IoT-based sensing system for phosphate detection using Graphite/PDMS sensors

This paper presents a novel IoT-based system for phosphate detection. The sensor patches in the system were developed using castings on 3D printed molds. Graphite and PDMS were used as electrodes and substrate respectively to fabricate the sensor patches. The testing of the prototypes was done in two phases, using an impedance analyzer and a microcontroller-based system. The electrodes of the sensor patches operated on a capacitive principle due to their interdigital structure. The reactance and impedance values from the sensor patches were analyzed during experimentation. The sensors showed a sensitivity of 0.0498 Ω/ppm, for the four different samples ranging between 0.03 ppm and 30 ppm. The sensor patches were also tested with unknown samples spiked with phosphate concentrations equivalent to different water bodies. They displayed repeatable responses having less than 3% deviation for each concentration. The optimal frequency value obtained from the testing of the sensor patches with the impedance analyzer was used as the operating frequency in the IoT-based system which consisted of an impedance analyzer AD 5933, Wi-Fi embedded Arduino Uno and 2:1 multiplexer ADG849. The data obtained from the IoT-based system were sent to the cloud server to represent the usage of the proposed system for real-time applications of phosphate detection in different water bodies.