Study On A New Fluorescence Method For The Determination Of Doxycycline By Fluorescence Quantum Dots Based On Internal Filtration Effect

Fluorescent quantum dots（QDs）are a new type of fluorescent nano-materials,whose size is less than 10 nm.Many kinds of QDs can be prepared based on the source of different elements and synthesis methods.For example,carbon quantum dots,silicon quantum dots,fluorescent copper clusters and gold clusters can be prepared from carbon,silicon,copper and gold sources.Due to the different properties of different elements,the luminescent and surface properties of QDs can be adjusted by doping elements,which will promote the application of QDs in biosensing and bioanalysis.Doxycycline（DC）is a widely used broad-spectrum antimicrobial tetracycline.It has antibacterial activity against Gram-positive bacteria and Gram-negative bacteria,Chlamydia,Rickettsia and Mycoplasma,and can be used to treat certain respiratory tract infection,urinary and biliary tract infections.In the treatment of Novel coronavirus pneumonia（COVID-19）patients with hydroxychloroquine combined with antibiotics,tetracyclines（such as doxycycline）may be a better choice than macrolides and quinolones for patients with cardiovascular diseases.In veterinary medicine,doxycycline is extensively used in animal husbandry,shrimp farming and fish to prevent and treat infection in food animals.However,excessive use of doxycycline can cause a range of problems that affect human health.Therefore,doxycycline concentration monitoring in different areas is a very important work.In this work,the optical properties of fluorescent quantum dots（QDs）,such as carbon quantum dots（CDs）and silicon quantum dots（SiNPs）,which have good luminescent properties,are investigated,thus,DC determination based on the signal variation of two kinds of fluorescent quantum dots is established,and various complicated practical systems are determined,and the quenching mechanism is further investigated.The research contents of this thesis are divided into the following two parts:Chapter one:The feasibility of determination of doxycycline based on the effect of internal filtration and the fluorescence detection of doxycycline using carbon quantum dots as probeIn this chapter,CDs with stable luminescence property and good compatibility is used as fluorescent probe.In phosphate buffer system,DC reacts with CDs which quenches the fluorescence emission of CDs.A simple and fast analytical method was established for the DC detection.By comparing the UV Absorption Spectra of different antibiotics and DC and the effect of DC on coumarin-6,Tam and Fam,it is proved that DC quenching CDs is an internal filtering effect.Then,it is verified that the interaction between DC and CDs is based on the internal filtering effect by infrared spectra and fluorescence lifetime.On this basis,the fluorescence quenching efficiency F₀-F/F₀ of CDs has a good linear relationship with C_DC when the concentration of DC varies in the range of 5-30μM.The fitting linear equation is y=0.01249*C_DC+0.03625,R²=0.9987,the detection limit is 2.343μM（n=8）.It was successfully used in the recovery of doxycycline hydrochloride tablets and human serum samples.Results show that this method has a good prospect in the field of biomedicine and the drug quality control of DC.Chapter two:Application of silicon quantum dots as fluorescence detection signal in the detection of doxycyclineIn this chapter,silicon quantum dots（SiNPs）with high quantum yield are designed for the defects of low sensitivity of DC and low quantum yield of CDs.In the same phosphate buffer system,the interaction between DC and SiNPs and the quenching of the fluorescence emission of SiNPs based on the principle of internal filtering effect,a simple and rapid analytical method was established for the detection of DC.The results show that the fluorescence quenching efficiency F₀-F/F₀ of SiNPs has a good linear relationship with C_DC when the concentration of DC varies in the range of 1-40μM.The linear fitting equation is y=0.0104*C_DC+0.0333,R²=0.992 and the detection limit is0.396μM（n=8）.In addition,the standard addition and recovery tests of doxycycline hydrochloride tablets,human serum plasma samples and milk samples were performed.The results showed that the method exhibited obviously improved analitycal performance,which wide the application of this method in DC concentration monitor,quanlity control and the DC residues in food was feasible for the determination of doxycycline.