Electrochemiluminescence Biosensors Based On Diatomic Co-doped Carbon Dots As Emitter And Their Application In Bio-analysis

Electrochemiluminescence（ECL）analysis technology combines the advantages of electrochemical and chemiluminescence technology,which possesses high sensitivity,simple optical setup,excellent temporal and spatial controllability,and low background signal without a light source,has become a powerful technique for metal ion,small molecule and biomarker detection,environmental monitoring,and food and water testing.Currently,much effort has been devoted to improving the sensitivity of ECL detection methods to make them more reliable and applicable.Carbon dots（CDs）have been developed as a novel nanomaterial with great potential in applications such as optoelectronic devices,biosensing,imaging and catalysis due to their excellent optics,stable chemistry and low toxicity.However,the ECL efficiency of common undoped CDs is still unsatisfactory,which limits their further application in the field of ECL.Heteroatom doping is a widespread and effective method to enhance the ECL of CDs,which benefited from the modulation of electronic and chemical properties.In addition,nucleic acid signal amplification technology can convert the target into a large number of output nucleic acids,which can achieve signal amplification of the target and enhance the detection sensitivity of ECL biosensors.Based on this,this study focuses on the synthesis of a variety of heteroatom-doped CDs with excellent ECL performance as emitters combined with a new strategy of nucleic acid amplification to construct ECL biosensors for the sensitive detection of biomarkers.The specific research work can be divided into the following parts:1.Electrochemiluminescence biosensor based on fluorine and nitrogen co-doped carbon dots as emitter for ultrasensitive detection of HIV-DNA fragmentHeteroatom doping has been employed to improve the surface state of CDs and enhance ECL emission.It is noteworthy that N-doping has found to be an effective approach to optimize the surface state for improving the ECL performance of CDs.However,the ECL efficiency of single atom doping CDs was still unsatisfactory due to the restricted active sites,which limited its application in the ECL field.In this work,fluorine-nitrogen co-doped CDs（FNCDs）was synthesized by the solvothermal method,which only effectively formed hydrogen bonds to hinder the free rotation of CDs for increasing the radiation transition probability,but also changed the charge distribution of CDs leading to a narrower energy gap,thus improving the ECL intensity and stability of FNCDs.In addition,the Y-supported 3D network DNA nanostructure amplified formed by the elaborately designed horizontal hybridization chain reaction（H-HCR）was different from the simple linear amplification of conventional HCR,which not only enabled the insertion of large amounts of ferrocene,but also shortened the electron transfer distance between ferrocene and electrode,making the detection more sensitive.Finally,Exo III-assisted multiple recycling amplification could convert trace HIV-DNA into an abundance of output DNA to achieve the amplification of the target nucleic acid to trigger H-HCR.Therefore,combining these advantages,an“on-off”ECL biosensor was constructed for the ultrasensitive detection of HIV-DNA fragments with a detection limit of6.34 amol/L,which has a broad application prospect in biochemical analysis and early clinical diagnosis.2.Electrochemiluminescence biosensor based on selenium and nitrogen co-doped carbon dots as emitter for ultrasensitive detection of micro RNAMultiatoms co-doping has been demonstrated to provide more reactive active sites and thus enhance ECL emission.Nevertheless,limited by the low active site reactivity,the ECL efficiency is still unsatisfactory.Herein,selenium and nitrogen co-doped carbon dots（Se N-CDs）with excellent ECL performance was synthesized under mild conditions,in which selenium with excellent redox activity introduced new efficient redox active sites and could serve as a coreaction accelerator for accelerating the generation of abundant sulfate radicals(SO₄^·–)from the coreactant(S₂O₈^2–).Furthermore,the target-induced T7 Exo-assisted double cycle amplification strategy overcame the disadvantage of low conversion efficiency of single-cycle amplification and could convert the trace target micro RNA-221 into a large amount of output DNA to capture 3D nanostructures loaded with abundant ferrocene as ECL signal quenching probes.The constructed biosensor responded linearly to micro RNA-221 in the concentration range of 10 amol/L to 100 pmol/L with a detection limit as low as 2.3 amol/L,and was successfully applied to detect micro RNA-221 in Hela and MHCC97-L cancer cell lysates,which provided a promising path for biomarker detection and disease diagnosis.