A flexible printed non-enzymatic glucose sensor based on CeO2-doped ZnO nanostructures for plant applications

Abstract

In this study, a non-enzymatic glucose sensor for plants was developed and tested. Firstly, a three electrode sensor design was chosen and comprised of silver reference electrode and contacts, and carbon auxiliary and working electrodes. Experiments with varying concentrations of glucose were done to determine which printing method between inkjet printing and screen printing produces the better sensor. This was achieved by modifying the working electrode with commercial zinc oxide nanoparticle ink and glucose oxidase in order to ensure as best as possible the only variable was the printing technique. The printing technique selected was screen printing, as it generated more current for the same concentration of glucose compared to the inkjet printed electrode. Afterwards, research was done as to an appropriate dopant to improve sensitivity. This was selected to be cerium(IV) oxide due to its reported enzymatic-like properties. Zinc oxide nanoparticles with 1.7% doping and 10% doping concentrations were then synthesised. These were then used to modify the working electrode and evaluate glucose sensitivity. The 1.7% doping generated the highest current, obtained a normalised sensitivity of 190.6 μA·mM−1 ·cm−2, and was used in a plant based experiment to evaluate if it could differentiate a difference in glucose production when a plant was subjected to salt stress. The sensor was inserted into the plant, and plant sap was mixed with the appropriate electrolyte and used with the standard addition test. The results currently indicate promise with the sensor recording different current readings for a stressed and unstressed plant. These results were validated qualitatively by a glucose assay test on the same plant sap.