Development And Application Of Novel Carbon Nanomaterials Based Biosensors

With the development of bioscience, the requirement of measurement andanalysis for the related substances resulting from metabolical processes is growinghigh. In order to obtain accurate and comprehensive bioinformation, some analysisand measurement methods with high sensitivity, high selectivity, ease to operationand cost effective are badly in need of development. Biosensor is a detectiontechnology developing from the multi-disciplinarity involving biology, chemistry,physics, medicine, microelectronics and so on. Because the technology has theadvantages of ease to operate, high sensitivity, good selectivity and fast analysis, ithas been paid high attention, and will be widely applied in the field of bioanalysis.In recent years, study on carbon nanomaterials becomes a wordwide hot spot, and thus various carbon nanomaterials with all kinds of structures and morphology have been synthesized, such as zero dimensional fullerenes, one-dimensional carbon nanotubes, two-dimensional graphene and etc. As a class of the common nanomaterials,because of the advantages of good biological compatibility, excellent catalysis and electrical conductivity, and large specific surface area, carbon nanomaterials are widely and effectively applied in the field of biochemical analysis. Specially, the development of biosensor is greatly promoted by the introduction of different structure of carbon nanomaterial which can effectively improve the sensitivity and stability of the biosensor.In this thesis, we prepare several new types of carbon nanomaterials by chemicalvapor deposition method, design several novel biosensors, and apply them todetecting heavy metal ions, small molecules and DNA. The main contents of thisthesis are as follows:（1）Based on the remarkable difference in affinity of GO with ssDNA containingdifferent number of bases in length, we constructed a graphene–DNAzyme basedsensing system for amplified fluorescence "turn-on" detection of Pb²⁺. TheDNAzyme-substrate hybrid containing a large ssDNA loop make the fluorophoreclose to the GO surface to the greatest extent to afford a high quenching efficiencyand a low background fluorescence. Upon the addition of Pb²⁺, the DNAzyme wasactivated and cleaved the substrate strand, releasing a short FAM-linkedoligonuleotide fragment, a related long oligonuleotide fragment and the DNAzymestrand. The DNAzyme strand can hybridize with another substrate strand and then induce the second cycle of cleavage by binding Pb²⁺. The introduction of GO into thesensing solution will result in weak quenching of the fluorescence of FAM due to theweak affinity of the short FAM-linked oligonuleotide fragment to GO, and thefluorescence intensity should gradually increase with increasing Pb²⁺concentrationadded. Our proposed biosensor exhibits a high sensitivity towards target with adetection limit of300pM for Pb²⁺.（2） we developed a magnetic graphitic nanocapsule nanomaterial for nucleicacid detection. Combining the unique properties of graphene and magneticnanoparticles, a core-shell magnetic graphitic nanocapsule material was firstsynthesized. Then, by means of π-stacking interactions between the nucleotide basesand the MGN outer shells, stable ssDNA/MGN complexes could be formed. Theheart of this biosensor is the efficient quenching for DNA detection. However, tofurther functionalize this biosensor, we designed a multipurpose DNA captur ing andreleasing strategy for programmed and targeted fishing, enrichment and detection ofDNA. With MGN nanomaterials and this simple, nonenzymatic strategy, the LOD ofour snesing platform was observed down to50pM, approximately three orders ofmagnitude better than common carbon nanotube-and graphene-based fluorescentbiosensors.（3）we developed a method of synthesizing hollow graphitic nanocapsules （HG N）and using them as an electrode material for hydrogen peroxide detection. TheseHGNs were used as three-dimensional matrices to effectively immobilize enzymes,proteins and small molecules. Specifically, a reagentless amperometric biosensor wascreated by coimmobilization of methylene blue （MB） electron mediators andhorseradish peroxidase （HRP） enzyme on the HGN-coated electrode. The positivelycharged HRP and MB molecules were anchored on the HGN surface throughelectrostatic adsorption. As a consequence of the extra strong π-π interaction, HGNsexhibited a high loading capacity for the MB electrochemical mediator-molecules.The constructed HGN-HRP-MB platform ably facilitated electron shuttling betweenthe active center of HRP enzyme and the surface of the electrode. Thus, by usingHGN as the electrode matrix, together with a simple MB and HRP assembly strategy,the sensing platform demonstrated the ability to detect hydrogen peroxide with highsensitivity, selectivity, reproducibility and stability.