Study On The Highly Sensitive Optical Nano-biosensor Based On Graphene Oxide

In this dissertation, a new kind of nanomaterial——water-soluble graphene oxide, was introducedinto designing of optical biosensors. By using the good biocompatibility, high fluorescencequenching efficiency and large surface area of graphene oxide, we developed severalnanobiosensors with high sensitivities, selectivities and stabilities for the detection of heavy metalionsandbiologicalmacromoleculesintheenvironmentandlivingbody.Firstly,wedesignedamultifunctionalsensingplatformforconvenient,rapidandsensitivedetectionof hybridization and hydroxyl radical of DNA, as well as single-strand-specific S1 nuclease and itsinhibitor based on water-soluble graphene oxide (WSGO). The complex of dye-labeled ssDNAandWSGOwas used as aversatileunit to assaythe DNAandS1 nuclease.Thefluorescence ofthedyewas strongly quenched by WSGO due to the strong noncovalent binding between them, whichcorresponding to a fluorescence quenched status. Upon addition of the complementary DNA, theformation of the DNA duplex will release the dye-labeled probe from the surface of WSGO andlead to the ?uorescence recovery. However, when the complementary DNA is hydrolyzed by S1 nuclease or hydroxyl radical into small fragments, the ?uorescence remain quenched because the small fragments can not form duplex any more. The limit of detection for S1 nuclease can reach2.50×10^-5units/ul. Furthermore, the enzymatic and oxidative activities as well as their inhibitorscouldbequantitativelyanalyzedbythemultifunctionalbiosensor.Secondly, we developed a highly sensitive and selective,"turn-on"and simple mercury (II)biosensor by using water-soluble graphene oxide (WSGO) and dye-labeled mercury(II)-specificoligonucleotide (MSO) probe. The probe is rich of thymine (T) and can readilyform the stem-loopstructure consists of the T-Hg²⁺-T configuration. In the absence of Hg²⁺, the probe exists as arandomcoilconformationandthefluorescenceofthedye-labeledMSOis stronglyquenched.Uponaddition of Hg²⁺, the formation of the T-Hg²⁺-T structure release the MSO from the surface ofWSGO, resulting in a restoration of the fluorescence of dye-labeled MSO. By using thefluorometric method, the limit of detection for Hg²⁺ can reach picomolar range (187 pM), and it isdemonstratedthatthebiosensorishighlyselectiveandonlyminimallyperturbedbyawiderangeofnon-specificmetalions.Magnetic microparticles (MMPs) are widely used in the immobility and/or enrichment of the biomolecules and/or analytes. A new highly sensitive biosensor for the detection of lead (II) wasdeveloped using 8-17 DNAzyme and biofunctional MMPs. MMPs assembled 8-17 DNAzyme onthe surface act as recognition element to capture target ions. In the presence of Pb²⁺, the enzymechain is activated and then cleave the substrate at rA site. In this case, dehybridization of 8-17DNAzyme allows the substrate fragment labeled with fluorescein apart away from the surface ofmagnetic particles. When collecting and detecting the solution contain the fluorescein, a highfluorescence emission of the solution shows the existence of Pb²⁺. The biosensor exhibits goodspecificityand the detection limit is 31 nM. Additionally, it is hopeful to improve the sensitivitybyadding the water-soluble conjugated polymer to the detection system, which results in an efficientFRETfromthepolymertothefluorescein.