Adaptive Stem-Growth Microneedle Array Sensor for Tracking Plant Nutrient Demand

Conventional soil nutrient measurement methods can only indirectly estimate plant nutritional status. They fail to accurately capture the dynamic in vivo nutrient status of plants. This study proposes a method for detecting nutrient status using stem-mounted sensors, comprising a bionic growth-accommodating structure and a microneedle array. The system achieves in situ monitoring within plants through minimally invasive implantation, enabling the tracking of evolution patterns in electrophysiological parameters of tomato seedlings under varying gradients of nutrient stress. Results reveal the biomimetic structure’s adaptive preload characteristics. As stem diameter increases, clamping force increases, improving electrode stability. Meanwhile, the bionic structure did not significantly affect the growth of tomato seedlings. The microneedle’s bending force reached 1.352 × 102 N, withstanding 100 insertions with only a 5.53% wear rate, maintaining 100% array integrity and zero deformation. In addition, the changes in indicators such as Z and Zi in tomato seedlings are consistent with the changes in bound water ratio. They first increase and then decrease as nutrient stress concentration increases, and they can serve as indicators for nutrient detection. The sensor maintains stable stem attachment during plant growth, making continuous data collection possible and providing technical support for precise nutrient management in the future.