Construction Of Double-hue Ratiometric Fluorescent Probes And Their Application In Visualization Analysis

Fluorescence visualization detection has been widely applied to environmental monitoring,food analysis,medical diagnosis and treatment,pharmaceutical analysis,and other fields due to its high sensitivity,excellent visualization effect and portable monitoring with ultraviolet lamp.At present,fluorescence detection methods are generally divided into single-wavelength detection and ratiometric fluorescence detection.The former system has only single emission peak under the excitation of ultraviolet light,and during the detection process,the intensity of fluorescence peak increases or decreases,so that it lacks self-calibration and suffers from background interference easily.When the fluorescence peak is in the visible region,color change mode is‘turn on’or‘turn off’but it is single.On the other hand,the latter can emit two or more fluorescence peaks under the excitation of ultraviolet light.In the process of detection,the two peaks change with the content of the substance to be measured,so it can overcome the influence of environmental factors and background interference and improve the sensitivity and accuracy of the detection method.But sometimes one or two emission peaks are outside the visible region,and the visualization is affected.When two/more fluorescence peaks are located in the visible region,emission peaks are appropriately separated,and the changing trends of the two peaks are different with the content changing of the substance to be measured,the fluorescence color of the system can change between two or more hues and the visualization effect is more sensitive.However,for ratiometric fluorescence sensor system,in order to realize sensitive visual analysis,arriving at the above three conditions is not easy,simultaneously.In conclusion,it is of great practical significance to develop ratiometric fluorescence sensors for two/more hues visual analysis detection.Based on the above mentioned,this work established three different ratiometric fluorescence sensors whose two emission peaks are located in the visible region and far apart,and applied them to realize the double hues visual detection of aluminum ion(Al³⁺)and berberine hydrochloride（BRH）.Their details are described as follows:（1）A sensitive ratiometric fluorescence method for visual detection of aluminum ion based on chelation-enhanced photoluminescence.Ciprofloxacin hydrochloride（CIP）can sensitize europium ion(Eu³⁺)to emit red fluorescence based on antenna effect easily,so we can construct bule-red ratiometric fluorescence probe successfully.When Al³⁺was added into the system,the blue fluorescence intensity increased and the red fluorescence intensity decreased due to the Chelation-Enhanced Photoluminescence（CHEP）between Al³⁺and CIP.Therefore,with the increasing of Al³⁺concentration,the fluorescence color changes from red to blue little by little.And the ratiometric fluorescence intensity is proportional to the content of Al³⁺and the assay exhibits good selectivity and sensitivity with a limit of detection（LOD）of 0.60μmol/L and a linear range of 0-120μmol/L.The simple,sensitive and selective ratiometric fluorescence assay was proposed and it has been successfully applied for Al³⁺sensing in real samples.Fluorescence lifetime,Scanning electron microscopy（SEM）images,Fourier transform infrared（FTIR）spectra,UV-Visible absorption（UV-Vis Abs）spectra and X-ray photoelectron spectra（XPS）were characterized for the mechanism study.（2）Synthesis of Terbium ions modified carbon dots and its application for aluminum ions visualization detection.Although the ratiometric fluorescence sensor of Al³⁺was successfully constructed in the last work,the anti-interference ability to ferric ion(Fe³⁺)and cupric ion(Cu²⁺)was not enough,which limited its practical application in other fields.So,in this work,ciprofloxacin hydrochloride（CIP）used as the carbon source and dimethyl sulfoxide（DMSO）used as the solvent,we synthesized the high quantum yield blue carbon dots（CDs）via a simple solvothermal method.Then CDs can be modified by terbium ions(Tb³⁺)based on antenna effect,the green fluorescence attributed to Tb³⁺can be excited and the apart blue fluorescence of CDs still remains,so a new blue-green emission fluorescence probe can be constructed successfully.The fluorescence probe has excellent specificity response to Al³⁺,with adding Al³⁺into assay system,the blue fluorescence intensity recovers and the green fluorescence intensity decreases,meanwhile the fluorescent color changes from blue to green.The ratioratiometric fluorescence intensity has a good linear correlation with Al³⁺content,with a linear range of 0-8.0μmol/L and a limit of detection（LOD）of 39.31 nmol/L.Comparing with the last work,the LOD went down by an order of magnitude.And it is worth mentioning that this system has enough anti-interference ability to Fe³⁺and Cu²⁺so that it has been successfully applied to the visual detection of Al³⁺in real water samples.Transmission electron microscopy（TEM）images,X-ray photoelectron spectra（XPS）,Raman spectroscopy,Fourier transform infrared spectroscopy（FTIR）,Fluorescence lifetime,Fluorescence spectra and so on were used to carry out the mechanism research.（3）Visual analysis and detection of berberine hydrochloride based on double emission fluorescent carbon dots.The above two works realized the construction of ratiometric fluorescence sensors depending on two different components,but the processes are little tedious.Therefore,in this work,3-aminophenol as nitrogen source and succinic acid as carbon source,the blue and green emission carbon dots（named D-CDs）were synthesized in one step by hydrothermal method.The D-CDs have an excellent specificity response to berberine hydrochloride（BRH）and wit h the increasing of BRH content,the fluorescence color of the D-CDs changes from blue to green,so the visual effect is obvious.The ratio of blue to green fluorescence intensity is directly proportional BRH concentration.The detection assay has good selectivity and sensitivity with a linear range of 0-150μmol/L and a detection limit of（LOD）0.70μmol/L.The system can detect the content of BRH in urine by standard addition method.In order to explore the detection mechanism,we divided D-CDs into two different CDs by column chromatography and discussed their interactions with BRH respectively.In summary,this paper focused on the establishment of double hues ratiometric fluorescence detection system and realized the highly sensitive and good visual analysis of Al³⁺and BRH.Meanwhile,we applied them to the actual sample detection and discussed the detection mechanism,respectively.