Aptamer-conjugated core–shell magnetic nanoparticles for quick and specific separation of gram-negative bacteria

Quick separation of gram-negative bacteria, such as <i>Escherichia coli</i> (<i>E. coli</i>), from water sources is crucial for ensuring timely public health protection and promoting environmental sustainability. This study demonstrates that aptamer-conjugated core-shell magnetic nanoparticles (MNPs) can quickly capture <i>E. coli DH5α</i> from water. The core-shell MNP composed of an iron (Fe₃O₄) core and a silica (SiO₂) shell has been bio-conjugated with aptamers using glutaraldehyde as a cross-linker. The Fe₃O₄ core has an average diameter of approximately 16 ± 5 nm, and the thickness of the silica shell is around 24 ± 4 nm. Our results show that 1 mg mL^-1 of the Aptamer-Fe₃O₄@SiO₂ nanoparticles (NPs) can efficiently capture and remove <i>E. coli DH5α</i> cells (1 × 10⁷ CFU mL^-1) from aqueous solutions in just 5 minutes when subjected to an external magnetic field of 2.0 kOe. The selective interaction between <i>E. coli DH5α</i> and the Aptamer-Fe₃O₄@SiO₂ NPs has been analyzed as compared to the interaction between the Aptamer-Fe₃O₄@SiO₂ NPs and different strains of <i>E. coli</i> and gram-positive bacteria. This work demonstrates that the conjugation of aptamers on Fe₃O₄@SiO₂ NPs is a powerful tool for fast bacterial detection and magnetic isolation, supporting future use in monitoring water quality and protecting public health.