Visual determination of hydrogen peroxide and glucose by exploiting the peroxidase-like activity of magnetic nanoparticles functionalized with a poly(ethylene glycol) derivative

A colorimetric assay is described for the determination of H2O2 and glucose based on the peroxidase-mimicking activity of Fe3O4 magnetic nanoparticles functionalized with a poly(ethylene glycol) derivative (PEG-MNPs). PEG ligands conjugated to a phosphine oxide and a phospholipid were synthesized and deposited on the surface of magnetic nanoparticles (MNPs). This leads to enhanced peroxidase-like activity of the MNPs by providing more monodispersed MNPs to be present in solution and by reducing self-aggregation. The PEG-MNPs were then used as enzyme mimetics that catalyze the oxidation of 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) to form a green product having an absorption maximum at 417 nm which enables a visual detection of H2O2. These findings are exploited in a highly sensitive and selective glucose bioassay based on the formation of H2O2 by glucose oxidase (GOx). The calibration plot covers the glucose concentration range from 5 mu M to 1 mM, and the limit of detection is as low as 3 mu M. The diagnostic capability of the method is demonstrated by analyzing glucose in human blood serum. It is perceived that the PEG-MNPs presented here also may act as potent peroxidase mimetics in other methods for the determination of clinically important analytes.