Enzymatic etching of gold nanorods by horseradish peroxidase and application to blood glucose detection

Abstract

Gold nanorods (AuNRs) have become some of the most used nanostructures for biosensing and imaging applications due to their plasmon-related optical response, which is highly sensitive toward minute changes in the AuNR aspect ratio. In this context, H₂O₂ has been used to trigger the chemical etching of AuNRs, thereby inducing a decrease of their aspect ratio. However, special conditions and relatively high concentrations of H₂O₂ are usually required, preventing the applicability of the system for biodetection purposes. To overcome this limitation we have introduced a biocatalytic species, the enzyme horseradish peroxidase (HRP) that is able to induce a gradual oxidation of AuNRs in the presence of trace concentrations of H₂O₂. Interestingly, the presence of halide ions has also been found to be essential for this process. As a consequence, other enzymatic reactions, such as those catalyzed by glucose oxidase, can be easily coupled to HRP activity, allowing the detection of different amounts of glucose. On the basis of these findings, we developed a highly sensitive and simple colorimetric assay that can be read out by the naked eye and allows the detection of physiological glucose concentrations in human serum.