Multimodal operation of printed electrochemical transistors for sensing in controlled environment agriculture

The global demand for food is the highest it has ever been due to the growing population and changing diets. This is happening at a time when agricultural production is extremely vulnerable to the changing climate and loss of arable land. Controlled environment agriculture (CEA) is a technology-based approach to grow plants indoors, which drastically reduces land and water use while sustaining high yields. To maintain optimal growing conditions, CEA agronomists need to continuously monitor the environmental parameters surrounding the roots of their crops. Here, we present a low-cost, fully screen printed sensor strip that can be used to measure three essential factors in CEA hydroponic fluids: the electrical conductivity (EC), temperature and pH. By utilizing both DC and AC biasing techniques, we demonstrate how a simple electrochemical transistor can exhibit multimodal sensing functionality. This printed device has a high sensitivity to EC of ∼ 8.7 mA/dec, a < 4 % error for temperature measurement and a Nernstian pH sensitivity of ∼ 59.3 mV/dec. We show that the flexible device can be used to monitor the key environmental growth factors in an active hydroponic growing system over 72 h. The results demonstrate that simple printed electronic (PE) sensing devices can be used effectively to enable precision CEA.