Cost Effective Soil pH Sensor Using Carbon-Based Screen-Printed Electrodes

This paper for the first time demonstrates a low cost, easy to make, disposable and paper-based soil pH sensor. The measurement of soil pH is performed using three electrode based electrochemical platform. The sensor is printed using screen-printing technique on a non-tearable hydrophobic paper. Carbon paste is modified with pH sensitive quinone moiety, alizarin, which shows 2e(-)/2H(+) redox process. The detection is carried out using square wave voltammetry at 25 +/- 1`degrees C. Eleven different kinds of soil have been collected from three different provinces in India. Samples are prepared using the standard protocolviz. 1M KCl and 0.01M CaCl2. The sensitivity is 60.61 mV/pH and 65.16 mV/pH for buffer solution containing 1M KCl and 0.01M CaCl2, respectively. Two consecutive scans are taken for accurately measuring the soil pH. The first scan shows two peaks which correspond to different types of redox behaviour of alizarin. The second scan shows the actual pH behavior which is demonstrated for the first time. Soil samples prepared using KCl solution show the relative error within 4.9%. For CaCl2 samples the relative error is within 2.9% for soil pH less than 7.3 and within 7.9% for pH greater than 7.3.