Fluorescein isothiocyanate-capped gold nanoparticles for fluorescent detection of reactive oxygen species based on thiol oxidation and their application for sensing glucose in serum

This study reports a simple and sensitive method for fluorescent detection of reactive oxygen species (ROS) based on the oxidation of 2-mercaptoethanol (2-ME) and 2-ME-induced increase in fluorescence of fluorescein isothiocyanate-capped gold nanoparticles (FITC-AuNPs). FITC molecules can be readily attached to the surface of citrate-capped AuNPs through their isothiocyanate group. FITC-AuNPs fluoresce weakly mainly due to the efficient fluorescence resonance energy transfer from FITC to AuNPs. It is found that the presence of 2-ME enables FITC to be removed from the surface of the AuNPs through the formation of Au S bonds, thereby restoring the fluorescence of FITC. In contrast, when 2-ME is oxidized with ROS under alkaline condition, the generated 2-ME disulfide is unable to remove FITC from the NP surface. As a result, the weak fluorescence of FITC-AuNPs increased gradually after adding increasing concentrations of ROS. The sensitivity of this method toward ROS was significantly improved after removal of the AuNPs by centrifugation. Because the glucose oxidase-catalyzed oxidation of glucose yielded gluconic acid and H2O2,, this method was also utilized to detect glucose. Under optimum conditions, the minimum detectable concentrations for H2O2, superoxide anion, hydroxyl radical, and glucose were found to be 1, 0.6, 0.6 and 1 1 mu M, respectively. This method has been successfully applied to the determination