Study On Detection Of Oxytetracycline Using Novel Fluorescent Biomimetic Sensing Probes Based On Carbon Dots And Luminescent Metal-Organic Frameworks

Oxytetracycline（OTC）is a tetracycline antibiotic that has been widely used to treat infectious diseases caused by pathogenic microorganisms due to its broad-spectrum antibacterial activity,effectiveness,and low cost.However,the excessive use of OTC can lead to its accumulation in the environment and food,posing a threat to human health.Therefore,developing rapid,highly sensitive,and cost-effective methods to monitor OTC residues in food is of great significance.Compared with traditional detection methods,fluorescence（FL）sensing methods show considerable advantages,such as convenient operation,low cost,high sensitivity,and fast response.At the same time,molecularly imprinted polymer（MIP）has specific recognition ability and high affinity for target analytes.Applying MIP to construct FL sensing probes can enhance selectivity and anti-interference ability.In this study,a series of FL biomimetic sensing probes were constructed to detect OTC in milk using MIP as recognition elements,carbon dots（CDs）and luminescent metal-organic frameworks（LMOFs）as fluorescent materials.（1）A fluorescent biomimetic probe（Ce,N-CDs@MIP）was constructed for OTC specific recognition and quantitative detection by encapsulating cerium and nitrogen co-doped carbon dots（Ce,N-CDs）into MIP.Ce,N-CDs with high fluorescence quantum yield（FLQY,33.69%）and bright blue FL were synthesized by hydrothermal method.Using Ce,N-CDs as fluorescent materials,in the presence of OTC（template molecule）,3-amino-propyl triethoxysilane（APTES,functional monomer）,tetraethoxysilane（TEOS,cross-linking agent）,and HAC（catalyst）,the sol-gel method was used to synthesize Ce,N-CDs@MIP.In this strategy,Ce,N-CDs with high FLQY and good FL characteristics served as fluorophores,enabling Ce,N-CDs@MIP to display a sensitive FL response to OTC through an effective inner filter effect（IFE）sensing mechanism.Due to the modification of the molecularly imprinted layer,the sensing probe had specific recognition performance for the target molecule OTC,which can improve the adsorption and binding ability for OTC,and had good anti-interference ability in complex detection environments.Owing to the comprehensive advantages of Ce,N-CDs and MIP,the sensing detection method based on Ce,N-CDs@MIP had a low detection limit(0.032μg m L^-1),wide linear range(0.125-20μg m L^-1),ideal selectivity and sensitivity,as well as good stability.Meanwhile,the constructed FL sensing probe was successfully used for the quantitative analysis of OTC in milk,and the determination results were basically consistent with those obtained by HPLC,demonstrating its accuracy and practical applicability.（2）Embedding Ce,N-CDs into cobalt-based metal-organic framework（ZIF-67）to form Ce,N-CDs@ZIF-67 as FL materials,using OTC as template molecules and APTES as functional monomers,an innovative fluorescent biomimetic probe（Ce,N-CDs@ZIF-67@MIP）was fabricated through a one-pot strategy and applied for the selective and sensitive detection of OTC.The Ce,N-CDs featured with bright blue FL and high FLQY（33.69%）were incorporated as a signal label to make the sensing probe generate measurable FL response signal according to IFE.The modification of the surface imprint layer enabled the sensing probe to possess favorable anti-interference ability and specific recognition performance.ZIF-67 with large specific surface area functioning as supporter significantly increased the mass transfer rate,shortened the response time,as well as improved the adsorption and detection performance of Ce,N-CDs@ZIF-67@MIP.Thanks to the integrated merits of MIP,ZIF-67 and Ce,N-CDs,the sensing method based on Ce,N-CDs@ZIF-67@MIP not only displayed a favorable linear range(0.05-20μg m L^-1)with a low detection limit(0.015μg m L^-1),but also showed good stability and selectivity.Ce,N-CDs@ZIF-67@MIP has been successfully utilized for the FL analysis of OTC in milk samples.The relevant results were highly in accordance with those obtained by HPLC method.Therefore,the proposed Ce,N-CDs@ZIF-67@MIP sensing probe is expected to provide an efficient and sensitive FL detection assay for OTC evaluation in dairy products.（3）A“on-off”type FL biomimetic sensing probe（NH₂-UIO-66（Zr）@MIP）based on MIP-coated amino-functionalized zirconium（Ⅳ）metal-organic framework was successfully constructed for ultrasensitive and selective determination of OTC.NH₂-UIO-66（Zr）with the maximum emission wavelength of 455 nm at 350 nm excitation was prepared by micro-wave-assisted heating method.The NH₂-UIO-66（Zr）@MIP sensing probe with specific recognition performance for OTC was acquired by modifying with MIP on the surface of NH₂-UIO-66（Zr）.The introduction of NH₂-UIO-66（Zr）as both signal tag and supporter can strengthen detection performance of the prepared FL sensing probe.The integration of MIP made NH₂-UIO-66（Zr）@MIP enjoy high selectivity,adsorption affinity and binding ability to OTC.The constructed FL sensing method based on NH₂-UIO-66（Zr）@MIP displayed a linear range of 0.05-40μg m L^-1 with a detection limit of 0.012μg m L^-1.Thanks to the combination of MIP and NH₂-UIO-66（Zr）,the prepared FL sensing probe not only exhibited specific FL response to OTC,but also showed good stability.The NH₂-UIO-66（Zr）@MIP FL sensing probe was applied to the detection of OTC in milk,and the results were comparable to those attained by HPLC approach.Hence,the NH₂-UIO-66（Zr）@MIP sensing probe possesses great application potential for accurate evaluation of trace OTC in dairy products.