The Preparation And Performance Study Of Long Wavelength Fluorescent Carbon Dots Based On Anhydrous Creatine

As a new star in the field of photoluminescent（PL）materials,carbon dots（CDs）have attracted great attention since they were first observed in 2004.CDs have numerous advantages over conventional quantum dots,such as tunable emission,high photostability,easy preparation from inexpensive raw materials,and surface modifiability.These advantages have stimulated the great potential of CDs for applications in bioimaging,ion sensing,drug delivery,and cancer therapy,especially in the biomedical field.However,most of the prepared CDs exhibit strong emission only in the blue-green light region under ultraviolet（UV）irradiation.To our knowledge,biological tissues show intense blue autofluorescence upon UV excitation.This may hinder the signal of CDs.In addition,UV irradiation is harmful to tissues and cells,and these drawbacks greatly limit the application of carbon dots in biomedical fields.In contrast,red-emitting CDs that can be excited by long-wavelength light obtained by tuning precursors and preparation strategies show great potential in biomedical fields due to their good tissue penetration.Of course,there are some problems with these long-wavelength carbon dots,such as the single method and type of synthesizing long-wavelength carbon dots and the complicated synthesis strategy.These defects limit the practical applications of long-wavelength carbon dots.Therefore,there is an urgent need to develop more methods for preparing long-wavelength carbon dots to broaden their application areas.Based on the above background,this paper provides an in-depth discussion on the controllable preparation of long-wavelength carbon dots and their applications in the fields of sensing detection and environmental monitoring.The main contents are as follows.Firstly,the advantages of carbon dots over traditional quantum dots are systematically analyzed in terms of the synthesis methods and properties of carbon dots,taking the classification of carbon nanomaterials as the starting point.After that,the surface states,optical properties and cytotoxicity of carbon dots under different structures are described,starting from their structures.This is followed by a summary of the progress of the formation mechanism of carbon dots and the emission mechanism of fluorophores.Finally,the research ideas of this paper are presented for some problems of carbon dotsIn the next work,we optimized the preparation process of carbon dots by hydrothermal method and synthesized excitation-independent orange carbon dots with an optimal emission peak at 578 nm.Then we systematically investigated the relationship between fluorescent carbon dots and ferric ions,and further studied that the fluorescence could be selectively burst by ferric ions.Based on this,we constructed an iron ion fluorescent probe.It showed a linear relationship with the fluorescence intensity of the orange carbon dots when the iron ion concentration was in the range of 0～50μM.The correlation coefficient R²was 0.99,and the detection limit was 1.16μM.Based on the above work,we next prepared pH-dependent red-blue dual-emission ratiometric fluorescent carbon dots（R-CDs）by changing the carbon source.R-CDs have an inherent pH-sensitive response behavior,and their fluorescence intensity shows ratiometric fluorescence emission(F_{490 nm}/F_{640 nm})with the change of pH.Through an in-depth study of the pH response mechanism of R-CDs,we concluded that the inherent pH-sensitive response behavior of R-CDs originated from their protonation and deprotonation processes in pH-different media.We then constructed a biosensor platform for pH change visualization based on R-CDs for sensitive tracking of pH changes.The specific detection and visualization properties of this sensor offer more advantages than the conventional single fluorescence detection,providing a theoretical basis for its potential application in biomedicine.