Construct And Application Of Carbon Quantum Dots-sulfadiazine Imprinted Fluorescence Sensor

As a new type of fluorescent material,carbon quantum dots are widely used in biological imaging,fluorescent chemical sensors,and photocatalysis due to their excellent fluorescent optical properties,simple preparation methods,cheap raw materials,good biocompatibility,and nontoxicity field.However,the fluorescence emission mechanism of carbon quantum dots is still controversial.In addition,when carbon quantum dots are used as fluorescent response materials to detect sulfadiazine,there are disadvantages such as poor selectivity,poor sensitivity,and susceptibility to environmental interference.Therefore,it is of great significance to study the fluorescence mechanism of carbon quantum dots and realize a carbon quantum dot fluorescence sensor with high selectivity,high sensitivity and anti-interference.Sulfadiazine as a member of antibacterial drugs,excessive use of sulfadiazine is likely to cause bacterial resistance,so the detection of sulfadiazine is still very important.This article will focus on the theme of carbon quantum dots,mainly for the preparation,physical and chemical properties,fluorescent properties,fluorescence mechanism,quenching mechanism of carbon quantum dots and as a fluorescent response material to achieve single emission with high selectivity and high sensitivity detection of sulfadiazine,and the ratio fluorescence sensors with anti-interference are systematically studied.Specific research includes the following:1.Using sulfadiazine as a precursor,double-emission carbon quantum dots（DCQDs）with the highest quantum yield of up to 82.15%were synthesized using the hydrothermal method under the optimal reaction conditions.Through a series of characterization results,it can be found that DCQDs had two emission wavelengths and both have excitation wavelength independence property.The fluorescence emission wavelength and fluorescence intensity were reversible between acidic and alkaline.Structurally,DCQDs had a better graphene structure and clear lattice.Based on the excellent dual-fluorescence properties of DCQDs,the fluorescence mechanism of carbon quantum dots was studied using an improved intercept method.It was found that there were four different energy gap bands for carbon quantum dots,which are 4.93eV,4.00 eV,3.66 eV and 3.06 eV.And,based on the carbon quantum dot bandgap,the fluorescence mechanism was well cconsisted with the change law of carbon quantum dot fluorescence under different excitation wavelengths.At the same time,DCQDs were used to detect Fe³⁺,and the improved intercept method was used to study the fluorescence quenching mechanism of carbon quantum dots in the presence of Fe³⁺.As a result,it was found that the improved intercept method was feasible to distinguish the fluorescence quenching mechanism.2.Ratio-type fluorescent sensors generally require two types of fluorescent materials,one was a reference fluorescent material and the other is a response fluorescent material.In order to ensure that the prepared ratio-type fluorescent sensor can be green and non-toxic,and can maximize the performance in selectivity and sensitivity,the carbon quantum dot imprinted fluorescent sensor and the semiconductor quantum dot imprinted fluorescent sensor were studied separately in order to compare the two of the selectivity,sensitivity and detection range of molecularly imprinted fluorescent sensor in the detection of sulfadiazine to determine the best fluorescent response material and the best fluorescent reference material.Using citric acid as a precursor,carbon quantum dots prepared by hydrothermal method and manganese-doped zinc sulfide quantum dots prepared by precipitation method were used as response fluorescent materials to prepare single-emission molecularly imprinted fluorescent sensors.Scanning electron microscope,Fourier Infrared spectroscopy and other characterization results of two single fluorescent imprinted sensors showed that both types of fluorescent sensors had a core-shell structure and were spherical.The minimum detection limits of carbon quantum dot imprinted fluorescent sensors and manganese-doped zinc sulfide quantum dot imprinted fluorescent sensors were 4μmol/L and 0.24μmol/L,and the linear detection ranges were 10μmol/L-60μmol/L and 5μmol/L-40μmol/L,respectively.The quenching mechanism is photo-induced electron transfer.The minimum detection limit of the carbon quantum dot imprinted fluorescent sensor was lower than that of the manganese-doped zinc sulfide quantum dot imprinted fluorescent sensor,and the linear detection range was better than that of the manganese-doped zinc sulfide quantum dot imprinted fluorescent sensor.In the selectivity study,it was found that the selectivity of carbon quantum dot imprinted fluorescent sensors was much better than that of manganese-doped zinc sulfide quantum dot imprinted fluorescent sensors.And selectivity was a core and important factor of molecularly imprinted fluorescent sensors,from which it can be concluded that carbon quantum dots had greater advantages as response materials for ratio-type fluorescent sensors.3.After comparing the results of the detection of sulfadiazine by a single emission molecularly imprinted fluorescent sensor made of carbon quantum dots and semiconductor quantum dots as fluorescent response materials,it was found that carbon quantum dots are more suitable as fluorescent response materials to achieve high selectivity,high sensitivity and for ratio-type fluorescent sensors with anti-interference ability,semiconductor quantum dots were feasibly to be used as fluorescent reference materials.Compared with manganese-doped zinc sulfide quantum dots,the fluorescence efficiency of cadmium telluride quantum dots was higher and there is no impurity peak.Using it as a reference fluorescent material was superior to manganese-doped zinc sulfide quantum dots.Based on the above results,a ratio-type molecularly imprinted fluorescent sensor was prepared by combining polymer nanospheres,molecular imprinting technology,carbon quantum dots,and cadmium telluride quantum dots.The ratio fluorescence sensor was characterized by scanning electron microscope and Fourier infrared spectroscopy.The results showed that the ratio fluorescence sensor had good dispersion,the minimum detection limit was 2.6μmol/L,and the linear detection range was 10μmol/L-60μmol/L,showing potential application value in the actual detection of sulfadiazine.And found that compared with single emission carbon quantum dot imprinted fluorescent sensor,there have a wider linear detection range,the minimum detection limit has been reduced,which indicated that the sensitivity has increased.In summary,a ratio-type imprinted fluorescent sensor with high selectivity,high sensitivity,anti-interference ability and practical application value was successfully realized.