Detection Of Cephalexin Using Molecularly Imprinted Polymer Capped Mn-doped ZnS Phosphorescent Quantum Dots

Cephalexin（CEX）is a kind ofβ-lactam antibiotic with broad-spectrum antibacterial activity.As a veterinary drug,CEX can prevent and treat bovine mastitis and other infectious diseases.However,CEX residues in milk and other foods can have harmful effects on human health,such as allergic reactions.They may also increase the antibiotic-resistance of deleterious bacteria.Conventional detection methods have the disadvantages of time consuming and high cost.Therefore,developing a novel method for the highly effective detection of CEX is essential for monitoring food quality and guaranteeing public health.In this study,quantum dots（QDs）and molecular imprinting technology（MIT）were combined to prepare highly sensitive and highly selective CEX molecularly imprinted phosphorescent probes.The preparation methods,optical and morphological characteristics,and adsorption properties of phosphorescent probes were investigated.At the same time,a novel method for detecting CEX residues in actual samples based on aphosphorescent probes was established.The main results were listed as follows:1.Combining sol-gel polymerization method and surface molecular imprinting method,molecularly imprinted phosphorescent probes（SiO₂-QD-MIPs）and molecularly non-imprinted phosphorescent probes（SiO₂-QD-NIPs）were prepared on the surface of SiO₂-QDs nanoparticles using CEX as template molecules.According to the single factor test,the optimal preparation conditions of phosphorescent probes were as follows:50μL of APTES,90μL of TEOS,and 5 m L of SiO₂-QDs.2.Various optical and morphological characterization experiments have been performed on the phosphorescent probes.The results showed that the Thioglycolic acid modified Mn-doped ZnS quantum dots（TGA-QDs）have been successfully grafted onto the surface of SiO₂ nanoparticles through amide bonds,and the imprinting layers were coated on the SiO₂-QDs surfaces.The prepared probes have a unique core-shell structure with an average particle diameter of 250-300 nm,and excellent phosphorescent properties.3.The dynamic and static adsorption results of the phosphorescent probes showed that the adsorption amount is positively correlated with the adsorption time,the adsorption velocity is fast at first and then become slow.Moreover,the saturated adsorption capacity of SiO₂-QD-MIPs is much higher than that of SiO₂-QD-NIPs,indicating that SiO₂-QD-MIPs have better affinity for CEX.In addition,the probes also have good selectivity.4.Under the optimal detection conditions（pH 7.0,40-fold dilution of SiO₂-QD-MIPs and reaction time 30 min）,the phosphorescence quenching of SiO₂-QD-MIPs by CEX comply with the Stern-Volmer equation and belong to dynamic quenching.Its linear range was calculated to be 2.5-50μg/L,and detection limit（LOD）was calculated to be 0.81μg/L.The recoveries of the spiked samples ranged from 91.7 to 103.7%,and the results were highly consistent with the HPLC-UV controlled trial（R²>0.98）.