Development of Ion-Selective Optrodes for Interplanetary Food Production and Water Sampling

Kurzfassung

The confirmation of atmospheric jets on Enceladus via Cassini has led to speculation of possible extraterrestrial life close to thermal hydrogen vents on the ocean's floor. Instantaneously sensing the ionic constituents, fundamental to biological building-blocks, in the water on distant moons is essential to validating the possibility of extra-terrestrial life. The second major application of instantaneous ion sensing will be in closed, feedback driven bio-regenerative life support systems on future missions to Mars. This includes the cultivation of crops, the processing of human/plant waste during interplanetary transit and stays on the Moon/Mars. Currently, the height of ion sensing comes from high-performance liquid chromatography (HPLC). HPLC is accurate but has shortcomings. HPLC is very cumbersome, expensive, requires many consumables and takes many hours to process samples; reducing its validity for use in space. While commercial ion-selective electrodes (ISE) are available, instantaneous and feedback driven/autonomous bulk sensors are not. ISE limitations include their susceptibility to high electrical interference, drift, temperature sensitivity and short operating lifespan. In hydroponic systems within future space-based biological life support systems, these can result in inaccurate measures of ion concentrations, resulting in non-optimal crop yields. I propose the use of reversible, low mass and low cost in-situ ion-selective optrodes. This is a new technology that is in development at the University of Guelph and being tested inside the EDEN ISS module, under construction by The German Aerospace Center (DLR) in Bremen, Germany. The optrodes are essentially a fiber optic cable, coated with a polymer film that includes a precise mixture of an ionophore, chromionophore, plasticizer and a stabilizing matrix that can be customized to react with an ion of interest. The fiber optic is then run through a 3D titanium printed housing. When binding to a selected ion in solution, the film will undergo a color change which is measured via mini-spectrometer. This change in light absorbance can then be run through a model to compute the concentration of the analyte in question. These optrode sensors have application for use within nutrient solution sensing for space-based bio-regenerative life support systems due to their low mass and power requirements.