Graphene-based Electrochemical Biosensing

Graphene, a single layer of carbon atoms in a closely packed honeycomb two-dimensional lattice, is a new carbon nanomaterial which has novel properties such as good mechanical strength, zero band gap, high carrier mobility, large specific surface area and outstanding electric conductivity. It has great potentials in the field of electric device, sensor, drug carrier, energy storage and supercapacitor applications. Furthermore, biosensor is the important field of life analytical chemistry and biomedicine, which have been widely used in the filed of clinic cancer diagnosis and therapy. Thus, studying the applications of graphene in the field of biosensor is very important to both fundamental research and practical application.This dissertation focuses on the studies on the applications of graphene in the field of biosensor and drug delivery based on the functionalized graphene with the combination of nanotechnology, analytical chemistry and biotechnology. The main contents were summarized as follows:1.The functionalized graphene nanosheets (PDDA-G) with (diallyldimethylammonium chloride) (PDDA) were synthesized and used to combine with room temperature ionic liquid (RTIL). The resulting RTIL/PDDA-G composite displayed an enhanced capability for the immobilization of hemoglobin to realize its direct electrochemistry. Moreover, the RTIL/PDDA-G based biosensor exhibited excellent electrocatalytic activity for the detection of nitrate with a wide linear range from 0.2 to 32.6μM and a low detection limit of 0.04μM at 3σ. Meanwhile, the proposed sensor show good stability and anti-interference.2.A sensitive electrochemical immunosensor with graphene-assisted signal amplification has been developed. In order to construct the base of the immunosensor, a novel hybrid architecture was initially fabricated by combining poly (diallyldimethylammonium chloride) functionalized graphene nanosheets (PDDA-G) and gold nanoparticles (AuNPs) via a simple sonication-induced assembly. The formed hybrid architecture provided an effective matrix for antibody immobilization with good stability and bioactivity. Subsequently, a smart, multilabel, and graphene-based nanoprobe that contains gold nanoparticles functionalized exfoliated graphene oxide and horseradish peroxidase-secondary antibodies was designed for constructing a novel sandwiched electrochemical immunosensor. Enhanced sensitivity was obtained by combining the advantages of high-binding capability and excellent electrical conductivity of hybrid architecture with the multilabel signal amplification. On the basis of the dual signal amplification strategy of graphene-based architecture and the multilabel, the immunosensor displayed excellent analytical performance for the detection of human IgG (HIgG) range from 0.1 to 200 ng/mL with a detection limit of 0.05 ng/mL at 3σ.Moreover, the proposed method showed good precision, acceptable stability and reproducibility, and could be used for the detection of HIgG in real samples.3.A green and facile method for the preparation of gelatin functionalized graphene nanosheets (gelatin-GNS) was reported by using gelatin as a reducing agent. Meanwhile, the gelatin also played an important role as a functionalized regent to prevent the aggregation of the graphene nanosheets. The obtained biocompatible gelatin-GNS exhibited excellent stability in water and various physiological fluids including cellular growth media as well as serum which were critical prerequisites for biomedicine application of graphene. Cellular toxicity test suggested that the gelatin-GNS was nontoxic for MCF-7 cell even at a high concentration of 200μg mL Furthermore, the anticancer drug was loaded onto the gelatin-GNS at a high loading capacity via physisorption for cellular imaging and drug delivery. The doxorubicin/gelatin-GNS composite exhibited a high toxicity to kill MCF-7 cell and experienced a gelatin-mediated sustained release in vitro which have potential advantage to increase therapeutic efficacy.4.An electrochemical sensor based on chemically reduced graphene (CRG) was developed for the sensitive detection of rutin. To construct the base of the sensor, a novel composite was initially fabricated and used as the substrate material by combining CRG andβ-cyclodextrin (β-CD) via a simple sonication-induced assembly. Due to the high rutin-loading capacity on the electrode surface and the upstanding electric conductivity of graphene, the electrochemical response of the fabricated sensor was greatly enhanced and displayed excellent analytical performance for rutin detection from 6.0×10-9 to 1.0×10-5 mol L-1 with a low detection limit of 2.0×10-9 mol L-1 at 3σ. Moreover, the proposed electrochemical sensor also exhibited good selectivity and acceptable reproducibility and could be used for the detection of rutin in real samples.