Dendrimer Encapsulated Pt Nanoparticle-Immobilized Glassy Carbon Electrode with High Electrocatalytic Redox Activity to Hydrogen Peroxide and Its Application for Biosensing

Abstract

Dendrimers, which are highly-branched monodisperse macromolecules with well-defined size, shape, and surface functionality, have been widely used in the modification of electrode surfaces due to their good biocompatibility and adequate functional groups. The intriguing properties of dendrimers allow the dendrimer-coated surfaces to be utilized in a variety of fundamental and applied researches. For example, the use of dendrimers has been proposed for the design of microarray chips because dendrimer-immobilized surfaces provide a unique three-dimensional architecture with flexible branched arms connected to numerous functional groups. This allows for the effective immobilization of biomolecules with a high density as well as minimization of biomolecule denature. In addition, dendrimer-immobilized surfaces have been proven to be useful in improving sensitivity as well as selectivity for biosensing applications. Recently, we also reported facile surface modification of carbon-based materials with amine-terminated dendrimers and its applications to construct catalytic bifunctional surfaces for electrochemical reactions of chemicals such as hydrazine and oxygen. Here, we report the electrochemical modification of glassy carbon electrodes (GCEs) via electrooxidative coupling of the dendrimers encapsulating electrocatalytic Pt nanoparticles and the promising potential of the resulting dendrimer encapsulated Pt nanoparticle-decorated GCEs as biosensing platforms. Since Pt nanoparticles were encapsulated inside the cores of dendrimers, the electrooxidative coupling of the dendrimers onto GCEs resulted in modification of GCEs with the catalytic Pt nanoparticles. As illustrated in Scheme 1, we synthesized dendrimer encapsulated Pt nanoparticles (Pt DENs, diameter 2.1 ± 0.3 nm) using amine-terminated sixth-generation polyamidoamine (G6-NH2 PAMAM) dendrimers and immobilized the Pt DENs on GCEs via electrooxidative coupling of the terminal amino groups of dendrimers. The resulting Pt DEN-immobilized GCEs showed much higher electrocatalytic activity toward redox reactions of H2O2 than that shown by bare GCEs. The enhanced electrocatalytic activity of Pt DEN-decorated GCEs was further applied to glucose sensing. Figure 1 shows a TEM image and a corresponding histogram of the particle size distribution of the as-synthesized Pt DENs denoted as G6-NH2(Pt250), where the numerical subscript of Pt represents the original PtCl4 :G6-NH2 ratio used for the synthesis and thus the average number of Pt atoms in each dendrimer. The Pt nanoparticles were found to be nearly monodispersed in size and rarely aggregated due to stabilization of the nanoparticles via their encapsulation inside the dendrimers (Figure 1). The measured average diameter (2.1 ± 0.3 nm) of the Pt DENs was slightly larger than the theoretical value (1.9 nm) for nanoparticles containing 250 Pt atoms (Figure 1, inset), which is presumably