Plant active small molecules play an indispensable role in plants. They form the basis of the core physiological mechanisms that regulate the plant growth and development and enhance resilience to environmental stress. Achieving highly precise quantitative analysis of these active small molecules is therefore vital for promoting precise management practice in the agricultural and accelerating the development of smart agriculture. Currently, various technologies exist for the detection and analysis of these small molecules in plants. Among them, electrochemical sensing platforms have attracted extensive attention due to their significant advantages, including high sensitivity, excellent selectivity, and low cost. These advantages enable them to effectively detect trace levels of various active small molecules in plant samples. They also have the potential for real-time and in-situ detection.

Based on a comprehensive review of relevant academic literature, this article systematically summarizes the current research progress and status of electrochemical sensors applied in detecting plant active small molecule. Based on this, the article further analyzes the core sensing mechanisms of different electrochemical sensors types, signal amplification technologies for enhancing detection performance, and their huge potential in practical applications. Furthermore, this paper explores a notable development direction in this field: Sensor technology is evolving from the traditional in vitro detection mode to more challenging in vivo detection and in-situ realtime monitoring methods. Meanwhile, the article particularly emphasizes and elaborates in detail the indispensable and significant role of nanomaterials in key links such as constructing high-performance sensing interfaces and significantly enhancing detection sensitivity and selectivity. Finally, it prospectively discusses the innovative integration of electrochemical sensors with cutting-edge flexible electronic technology and powerful artificial intelligence (AI)-based data analysis, along with their potential for broad application.

This article comprehensively identifies and summarizes the core technical challenges that electrochemical sensors currently face in detecting plant active small molecule. In terms of environmental detection, due to the influence of the complex matrix within plants, the response signal of the sensor is prone to drift, and its stability and sensitivity show a decline. Regarding electrolytes, the external application of liquid electrolytes dilutes the target molecules concentration in plant samples, lowering the detection accuracy. Furthermore, the transition from principle development to mature productization and industrialization of electrochemical sensors is relatively lengthy, and there are few types of sensors available for the detection of plant physiological indicators: Limiting their application in actual agricultural production. On this basis, the article prospectively analyzes the key directions of future research. First, continuously improving sensor performance indicators such as sensitivity, selectivity and reliability. Second, exploring and optimizing electrolyte material systems with stronger adaptability to significantly improve detection accuracy and long-term stability. Third, promoting deeper integration and innovation of sensor technology with advanced micro-nano electronic technology and powerful AI algorithms. The core objective of this review is to provide a theoretical guidance framework for in-depth research and systematic performance optimization of electrochemical sensing technology for plant active small molecules, as well as practical guidance for the actual application of related sensors in complex plant substrate environments.

Brassinolide is an important endogenous plant hormone. In this work, an electrochemical immunosensor for in situ detection of brassinolide was constructed using screen-printed electrode (SPE).

Au nanoparticles (AuNPs) were firstly electrodeposited on the surface of SPE electrode by electrochemical workstation, and then CuCl₂ nanowires (CuCl₂ NWs) were added to the electrode, which can not only increase the conductivity of the electrode, but also Cu²⁺ can be used as a REDOX probe for the sensor. Finally, Mxene and polydopamine nanocomposite (Mxene@PDA) were selected as the modification materials for SPE electrodes because Mxene has the advantages of large surface area and good electrical conductivity, which can further amplify Cu²⁺ signals. However, Mxene is easily oxidized and unstable in air. Polydopamine (PDA) contains a large number of catechol and amino groups, which are coated on the surface of Mxene after self-polymerization by dopamine, cutting off the path of oxygen penetration, making Mxene difficult to be oxidized. Mxene@PDA can also be used as a coupling agent to fix more antibodies on the electrode surface, improving the overall biocompatibility, and improve the overall biocompatibility.

The sensor has a wide linear detection range: 0.1 pg/mL to 1 mg/mL, and the detection limit was 0.015 pg/ml (S/N=3). In addition, the content of endogenous brassinolide in wheat was detected by SPE electrodes in vitro and the recovery rate was 98.13% to 104.74%.While verifying the accuracy of the sensor, it also demonstrated its superior stability and sensitivity. Besides, the sensor also showed excellent application potential in the in situ detection of brassinosteroids from wheat leaves. Compared with other brassinolide detection methods, the immunosensor developed in this study has better analytical performance.

An electrochemical immunosensor for in situ detection of brassinolide was developed for the first time, providing a good electrochemical platform for in situ determination of brassinolide in plant leaves, which has great application potential in precision agriculture.