Study On The Optical Chemical Sensors & Biosensors Based On The Carbon Quantum Dots And Intelligent Hydrogel

The fast and precise detection of some chemical and biological substances in environment and human body such as Fe³⁺,dopamine,glucose and cholesterol are very important to environment monitoring and human health.Optical chemical sensors and biosensors are the detection instruments which can selectively and continuously change the chemical and biological information of the analytes into the easily detectable optical signals.They can perform the real time and online detection for many single and multi detection objects,and become the important detection means for many biological substances,molecules and ions.Optical chemical sensors and biosensors have a lot of advantages such as high sensitivity,fast response,strong ability to resist disturbance,among them,the fluorescence probes and fiber optic chemical sensors and biosensors are more sensitive,easy to operate,and more conducive to commercialization,therefore,they are effective means to realize the fast and online detection for chemical and biological substances.Carbon dots are zero dimension carbon nanomaterial.As a newly developed fluorescence probe,carbon dots have many advantages including excellent fluorescence properties,good biocompatibility,strong chemical stability and low toxicity.Thermosensitive intelligent hydrogels are a kind of hydrogels which can respond to temperature stimulation.When the environment temperature changes,thermosensitive hydrogel can perform the reversible“swelling-shrinkage”changes.This characteristic makes them have potential applications in the field of intelligent temperature controlling detection.If we combine the advantages of carbon dots,thermosensitive intelligent hydrogels and optical chemical sensors and biosensors,and use them in the detection of some important chemicals and biomasses in environment and human body,it is expected to obtain excellent detection results.This kind of researches will have important research significance and application value for the development of chemical and biological detection technology.This thesis was funded by the National Nature Foundation of China(No.61575150).In this thesis,carbon dots,sensing film based on carbon dots,intelligent hydrogel and immobilized enzymes were used to fabricate the fluorescent probes and fiber optical chemical sensors and biosensors based on fluorescence quenching.The structures,preparation conditions and sensing properties of the carbon dots fluorescent probe and fiber optic chemical sensors and biosensors were studied.The effective detections of Fe³⁺,dopamine,glucose and cholesterol were performed.The main works are in the following:1.Citric acid monohydrate and L-Cysteine were used as the carbon source,and microwave assisted heating method and hydrothermal method were used to prepare the carbon dots of different systems.The influence of the preparation conditions on the properties of carbon dots was studied and the optimal preparation conditions were obtained.The structures,morphology and optical properties of the prepared carbon dots were characterized and studied.The fluorescence quantum yield was as high as 85%,and the cell inhibition rate(cultured for 24 h)was almost 0%,indicating their excellent biocompatibility.2.The fluorescence quenching of carbon dots by dopamine was studied and the quenching principle was investigated.The influence of factors such as solution p H and temperature on the fluorescence quenching was researched.The linear relationship between dopamine concentration and fluorescence intensity of carbon dots was obtained.The detection range of this fluorescent probe for dopamine is 0?40?mol/L and the detection limit is 0.75?mol/L.The detection of dopamine in practical samples was performed by the fluorescent probe and it has the recovery rate range of97.7%?103.3%.3.Folic acid was used as carbon source,carbon dots which were used as Fe³⁺fluorescence probe were prepared by using hydrothermal method.This probe has the detection range of 0.1?1.0 mmol/L and the detection limit of 0.05 mmol/L.The carbon dots/CA sensing membrane were prepared by using chemical crosslinking method.The structures,morphology and optical properties of this sensing membrane were characterized and studied.The fiber optic Fe³⁺sensor based on this sensing membrane and lock-in amplifier technology was prepared,and the influence of factors such as solution p H and temperature on the Fe³⁺detection by this sensor was studied.The standard curve of Fe³⁺detection by this sensor in the concentration range of 0.1?1.0mmol/L was obtained.The detection limit of this sensor is 0.03 mmol/L.4.SiO₂nanoparticles were prepared using hydrolysis method.The carbon dots were immobilized on the surface of SiO₂nanoparticles and the SiO₂nanoparticles immobilized carbon dots were obtained.By using freezing method,the thermosensitive intelligent hydrogel,which has the low critical solution temperature(LCST)of 32?,and the hydrogel-SiO₂nanoparticles immobilized carbon dots complex were prepared,and their surface topography,internal structure and properties were characterized and studied.The Fe³⁺fluorescent probe based on this complex was prepared and its properties and influence factors were studied.The intelligent temperature controlling detection of Fe³⁺was realized with this probe and the detection range is 0?50?mol/L;5.The SiO₂nanoparticles immobilized enzymes and the thermosensitive intelligent hydrogel-SiO₂nanoparticles immobilized enzyme complex were prepared.The structures and morphology of this complex was characterized.The two-parameters fiber optic biosensors based on this complex and lock-in amplifier technology was prepared.By controlling temperature,the continuous detection of cholesterol and glucose was realized.The sensor has the detection range of 20?250 mg/d L for cholesterol and the detection range of 50?700 mg/d L for glucose.The response time for both cholesterol and glucose are 200 s.This sensor has good repeatability and ability to resist disturbance.The detection of practical samples was performed and the sensor has the recovery rate range of 95.6%?102.4%for cholesterol and the recovery rate range of 95.5%?103.1%for glucose.