Preparation Of Carbon Dots-Based Dual-Emission Materials And Their Application In The Detection Of Heavy Metal Ions And Anthrax Biomarker

Carbon dots（CDs）,as a type of fluorescent nanomaterial with low toxicity and free of heavy metals,have promising practical applications in the field of fluorescence sensing.Recently,ratiometric fluorescence methods have become a research hotspot due to their ability to provide internal self-calibration to eliminate environmental and instrumental interferences for accurate quantitative analysis.Currently,most of CDs-based ratiometric fluorescent probes rely on simple physical mixing of single-emission CDs with other single-emission fluorescent materials,which has the disadvantages of cumbersome preparation steps and poor stability,limiting the application of probes for real-time field analysis.Therefore,it is of great importance to develop fluorescent materials with dual emission centers at a single excitation wavelength.In this thesis,three CDs-based dual-emission materials were fabricated through different synthetic strategies,and ratiometric fluorescent probes were successfully applied to the quantitative detection of heavy metal ions and anthrax biomarker.The main studies are as follows:1.A one-pot hydrothermal method for the preparation of dual-emission carbon dots（BYCDs）from o-phenylenediamine and glycine was proposed.The prepared BYCDs had two independent fluorescence emission peaks at 426 nm and 543 nm under a single excitation wavelength.Based on the change in the intensity ratio of the two fluorescence emission peaks after the addition of Hg²⁺,a ratiometric fluorescence probe was constructed for the highly selective and accurate detection of Hg²⁺with both static and dynamic quenching mechanisms,a linear range of 0.95-50μM and a detection limit of 0.27μM.In addition,the recovery rate was between 96.4%and 106.8%in the spiked recovery experiments of real water samples and can be applied to the quantitative analysis of Hg²⁺in real environmental water samples.2.The europium-doped carbon dots（Eu-NCDs）were synthesized by a facile one-step hydrothermal method using ethylenediaminetetraacetic acid disodium salt and diethylenetriamine as reaction precursors and introducing Eu³⁺into the reaction precursors,and the prepared Eu-NCDs showed blue emission at 435 nm.After the addition of the anthrax biomarker（DPA）,DPA was stably coordinated to Eu³⁺and its characteristic emission at 616 nm was enhanced by the antenna effect.The abundant carboxyl and amino groups found on the surface of Eu-NCDs were able to displace the water molecules from the doped Eu³⁺and act as an auxiliary ligand and a reference signal insensitive to DPA.Then a ratiometric fluorescent probe was constructed for the detection of DPA.The linearity range was 0.05-50μM with a detection limit as low as 0.012μM.In addition,a smartphone and color analyzer software were used for the instant visual detection of DPA.3.A novel dual-emission composite（CDs@IRMOF-3）was developed by encapsulating yellow CDs prepared from o-phenylenediamine in IRMOF-3 using rapid precipitation at room temperature.The prepared CDs@IRMOF-3 showed two fluorescence emission peaks at 431 nm and 562 nm,and the structural composition of the prepared CDs@IRMOF-3 was investigated using various modern characterization methods.A ratiometric fluorescence sensing platform was also established based on the fluorescence response signal of CDs@IRMOF-3 for Fe³⁺with a linear range of 0.5-25μM and a detection limit of 0.14μM.