gamma-Fe2O3 (maghemite)-silica nanocomposite particles were synthesized using a sol-gel method. The condensation products of 3-glycidoxy propyltrimethoxy silane (GPTMS) and nitrilotriacetic acid (NTA) were introduced onto the surfaces of the gamma-Fe2O3 silica nanocomposite particles and subsequently, these modified surfaces were complexed with cobalt (Co+2) metal ions. A possibility of using these surface modified gamma-Fe2O3-silica particles for the purification of 6 x histidine tagged recombinant benzaldehyde lyase (BAL, EC 188.8.131.52) based on magnetic separation was investigated. X-ray diffraction (XRD), thermal analysis, and vibrating sample magnetometry (VSM) methods were used to characterize the surface modified superparamagnetic gamma-Fe2O3 (maghemite)-silica nanoparticles. XRD (Scherer's equation) results indicate that the primary particle size of maghemite was around 11 nm. Magnetic characterization results confirmed that the gamma-Fe2O3 (maghemite)-silica nanoparticles were superparamagnetic. According to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results, these superparamagnetic nanoparticles specifically capture 6 x His-tagged BAL from crude extract of Escherichia coli (E. coli) BL21(DE3)pLysS/BAL(HIS). This study shows that the surface modified gamma-Fe2O3 (maghemite)-silica nanoparticles are eligible for immobilized metal-ion affinity adsorption for histidine tagged recombinant proteins with its high capacity (3.16 +/- 0.4 mg/g) and selectivity. (C) 2011 Elsevier Ltd. All rights reserved.