Construction Of Novel Electrochemiluminescence Biosensor Based On Graphite-like Carbon Nitride Nanomaterials

Graphite-like Carbon Nitride（g-C₃N₄）is a polymeric semiconductor material composed of two elements,carbon and nitrogen.It has a layered structure similar to graphite.Because of its unique advantages such as low density,good biocompatibility,adjustable optical band gap,and stable chemical properties,it has been widely used in the field of electrochemiluminescence（ECL）sensing in recent years.Based on the excellent ECL properties of g-C₃N₄ nanomaterials,this paper designs and synthesizes modified g-C₃N₄ and its composite materials,combining co-reaction promoter signal amplification strategy,new co-reaction reagent amplification strategy,and ECL resonance energy transfer（ECL-RET）method to develop three ECL biosensors for the detection of anticancer drugs,amino acids and peptides.The constructed sensors have the advantages of high sensitivity,good selectivity,low cost,simplicity and quickness,etc.,which has expanded the application of g-C₃N₄ nanomaterials in the field of analytical sensing.The specific research is as follows:1.Fe-Co-Co prussian blue analogues as a novel co-reaction accelerator for ultrasensitive electrochemiluminescent biosensor constructionThe introduction of co-reaction accelerators provides a new way to improve the luminous efficiency of luminescent reagents.In this work,Fe_yCo_3-y[Co（CN）₆]₂Prussian blue analogs（Fe-Co-Co PBAs）was used as an efficient co-reaction accelerator of the carboxylated graphene-like carbon nitride/peroxydisulfate(C-g-C₃N₄/S₂O₈^2-)ECL system improves the efficiency of the luminophores and the co-reactant,and obtains a stronger and stable ECL signal.We have synthesized a core-shell Fe-Co-Co PBAs@C-C₃N₄ ECL prober with a core-shell structure that integrates the luminophores and the co-reaction accelerator by electrostatic adsorption.The excellent magenetism of Fe-Co-Co PBAs allows reaction products to be quickly and easily separated from complex sample solutions,meanwhile,its electrochemical regenerable property greatly improves the ECL signal enhancement efficiency of coreaction accelerator.Based on this,an ultra-sensitive ECL sensor was constructed for quantitative detection of methotrexate（MTX）.The linear range of the sensor is 5pmol·L^-1 to 10μmol·L^-1,and the detection limit is 1.1 pmol·L^-1（S/N=3）.Therefore,this method provides a new perspective for the research of PBAs nanomaterials in biosensing,and provides new ideas for the rapid detection of MTX.2.Research on construction of"off-on"ECL sensor based on electrochemiluminescence resonance energy transfer system for cysteine detectionSo far,most ECL sensors based on g-C₃N₄ nanomaterials are signal-off.However,in complex biological analysis,the signal-off strategy is prone to generate false positive results,and the signal-on strategy can avoid this phenomenon.Therefore,in order to improve the accuracy of the analysis,we synthesized manganese dioxide/carboxylated graphite-like carbon nitride（MnO₂/C-g-C₃N₄）nanocomposites as a L-cysteine（CySH）detection probe in a simple one-step method Needle,based on the ECL-RET between C-g-C₃N₄ and MnO₂,built an ultra-sensitive signal"off-on"ECL sensing platform.In this nanocomposite,C-g-C₃N₄ and MnO₂ act as energy donors and energy acceptors,respectively.The ECL signals of C-g-C₃N₄ nanosheets are quenched by MnO₂ nanosheets through ECL-RET.When CySH was present,MnO₂ was reduced to Mn²⁺,ECL-RET was eliminated,allowing the ECL signal to fully recover.Under optimized conditions,CySH has a good linear relationship with the ECL signal in the concentration range of 0.50 nmol·L^-1 to 1.0μmol·L^-1,and the detection limit is 0.18 nmol·L^-1（S/N=3）.This method had good selectivity for CySH and was used for the determination of CySH in actual samples with satisfactory results.This work provides a new method for fast and sensitive detection of CySH.3.Poly-L-lysine as efficient co-reactant for enhanced electrochemiluminescence of silver-doped graphite carbon nitride and its sensing glutathioneThe way to introduce a co-reaction reagent into the ECL system to enhance the luminous efficiency of the luminescent group and then amplify the ECL signal is an important means to improve the detection sensitivity of the ECL biosensor.In the present work,we found that poly-L-lysine（PLL）could act as an effective co-reactant for the anodic ECL of silver-doped graphite carbon nitride（Ag-g-C₃N₄）.Meanwhile,the possible anodic ECL reaction mechanism of the Ag-g-C₃N₄/PLL system was discussed.The study found that nano-silver’s electron transfer and storage capacity can effectively alleviate electrode passivation caused by the excessive injection of electrons into the g-C₃N₄ film,thereby improving the ECL stability of the g-C₃N₄,and the good biocompatibility and water solubility of the PLL can successfully improve the luminous efficiency of Ag-g-C₃N₄ and achieve signal amplification.On the basis of the quenching effect between the PLLradical and the free radical scavenger glutathione（GSH）,the single-off ECL sensor was successfully constructed for GSH analysis.The linear response range of this method is 1.0 nmol·L^-1～1.0 mmol·L^-1,and the detection limit is 0.32 nmol·L^-1（S/N=3）,which provides a new idea for the rapid detection of GSH.