Synthesis, characterization and properties of magnetic microspheres for fish environmental DNA monitoring

In the context of Aquatic ecological conservation policies in China, such as the Yangtze River fishing ban, traditional net-based fish monitoring methods have become restricted in major water bodies like the Yangtze River. Environmental DNA (eDNA) analysis, owing to its non-invasive nature and operational simplicity, has gradually been applied to fish monitoring. However, current eDNA analysis still suffers from inefficiencies in nucleic acid purification and separation, which may lead to the loss of some valuable biological information. To address this issue, this study prepared Fe₃O₄-SiO₂-PMIDA magnetic microspheres and systematically characterized them using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and thermogravimetric/differential thermal analysis (TG/DTG). The results showed that the prepared microspheres exhibited good dispersibility, superparamagnetic behavior, and abundant surface functional groups. Under optimized conditions, the material achieved a maximum DNA adsorption capacity of 33.81 μg/mg for salmon sperm DNA, with an elution efficiency of 87.14%. Adsorption isotherm analysis indicated that the DNA adsorption process followed the Langmuir model, suggesting homogeneous monolayer adsorption. Kinetic studies showed that the adsorption followed the pseudo-second-order kinetic model, indicating that chemical coordination was the rate-limiting step. In the extraction of eDNA from actual environmental water samples, compared with a commercial DNA extraction kit, the Fe₃O₄-SiO₂-PMIDA magnetic microspheres demonstrated higher extraction efficiency, increasing the number of OTUs by 21.55% and detecting more fish species. In summary, the magnetic microspheres show promising potential for application in fish eDNA monitoring.