Analysis of the heterogeneous structure of iron oxide/gold nanoparticles and their application in a nanosensor

•A heterogenous nanoparticles, IONPs-AuNPs using electrostatic- self- assembly technique is proposed.•This technique manipulates the positive (IONPs) and negative (AuNPs) surface charge.•Modification of carboxylate-IONPs-AuNPs for glucose oxidase immobilisation.•Application of immobilised glucose oxidase on IONPs-AuNPs for glucose detection. Magnetic iron oxide-gold nanoparticles (IONPs-AuNPs) could provide a useful platform for biosensing purposes. The aim of this study was to investigate the formation of such particles using a simple electrostatic self-assembly technique, and then to demonstrate their application using a glucose detection assay. AuNPs were attached to the IONPs surface by ionic interaction, as verified using UV–vis spectrophotometry. Then, a carbodiimide-coupling technique was used to covalently attach glucose oxidase (GOx) onto the nanoparticles’ surface and the bioactivity was measured using an ABTS colorimetric assay. For characterization, UV–vis spectrophotometer, DLS, zeta potential, TEM, EDX, XPS and FTIR techniques were used. The particle diameter obtained from TEM was 16.1±11.1nm and EDX confirmed the presence of Au and Fe elements. In addition, FTIR results exhibited strong vibrational modes around 1654, 1546 and 3369cm−1 that appeared to be primarily due to immobilization of GOx onto Fe/Au. The colorimetric assay also showed a significant increase in green color intensity, due to oxidation of ABTS, with increasing glucose concentrations ranging from 20μM to 100μM. IONPs/Au nanoparticles showed a good potential for application in this colorimetric assay, thus suggesting an excellent basis for a nanosensor system using these particles.