonstrate the feasibility of developing nanoscale sensors for quantifying the supply of Fe to eukaryotic phytoplankton in coastal seawaters. The broader goal is to establish the viability of nanotechnology for sensing bioactive substrates in the marine realm.