High-sensitivity pesticide detection on mango skins by terahertz spectroscopy with graphene oxide sensors

Regular monitoring of pesticides in agricultural farmland is essential to prevent the misuse of toxic pesticide chemicals. As crop samples are typically disintegrated to extract the pesticide residue for chromatographic analysis, non-destructive techniques for pesticide monitoring are ideal for preventing the unwanted destruction of crops. This, however, requires analytical techniques that can detect trace pesticide amounts. Here, we show that terahertz (THz) spectroscopy in attenuated total reflection mode, combined with low-cost graphene oxide (GO) plasmonic sensor, can be used for sensitive, fast, and non-destructive pesticide detection on mango skin. After the application of pesticide solution onto the mango skin, the dried pesticide residue was transferred to the GO sensor by pressing it in contact with the mango skin surface. Due to the adsorption of the pesticide molecules onto the oxygen-rich GO surface, a signal in the THz range was obtained corresponding to the pesticide’s chemical fingerprint. With this technique, pesticide surface concentrations of approximately 1 µg/cm2 on mango skins can be detected.