Studies On The Synthesis Of Red Emissive Carbon Dots And Their Applications In Multichannel Sensing And Cancer Theranostics

Carbon dots?CDs?are a newly emerged type of fluorescence?FL?nanomaterials,typically with a size under10 nm,have inspired intense research efforts in recent years.Comparing with traditional organic FL dyes and semiconductor quantum dots,CDs hold many merits including facile preparation,superior optical properties,easy surface functionalization,chemical inertness,low toxicity and good biocompatibility.Hence,CDs are demonstrated many potential applications,such as photocatalysis,optoelectronics,sensing,bioimaging,and theranostics.Although many kinds of CDs had been reported so far,most of them show intense emission only at blue-to green-light regions under excitation with ultraviolet-or blue-light.Such drawbacks restrict their further applications,particularly in the fields of biomedicine,because of the well-known blue auto-fluorescence of biological matrix and severe photodamage of ultraviolet excitation light.And,even the few reported red emissive CDs still suffering from low quantum yields?QYs?,not pure red emission,and/or complicated synthesis/separation procedures.Therefore,it's highly significant to achieve high-efficient red-light emissive CDs that can be excited with long-wavelength lights as well.In this thesis,studies on the synthesis of red emissive carbon dots and their applications in multichannel sensing and cancer theranostic are presented.The main research contents of this paper are as follows:In chapter 1,we firstly introduced the basic properties of several typical carbon nanoallotropes,including the fullerene,carbon nanotube,graphene,and carbon dots.In next part,we focus on the synthesis methods,physicochemical properties and potential applications of CDs.Especially,the discussion on unique applications of red emissive CDs are also provided.Finally,based on the unaddressed issues in CDs related field,the significance of this paper is proposed.In chapter 2,CDs-metal ions ensembles are designed as a triple-channel FL sensor array for the detection and discrimination of various phosphate anions?e.g.ATP,ADP,AMP,PPi,and Pi?.Owning to covering abundant functional groups on the surface of red emissive CDs and which making them possible to interact with metal ions,Ce³⁺,Fe³⁺and Cu²⁺are screened and selected to coordinate with the CDs,resulting in quenching their FL due to aggregation.With the addition of phosphate anions,disaggregation or further aggregation of CDs-metal ions ensembles occur depending on the used metal ions,thus inducing FL recovering or further quenching.Based on the distinguished FL changes of red emissive CDs,these phosphate anions can be well identified and differentiated.Moreover,quantitative detection of ATP using this array and its potential applications for the identification of phosphate anions in complex media?e.g.blood serum?and blind samples were also demonstrated.In chapter 3,based on our previous work,further studies on the high-efficient red emissive CDs?R-CDs?are displayed.The as-prepared R-CDs are confirmed to be not only low cytotoxicity,respectable QY and high photostability,but more importantly,excellent two photo excitation fluorescence?TPEF?feature,ease of conjugation,and high photothermal conversion efficiency.Moreover,the R-CDs are confirmed to be able to selectively stain RNA-rich nucleolus,carry fluorescein isothiocyanate?FITC?into living cells,and used for photothermal cancer therapy in vitro.These findings demonstrated that the as-prepared R-CDs could be potentially employed as multifunctional theranostic agents for nucleolus imaging,drugs/genes delivery,and photothermal therapy?PTT?.In chapter 4,a new concept,loading a small amount of photosensitizers?PSs?onto a PTT agent?both of them can be triggered by a single near-infrared?NIR?laser?was proposed to evade the shortcomings of PTT and photodynamic therapy?PDT?.Further research demonstrated that Ce6-modified RCDs?named Ce6-RCDs?offer much higher cancer therapy efficacy under a reduced laser power density?i.e.,0.50W/cm² at 671 nm?in vitro and in vivo than that of the equivalent RCDs or Ce6 under the same irradiation conditions.Besides,the Ce6-RCDs also exhibit multimodal imaging capabilities?i.e.,fluorescence?FL?,photoacoustic?PA?and photothermal?PT??,which can be employed for guidance of the phototherapy process.This work suggests not only a strategy to enhance cancer phototherapy efficacy,but also a promising candidate?i.e.,Ce6-RCDs?for multimodal FL/PA/PT imaging-guided and single-NIR-laser-triggered synergistic PTT/PDT for cancers by a reduced irradiation power.In chapter 5,we summarized the main conclusions of the above-mentioned works.Although many progresses have been made on the preparations and applications of red emissive carbon dots,some unaddressed issues are still needs to be solved to take full use of their potential.