Surface engineered magnetic nanoparticles (Fe(3)O(4)) were synthesized by facile soft-chemical approaches. XRD and TEM analyses reveal the formation of single-phase Fe(3)O(4) inverse spinel nanostructures. The functionalization of Fe(3)O(4) nanoparticles with carboxyl (succinic acid), amine (ethylenediamine) and thiol (2,3-dimercaptosuccinic acid) were evident from FTIR spectra, elemental analysis and zeta-potential measurements. From TEM micrographs, it has been observed that nanoparticles of average sizes about 10 and 6 nm are formed in carboxyl and thiol functionalized Fe(3)O(4), respectively. However, each amine functionalized Fe(3)O(4) is of size similar to 40 nm comprising numerous nanoparticles of average diameter 6 nm. These nanoparticles show superparamagnetic behavior at room temperature with strong field dependent magnetic responsivity. We have explored the efficiency of these nanoparticles for removal of toxic metal ions (Cr(3+), Co(2+), Ni(2+), Cu(2+), Cd(2+), Pb(2+) and As(3+)) and bacterial pathogens (Escherichia coil) from water. Depending upon the surface functionality (COOH, NH(2) or SH), magnetic nanoadsorbents capture metal ions either by forming chelate complexes or ion exchange process or electrostatic interaction. It has been observed that the capture efficiency of bacteria is strongly dependent on the concentration of nanoadsorbents and their inoculation time. Furthermore, these nanoadsorbents can be used as highly efficient separable and reusable materials for removal of toxic metal ions. (C) 2011 Elsevier B.V. All rights reserved.