Flexible Electrodes Decorated with Mesoporous WO₃-Dots Using Electrospray and Evaporation Induced Self-Assembly (EISA)

Materials fabricated through electrospraying methods exhibit enhanced mechanical and electrical properties for various applications. Mesoporous structures with surface porosities of 20-50 nm provide numerous active sites, enabling high sensitivity, mechanical robustness, and rapid response and recovery. However, surface modification is essential to improve the electrochemically active sites for high-sensitivity, non-enzymatic biosensors compared to flat surfaces.<br/>Evaporation-induced self-assembly (EISA) is a powerful nanostructuring method that creates electrochemically active surfaces. This technique offers significant advantages in material fabrication and structural control. Tungsten trioxide (WO₃), a metal oxide semiconductor, is notable for its rapid electron transport and diverse structural forms, making it attractive for sensor applications.<br/>This study investigates the fabrication of flexible polyimide (PI) electrodes decorated with mesoporous WO₃ for the highly sensitive detection of catechol (CC) and hydroquinone (HQ), which are critical environmental pollutants due to their low degradability and ecological toxicity. Organic-inorganic composite dots were formed on flexible PI electrodes through EISA and electrospraying. EISA was conducted with high-voltage biasing and substrate heating for a temperature gradient. During solvent evaporation, randomly distributed precursors formed micelles, followed by well-ordered thin films. Partially decomposed organic components were removed using O2 plasma, forming mesoporous structures. The increased specific surface area of the mesoporous structures facilitated effective redox and adsorption-desorption reactions.<br/>Differential pulse voltammetry (DPV) and cyclic voltammetry (CV) measurements confirmed a linear increase in cathodic peak current with increasing sample concentration. Computational studies supported the spontaneous adsorption of CC and HQ molecules on the modeled WO₃ surface.<br/>The proposed sensor successfully measured CC and HQ simultaneously and individually on the WO₃-PI electrode. It demonstrated high sensitivity, wide linear range, and low detection limits when CC and HQ were present either individually or concurrently. The sensor's practicality was validated using real river water samples.<br/>The results indicate that flexible PI electrodes decorated with mesoporous WO₃, fabricated via EISA and electrospraying, provide an efficient and reliable method for detecting these phenolic compounds. This approach suggests a promising method for developing electrochemical sensor materials aimed at environmental safety.<br/><br/>This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (RS-2023-00243390). This study was also supported by the Basic Science Research Program through the National Research Foundation of Korea, funded by the Ministry of Education (2022R1A6A3A13063381 and 2022R1A3B1078163).