Novel Fluorescent Sensing Methods Based On Fluorescent Polydopamine Nanoparticles

Fluorescent biosensing technology,as an important tool for life science research,has significant advantages in analysis speed,sensitivity,selectivity,and operation cost.In recent years,popular nanomaterials with unique oxidation properties,optical effects and surface effects have opened up new directions for the researches of fluorescent biosensors.And it is of great significance to apply these excellent properties of nanomaterials in the construction of biosensors.Because they can avoid some shortcomings of previous sensors,simplify the design processes,reduce the harm to human body.Therefore,many workers have been dedicated to designing biosensors with simple,smart,safe and reliable.In this dissertation,a new type of polydopamine（PDA）nanoparticles with fluorescent properties was synthesized.And we constructed three simple,low-cost,label-free biosensors using these fluorescent PDA nanoparticles,which have achieved the analysis of ascorbic acid（AA）,pyrophosphate（PPi）,hypochlorite（ClO^-）.The main contents are as following:（1）In chapter 2,as an important biological small molecule,ascorbic acid（AA）plays a key role in many bioprocesses.Here,it was the first time that fluorescent PDA nanoparticles were synthesized through oxidation by CoOOH nanosheets.And a novel method to evaluate AA based on the redox reaction between CoOOH and AA was developed.In our work,a nanosystem was constructed with fluorescent polydopamine（PDA）nanoparticles and CoOOH nanosheets,which were used as signal indicators and an oxidant respectively.In the absence of AA,dopamine was oxidized to quinone derivatives and further spontaneously polymerized into fluorescent PDA nanoparticles which had strong fluorescence signals.When there was AA in the reaction system,CoOOH nanosheets would be reduced to Co²⁺,which would prevent the synthesis of fluorescent PDA nanoparticles due to the absence of oxidant CoOOH,resulting in weak fluorescence.Hence,AA concentration was detected by using the fluorescence intensity of the PDA nanoparticles.The fluorescence of this sensing platform was linear with the concentration of AA in the range of 0-500μM with a detection limit of4.8μM.In addition,the sensor was simple,fast,label-free,and low cost,and it is hopeful to apply this principle to design and test other small molecules with redox properties.（2）In chapter 3,a fluorescent biosensor for the detection of PPi was designed using the coordination interaction between synthesized fluorescent PDA nanoparticles and Cu²⁺,as well as coordination interaction between Cu²⁺and PPi.In this work,Cu²⁺could be associated with the catechol of the fluorescent PDA nanoparticles.At this time,Cu²⁺as an electron acceptor,electron transfer took place between fluorescence PDA and Cu²⁺,resulting in fluorescence quenching of fluorescent PDA nanoparticles.The PPi,as a kind of commonly used Cu²⁺complexing agent,has strong coordination ability towards Cu²⁺,which led to form the PPi-Cu²⁺compound,therefore,the fluorescence of fluorescent PDA nanoparticles were restored.Thus,the detection of PPi was achieved through the competition of the coordination interaction.The linear range was 0-300μM,and the detection limit was 11.7μM.Compared with the traditional detection methods,this method had the advantages of simplicity,low cost,and it has a good application prospects.（3）In chapter 4,a"turn-off"analysis method for label-free,rapid detection of ClO^-was constructed based on the optical properties of fluorescent PDA particles and the oxidation properties of ClO^-.The fluorescence of original nanoparticles was strong,but when adding the ClO^-,the fluorescence of fluorescent PDA was quenched.According to the research,the quenching mechanism maybe was oxidation.Some functional groups on the surface of the fluorescent PDA were oxidized by ClO^-,leading to the fluorescence quenching.Therefore,the ClO^-concentration detection was reached by monitoring the change of fluorescence signals.And the detection limit was 2.2μM.The sensor used a new type of fluorescent material,which had some advantages with synthetic simple,low cost.In addition,the study of its application has been also less,therefore,it is expected to take advantage of its majority properties to design more biosensors.