A Flexible Microsensor Array for Root Zone Monitoring of a Porous Tube Plant Growth System for Microgravity

Control of oxygen and water in the root zone is vital to support plant growth in the microgravity environment. The ability to control these sometimes opposing parameters in the root zone is dependent upon the availability of sensors to detect these components and provide feedback for control systems. The objective of this work was to design and build advanced sensor technology that could be adapted to future hardware systems and monitor the balance between water and oxygen availability. Here we demonstrate the feasibility of using microsensor arrays on a flexible substrate for dissolved oxygen detection, and a four-electrode impedance microprobe for surface wetness detection on the surface of a porous tube (PT) nutrient delivery system. The Flexible Dissolved Oxygen Microsensor (FDOM) reported surface oxygen concentrations that correlated with the oxygen concentrations of the solution inside the PT when operated at positive pressures. But it showed convergence to zero oxygen values at negative pressures due to inadequate water film formation on the porous tube surface. The four-electrode microprobe (FEM) is useful as a basic wetness detector as it provides a clear differentiation between dry and wet surfaces. This is important as the output of the FDOM is dramatically affected by the differences in oxygen concentrations in gas and aqueous phases. The unique features of the FDOM array and FEM include small size, simple structure, mechanical flexibility, and multipoint sensing. The demonstrated technology is anticipated to provide reliable sensor feedback monitoring specialized plant nutrient delivery systems in both terrestrial and microgravity environments.