Non-invasive early monitoring plant health using terahertz spectroscopy

The state-of-the-art Terahertz sensing technique has emerged as a powerful tool for identifying various types of plant leaves and enabling early detection of plant diseases. This innovative approach utilizes both transmission and Attenuated Total Reflection modes within a frequency range of 0.1 to 3.5 THz. The motivation behind this work stems from the challenges encountered when analyzing thin plant leaf samples with high water content and non-uniform fiber distribution. These factors often result in a low signal-to-noise ratio, and the absorption peaks of targeted plant substances or chemicals associated with plant diseases are typically at trace levels. Traditional THz transmission testing schemes struggle to identify these peaks effectively. In response to these challenges, we developed and implemented a novel ATR measurement technique. This technique leverages a low-cost graphene oxide thin film sensor for plasmonic enhancement, aiming to significantly improve the detection SNR and sensitivity compared to conventional transmission testing methods. In this study, we conducted direct testing on fresh leaves affected by two different leaf diseases, Coleosporium Plumeriae (Frangipani Rust) and Pseudocercospora. The successful identification of the disease chemical absorption peaks using our enhanced ATR method demonstrates the high sensitivity detection capabilities of our approach. The findings from our direct testing on fresh leaves, combined with the graphene oxide thin film enhancement of the intensity and sensitivity (> 100%) in the ATR mode, showcase the promising potential of Terahertz sensing for future applications in agricultural monitoring.