Microsensor for limonin detection: An indicator of citrus greening disease

Abstract

Limonin is a biomolecule which is responsible for the bitter taste in citrus fruits such as oranges, grapes etc. The abnormally high level of limonin is indicative of citrus greening disease which results in stunted tree growth and affects fruit quality in terms of nutritional value, taste, texture and aroma. Therefore, quantification and detection of limonin is crucial for an early management of citrus greening disease to save the multibillion dollar citrus industry. To this end, an organic electrochemical transistor (OECT) functionalized with Ceria Nanoparticles (CNPs) as transducer has been developed to detect ultralow concentration of limonin. The device exhibited high sensitivity (detection limit: 10 nM) and selectivity towards limonin with response time in seconds. The detection is attributed to the switching of Ce3+ to Ce4+ at the gate electrode which decreases the overall effective gate voltage resulting in an increase in the output current. The increase in output current was observed in transfer characteristics as well as time-current curve. In-situ spectro-electrochemical studies were also performed to analyse the change in oxidation state of CNPs in the presence of limonin. This novel biosensor successfully detected the increase in limonin in infected juice samples as compared to healthy ones with a sensitivity of ∼10 μA/μM. A rapid, easy and on-site testing tool to detect and quantify the amount of limonin for an early detection of citrus greening disease has been demonstrated for the first time.