The Sensing Method Based On DNA Nanomachine And Fluorescent Polydopamine Nanoparticles

Biosensing technology is an important technology,which is established by various disciplines,and it has been widely applied in the fields of food,medicine,environmental monitoring and so on.The development of biosensing technology has been affected many other technology.However,with the change of social demand,it is urgent to develop the novel sensors with high sensitivity,good specificity,high accuracy,rapid response and strong operability.Due to the specific advantages of nanomaterials and DNA nanotechnology,biosensing technology has been further developed.Hence,according to the characteristics of nanomaterials and DNA nanotechnology,several biosensors with high accuracy,fast response and simple operation for the detection of biomolecules have been developed in this article.The contents of the study are as follows:（1）In chapter 2,RNase H is an endoribonuclease that is involved in many biological processes,and its activity is related to some diseases,so it could be used as a potential therapeutic target.Based on this,we constructed a novel DNAzyme motor for the sensitive detection of intracellular RNase H activity.DNAzyme motor contains the locked-DNAzyme with hairpin structure（the stem part is DNA/RNA hybrid duplexes）and the corresponding substrate strand,both of are connected to the gold nanoparticles（Au NPs）by Au-S bonds.Initially,the fluorescence of the FAM in the substrate was quenched.When the DNAzyme motor enters the cell,the intracellular RNase H could specifically degrade the RNA fragments in the DNA/RNA hybrid duplexes,resulting in the disintegration of the hairpin structure and released the active DNAzyme.Further addition of Mn²⁺,the active DNAzyme could effectively cleaved its substrate strand,releasing the FAM-labelled DNA fragment.Due to the hybrid thermodynamic instability between the DNAzyme and cleavage products,the DNAzyme could become free again and hybridize with another adjacent substrate,resulting in the next cyclic cleavage and dissociation until the most of the substrate strand were cleaved.Each cleavage step could release a FAM-labelled DNA fragment from the Au NP surface,resulting the fluorescence was restored.Our method has the advantages of the strong operability,high specificity and low detection limit,and could effectively realized the sensitive detection of intracellular RNase H activity.（2）In chapter 3,ascorbic acid（AA）,as an important neuromodulator,is involved in many physiological processes.In this chapter,based on the principle of Mn O₂ nanosheets oxidization of dopamine to synthesized fluorescent polydopamine（F-PDA）nanoparticles,we constructed a facile biosensor for rapid and reliable detection of ascorbic acid.Mn O₂ nanosheets have strong oxidation properties,which could oxidize dopamine to the corresponding derivatives of quinone,and the further sel-polymerization was occured to form F-PDA nanoparticles.However,ascorbic acid,as a reducing agent,could effectively reduce the Mn O₂ nanosheets to Mn²⁺without the ability to oxidize dopamine,thus preventing the formation of F-PDA nanoparticles and producing weak fluorescence signals.Detection limit of this sensing method was as low as 1.14μM.In addition,the method has the advantages of sim ple operation,fast response,low cost,and has a good development prospect.（3）In chapter 4,cysteine（Cys）is involved in many cellular and physiological processes in the human body,and its abnormal expression is also the cause of many physical diseases.Therefore,it is important to construct an effective detection platform for the detection of cysteine.Based on this,we synthesized a fluorescent polydopamine nanoparticle that could be quenched by Cu²⁺for the efficient detection of cysteine.Cu²⁺could coordinate with the catechol group on the fluorescent PDA nanoparticles and futher quenched the fluorescence of PDA nanoparticles.Whereas,the cysteine could bind to Cu²⁺through the strong affinity of sulfhydryl groups with Cu²⁺,forming a cysteine-Cu²⁺complex,which hinder the binding of Cu²⁺to fluorescent PDA nanoparticles and the fluorescence was recovered.This sensor could effectively detect the cysteine and the detection method was fast,simple,and has a wide application prospect in sensor.