Study On Trace Nitrite Contamination Analysis By Fluorescent Carbon Dots With Smart Device

As a new type of fluorescent carbon-based nanomaterial,carbon dots luminescent materials have attracted much attention for their easy structural tuning,functional diversification and excellent luminescent properties.In addition,this material has very broad potential applications in the fields of pollutant detection,bioimaging,sensing,catalysis and light-emitting devices due to its proven low toxicity,environmental reliability,and other advantages.Microfluidic paper chip is a paper-based substrate,which is used to design hydrophilic or hydrophobic channels,to build a"paper laboratory",also mentioned as,"microfluidic paper-based analytical device".The paper-based chip is rapidly developing as a research hotspot due to its natural advantages of low cost,environmental protection,biodegradable,capillary action self-driven,and good biocompatibility of paper materials.Currently,paper-based chips combined with intelligent detection devices can be used in research areas such as food safety,life sciences and environmental testing.In this thesis,we prepared and characterized the carbon dot luminescent material and studied the fabrication of carbon dots paper-based chips,developed and optimized the intelligent detection devices,and further explored the qualitative and quantitative detection of trace nitrite contaminants by applying carbon dot paper-based chips combined with intelligent detection device.Firstly,o-phenylenediamine,which is highly cross-linked and has a high carbon number,was chosen as the carbon source,and dopamine hydrochloride,which also has a high carbon number,was chosen as the modifier,unlike the main carbon source,which is not suitable for cross-linking but has an abundant-OH group to improve the hydrophilicity of carbon dots.After characterization,the products were separated using column chromatography and prepared as a series of excitation light stable and monochromatic luminescent carbon dots.After characterization,the selected yellow-green carbon dot materials have structures rich in C=C,C=N,C=O,and O-H bonds,are salt-resistant and stable in the concentration range of 0～1.0μg·m L^-1,and have good fluorescence intensity between p H 6～12,with an optimal p H range of 7～11.The size is about 5 nm,a graphite-like structure exists,and the quantum yield of the fluorescently labeled material is 10.20%.Then,after screening experimental studies of various contaminants such as common metal ions and anions in water,it was shown that the isolated yellow-green carbon dots（λex=440 nm,λem=535 nm）had a high sensitivity and fast specific response to NO₂^-in the range of 0～50μg·m L^-1 in accordance with the Stern-Volmer equation（F0/F-1=K[Q]）,with good fluorescence linearity（R²=0.9937）in the detection range of 0～10μg·m L^-1 and 12～50μg·m L^-1.The detection limit was up to 0.0129μg·m L^-1（S/N=3,n=3）.Secondly,the carbon dots paper chips that can be used for intelligent detection were produced.The optimal conditions for the immersion method were:100μg·m L^-1carbon dots ethanol solution immersion solution,the paper is immersed in shade for 6h.In addition,patterned carbon dots paper chips can be produced by the inkjet printing method,where carbon dots ethanol solution,polyethylene glycol and polyvinylpyrrolidone are mixed in a certain ratio to make carbon dots ink,and carbon dots are printed the carbon dot university emblem directly on paper by commercial printers,as well as,carbon dots ink is made by ultrasonically mixing carbon dots ethanol solution and glycerin in a homogeneous way,to obtain a handwritten carbon dots paper-based chips by writing method,etc.Then,the carbon dots paper-based chips with stable luminescence intensity was further applied to detect NO₂^-in real water samples by immersion.The response curve of the carbon dot paper chip was in accordance with the Stern-Volmer equation（F0/F-1=K[Q]）,with a good fluorescence linear response（R²=0.97717）in the concentration range of 0～10μg·m L^-1 and a detection limit of 0.0292μg·m L^-1（S/N=3,n=3）,which meets the requirements of the national standard for domestic water(≤1μg·m L^-1).Finally,the hardware and software of the intelligent detection devices are optimized to construct a intelligent detection platform for carbon dots paper-based chips suitable for rapid detection contaminants response applications.Based on a novel,convenient,low-cost,real-time datable concept,a intelligent detection device for the qualitative and quantitative detection of NO₂^-in samples with carbon dots paper-based chips were explored.The intelligent detection method is simple,the device is low-cost and stable.The RGB data is mainly read by an app application that integrates picture and data analysis through self-developed smartphones,enabling the transformation of picture information into data-based detection.In the experiments,the reproducibility of the results was verified by the detection of NO₂^-in three real water samples and the spiked recoveries.The results showed good linearity（R²=0.9952）in the range of 0～20μg·m L^-1,with the working curve conforming to the Stern-Volmer equation（F0/F-1=K[Q]）and the recoveries range of 99.4%to 114.3%.The intelligent detection device is simple,with good device portability,low cost and good stability,and meets the requirements for trace detection of contaminants in real water samples with reliable results.In summary,the carbon dot luminescent material prepared in this paper achieves the application of rapid and specific intelligent detection of NO₂^-contaminants in real water samples,with low detection limit of the method,meeting the requirements of the Chinese national standard,which can provide the theoretical basis for the preparation and application of specific contaminants-responsive carbon dots materials.The carbon dots paper-based chips combined with the intelligent detection devices and the application software APP were further developed,which has a great potential to be applied in the detection of contaminants,especially toxic nitrite contaminants in water bodies,and can be used as an important supplementary means for water quality monitoring in water sources.