The Application Of Graphene Oxide And Graphene Quantum Dots In Biological Detection

Graphene is a two-dimensional carbon material with only one atomic-layer thickness. Its discovery completes the carbon material system, from zero-dimensional fullerene, one-dimensional carbon nanotube, two-dimensional graphene to three-dimensional diamond or graphite. Graphene material affords excellent electroconductivity, mechanical strength, ductility, light and thin, which might be applied in the fields of fast-charging fuel cells, supercapacitors, foldable solar cells and biomedicine in future. Therefore, it is promising to improve people’s living environments. Scientists also predict that graphene materials might subvert the silicon materials in the next ten to twenty years.As one member of the graphene family, graphene quantum dots(GQDs) not only exhibit the excellent properties of graphene, but also afford others new properties due to their quantum confinement effect and edge effect, which are attracting most fields of scientists’ attentions. At present, researches focused on the photoluminescence properties of GQDs for their promising candidates for biomedical applications like cell imaging, phototherapy, drug delivery, gene transfer and biosensors, due to their excellent biocompatibility, lower toxicity, chemical inertness and thermal conductivity.In the field of fluorescence sensors, graphene are usually employed as an efficient fluorescence quencher, and GQDs can be served as fluorescence probes. The fluorescence intensity can be changed by controlling their assembly/disassembly. Based on the structural and property of graphene and GQDs, we wish to design a series of rapid and sensitive fluorescence probes for biological detection. In preface part, we give a short introduction on properties, preparation and functionalization of graphene materials. Then we summarize their applications in biological fluorescence probes. Inspired by these researches, we carry out our research from the following four parts:Glycoprotein is one of the most important proteins in organism, and it affects the biological recognition of cells and molecules. So we think it is necessary to investigate the glycoproteins. In this chapter, we develop a new biosensor to detect glycoproteins though the glycoprotein- carbohydrate specific recognition. Concanavalin A(Con A) is a multimeric protein and can specific recognized with multiple carbohydrates, so we can design a graphene oxide(GO) based fluorescence sensor through carbohydrate-Con A specific recognition. Glucosamine are covalently modified to the surface of GO and CdTe Quantum dots via amide bond to form GO-G and QDs-G complex, respectively. Due to the tetradentate structure, Con A can interact with the glucosamine of GO-G to form GO-G/Con A conjugates, and further recognize with the glucosamine of QDs-G to close the distance between QDs and GO, resulting in the fluorescence resonance energy transfer(FRET) from QD to GO and fluorescence quench of QDs. Therefore, we can develop a sensitive detection of Con A by the change of fluorescence intensity.Pharmaceutical analysis is very crucial in the field of biological analysis. Accurate administration and dosage of drugs not only helpful for treatment of diseases, but can also avoid bad symptoms. Organic fluorescent molecules can usually interact with large ringed host molecules, However, some drugs also can competitively interact with the complex, which causing the change of fluorescence intensity and the detection to the drugs. We developed a new biosensor for the detection of amantadine based on the competitive host-guest interaction of amantadine and rhodamine 6G(R6G) with β-cyclodextion(β-CD). β-CD modified graphene oxide(GO-CD) can interact with R6 G via the specific recognition, and GO is served as a high efficient quencher to quench the fluorescence of R6 G due to FRET between R6 G and GO-CD complex. However, the affinity of amantadine to β-CD is stronger than that of R6 G, R6 G would be released from the inner cavity of GO-CD and resulted in the fluorescence recovery when amantadine was added to the GO-CD/R6 G complex system. The proposed system can be used for quantitative detection of amantadine through the change of fluorescence intensity. Furthermore, it is also successfully applied to determine the amantadine in pharmaceutical capsule with good accuracy and satisfactory recovery.Graphene quantum dots afford excellent biocompatibility and stable fluorescence emission, and might be the candidates in designing biological fluorescence sensors. The size of prepared graphene quantum dots(GQDs) was distributed in 20-40 nm. Our developed GQDs show the strongest emission peak at 540 nm when excited at 480 nm, which is potential for the detection in vivo. In this chapter, we develop a new fluorescence sensor based on GQDs for tyrosine and cysteine. Tyrosine can be oxidized to dopaquinone structure in the presence of tyrosinase to quench the fluorescence of GQDs via electron transfer. On the contrary, cysteine can inhibit the tyrosinase ability and reduce the produced dopaquinone to polyphenol processors, which makes the fluorescence intensity recovered. So we can detect the content of tyrosine and cysteine from the fluorescence “Off” and “On” of the system respectively.Stronger recognition interactions are crucial for the sensitivity and detectability of fluorescence biosensors. We design and synthesize a water soluble poly(amido anime) dendrimer terminated with 128 guanidine groups(PAMAM-Gu+). The multiple positively charged PAMAM-Gu+ can electrostatic interact with negative GQDs to improve the fluorescence transfer efficiency. GQDs can self-aggregate and fluorescence is quenched when added small amounts of PAMAM-Gu+. However, the addition of highly negatively charged heparin(Hep) or chondroitin sulfate(CS) into the fluorescence sensing system resulted in the fluorescence recovery. Because the multi-positively charged PAMAM-Gu+ would prefer to bind with highly negatively charged Hep or CS, resulting in the de-aggregation of GQDs. We also find the fluorescence recovery extent of Hep is higher than that of CS for its higher negativity. Also, the tight binding between the multi-positively charged PAMAM-Gu+ and negatively charged polysaccharide affords the turn-on method higher sensitivity and selectivity. And this proposed method was applied to the determination of Hep or CS in commercial medicinal solutions with satisfactory results.