Hydrophobically modified chitosan (HMCS), synthesized by reacting dodecyl aldehyde with chitosan (CS) has good hemostatic properties and can, by means of its hydrophobic tail, coagulate blood cells. In this work, the ability of synthesized HMCS to coagulate Escherichia coli cells was demonstrated. In order to facilitate the removal of coagulated E. coli cells using an applied magnetic field, HMCS was grafted on to the surface of magnetic nanoparticles (MNPs). Such modified MNPs interacted with Gram-negative bacteria such as E. coli by means of strong hydrophobic forces between the hydrophobic tails of HMCS and outer membrane of E. coli. The highest E. coli removal capacity achieved by MNPs@HMCS was 1.38 x 10(8) cells/mg. The characterization of CS, HMCS, CS/HMCS grafted MNPs (MNPs@CS, MNPs@HMCS) were carried out by Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The degree of deacetylation (DDA) and the degree of substitution (DS) of the synthesized HMCS are 81% and 11%, respectively.