Mechanisms And Methods Of Doxycycline Detection Using Terahertz Metallic Hole Array

The residues of tetracycline antibiotics will cause some harm to the ecological environment and human health,while traditional detection technology still has limitations in practical applications.Terahertz(THz)spectroscopy,especially THz time-domain spectroscopy,has demonstrated attractive potential for biological and chemical compounds analysis due to the properties of non-ionization,timesaving and capacity to reflect the low frequency vibration information of molecules.However,the interaction between free-space THz waves and samples is weak and THz signal is strongly absorbed by polar liquids such as water,which limit the further development and applications of THz spectroscopy with respect to its detection sensitivity and the states of samples.Spoof surface plasmon-based THz devices,represented by metamaterials,can enhance the interaction between THz waves and samples and promote the ability to obtain effective signals of samples,which have been studied for detecting trace amount substances at present.In this thesis,doxycycline hydrochloride(DCH),widely used in aquaculture production,was chosen as the detection object.THz metallic hole array(THz-MHA),which can be fabricated through large-throughput and convenient processing methods,was employed to conduct research on DCH detection based on THz time-domain spectroscopy technique.Systematic methods for fast and sensitive detection of DCH samples in drying and aqueous solution states were explored and established,which could provide new solutions to push for addressing the common problems in THz sensing,and also offer new ideas and perspectives for the rapid detection of antibiotic residues.The main research contents and results of this thesis are as follows:(1)The absorption and dispersion characteristics of DCH in the THz range were analyzed by pressing the solid powder samples into pellets,and the transmission characteristics of THz metallic mesh device(THz-MMD)at different test angles were studied.On this basis,THzMMD was utilized to implement the transmission test for DCH samples with different contents by dropping-and-drying method,reaching a minimum detection limit to 205 mg/L.(2)A fast and convenient method for analyzing DCH aqueous solutions using THz-MMD was explored and established.Numerical simulations and experimental measurements were conducted to investigate the relationship between the reflection characteristics of THz-MMD and the test azimuth.On this basis,THz-MMD was served as a sensor for rapid determination of DCH aqueous solution with a concentration as low as 10 mg/L,and the sensing mechanism was also explored through simulation analysis.(3)A THz parallel plate resonator integrated with MMDs was constructed and utilized for doxycycline detection.The influence rules of key parameters of the THz parallel plate resonator were mastered,which was explained using the multi-beam interference theory.Furthermore,the THz parallel plate resonator incorporated with THz-MMDs was utilized to detect DCH by dropping-and-drying method,which is able to determine 1 mg/L of DCH solution.Compared with detection using simple THz-MMD,the sensitivity was improved by about two orders of magnitude.(4)A THz microfluidic device integrated with graphene-MHA structure was constructed and used for rapid detection of DCH aqueous solutions.The resonance modes were significantly attenuated after transferring a single layer of graphene onto the MHA structure,which was analyzed through numerical simulations and experimental measurements.The graphene-MHA structure was further integrated into THz microfluidic device for rapid determination of DCH aqueous solution with a concentration as low as 0.1 mg/L,which met the maximum residue limit of doxycycline in animal-derived food specified in the national standard.