Modulation Of Quantum Dots Fluorescence Properties Based On Nanogold And Construction Of Highly Sensitiive Biosensors

The fluorescent sensors have extensive applications in fields such as disease diagnosis,food detection,and environmental monitoring.The emergence of nanomaterials has improved the detection performance of fluorescence sensors and promoted the development of fluorescent sensors.Quantum dots（QDs）,as a common new type of semiconductor fluorescent nanomaterial,are employed extensively in the biomedical fields of biological detection,imaging,and dynamic tracing due to their distinctive optical features.However,the current application of quantum dots in the field of biomdical detection requires surface modification of hydrophobic quantum dots,and due to a series of problems such as complex biological environments,the fluorescence performance of quantum dots is damaged,resulting in limited sensitivity of quantum dots in biological detection.Meanwhile,due to the fact that disease biomarkers start at very low levels,highly sensitive detection is needed to achieve early prevention and screening of diseases.Due to a unique local surface plasmon resonance effect,precious metal nanoparticles can improve the fluorescence quantum yield and stability of nearby fluorescent materials.This phenomenon is called metal enhanced fluorescence（MEF）effect.Based on the effect,it is anticipated to improve the fluorescence performance of quantum dots and enhance their sensitivity in biological detection.Therefore,in order to improve the fluorescence performance of quantum dots and achieve early and highly sensitive detection of disease marker,the thesis employs the metal enhanced fluorescence effect.The following is the primary content:（1）The C-reactive protein（CRP）is a kind of protein related to infection.The traditional methods are insufficient to predict the risk of cardiovascular diseases due to the lack of high sensitivity.In view of this,we design a metal enhanced quantum dot fluorescence system for signal amplification,which allows us to quickly,high sensitivity,high throughput detects CRP by quantum dot-based fluorescent linked immunosorbent assay（QLISA）.Firstly,Cd Se/Zn S core/shell quantum dots with high stability and high quantum yield are firstly prepared by using the self-owned“phosphine-free”,“low temperature injection and high temperature growth”technology.Cd Se/Zn S quantum dots modified by self-synthesized amphiphilic polymers maintain the integrity of the original ligand of hydrophobic quantum dots,thus obtaining quantum dots with high quantum yield（～92.6%）,high stability and good biocompatibility.Secondly,anisotropic gold nanospheres（Au NSs）are synthesized by seed growth method.It has a large number of sharp branches acted as"hot spots",an adjustable size,and a local surface plasmon resonance（LSPR）peak,all of which can be used to greatly enhance the local electromagnetic field of adjacent quantum dots,thus improving the radiation emission rate of quantum dots,and the fluorescence performance（increasing fluorescence intensity and fluorescence stability）.Then the self-assemble monolayers（SAMs）of Au NSs are formed on the ELISA plate through Au-S,the antibody is orderly coated on the substrate by dithiothreitol（DTT）,which can increase binding efficiency of the antibody.Finally,a highly selective and sensitive immune detection platform is constructed based on metal-enhanced fluorescence effect between quantum dots and Au NSs.The scheme not only provides a wide detection range（0.25 ng/m L-1000 ng/m L）and a low limit detection（0.056 ng/m L）,but also has short detection time（20 minutes）for CRP detection.More interestingly,the plasmonic ELISA plate shows～3-fold fluorescence enhancement and～17-fold sensitivity improvement comparing with the normal ELISA plate where no Au NSs is laid.More importantly,the assay is used for the detection of whole blood samples and tissue samples with high accuracy and sensitivity.（2）The early diagnosis of Alzheimer’s disease has always been a huge challenge in clinical diagnosis.In view of this,we design a dual signal amplification sensor based 3D DNA walking machine and metal-enhanced fluorescence.Firstly,green and environmentally friendly In P quantum dots are synthesized in organic solutions at high temperatures.Through ligand exchange at low temperatures,biocompatible In P quantum dots with 3-MPA are subsequently produced.Zn²⁺in ZnCl and S^2-in 3-MPA are excited by ultraviolet radiation to grow Zn S outer shells on the surface of In P quantum dots.The addition of the Zn S shell slows down the flow of excitons within In P quantum dots,successfully enhancing the stability of the water-soluble In P quantum dots and maintaining their favorable fluorescence properties.The 3D DNA walking machine is carried by magnetic nanoparticles with good magnetic guidance and controllability.And the DNA walking machine has great signal amplification capabilities,high walking efficiency,and the ability to significantly improve detection sensitivity.The 3D DNA Walker is activated after Protects（the strand that makes the Walking stationary）captures a Target（mi R-574-5p）,and the Walking strand（Walking）is complementarily paired with the BHQ-modified Support to produce a site specifically recognized by the Nt.A1WI nicking endonuclease.The BHQ intermediate is complementarily paired with In P@MPA@NH₂-DNA,at which point the In P@MPA@NH₂-DNA fluorescence is OFF.Subsequent addition of Au NSs@SH-DNA prepared by the salt aging method resulted in a Super ON fluorescence state,resulting in a recovery of In P@MPA@NH₂-DNA fluorescence and an enhanced fluorescence signals.The highly sensitive detection of mi R-574-5p was achieved by capturing a target by 3D DNA Walker to generate multiple intermediates for nucleic acid signals amplification and anisotropic gold nanospheres to enhance quantum dot fluorescence signal amplification.