| The over-use of antibiotics has caused residue problem which has become a harsh issue in the security of agro-products/food and global public health.There are still some limitations in traditional detection technology for practical applications.Hence,it is in urgent need to develop novel sensing techniques for rapid and sensitive analysis.Terahertz(THz)spectroscopy has demonstrated unique advantages and broad application prospects in molecular information perception due to its attractive characteristics,including non-ionization,non-destruction,timesaving and capacity to reflect molecular fingerprint spectrum.However,in the development of THz sensing technology,some critical and common problems,such as weak interaction between THz wave and samples,extreme signal attenuation by polar liquid like water,and complicated machining of signal enhancement devices,are limiting the performance improvement and applications of this technology.Artificial microstructures,typified by metamaterials,which have obvious signal response in the THz region,can effectively enhance the capability of information acquisition.Nanomaterials have excellent characteristics suitable for sensing,such as small-size effect,large specific surface area,and easy modification,but of which the THz signal response is weak due to the size mismatch between nanomaterials and THz wave.Therefore,it is of great significance to integrate artificial microstructures with nanomaterials for further improving the performance of THz technology in sensing biochemical substances.In this thesis,tetracycline antibiotics,widely used in stockbreeding and aquaculture production,were chosen as the target analytes.The research mechanisms and methods of THz sensing technology for detecting antibiotics assisted by nanomaterial and artificial microstructures were explored and established.And the potential of nanomaterials cooperated with artificial microstructures in boosting the performance of THz sensing was thoroughly studied,which could provide new ideas for solving the key and common problems in THz sensing,and also offer new solutions for monitoring the quality and safety of food and agricultural products.The main research contents and results in this thesis are illustrated as follows:(1)A quick and simple method for sensing doxycycline hydrochloride(DCH)based on the substrate-free and flexible metamaterial was established.THz metamaterials can be fabricated quickly using laser engraving technique.The processing method of reproducing the metamaterial was determined by optimizing the parameters of laser engraving.Theoretical simulations and experimental measurements were conducted to study the detection performance of the fabricated metasurface.On this basis,the dropping-and-drying method was used to detect DCH samples of different contents,reaching the limit of detection(LOD)of 4.90mg/L.(2)A high sensitive and specific method for sensing tetracycline hydrochloride(TCH)based on the carbon nanotube(CNT)-based THz metamaterial was established.THz metamaterials using several different materials were fabricated on the basis of the simulated parameter optimization.Sensing performance of metamaterials made of different materials was comparatively analyzed.CNT-Au hybrid metamaterial was used to detect TCH with the LOD of 0.032 mg/L.Additionally,specific detection of TCH was realized through the functionalized modification of CNTs.(3)A THz microfluidic system integrated with graphene-metasurface structure was constructed for rapid analysis of DCH in aqueous solutions.The sensing mechanism was clarified and the sensing method based on biochemical-electric-optical signal gain transformation was established.A DCH aqueous solution of 0.1 mg/L was successfully detected,which met the detection requirement of the maximum residue limit of tetracyclines in animalderived food specified in the national standard.The rapid,accurate,and label-free detection of DNA sequences of Escherichia coli O157:H7 was also realized using the graphene-metasurface integrated THz microfluidic system.(4)A sensing method based on gold nanorods with laser irradiation in the THz region was explored for detecting TCH in aqueous solutions.Comparative analysis of the THz response characteristics based on the silicon,silicon coated with a layer of gold nanorod film,and gold nanorod aqueous solution under laser illumination was conducted.The mechanism of THz modulation based on gold nanorods with laser irradiation was clarified.On this basis,a THz liquid micro-channel combined with aptamer-modified gold nanorods was utilized for sensitive,and rapid detection of TCH aqueous solutions with a LOD of 0.01 mg/L.The above research results proved the advantages of nanomaterial-artificial microstructure assisted terahertz sensing techniques for sensing antibiotics and its great potential for sensing antibiotic residues.The key technologies discussed in this thesis,including that the sensitivity and specificity of detecting the film samples of antibiotics was improved based on the high adsorption and easy modification of CNTs and the rapid processing method of metamaterials,and that the sensing performance of detecting antibiotics in aqueous solution was boosted based on the synergistic effect between graphene and metamaterials as well as the photothermal effect of gold nanorods.The results provide a new idea and method for solving the common problems in safety detection of agro-products/food based on THz technology. |
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