Synthesis And Characterization Of Carbon Dots And Their Application In The Detection Of Antibiotic Drugs

Currently,room temperature phosphorescence（RTP）materials have been successfully applied in sensing,bioimaging,optoelectronic devices and information encryption due to their excellent afterglow emission properties.However,conventional room-temperature phosphorescence materials are usually inorganic compounds containing rare earth,metallic compounds and pure organic compounds,which are complicated to be prepared.Metals are toxic and non-renewable,thus limiting the prospects for long-term applications.Therefore,it is imperative to develop a new generation of room temperature phosphorescent materials with long afterglow life,easy availability and low toxicity.Carbon dots（CDs）are very attractive owning to their desirable optical properties,low cost and low toxicity.Several efficient room-temperature phosphorescent emission are achieved by embedding carbon dots into complex matrices,doping with different elements,and forming self-protective structures.In this paper,diethylenetriamine pentamethylene phosphonic acid and alizarin red s are served as the precursor respectively,thus the carbon dots with extraordinary luminescence have been successfully prepared.Furthermore,these carbon dots are employed to the detection of antibiotic drugs,anti-counterfeiting and pH sensing.The specific research contents are listed as follows:1.Synthesis and characterization of room temperature phosphorescent carbon dots and the detection of metronidazoleChemical doping with halogens,nitrogen or phosphorus can promote the spin-orbit coupling of carbon dots and the generation of abundant surface states,thus effectively facilitating the inter-system crossing process（ISC）and protecting triplet excitons from non-radiative effects,enabling the RTP of carbon dots.The solutions of the synthesized N、P-CDs were light brown under the sunlight and emitted bright blue fluorescence under the UV lamp.When the carbon dots were loaded on the filter paper or lyophilized into powder,green phosphorescence was observed,mainly due to the self-protective structure formed by the N、P-CDs after lyophilization and the use of filter paper as a substrate not only stabilizing the N、P-CDs triplet excitons but also suppressing the radiation-free jump to achieve RTP emission.Secondly,the N、P-CDs were characterized by using high-resolution transmission electron microscopy（HR-TEM）,dynamic light scattering（DSL）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XSP）.The results showed that the carbon dots were uniformly distributed and the size of it was in the range of 1.01～4.70 nm.The carbon dots mainly contained the elements of C,N,O and P,and there were abundant functional groups on the surface,such as C=O/C=N,phosphate and so on.Again,this experiment synthesized silica-based carbon dots from N、P-CDs,then coated the carbon dots with silica to achieve their phosphorescence in the aqueous solution.After the introduction of water,the lifetime of N、P-CDs was shortened,while Si O₂-N、P-CDs remained in the order of seconds,which could be used as a kind of RTP ink for the information encryption.Importantly,N、P-CDs could respond to nitroimidazole antibiotics as probes.Therefore,a dual-signal of fluorescence and phosphorescence method was established to detect metronidazole.To be specific,the linear range of fluorescence assaying was 2 nmol/L～200μmol/L with the detection limit of 0.98nmol/m L;the linear range of room temperature phosphorescence detection was 50nmol/L～2.0 mmol/L with the detection limit of 38.2 nmol/m L.Electron transfer and f o?rster resonance energy transfer were the leading causes of fluorescence and phosphorescence bursts in the carbon dots.More meaningful,phosphorescence sensing extended the linear detection range and improved the accuracy of the detection.2.Synthesis and characterization of yellow fluorescent carbon dots and their application in pH sensing and detection of tigecyclineFirstly,in this experiment,nitrogen and sulphur co-doped carbon dots（N、S-CDs）were prepared in one step,using a hydrothermal method.Specifically,alizarin red s and ethylenediamine were applied as the raw materials,alizarin red s provided the carbon source and ethylenediamine was used as a dopant.The prepared N、S-CDs exhibited bright yellow fluorescence under UV lamps with the optimum emission wavelength of547 nm under the excitation at 470 nm.Besides,the fluorescence quantum yield of N、S-CDs was 13.2%.Secondly,the N、S-CDs were characterised using HR-TEM,DSL,FITR and XPS.The experimental results showed that the average particle size of the carbon dots was 4.47 nm,and the dispersion of it was good.In addition,the carbon dots were mainly composed of four elements including C,N,S and O,and had functional groups such as C=O/C-N and sulphite.Meaningfully,the fluorescence intensity of N、S-CDs decreased with acidic conditions,thus enabling pH sensing in the acidic range of2 to 7 with good repeatability.Specifically,a large amount of-COOH reacted with H⁺on the surface of the carbon dots with pH decreasing,changing the surface state structure of the carbon dots and thus causing the fluorescence burst of the N、S-CDs.Finally,tigecycline also attenuated the fluorescence intensity of carbon dots,which was mainly due to the formation of hydrogen bonds between N、S-CDs and tigecycline,and static sudden extinction reduced the fluorescence intensity of N and S-CDs.Therefore,an analysis method could be established for detecting tigecycline by N、S-CDs.The reduced fluorescence values of N、S-CDs probes were linearly related to the concentration of tigecycline in the range of 7 nmol/L～200μmol/L.This experiment successfully extended the application of carbon dots in the analytical detection of tigecycline.The above experimental work investigated the preparation of room-temperature phosphorescent carbon dots,elucidated the structural characteristics of the prepared carbon dots and their functional groups using various characterization methods.Moreover,we established a dual-channel method for the detection of antibiotic drugs by phosphorescence and fluorescence,which provided a specific reference value for our in-depth knowledge and study of carbon dots and further expanded the application of room-temperature bright carbon dots in the field of detection.