Highly Sensitive Cellulose Gauze Patch for the Detection of Morpholine Coating on Fruits

Morpholine, one of the chemicals that is used to achieve glazed waxy surface over fruits such as apple, possesses fungicidal properties, is pest-repellent and regulates humidity around the fruit. Despite having these advantages, it is proven to be a carcinogenic adulterant and extremely fatal for the human body, if consumed in excess above the safe dose of 0.48 µg/mL. Though the conventional methods of detecting morpholine are accurate, they are expensive, laborious, time-consuming, and require technical expertise. Hence, there is a demand for a simple, portable, and rapid device for on-site sensing of morpholine. In this present investigation, we have developed cellulose gauze patch for detecting morpholine coating on apple within 5 min by utilizing two different approaches, qualitative Simon’s based and quantitative pH-based colorimetric tests. The qualitative response is inferred by the colour change from brown to navy blue upon rubbing the cellulose gauze patch over the apple surface. The quantitative signal is deduced from the colour change from yellow to pink. In addition, there is a proportionate increase in the G-channel intensity of the pink colour obtained through the phenol red-based pH test, owing to the basic nature of morpholine and the increase in the pH value with the increase in its concentration, with a limit of detection (LOD) of 10 µg/mL.