Novel Fluorescent Biosensor Based On Cobalt Oxyhydroxide And Polydopamine Nanomaterial

In recent years,nanomaterial appeared in many fields with a wide range of applications because of its unique electronic properties and large specific surface area.Many analysts have made efforts to combine nanomaterial with biosensor and advance the development of intelligent and integrated biosensor.In this thesis,novel,simple and low-cost fluorescent biosensors were constructed to detect thrombin,ascorbic acid(AA)and Fe3+ in the presence of new nanomaterial,cobalt oxyhydroxide(CoOOH)nanosheets and polydopamine(PDA)nanoparticles.The details are as follows:In chapter 2,an aptasensor based on a fluorophore-labeled aptamer and CoOOH nanosheets was developed for determining the concentration of thrombin.We first found that the CoOOH nanosheets had the ability to distinguish a G-quadruplex from single-stranded DNA(ssDNA)due to the different abilities of the nanosheet to absorb these two DNA forms.The absorption of 6-carboxyfluorescein(6-FAM)labeled aptamer(ssDNA)on the surface of the CoOOH nanosheets resulted in quenching of the fluorescence of the FAM through fluorescence resonance energy transfer(FRET)between the FAM and the CoOOH nanosheets.However,the binding of the aptamer to its target resulted in the formation of an antiparallel G-quadruplex complex,for which the CoOOH nanosheets had weak affinity,resulting in a recovery of fluorescence.We applied this strategy to the detection of thrombin.The intensity of the fluorescence recovery was found to be linear with the logarithm of the thrombin concentration in the range of 0.5 to 100 nM,and the limit of detection(LOD)was determined to be 0.5 nM.Because of the high selectivity of the aptamer and strong quenching ability of the CoOOH nanosheets,similar aptasensor but with different specific aptamers may potentially serve as platforms to detect a wide range of analytes,and may hence have promising applications in clinical diagnosis.In chapter 3,a "turn-on" fluorescent biosensors based on CoOOH nanosheets and FAM labeled ssDNA had been developed for the detection of AA.CoOOH nanosheets had the ability to absorb FAM labeled ssDNA and resulted in quenching of the fluorescence of the FAM through FRET.With the addition of AA,redox reaction occurred between AA and CoOOH nanosheets due to AA's strong reduction.FRET was blocked because CoOOH nanosheet was reduced to Co2+.And then the fluorescence of FAM was restored.The quantitative detection of AA could be achieved by monitoring the change of fluorescence intensity.By calculating,the detection limit of AA based on this biosensor was about 35 ?M.The method is simple and low cost,and can achieve rapid and sensitive detection of AA.In chapter 4,we synthesized the PDA nanoparticles with photoluminescence by oxidizing the dopamine under alkaline conditions.Fe3+ could coordinate with the catechol groups on the surface of PDA nanoparticles,leading to fluorescence quenching by electron transfer process.While AA could reduce Fe3+,leading to fluorescence recovery of PDA nanoparticles.Through monitoring the fluorescence intensity of PDA nanoparticle,we achieved free labeling to detect Fe3+ and AA.The detection limits of Fe3+ and AA by this method were 21.5?M and 180 ?M,respectively.Compared with the traditional methods,this method is simple to synthesize,rapid detection,no extra operation and expensive instruments.And based on the characteristics of fluorescent PDA nanoparticles,it can be developed more promising sensor applications.