Study On Novel Electrochemiluminescence Probe For Mercury/Arsenite Ion Detection

Environmental pollution problems have been receiving widespread attention.Among them,the pollution of heavy metal ions is one of the most severe environmental problems.At present,the detection of heavy metal ions is mostly based on expensive instruments such as atomic absorption spectrometers,and the sample prepared processing is complicated.Electrochemiluminescence(ECL)has received quite a lot of attention as an emerging detection method in recent years due to its low background signal and high sensitivity.Nanomaterials has been widely used in ECL biosensing with unique optoelectronic properties,large specific surface area,and good biological compatibility.,tris(2,2'-bipyridyl)ruthenium(II)(Ru(bpy)32+)as a common ECL emmiter whose traditional coreactants like tripropylamine are highly toxic and volatile.It is urgent to develop a new ECL coreactant based on nanomaterials.Eco-friendly ECL systems used to detect heavy metal ions can avoid secondary pollution to the environment and realize sensitive and selective monitoring of heavy metal ions in the environment.In this dissertation,different ECL sensing platforms were constructed using carbon nitride or covalent organic framework(COF),which were successfully applied to analyze mercury ion and arsenite in environmental water samples.The main research contents are as follows:1.Combined the specific recognition of Hg2+ and T bases with the electrochemiluminescence energy resonance transfer(ECL-RET)effect between silver clusters(DNA-Ag NCs)and carbon nitride nanosheets(g-C3N4 NSs),an "on-off-non" ECL biosensor was constructed to detect Hg2+.First g-C3N4 NSs and chitosan(CS)were coated on glassy carbon electrode(GCE),which shows a strong cathodic ECL with K2S2O8 as coreactant.Then the carboxyl-modified capture DNA(cDNA)was modified on the electrode surface due to the amide reaction.DNA-Ag NCs futher modified on the electrode surface via complementary hybridization between A-T bases.Owing to the ECL-RET between g-C3N4 NSs and DNA-Ag NCs,the ECL intensity of g-C3N4 NSs decreased,showing a signal "off" state.In the presence of Hg2+,the T bases in the free nucleotide fragments of DNA-Ag NCs can bind to Hg2+ and form a stable T-Hg2+-T complex via N-Hg2+-N bonds which are tighter than the hydrogen-based A-T base pairs in the chain.Therefore,DNA-Ag NCs cannot be modified on the surface of the CS/g-C3N4/cDNA electrode,which leads to the recovery of the ECL-intensity of g-C3N4 NSs,displaying an "on" state again.As results,the ECL signal biosensor was constructed successfully and can realize sensitive and selective detection of Hg2+in environmental water samples.2.It was first discovered that gold nanoparticles(AuNPs)functionalized g-C3N4 NSs(Au-g-C3N4 NSs)modified GCE can be used as a cathodic coreactant for Rulopy)32+to enhance its cathodic ECL and a ratuometumc ECL sensor for Hg2+detection is developed based on the novel Au-g-C3N4/GCE-Ru(bpy)32+system.AuNPs loaded on g-C3N4 NSs surface can catalyze the reduction of Ru(bpy)32+at the cathode to generate more Ru(bpy)3+.And the dissolved oxygen generates reactive oxygen species at negative potential which oxidize Au-g-C3N4 NSs to oxidized Au-g-C3N4 NSs free radicals,then Ru(bpy)3+ reacts with strongly oxidized Au-g-C3N4 NSs free radicals to generate excited Ru(bpy)32+*,greatly enhancing the cathodic ECL signal of Ru(bpy)32+.Therefore,Au-g-C3N4 NSs modified GCE can serve as cathodic ECL coreactant of Ru(bpy)32+.When Hg2+is present,the formation of gold amalgam at the cathode inhibites the catalysis of Au-g-C3N4 NSs to the reduction of Ru(bpy)32+ and consumes the generated ROS,leading to the weakened cathodic ECL signal of Ru(bpy)32+.At the same time,Hg2+ enhanced the anodic ECL signal of Ru(bpy)32+by improving the anodic ECL efficiency of the Au-g-C3N4/GCE-Ru(bpy)32+system.The concentration of Hg2+ was linearly related to the ratio of the anodic ECL intensity of Ru(bpy)32+to the cathodic ECL intensity of Ru(bpy)32+.Therefore,ratiometrlc detection of Hg2+ can be achieved selectively and sensitively without any complicated modification.3.Bipyridine-containing covalent organic framework(Tp-Bpy COF)overcoming its poor conductivity was first explored to be cathodic coreactant of Ru(bpy)32+and iridium(Ir(ppy)3)to enhance their cathodic ECL.Based on the coreactant effects of Tp-Bpy COF,a dual-wavelength ratiometric ECL biosensor was constructed for arsenite(As(III))detection by a dual amplification effect.First,the mixture of Tp-Bpy COF and chitosan(CS)were coated on glassy carbon electrode(GCE),then the carboxyl-modified single strand of(AC)29 was modified on the electrode surface due to the amide reaction.When no As(?)exists,(GT)29 further modified on the electrode surface via complementary hybridization to form a double strand.Ru(bpy)32+is embedded in the double strand via electrostatic interaction,then ECL-RET occurs from Ir(ppy)3 to Ru(bpy)32+,coupling with the competition for the enhanced effect of COF.Therefore,the ECL of Ru(bpy)32+at 620 nm increased,and the ECL of Ir(bpy)3 at 505 nm decreased.While As(?)is present,As(?)specifically binds to(GT)29,resulting in the inability of Ru(bpy)32+to be introduced on the electrode surface.Therefore,the ECL signal at 505 nm increases and the ECL intensity at 620 nm quenches.The change in the ratio of the ECL signal at 505 nm and 620 nm realized the quantitative detection of As(?),and it was successfully applied to monitor As(?)in environmental water samples.