Preparation Of Functional Carbon Dots And Their Application In Phosphateanalysis

Phosphoric substances are important components in living organisms,maintaining the basic life processes of organisms.Abnormal contents in organisms can be important signals for certain diseases.Therefore,simple,rapid,sensitive,highly selective and real-time analysis of phosphoric acid is of greatvalue.Among the reported methods,fluorescence analysis is considered to be the most ideal method for detection of phosphoric acid in complex system and real-time imaging and analysis of intracellular phosphoric acid because of the high sensitivity and the advantages of high space-time resolution imaging.Carbon dots,a new star in carbon materials,have good biocompatibility,light stability and long Stokes shift,and are expected to be ideal materials for biosensing.In this paper,the phosphates-responsivefunctionalized carbon dots and their derivatized probes are used as the main tools for qualitative and quantitative imaging analysis of extracellular and intracellular phosphoric acid.The main contents are as follows:1.The construction of carbon quantum dots-ruthenium complexesand analysis of phosphoric acid in fingerprint sweat.In this part of work,we first carbonization citric acid and L-cysteine at high temperature to obtain bright blue fluorescent carbon quantum dots.And thena cerium nitrate solution is added to the prepared carbon quantum dots and then adjust the pH to obtain a large particle of carbon quantum dot-ruthenium complex.There is Dexter energy transfer between the carbon quantum dots and the ruthenium,so the prepared carbon quantum dot-ruthenium complex simultaneously has blue and red fluorescence emission.Due to stronger binding of phosphate and ruthenium,the structure of the complex is destroyed after the phosphate contacted with the carbon quantum dot-ruthenium complex,and the fluorescence signal exhibits blue fluorescence recovery and red fluorescence reduction.Subsequently,we embedded the carbon quantum dot-ruthenium complex into the electrospun nanofilm.During the daylight,the electrospun nanofilm is white,and under ultraviolet light,it emits a purple-red color.After touching with finger,no trace was observed on the electrospun nanofilm under the daylight,however,a blue fingerprint was visible under the ultraviolet lamp.These fingerprints are caused by phosphate in the fingerprint secretions.Basedon thiselectrospun nanofilm,we successfully analyzed the phosphoric acid in fingerprint sweat.And this "invisible" blue fluorescent fingerprint analysis method can be used infingerprintidentification,file security and secret communication.2.Positively charged single-layer graphene quantum dots with double recognition sites for mitochondrial ATP imaging.In this part of work,we have obtained functionalized single-layer graphene quantum dots through the in-situ functionalization strategy from the selection of raw materials and the optimization of synthesis conditions.In terms of raw material selection,we chose perylenetetracarboxylic anhydride with a large aromatic conjugated structure and polyethyleneimine with a rich amino group to help build a plurality of positively charged sites as a reaction raw material.In terms of synthesis conditions,we first selected a mild hydrothermal method as a synthesis method to maximize the retention of the functional structure and groups of the starting materials.Secondly,by optimizing the ratio of different reactants,we finally obtain a yellow fluorescent single-layer graphene quantum dot with a positive structure and a large hydrophobic conjugate plane which is expected to respond well to ATP.In addition,the single-layer graphene quantum dots also exhibit good mitochondrial targeting ability due to a certain degree of hydrophobicity and positive charge.Based on thisfunctionalized single-layer graphene quantum dots,we successfully monitored the fluctuation of ATP levels in mitochondria of living cells.3.Preparation of mitochondria-targeted dual-emission fluorescent carbon dots and their application in intracellular ATP imaging.To obtain the mitochondria-targeted carbon dots with dual fluorescence response to ATP,we used amino-rich polyethyleneimine and acetylethenetriphenylphosphine as the starting materials of preparing carbon dots.The surface of blue fluorescent carbon dots was rich in amino groups and triphenylphosphine(TPP)groups.Then,the fluorescein isothiocyanate(FITC)was modified on the surface of carbon dots,and finally TPP-CDs-FITC with strong blue fluorescence and weak green fluorescence were obtained.The addition of ATP leads to aggregation of the TPP-CDs-FITC composite probe and enhances the energy transfer of CDs to FITC,resulting in decreased blue fluorescence of TPP-CDs and enhanced fluorescence of FITC green.Due to the mitochondrial targeting performance of the TPP moiety in the composite probe and the ATP response of the CDs-FITC moiety,the intensity ratio of intracellular blue fluorescence to green fluorescence can be obtained after incubation of the TPP-CDs-FITC complex probe incubated with the cells.The monitoring of the changes in ATP concentrations in living cell mitochondria is more accurate and intuitive real-time.In general,taking advantageof abandance surface functional groups of carbon dots,we have prepared functionalized carbon dots and their derivatives that have special responses to phosphoric acids.Due to the good biocompatibility,long Stokes shift,and high light stability,these functionalized carbon dots and their derivatives have been successfully applied to phosphoric acid sensing in fingerprints and ATP imaging in mitochondria.This study provides new research ideas for the preparation and derivatization of functionalized carbon dots,and also has important significance for the application of carbon dots in analytical sensing,bioimaging and drug delivery.