Online Monitoring of Indole-3-acetic Acid in Living Plants Based on Nitrogen-Doped Carbon Nanotubes/Core–shell Au@Cu₂O Nanoparticles/Carbon Fiber Electrochemical Microsensor

Electrochemical sensing is an effective method for trace determination of specific substances. However, there are many active substances in plants, and the pH environment of plant organs varies. These factors directly affect the performance of electrochemical sensors and make it difficult to realize real-time detection accurately. Here, an online intelligent monitoring system for indole-3-acetic acid (IAA) was proposed, including reusable microsensor, portable electrochemical workstation, and online cloud platform. The microsensor was fabricated by depositing nanocomposites of nitrogen-doped carbon nanotubes/core–shell Au@Cu2O nanoparticles on the carbon fiber microelectrode. The IAA microsensor has a wide concentration range of 1–10 000 ng/mL and an ultralow detection limit of 10.8–57.8 pg/mL at a pH range of 4–8. The influence of different pH values on IAA detection was investigated. It is also revealed that the IAA microsensor has good anti-interference ability, repeatability, and stability which are suitable for real-time detection of IAA in living plants. Artificial neural network (ANN) algorithm is employed to establish the relationship between electrochemical signal and IAA concentration, and the ANN model is then configured in the online monitoring system to intelligently obtain the IAA concentration. Based on this system, real-time and online monitoring of the IAA concentration in a living cabbage stem was realized for a long time of 12 h. This study provides a feasible solution based on electrochemical sensing to monitor online the living plant for precision agriculture.