The Application Of Fluorescence Sensor Based On Quantum Dots/Aptamer In The Detection Of Biomolecules And Ions

As a new type of fluorescent probe,quantum dots have attracted more and more attention due to their unique optical properties and photoelectric properties.Aptamers have been considered as an effective tool for molecular recognition and detection of target materials due to their specific recognition.Combined with the advantages of quantum dots and aptamers,the sensor can realize highly sensitive,highly selective,simple and rapid recognition and detection of target molecules.Cd Te quantum dots?QDs?,one of the most studied quantum dots,possess extensive tunability,from ultraviolet to infrared,which can be achieved by varying the size and the composition of QDs.Cu In S₂ QDs are near infrared?NIR?quantum dots,which have great potential in the field of medical diagnose and fluorescence imaging.In this paper,we have developed two systems for sensitive detection of mercury ions(Hg²⁺)and adenosine-5?-triphosphate?ATP?based on Cd Te QDs,Cu In S₂ QDs,Hg²⁺-binding aptamers and ATP-binding aptamers.In chapter 1,we introduced the properties and synthetic methods of QDs,screening methods and modification of aptamers,and the application of QDs in the field of biochemistry.In chapter 2,we have developed an ultrasensitive fluorometric assay for Hg²⁺,which is based on the different affinities of gold nanoparticles?Au NPs?for unfolded and folded aptamers.In the condition of high ionic strength,Au NPs can recognize conformational changes of aptamers.Hg²⁺-binding aptamers could adsorb on the surface of Au NPs,preventing the salt-induced aggregation of Au NPs.Finally,the red Au NP/aptamer system reduces the green fluorescence of Cd Te QDs.However,in the presence of Hg²⁺,aptamers specifically react with Hg²⁺,and the Au NPs therefore form blue aggregates because they are not protected by aptamers under conditions of high ionic strength.The blue aggregates cannot quench the fluorescence of Cd Te QDs.So the fluorescence of Cd Te QDs is recovered with the addition of Hg²⁺.Fluorescence intensity is linearly proportional to the concentration of Hg²⁺ in the 50 p M to 1.0 n M concentration range,with a 2.5 p M detection limit.This ultrasensitive method has been applied to the determination of mercury in water with satisfactory results.Besides,this method shows a large potential of environmental monitoring Hg²⁺ ion,and is suitable for other ions if aptamers are available.In chapter 3,we have developed a NIR fluorescent aptamer-based sensor for sensitive detection of ATP by using ATP-binding aptamers and ?-cyclodextrin-Cu In S₂ quantum dots??-CD-Cu In S₂ QDs?.Due to the host-guest recognition between aptamers and ?-CDs,the fluorescence of ?-CD-Cu In S₂ QDs could increase with the addition of ATP-binding aptamers.After adding ATP,aptamers will bind to ATP thus forming G-quadruplexes.Aptamer-ATP complexes could enter into the hydrophobic cavities of ?-CDs,resulting in great enhancement of the fluorescence intensity.Under optimum conditions,the fluorescence intensity of ?-CD-Cu In S₂ QDs is proportional to the concentration of ATP,which shows a good linear response towards ATP concentration range of 6¹200 ?M,the detection limit for ATP is 3 ?M.The present assay has been applied to the determination of ATP in human serum samples with satisfactory results.