Efficient Synthesis of Magnetic-Silica Particles for Nucleic Acid Extraction in Diagnostics Based on Washing-Free Magnetic Fine Nanoparticles

Magnetic-silica particles (MAGSi) have been widely used for rapid and large-scale nucleic acid extraction. However, the synthesis procedure normally involves washing steps, which will produce chemical waste and are time-consuming. In this study, we synthesized magnetic-silica fine particles by eliminating the washing step in magnetic nanoparticle production, thereby improving environmental sustainability and reducing synthesis time. First, magnetic nanoparticles (MNP) with sizes averaging around 100 nm (based on dynamic light scattering (DLS) data) were synthesized via co-precipitation continued with silica coating by the Stöber method, without washing the Fe₃O₄ nanoparticles. Compared to the washed MNP, the unwashed MNP exhibited similar magnetization, with 47.85 emu/g for the unwashed and 47.10 emu/g for the washed MNP. The unwashed MNP was also successfully coated with silica, which resulted in a decrease in magnetization (5.00 emu/g) with a Fe₃O₄:SiO₂ mass ratio of 1:8. Compared to MAGSi synthesized by washed MNP, the unwashed MNP produced MAGSi with a larger size (~ 1700 nm compared to 320 nm based on the DLS data), more pronounced SiO₂ FTIR peaks, and lower magnetization due to a thicker SiO₂ layer. The MAGSi synthesized using the unwashed MNP is still effectively able to extract RNA and DNA from viral (SARS-CoV-2 and Canine Distemper Virus) and bacterial (Leptospira spp.) samples, as validated through PCR and qRT-PCR. This work introduces a practical and sustainable approach for synthesizing MAGSi, demonstrating their utility in nucleic acid extraction without compromising performance.