Preparation and characterization of nitro-functionalized magnetic maghemite nanoparticles using a dendritic molecule

JULIETA I. PAEZ; ARIEL CAPPELLETTI; VERONICA BRUNETTI; MIRIAM C. STRUMIA

Simposio; V Argentine-Chilean Polymer Symposium; 2009

Dendritic molecules have proved to be useful for functionalization of metallic surfaces due to their monodisperse nature that provides precisely controlled size, shape and functionality.[1] In our group, we have been working on functionalization of gold and carbon electrodes with a dendritic molecule (D-NO2).[2,3] The promising results obtained on these surfaces, encouraged us to explore the functionalization of magnetic nanoparticles (MNPs) with such molecule.[4] MNPs possess high surface area and unique magnetic properties with a broad range of potential biomedical applications[5-8] (e.g., diagnostic medicine, hyperthermia, cell labeling and sorting, separation o cells), and other nonbiomedical uses[9] (e.g. high-density memory devices, magnetic sensors, imaging reagents, ferrofluids). In recent years there has been a significant progress in the application of these novel nanomaterials in biosensors.[10] In this opportunity, we present the preparation and characterization of dendritic molecule-coated MNPs. Afterwards, the immobilization of these modified MNPs onto glassy carbon electrodes (GCE) was explored to generate a novel platform promising for the development of biosensors.

METHODS 

Maghemite magnetic iron oxide (g-Fe2O3) nanoparticles (MNPs) were functionalized with 3-(aminopropyl)trimethoxysilane (APS) as silane coupling agent.  Subsequently, a dendritic molecule (D- NO2) were covalently attached to the modified MNPs, achieving nitro-functionalized magnetic nanoparticles, (MNPs-APS-D-NO2) as is shown in Fig. 1.

Fig. 1. Synthesized dendritic molecule-coated MNPs.

Infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and transmission electronic microscopy (TEM) were used to characterize the derivatised surface. Then, the dendronized MNPs were attached onto GCE following a self-assembly procedure, and the obtained system was electrochemically characterized.

RESULTS AND DISCUSSION

FT-IR confirmed the planned modifications were achieved. Besides, TGA showed weigh-loss profiles that would demonstrated the grafting was successful, as was previously reported.[11] Also, TEM studies suggested the MNPs with different derivatization degree experiment changes in aggregation phenomena. It is important to notice that an increase in the solubility in organic solvents was observed after the organic derivatization. All carried-out studies indicated the achieved derivatization degree is low. However, the immobilization of MNPs-APS-D-NO2 onto GCE was successfully achieved (see Scheme 1). The nitro-functionalized g-Fe2O3 nanoparticles exhibit an spontaneous self-assembly onto GCE.  The attachment of the dendron was monitored through the observation of the electrochemical signal of the nitro group.[2,3] The voltammetric feature is similar to that observed for D-NO2 attached directly onto carbon surface (Fig. 2). The main difference, however, lies in the total amount of the charge related to nitro moiety which, in this case, is considerably smaller. These results are in a good agreement with the low degree of MNPs functionalization achieved. In addition, the electrochemical results show the reduction of Fe3+ to form Fe0, indicating a composite electroactivity, which can be exploited in electrochemical systems or devices.

Scheme 1. Physical immobilization of dendron-coated maghemite onto GCE.

Fig.2. Cyclic voltammograms at 0.1 Vs for MNPs-APS-D-NO2 modified GCE in 0.1M PBS (pH 7). First scan (dashed line) and second scan (solid line). 

CONCLUSIONS

Dendritic molecule-coated MNPs were synthesized and characterized. These results point out a simple method to add magnetic material in carbon electrodes and thus generate promising surfaces for the development of biosensors. They also pave the way for many applications such as biocompatible delivery systems and electronic and photonic devices.