Title : Low-cost in-field determination of soil ion concentration using a portable 3D printed device based on ion-selective electrodes and textile threads
This work reports the fabrication and characterization of a low-cost device for the continuous monitoring of the concentration of plant nutrients based on ion-selective electrodes and textile threads that work in direct contact with soils. Here, we developed a thread-based, microfluidic sensor platform as proof of concept.We utilized traditional polymer membrane-based ion-selective electrodes (ISEs) for nitrate, ammonium, potassium, and pH. Four ion-sensitive membranes for each ion and one for the reference electrode were drop-casted directly on top of a miniaturized, 3D-printed holder. Electrical contact is established via graphite-based contacts link to the electrochemical signal reader via electrical wires. The sensor platform was enhanced by the addition of five 30 cm long textile threads connected to an absorption pad on the opposite side. This is the key innovation as these threads mimic the roots and via capillary action wick the moisture from the soil to the sensing area. The device is placed next to the soil that is going to be analysed inserting the threads in the soil sampling area. Figure 1 illustrates the device.
Preliminary results show that the thread-based sensor system is reproducible and consistently provides a near-Nernstian sensitivity of 55±5 and 50±3 for potassium, -58±1 and -63±2 for nitrate, and 60±1 and 60±12 (mV/decade) for ammonium between 2.8x10-6 and 1.3x10-2 M without (directly in solution) and with textile threads respectively. Analysis of soil samples with different soil moisture content (100%, 75%, 50% and 40%) using our low cost device gave a correlation coefficient of R2 = 0.91 for potassium and R2 = 0.92 for ammonium when compared to the values measured using traditional methods such as inductively coupled plasma optical emission spectroscopy (ICP-OES) and flow injection analysis (FIA), respectively. This low-cost device's promising performance is encouraging its use as an extended network to measure soil ion concentration at high temporal and spatial resolution.
Audience Take Away Notes:
This is the result of a research project, thus benefits are mostly intellectual. Practical benefits are expected in the short-to-medium future following thorough testing and evaluation. The audience will gain ideas for further research. The device will provide information on soil fertility with significantly improved spatial and temporal resolution than currently possible. It will assist in understanding nutrient fluxes and design of innovative practices for the sustainable use of fertilizers