Writing Sensors on Solid Agricultural Products for In Situ Detection

This study reports on direct analysis of agricultural products. An easy and environmentally friendly method for the fabrication of electrochemical sensors on solid samples is developed, and it enables in situ detection of electroactive molecules without sample extraction. Fabrication of the sensor involves writing two electrode inks on the sample. The inks are made by mixing chitosan with graphite powder (2:1, v/w) and silver powder (1:2, v/w), respectively. The written electrode can become solidified within 5 min at room temperature. The porous structure of the sensor makes the solution accessible to the surface of sample under the electrode, thereby enabling the detection without sample extraction. This sensor was used for in situ detection of methyl parathion and nitrite. The practical performance was evaluated using Fuji apple, Chinese chives, and Chinese cabbage. By writing the electrochemical sensor on solid samples, this method avoids the time-consuming and complicated sample extraction and provides a simple and green analytical strategy for on-site application.