Novel looped enzyme–polyamidoamine dendrimer nanohybrids used as biosensor matrix

We report the synthesis of a novel looped enzyme–polyamidoamine nanocomposite with high enzyme loading density and long-term retention of bioactivity. The horseradish peroxidase (HRP) is first immobilized on fourth-grade (G4) poly(amidoamine) (PAMAM) dendrimer to form relatively a small enzyme–PAMAM composite, which is allowed to grow up into a larger one. The looped horseradish peroxidase-polyamidoamine (HRP-PAMAM) nanohybrid was characterized by TEM. The material obtained shows promising features as applied to the fabrication of high sensitive and long lifetime biosensors. In the presence of the hydroquinone mediator in the solution, the immobilized HRP exhibited excellent electro-catalytical response to H2O2. Under the optimal conditions, the resulting biosensor showed a linear response to H2O2 over a concentration range from 3.1 × 10−6 to 2.0 × 10−3 mol L−1 with a sensitivity of 0.36 A L mol−1 cm−2 and a detection limit of 8.0 × 10−7 mol L−1. The sensitivity of the sensor response maintained over 70% of the original over 10 weeks. The catalytic activity of the looped enzyme–PAMAM nanohybrid form of HRP enzyme was obviously stabilized. As an extension, bienzyme sensor modified with glucose oxidase and HRP enzymatic PAMAM nanocomposites was constructed. The sensor exhibited improved performance and can be applied to the detection of glucose in real samples.