There is a rising need for inline sensors for continuous and non-destructive monitoring of crops status. As growth in agricultural productivity stagnates, farmers are increasingly adopting soil-implanted sensors that allow them to optimize their yields. In existing literature, plant bio-impedance has been shown to change accordingly with various biotic and abiotic stress factors, and thereby may constitute a marker of interest. Yet, to date, there is no widespread adoption of bio-impedance for plant health monitoring due to the low sensitivity of planar electrodes. This thesis is dedicated to the development of a plant impedimetric biosensor that utilizes micro-needles electrodes for enhanced sensitivity. The micro-needles have been designed to pierce the upper waxy layer (cuticle) of plants to measure impedance from the underlying layers. Moreover, a micromolding process has been utilized to fabricate the micro-needles at scale without sacrificing fidelity. The molds were fabricated using dip-in laser lithography to benefit from the high resolution and flexibility of the technique. Standard metal sputtering processes were then used to confer conductivity onto the micro-needles. Several micro-needle aspect ratios and geometries were explored and adapted for use on Barley (Hordeum vulgare L,) and Date Palm (Phoenix dactylifera). In order to assess the performance of the sensors, the impedance of several plant specimens was monitored using the developed sensors alongside planar electrodes. The impedance measured by the sensors was lower than that reported by planar electrodes at low frequencies, indicating successful bypassing of the cuticle, as desired. No adverse effects were observed on the plant tissue post micro-needle attachment for seven days. Furthermore, a cyclical diurnal pattern of impedance was observed in both plants that was entrained by light. Finally, the micromolding technique developed in this thesis can help produce high- fidelity 3D electrodes for bio-impedance monitoring. Once the mold is fabricated, the electrodes can be produced at scale without the need of clean-room equipment. Furthermore, the fabricated sensors can monitor bio-impedance of plant specimens for extended durations of time and may offer a platform that can be functionalized to selectively quantify specific phytohormones of interest.
|Date made available
|KAUST Research Repository