Excessive use of oxytetracycline (OTC) has posed significant threats to microbial communities, soil quality, and public health via the food chain. It can often accumulate in soil from protected agricultural facilities. Therefore, there is an urgent need to develop rapid, sensitive, and cost-effective detection for the OTC residues. In this study, a photoelectrochemical (PEC) aptasensor was constructed using biochar/protected (ZnO@BIO-C) nanocomposites for the ultrasensitive detection of OTC residues in soil. The BIO-C support was derived from Magnolia grandiflora leaves via a microwave-assisted pyrolysis, followed by hydrothermal synthesis to grow ZnO nanoparticles onto the BIO-C surface. Various techniques were used to characterize the nanocomposites, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the ZnO nanoparticles were uniformly dispersed on the layered BIO-C matrix without significant agglomeration. The BIO-C matrix was introduced to significantly enhance the visible light absorption range for the separation and transport of photogenerated charge carriers, effectively suppressing electron-hole recombination. Photoelectrochemical measurements revealed that the ZnO@BIO-C composite with an optimal BIO-C doping ratio of 2% exhibited a photocurrent intensity 2.6 times higher than that of pristine ZnO, indicating superior PEC performance. A PEC aptasensor was then fabricated to immobilize an OTC-specific aptamer onto the ZnO@BIO-C-modified indium tin oxide electrode. The sensing mechanism relied on the specific recognition between the aptamer and OTC, leading to the dissociation of the OTC-aptamer complex from the electrode surface. The steric hindrance was reduced to restore the electron transfer pathway, resulting in a concentration-dependent increase in photocurrent. The PEC aptasensor exhibited a wide linear range from 1.0 × 10⁻¹² to 5.0 × 10⁻⁸ mol/L under optimal conditions, with a low detection limit of 3.3 × 10⁻¹³ mol/L (S/N = 3). There was excellent selectivity against common coexisting substances, such as tetracycline, salicylic acid, and indole-3-acetic acid. The sensor was also attributed to the high specificity of the aptamer recognition element. The practical applicability of the aptasensor was evaluated using the soil samples from a greenhouse. The sensor with the standard addition achieved high recovery rates from 99.92% to 100.10%, compared with the standard deviations below 5.5%. The sensor fully met the performance requirements for trace antibiotic detection in soil, indicating the high accuracy, reliability, and resistance to matrix interference. A green and sustainable strategy was obtained to convert the agricultural waste into high-value functional materials for environmental monitoring. The ZnO@BIO-C nanocomposite, derived from Magnolia grandiflora leaves, provided an excellent photoactive substrate with enhanced charge separation and visible light response. The PEC sensor was integrated with aptamer technology for the trace detection of antibiotic residues. Nevertheless, the aptamer immobilization currently relies on physical adsorption, thus leading to gradual desorption and low long-term stability. The structural properties of biochar, such as pore size distribution and defect density, were highly dependent on pyrolysis parameters for the performance consistency. Moreover, a more systematic investigation is often required for the interfacial charge transfer kinetics and the influence of soil matrix variability on sensor response. Future research should focus on more robust aptamer anchoring strategies, biochar synthesis parameters, the sensor against standard analytical techniques, and its applicability to a wider range of emerging contaminants. Overall, this work can provide a promising technical pathway for on-site monitoring of antibiotic pollution in agricultural environments. The low-cost, biomass-derived materials can also be expected for advanced sensing applications.

Efficient rotation of cropping production is often required for automatic transplanting devices. However, seedling damage can frequently be found during operation. There are some challenges to the success of seedling transplanting. It is very important to understand the force condition of picking up seedlings in the process of automatic transplanting. In this study, a multi-pin pincette mechanical equipment was designed to examine various force conditions. The dynamic analysis was also carried out to pick up the seedlings from the growing tray cells. Among them, the pincette-type end effector was driven by multiple cylinders. Two fingers and four needles were efficiently configured for picking up seedlings. The ball screw linear was constructed to move the pincette-type end effector for picking up seedlings. The displacement sensor was selected to accurately detect the displacement. The tension/pressure sensor was utilized to examine the applied forces in the process of automatic picking. The high precision control and data acquisition were constructed using these sensors. Single-factor and orthogonal tests were conducted to take the target parameters as the size of the sliding needle and the running speed of picking seedlings. The mechanical test of grasping and picking root lumps for automatic transplanting vegetable seedlings was carried out under the different influencing factors. It was found that picking seedlings was a combination of multiple mechanical actions, such as inclined penetration, parallel grasping, and vertical extraction of sliding needles. A better performance was achieved in the sudden squeezing of the seedlings by the sliding needles at the maximum depth of penetration. Their roots were then loosened to take away from the growing tray cells. The grasping deformation of the root lumps was furthermore maintained to completely break away from the adhesion of the tray cells, in order to successfully pick up seedlings. The dynamic analysis was performed on picking up seedlings from their growing tray cells, according to the measured data. The statistical analysis of variance (ANOVA) showed that the size of the sliding needle shared a highly significant effect on the penetrating forces, and the running speed of picking seedlings had a significant effect on the desorption force and the pulling force. Furthermore, the pulling force in picking up seedlings from their growing tray cells was closely related to the desorption force of the root lumps. Specifically, the oblique penetrating force of the thick sliding needles with a diameter of 2 mm was 1.6 times that of the thin sliding needles with a diameter of 1.5 mm at the low-speed operating state. According to the measured seedling, the desorption forces of plug seedlings grown in the 72-cell trays were more than 10 times their own seedling weights. Automatic transplanting of plug seedlings was successfully realized in the growing trays. Among them, the applied forces were mainly used to overcome the adhesion forces between the seedling roots and the cell walls in the process of automatic picking. The better integrity of the seedling root lump was achieved in the fine needle with a diameter of 1.5 mm and a running speed of 25 mm/s. On the whole, the elastic thin needles with less disturbance to the root lumps were better than those of the rigid thick needles. Combined actions included inclined penetration, parallel grasping, and vertical extraction of sliding needles. After that, the plug seedlings transplanting was extracted from their growth cells. The integrity rate of root lumps was more than 97% in the picking up seedlings, indicating the better performance of transplanting. This finding can provide guidance for the optimal design of the high-efficiency and low-damage seedling-picking mechanism