Carboxyl-modified Tris(2,2′-bipyridyl)ruthenium(Ⅱ)-based Electrochemiluminescence Aptasensors For The Detection Of Lead Ion In Soil

Heavy metal pollution has become an important reason threatening soil quality safety and agricultural environment health in China.As one of the heavy metals with strong toxicity,lead ion(Pb²⁺)in soils can reduce crop yield,affect the quality safety of agricultural products,and finally endanger the agricultural environment and human health.In order to strengthen the prevention and control of Pb²⁺pollution in soils,realizing the precise detection of Pb²⁺is of great significance.As-developed instrumental analytical methods such as mass spectrometry and spectroscopy have the advantages of high accuracy and reliability,but they rely on expensive instruments and professional operations.Electrochemiluminescence（ECL）aptasensing method has attracted widespread attention due to high sensitivity,good selectivity,and simple operation.As ECL emitters,tris（2,2′-bipyridyl）ruthenium（II）(Ru（bpy）3²⁺)and its derivatives have laid the application foundation of ECL in the sensing field.Among them,carboxyl-derived Ru（bpy）₃²⁺emitters exhibit high luminescence efficiency due to the unique surface properties,and have excellent analytical performances in ECL aptasensors for the detection of Pb²⁺.However,the luminescence mechanisms of carboxyl-derived Ru（bpy）₃²⁺emitters are still unclear,and the sensitivity and accuracy of the sensor need to be further improved.For above problems,this thesis focuses on the development of sensitive and accurate ECL methods for Pb²⁺in soils,and starts with improving the sensitivity of ECL aptasensor,selecting six carboxyl-modified Ru（bpy）₃²⁺(Ru（dcbpy）₃²⁺)as the ECL emitter,elucidating the coreactant and the annihilation mechanisms of Ru（dcbpy）₃²⁺by the intrinsic property of carboxyl functional groups,having constructed a variety of high-performance ECL aptasensors by introducing signal amplification and ratiometric strategies,which have successfully achieved the precise analysis of Pb²⁺in soils.The main research contents are as follows:（1）In order to improve the sensitivity of Pb²⁺analysis,based on the surface property of Ru（dcbpy）₃²⁺,nitrogen-doped carbon quantum dots（NCQDs）were designed and prepared,and an intermolecular hydrogen-bond-induced quench-type ECL system was established by the quenching effect of Ru（dcbpy）₃²⁺ECL system by NCQDs,thereby a quenching mechanism involving the energy transfer from the excited state of Ru（dcbpy）₃²⁺to the intermolecular hydrogen bond was proposed.Furthermore,an ECL aptasensor was constructed using the principle that the specific binding of Pb²⁺and aptamer caused the abscission of NCQDs,thereby resulting in the recovery of ECL signal.The as-developed ECL aptasensor showed a linear response range of 1.0×10^-14 M～1.0×10^-8 M and a detection limit of 4.4×10^-15 M,which has been successfully applied to the sensitive detection of Pb²⁺in soil samples.（2）In order to further improve the sensitivity of the sensor,G-quadruplex signal amplification strategy was introduced to construct an ECL aptasensor for Pb²⁺detection using the synergistic effect between the abscission of quencher and the formation of G-quadruplex.It was clarified that the synergistic effect came from the intermolecular hydrogen bond between Ru（dcbpy）₃²⁺and NCQDs,and the synergistic effect effectively improved the sensitivity of the ECL aptasensor.The as-developed ECL aptasensor showed a linear response range of 1.0×10^-15M～1.0×10^-8 M with a low detection limit of 1.9×10^-16 M,and also exhibited excellent selectivity,repeatability,and stability.（3）The ratiometric strategy was introduced to further eliminate the potential interference of single signal from electrode modification methods,environment and other factors,thereby improving the accuracy of the sensor.According to theory calculation of energy level stability and electron-accepting ability,we designed and selected Ru（dcbpy）₃²⁺as only one emitter that could generate dual-potential ECL signals without any coreactant,and proposed its annihilation mechanism in aqueous phase.On this basis,a ratiometric ECL aptasensor was constructed based on the difference in the quenching degree of the dual-potential signals of Ru（dcbpy）₃²⁺by gold nanoparticles（Au NPs）,which improved the accuracy of the ECL aptasensor.The as-developed ratiometric ECL aptasensor showed a linear response range of 3.0×10^-12 M～1.0×10^-8 M with a detection limit of 1.3×10^-13 M,which has been successfully applied to the detection of Pb²⁺in soil samples.（4）Based on the above work,luminol as the second emitter was introduced to construct a dual-emitter ratiometric ECL aptasensor based on the resonance energy transfer（RET）between Ru（dcbpy）₃²⁺and luminol as well as surface plasmon resonance（SPR）between Ru（dcbpy）₃²⁺and Au NPs.The combination of RET and SPR amplification strategies ensured the reliability of the ECL aptasensor,further improving the sensitivity of the ratiometric ECL aptasensor.The as-developed ratiometric ECL aptasensor showed a low detection limit of 3.0×10^-14 M,which achieved the precise analysis of Pb²⁺in soil samples,and its reliability has been verified by inductively coupled plasma mass spectrometry（ICP-MS）.