| The combination of biotechnology and science materials promotes the research development of biosensors, which leads the traditional biological detection method to a higher level. As a kind of small biological molecule, nucleic acid aptamers can be produced through chemical methods in vitro, and it is easy to decorate. Aptamer can bind with its target specificity making the changes of its structure, it can be used to detect a variety of targets with the good specificity. Graphene oxide is regard as a new type of nanomaterial, and it can adsorb the single-stranded DNA and the stem-loop DNA onto its surface by π-π stacking, quenching the fluorescence of dye which has been inserted or labelled the DNA. While double-stranded DNA has the strong rigidity,which will not be adsorbed on the surface of graphene oxide. Therefore, it can reduce the background of biological detection, and improve the detection sensitivity.In this paper, we carried out the following work based on the special combination between nucleic acid aptamer and its target and the fluorescence quenching effect of graphene oxide:(1) We put forward a fluorescent sensor for detection of lead ion based on the replace of double-stranded DNA and the difference of fluorescent intensity of the SG between single-stranded DNA and double-stranded DNA. SG is regard as a kind of dye,it can insert the double-stranded DNA firstly, making the fluorescence intensity of SG stronger. The aptamer of lead ion will react with its complementary strand forming a stable double chain. When there is lead ion in the solution, lead ion can bind with its aptamer specificity, reducing the amounts of double-stranded DNA. We can detect the lead ion quantificationally according to the fluorescence intensity when the SG is added to the solution, and the method has the advantages of high sensitivity, strong specificity, the simpleness and speediness. The lowest detection concentration of lead ion is 2 nM.(2) The detection of Hg2+ is very important for environmental monitoring. A novel and convenient biosensor for Mercury(II) detection was developed based on toehold-mediated strand displacement isothermal enzyme-free amplification(EFA)technology and label-free fluorescence platform using SYBR Green Ι(SG) and graphene oxide(GO). The method is highly sensitive and selective, and thelogarithmically related Hg2+ linearity range is from 0.1 nM-50 nM with a detection limit 0.091 nM. Moreover, our strategy has a good potential in the environment surveys in the future.(3) We put forward a hybrid chain reaction amplification detection of adenosine triphosphate(ATP) based on auxiliary magnetic sensing strategy. The surface of magnetic nanoparticles is easy to be modified, and also the magnetic nanoparticles have the advantages of the convenient operation, the good separation effect and the higher selectivity for biological sensing. First of all, the biotin labeled ATP aptamer will connect to the surface of the magnetic nanoparticles which is modified with streptavidin based on the affinity between biotin and streptavidin. Then a single DNA which is complementary to the ATP aptamer is added to hybrid with ATP aptamer, and the unnecessary DNA will be removed by magnetic separation. When the targeted ATP is added to the solution, the ATP will bind with its aptamer specially by releasing the complementary single-stranded DNA, and the complementary single-stranded DNA will continue for the next step of hybridization chain reaction. The signal would be stronger after magnetic separation. The background will be reduced by the fluorescence quenching effect of the graphene oxide, and the method has high sensitivity and high selectivity for targeting ATP. The lowest detection concentration of ATP is 0.1 nM. |
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