Phage-Functionalized Magnetic Separation for Rapid and Selective Detection of Escherichia coli

Selective bacterial preconcentration remains a key challenge for improving downstream molecular detection. Here, we report carboxymethyl-dextran (CMD) coated magnetic nanoparticle clusters functionalized with lytic T4 bacteriophages (phage@CMD) for selective capture of Escherichia coli. Iron-oxide particles were synthesized by coprecipitation and characterized by dynamic light scattering (DLS), Fourier transform infrared (FT-IR) spectroscopy, and electron microscopy, revealing CMD-stabilized nanoparticle clusters with a hydrodynamic diameter of approximately 181 nm with moderate dispersity (PDI = 0.267). T4 phages were immobilized via EDC/Sulfo-NHS chemistry, yielding a functional loading of ∼5.54 × 10¹² PFU-equivalent g^-1 (∼0.053 phage per particle). An empirical Langmuir-type analysis was used solely to estimate surface loading capacity. Phage-functionalized particles enabled magnetic capture of E. coli, resulting in experimentally determined separation efficiencies of ∼20-40%, verified by CFU depletion and PCR analysis of particle-associated fractions. Magnetic preconcentration improved the practical PCR input threshold compared to direct amplification of untreated suspensions. While the study represents a proof-of-concept in laboratory media, limitations including random phage orientation, partial loss of activity after immobilization, and lack of complex-matrix validation are discussed. These findings support the use of phage@CMD as a modular magnetic preconcentration platform for bacteria prior to nucleic-acid-based analysis.