Detection of Ammonia Nitrogen in Neutral Aqueous Solutions Based on In Situ Modulation Using Ultramicro Interdigitated Array Electrode Chip

In this study, an in situ electrochemical modulation method based on an ultramicro interdigitated array electrode (UIAE) sensor chip was developed for the detection of ammonia nitrogen (NH3-N) in neutral aqueous solutions. One comb of the UIAE was used as the working electrode for both the modulating and sensing functions, while the other comb was used as the counter electrode. Utilizing its enhanced mass transfer and proximity effects, the feasibility of in situ modulation of the solution environment near the UIAE chip to generate an electrochemical response for NH3-N was investigated using electrochemical methods. The proposed method enhances the concentration of hydroxide ions and active chloride in the local solution near the sensor chip. These reactive species play a key role in improving the sensor’s electrocatalytic oxidation capability toward ammonia nitrogen, facilitating the sensitive detection of ammonia nitrogen in neutral environments. A linear relationship was displayed, ranging from 0.15–2.0 mg/L (as nitrogen) with a sensitivity of 3.7936 µA·L·mg−1 (0.0664 µA µM−1 mm−2), which was 2.45 times that in strong alkaline conditions without modulation. Additionally, the relative standard deviation of the measurement remained below 2.9% over five days of repeated experiments, indicating excellent stability.