Construction Of A Novel Fluorescence Sensor Based On DNA And Graphene Quantum Dots And Its Bioanalysis Applcation

At present,the design of the fluorescence sensors are mostly used the commercial organic dye as a fluorescent group with "on-off-on"signal conversion strategy as a promising method to improve the sensitivity of the sensor,which can not only largely reduce the background fluorescence signal,but also eliminate false-positive signal interference.Graphene oxide?GO?,carbon nanotubes?CNTs?and gold nanoparticles?AuNPs?,etc.have been used as quenchers to reduce the background fluorescence signal.There is no doubt that it will improve the sensitivity of detection,but also can make the experiment more cumbersome at the same time.Graphene quantum dots?GQDs?,a novel zero-dimensional fluorescent nanomaterial,have attracted tremendous attention.They display many characteristics,such as lower toxicity,better resistance to photo bleaching and good biocompatibility,compared with traditional semiconductor quantum dots?such as,CdTe and CdS?and commercial organic dyes.In this paper,a series of novel fluorescence sensors based on DNA-modified GQDs and DNA structure conversion strategy were designed to accomplish the detection for target DNA,heavy metal ions,organic small molecules and biological toxins with high sensitivity.?1?we made use of carbon nanoparticles?CNPs?obtained from candle soot as an ideal electron/energy acceptor.When bGQDs labeled HIV?human being disease-related gene human immunodeficiency virus DNA?probe and gGQDs labeled HBV?human being disease-related gene hepatitis B virus DNA?probe were mixed with CNPs,GQDs fluorescence was quenched;Subsequently,the added target HIV and HBV DNA can trigger the quenched fluorescence recovered.In addition,an exonuclease-assisted autocatalytic target recycling amplification was also integrated into the sensing system,which afforded the biosensor with high sensitivity toward two kinds of target DNA,resulting in a detection limit of 6.56 pM for HIV and 9.5 pM for HBV,respectively,which is about 60-fold lower than that of traditional unamplified homogeneous fluorescent assay methods.?2?we report the development of a new high-sensitivity fluorescent aptasensor for the detection of ochratoxin A?OTA?based on tuning aggregation/disaggregation behavior of GQDs by structure-switching aptamers.The fluorescence sensing process for OTA detection involved two key steps:1)cDNA-aptamer?cDNA:complementary to part of the OTA aptamer?hybridization induced the aggregation of GQDs?fluorescence quenching?after cDNA was added into the GQDs-aptamer bioconjugate solution and,2)the target of OTA triggered disaggregation of GQD aggregates?fluorescence recovery?.Such new fluorescent sensing platform can be used to monitor OTA with a linear range of 0 to 1 ng/mL and very low detection limit of 13 pg/mL.?3?we constructed a novel fluorescence sensor of microcystin-LR?MC-LR?by tuning the aggregation/disaggregation behavior of GQDs by 3WJ DNA machine.The detection process was divided into two parts:1)DNA hybridization formed 3WJ DNA structure induced the aggregation of GQDs?fluorescence quenching?;2)the target of MC-LR triggered disaggregation of GQD aggregates?fluorescence recovery?.The detection limit can be as low as 19.2 pg/mL and specially realize the successful evaluation of MC-LR concentration in practical tap water and Olympic lake water samples.In addition,recycled operation and reproducible detection could be realized based on the reversible assembly and disassembly.?4?A novel dual functional fluorescent sensor was developed to detect mercury ions(Hg²⁺)and melamine based on thymine-rich DNA functionalized GQDs.In the presence of Hg²⁺,thymine-rich DNA form a rigid hairpin structure due to the formation of the T-Hg²⁺-T base pairing,cause the fluorescence signal turn off,while the addition of melamine can emit a "turn-on" fluorescent signal due to the stronger coordination affinity between Hg²⁺ and melamine.This "on-off-on" fluorescence signal conversion strategy show a dual functional sensing platform for convenient detection of Hg²⁺ and melamine.Moreover,we developed a logic gate with Hg²⁺ and melamine as inputs,wherein the output "1" is obtained only when the input is Hg²⁺.