Fabrications And Applications Of Biosensors Based On Graphene/ Poly(Indole-6-Carboxylic Acid) Composites

Conducting polymers (CPs) have shown great promise for theirapplications in biosensors by virtue of their unusual properties such as rapid electron transfer, high sensitivity, specificity and biocompatibility. These functional materials, which are not only used as immobilization carriers but also have active effects on the transduction of biosensors. The hexagonal cell structure of graphene(Gr) contains π bond, interactions between conducting polymers and graphene through π-π action play an important role in the ultimate performance of Gr/CPs composites. These composites have improved and synergic properties of electrochemical activity and biocompatibility due to the excellent electrical conductivity, catalytic activity and larger specific surface area of graphene. A novel conducting nanostructured composites, graphene/poly(indole-6-carboxylic acid), has been prepared by electrochemical polymerization and designed to construct biosensors successfully. The finished major contents are as follows:1. Novel conducting nanostructured composite, electrochemical reduction graphene/poly(indole-6-carboxylic acid) (ERGO/PICA), was synthesized by electrochemical polymerization of indole-6-carboxylic acid (ICA) monomer with ERGO modified electrode in acetonitrile (ACN). As the results of cyclic voltammetry (CV) studies, ERGO/PICA composite film showed good redox performances and electrochemical activity. Scanning electron microscope (SEM) showed that graphene film was a tight layer of thin film, while the composite film presented as net-like structure. Compared with pure PICA, the nanocomposite possessed larger specific surface area and higher charge-transport properties. These properties may have great potential in applications and will help broaden the Gr/CPs composites in biosensing field.2. An electrochemiluminescence (ECL) biosensor was fabricated based on the ERGO/PICA composite film, which could detect thrombin with a low detection limit of 3 fM. The ECL sensor showed a wide linear range, from 0.0001 nM tolO nM. High sensitivity was achieved due to the ERGO/PICA nanocomposite and the amplification of nanoparticles. These assays have the potential to provide a simple, rapid and cost-effective approach for the early and accurate detection of thrombin by the utilization of nanotechnology and aptamers.3. A lable-free electrochemical immunosensor based on ERGO/PICA composite was fabricated to detect CEA antigen by measuring the change of electrochemical responses and the detection limit was 0.02 ng mL-1. The immunosensor showed a wide linear range, from 0 to 90 ng mL-1. The immunosensor exhibited excellent performances of simplicity, good sensitivity, specificity and reproducibility. The nanostructured ERGO/PICA composite provided high specific surface area and good biocompatibility. Ionic liquid (IL) has good electrical conductivity. Gold nanoparticles could act as wires or electronic channels in the electrochemical reaction, thus had synergistic effects on the electron transfer process. The immunosensor offers a new insight into the fabrication of immunoassays for detecting CEA and other relevant biomarkers and extends the practical application of Gr/CPs composite to the field of biosensors.