Citrate Salts Detection Based On Terahertz Metamaterial Sensor

Terahertz(THz)wave has become a research hotspot in the cross field of physics and biology because of the electromagnetic characteristics of wide bandwidth,strong penetration and low photon energy.Metamaterials have extraordinary physical properties,which can tune the amplitude and phase of THz waves and respond sensitively to the changes of surrounding dielectric environment.Therefore,the combination of THz spectroscopy and metamaterial sensing technology can provide a new way for qualitative and quantitative detection of substances.Citrate salts(CSs)is a kind of organic salt formed by the combination of citric acid anion and metal cation.Due to the special physical and chemical properties,it is often used as food additive or medicine.The dosage of CSs has strict requirements in food additives and drugs.The dosage of citrate has strict requirements in food additives and drugs.If the dosage is too high,it would result in side effects and even harm to human health.Moreover,different citrates have different curative effects and efficacy.It is of great practical significance on accurate detection and identification of citrate.At present,the detection methods for CSs are mainly high performance liquid chromatography(HPLC),ion chromatography,capillary electrophoresis and enzymatic methods.Although these methods are widely used for the determination of citrate in food or pharmaceuticals,they suffer from cumbersome detection steps,large interference factors,and insufficient sensitivity and reproducibility.Therefore,accurate detection and identification of CSs has important practical significance.Therefore,this thesis focuses on the use of terahertz metamaterial sensors for rapid,label-free detection and identification of low concentration citrate solutions to fill the research in the field of terahertz on citrate for pharmaceutical development and food safety.Non-destructive studies on proteins and organisms such as Staphylococcus aureus are also carried out as follows:1.The progress of THz metamaterial sensors in biological nondestructive testing was summarized.Starting from the theoretical level of metamaterial sensors,the sensing principle of metamaterial sensors was analyzed,the performance of sensors was evaluated,and the micro-nano manufacturing process of sensors was introduced.Two kinds of THz metamaterial sensors were designed by Finite Element Method(FEM),and their sensing performance was analyzed.2.According to the mechanism of Fano resonance,the high quality factor(Q value)is excited by breaking the symmetry of double-opening ring,and the sensor with asymmetric double-opening ring periodic array structure is proposed.The appearance of Fano resonance splits the transmission line into two parts,Dip 1 and Dip 2.Through modeling analysis,the asymmetric open ring structure has a higher Q value than the single open structure of the LC resonance,with Q values of 13 and 30,respectively.After the sensor structure is fabricated by the ultraviolet lithography process,the characteristic spectral curves of 6 kinds of CSs with the same mass concentration(0.613 mg/ml)covering the sensor surface were measured in turn.The results show that the frequency shifts in the transmission spectra are all different and have a relatively good discrimination.In order to verify the accuracy of the results,we carried out the tableting experiment of CSs.According to the experimental data,it was concluded that the refractive index values of the six CSs in the terahertz band were only slightly different but distinct.The results show that the frequency shift?f shows a good agreement with the order of refractive index change.However,the measurable frequency offset of frequency response can also be found in combination with metamaterial sensors.In order to explore the high sensitivity of the sensor in different concentrations of organic salts,four different concentrations of potassium citrate solutions were experimentally demonstrated,and the lowest measurable concentration is 0.02 mmol/L(m M).It is shown that the experimentally designed sensor also has a good discriminating effect on CSs with only slight difference in concentration.It shows that the terahertz metamaterial sensor has great potential in citrate measurement,and also provides a unique characterization technique for the sensing of various analytes based on refractive index.3.Based on the previously designed asymmetric split ring structure,we also designed an asymmetric double split square structure,and the Q values of the sensor were calculated to be11 and 30,respectively.We performed biosensing experiments using fabricated sensor samples for bovine serum albumin(BSA)and Staphylococcus aureus.The experimental results show that the resonance frequency shifted significantly with the increase of analyte concentration.The minimum detection concentration of BSA is 1??,and the corresponding resonance peak offset is 8 GHz;The minimum detection concentration of Staphylococcus aureus is 1×10~3cells/ml,and the corresponding resonance peak frequency shifts by 55 GHz.The application of the sensor in biological detection by sensing experiments is validated,which has guiding significance for rapid detection of low concentration biomolecules and disease diagnosis.