Phase control of nanostructured iron oxide for application to biosensor.

We report results of the studies relating to the phase transformation of bare Fe3O4 nanoparticles (NPs) to α-Fe2O3 NPs obtained during electrophoretic film deposition onto indium-tin oxide coated glass plates. The in situ oxidation of NPs during electrophoretic deposition can be circumvented using surface passivation of the Fe3O4 NPs with an organic shell (carbon) as well as an inorganic shell (silica), while retaining the biocompatibility of the Fe3O4 NPs. XRD and XPS studies reveal the transformation of Fe3O4 NPs to α-Fe2O3 NPs upon electrophoretic deposition, and the retention of the phase of the Fe3O4 NPs upon encapsulation with carbon and silica, respectively. The results of SEM studies indicate decreased agglomeration of the Fe3O4 NPs upon encapsulation during film deposition. Attempts have been made to compare the characteristics of cholesterol biosensors fabricated using Fe3O4@C and α-Fe2O3 NPs, respectively. The Fe3O4@C NPs based cholesterol biosensor shows response time of 60 s, a linearity range of 25-500 mg dl-1, a sensitivity of 193 nA mg-1 dl cm-2 and a Michaelis-Menten constant of 1.44 mg dl-1.