用于土壤中氮钾含量快速测定的非接触电导微流控芯片.

[Objective] Nitrogen and potassium are essential nutrients for crop growth and agricultural production. The content of these nutrients in the soil directly affects crop yield, making it a crucial indicator in agricultural production processes. Insufficient levels of these nutrients can impede crop growth and reduce yield, while excessive levels can result in environmental pollution. Rapidly quantifying the nitrogen and potassium content in soil is of great importance for agricultural production and environmental protection. Therefore, it is necessary to establish a rapid and reliable method for the detection of N and K in soil. [Methods] A rapid and quantitative method was proposed for detecting nitrogen and potassium nutrient ions in soil based on polydimethylsiloxane (PDMS) microfluidic chip electrophoresis and capacitively coupled contactless conductivity detection (C4D). Microfluidic chip electrophoresis enables rapid separation of multiple ions in soil. The electrophoresis microfluidic chips have a cross-shaped channel layout and were fabricated using soft lithography technology. The sample was introduced into the microfluidic chip by applying the appropriate injection voltage at both ends of the injection channel. This simple and efficient procedure ensured an accurate sample introduction. Subsequently, an electrophoretic voltage was applied at both ends of the separation channel, creating a capillary zone electrophoresis that enables the rapid separation of different ions. This process offered high separation efficiency, required a short processing time, and had a small sample volume requirement. This enabled the rapid processing and analysis of many samples. C4D enabled precise measurement of changes in conductivity. The sensing electrodes were separated from the microfluidic chips and printed onto a printed circuit board (PCB) using an immersion gold process. The ions separated under the action of an electric field and sequentially reach the sensing electrodes. The detection circuit, connected to the sensing electrodes, received and regulated the conductivity signal to reflect the variance in conductivity between the sample and the buffer solution. The sensing electrodes were isolated from the sample solution to prevent interference from the high-voltage electric field used for electrophoresis. This contactless measurement method reduced costs and improved economic efficiency while extending the service life of the sensing electrodes and reducing the frequency of maintenance and replacement. It provided strong support for long-term, continuous conductivity monitoring. [Results and Discussions] The voltage used for electrophoresis, as well as the operating frequency and excitation voltage of the excitation signal in the detection system, had a significant effect on separation and detection performance. Based on the response characteristics of the system output, the optimal operating frequency of 1 000 kHz, excitation voltage of 50 V, and electrophoresis voltage of 1. 5 kV were determined. A peak overshoot was observed in the electrophoresis spectrum, which was associated with the operating frequency of the system. The total noise level of the system was approximately 0. 091 mV. The detection limit (S/N = 3) for soil nutrient ions was determined by analyzing a series of standard sample solutions with v arying concentrations. The detection limited for potassium (K+), ammonium (NH4+), and nitrate (NO3-) standard solutions were 0. 5, 0.1, and 0. 4 mg/L, respectively. For the quantitative determination of soil nutrient ion concentration, the linear relationship between peak area and corresponding concentration was investigated under optimal experimental conditions. K+, NH4+, and NO3-exhibit a strong linear relationship in the range of 0. 5～40 mg/L, with linear correlation coefficients (R²) of 0. 994, 0. 997, and 0. 990, respectively, indicating that this method could accurately quantify nitrogen and potassium nutrient ions in soil. At the same time, to evaluate the repeatability of the system, peak height, peak area, and peak time were used as evaluation indicators in repeatability experiments. The relative standard deviation (RSD) was less than 4. 4%, indicating that the method shows good repeatability. In addition, to assess the ability of the C4D microfluidic system to detect actual soil samples, four collected soil samples were tested using MES/His and PVP/PTAE as running buffers. K+, NH4+, and Na+ were separated sequentially within 1 min. K+ and NH4+ could be completely separated and detected simultaneously. The detection efficiency was significantly improved. Chloride (Cl-), NO3-, and sulfate(SO43-) were sequentially separated within 1 min. To evaluate the accuracy of this method, spiked recovery experiments were performed on four soil samples. The recovery rates ranged from 81. 74% to 127. 76%, indicating the good accuracy of the method. [Conclusions] This study provides a simple and effective method for the rapid detection of nitrogen and potassium nutrient ions in soil. The method is highly accurate and reliable, and it can quickly and efficiently detect the levels of nitrogen and potassium nutrient ions in soil. Accurately assessing the soil nutrient status can result in more scientific and efficient agricultural production, which can improve crop yield and quality. This will effectively address the need for rapid soil nutrient testing on farms and provide a scientific basis and technical support for agricultural production. [ABSTRACT FROM AUTHOR]