Research On Highly Efficient Doped Quantum Dots To Construct Electrochemiluminescence Biosensor For Sensitive Detection Of MicroRNA

Electrochemiluminescence（ECL）is generated chemiluminescence by a series of redox reactions on the electrode surface through electrochemistry,and meanwhile the excited state returns to the ground state in the process,which possesses the advantages of low background signal,wide response range,high sensitivity,high spatial and temporal resolution,and easy operation.In recent years,rearchers have constructed ECL biosensors to realize the sensitive detection of biomoleculers,such as proteins,virus,RNA,DNA fragment,etc.The abnormal expression of microRNA（miRNA）is associated with tumor diseases,but the content of miRNA in tumor is low.Therefore,the stringent requirement is put forward for the sensitive and accurate detection of miRNA.In addition,quantum dots（QDs）as a branch of nanomaterials,have attracted much attention in the ECL field due to unique optoelectronic properties,tunable wavelength,and adjustable size,etc.However,the ECL efficiency of QDs is low as ECL emitters in the field of biology.It’s a challenging problem to improve the ECL fficiency of QDs and further construct ECL biosensors for sensitive and accurate detection of miRNA.Based on this,on the one hand,the novel doped QDs are synthesized by doping suitable elements into QDs,which are tuned the optoelectronic properties to overcome the defects of the ECL emitters.On the other hand,the new nucleic acid amplification strategies are designed to achieve high conversion efficiency between targets and signal probes,providing new ways to build highly sensitive and precisely selective ECL biosensors,which can be further applied to quantitative detection of miRNA and provide opportunities to realize practical applications for clinical diagnosis and bioassays.The research work is divided into the following sections:1.Highly efficient electrochemiluminescence of MnS:CdS@ZnS core shell Quantum dots for ultrasensitive detection of microRNACdS:Mn@ZnS QDs have the shortcomings of size mismatch and“self-purification”effect,which were prepared by ionic doping.What’s more,the ECL efficiency was only0.87%.In this work,MnS:CdS@ZnS QDs were synthesized by bimetallic clusters（Cd₂Mn₂O₄）doping exhibited high ECL efficiency of up to 15.84%with S₂O₈^2-as cathodic coreactant,which could solve these problems and achieve the surface defect passivation.A novel“signal on-off”ECL biosensor was developed for ultrasensitive detection of miRNA let-7a based on MnS:CdS@ZnS QDs as ECL emitters and strand displacement amplification（SDA）as target cycle strategy,in which the trace target miRNA let-7a was able to be converted to a number of output DNA labeled with ferrocene（Fc）.The well-designed ECL biosensor exhibited high stability and excellent sensitivity of a concentration variation from 10 amol/L to 1 nmol/L and a low detection limit of 4.1amol/L,which was further applied to the analysis of miRNA let-7a from cancer cell（MCF-7）lysate.Thus,this strategy provides a novel method to prepare high-efficient ECL emitters for the construction of ECL biosensing platforms in biological fields and clinical diagnosis.2.AgAuS Quantum Dots as a Highly Efficient Near-Infrared Electrochemiluminescence Emitter for the Ultrasensitive Detection of microRNAThe ECL efficiency of Ag₂S QDs in the S₂O₈^2-system was low.In order to improve the ECL efficiency of Ag₂S QDs,researcheres have taken a number of steps,such as doping toxic metal ions into Ag₂S QDs or combining with other nanomaterials to form nanocomplexes.However,some shortcomings including heavy-metal toxicity,poor biocompatibility and low ECL efficiency still limit their further applications in biosensing and medical imaging.In this work,the stable and efficient NIR ECL emission was achieved by employing alloyed silver gold sulfur quantum dots（AgAuS QDs）as ECL emitters with K₂S₂O₈ as the coreactant for the first time,which attributed to the narrowed band gap by alloying Au atoms.The ECL efficiency of AgAuS QDs was 34.91%,which was substantially improved compared with the ECL efficiency of Ag₂S QDs（10.30%）.Additionally,an improved localized catalytic hairpin self-assembly（L-CHA）system was developed to display increased reaction speed by improving the local concentration of DNA strands,which addressed the obstacles of time-consuming of traditional CHA systems.As a proof of the concept,based on AgAuS QDs as the ECL emitter and improved L-CHA systems as signal amplification strategy,a“signal on-off”ECL biosensor was developed to exhibit superior reaction rate and excellent sensitivity with a detection limit of 10.5 amol/L,which was further applied to the analysis of miRNA-222from cancer cell（MHCC-97L）lysate.This work pushes the exploration of highly efficient NIR ECL emitters to construct biosensor for ultrasensitive detection of biomolecules in disease diagnosis and NIR biological imaging.3.The Efficient Electrochemiluminescence Emitter of Ag Doped CdTe Quantum Dots for the Ultrasensitive microRNA DetectionIn order to improve the ECL performance of CdTe QDs,in this work,a new ECL biosensor with Ag-doped CdTe QDs as the highly efficient ECL emitters was designed for sensitive detection of miRNA-222.Compared with the ECL intensity of CdTe QDs,that of Ag-CdTe QDs was higher,which was attributed to the Ag NO₃ as a dopant during the synthesis process,which changed the crystal shape of QDs from octahedral to cubic to improve the ECL efficiency.Meanwhile,we employed the strand displacement amplification as the target recycle amplification strategy to convert miRNA-222 into a large amount of output DNA（S1 and S2）,and constructed a"signal on-off"biosensor to achieve a low LOD of 61.9 amol/L.In addition,this biosensor exhibited excellent selectivity and good stability.This protocol not only provides a new ECL emitter,but also offers a novel research pathway for clinical diagnosis and bioanalysis.