Ionic Liquid Functionalized Lanthanide Metal-organic Frameworks: Synthesis And Applications In Photoelectrochemical Immunosensing

Photoelectrochemical(PEC)immunosensing technology developed by combining the photoelectric conversion process with the identification of biological macromolecules is extensively investigated recently.PEC immunosensing system possesses many advantages including fast analysis speed and compact equipment,accompanying with low background and high sensitivity.Therefore,it possesses broadly prospective in clinical diagnosis,environmental monitoring and food safety etc.PEC immunosensing system often consists an excitation light source,photoelectric conversion material and biorecognition element.Photoactive materials are commonly used as a photoelectric conversion element.High-performance photoelectrochemical immunosensors are closely related to the property of photoactive materials.At present,many PEC immunosensing systems are designed based on the excitation of ultraviolet light or visible light in a relatively narrow light-absorption range.The UV/Vis light sources commonly cause light bleaching effect and high-energy carriers.High-energy carriers generated during the excitation process will damage the biological recognition element and biological activity,which will cause poor selectivity and stability.In order to improve the sensing performance of PEC immunosensors,exploring a novel photoactive material that can be excited in the near-infrared or visible region with excellent photoelectric conversion efficiency is vital for the construction of PEC immunosensors and theoretical study.The lanthanide metal organic frameworks possess light-harvesting properties and excellent light-emitting properties.Herein,novel ionic liquid functionalized lanthanide metal-organic framework compounds were prepared and applied for PEC immunosensing AFP and CEA.The main contents of this dissertation can be detailed as following:(1)An ionic liquid with a large heterocyclic structure was successfully synthesized and used as a ligand to coordinate with Eu³⁺ions to supply Eu-MOF nanorods.Through in-situ reduction of HAu Cl₄ on the Eu-MOF nanorod surface,gold nanoparticle-decorated Eu-MOF nanocomposites(Eu-MOF@Au-NPs)were prepared.The excellent conductivity of Au-NPs and the unique properties of MOFs work together to improve photoelectrochemical performance by reducing charge carrier recombination and utilizing a broader spectrum for light harvesting.Under white light illumination,the photocurrent of the Eu-MOF@Au-NPs nanocomposite-modified electrode was about 2.2-fold higher than that of the Eu-MOF modified electrode.A novel photoelectrochemical immunosensor for alpha-fetoprotein(AFP)was fabricated using Eu-MOF@Au-NPs as the photoactive elements.When anti-AFP was immobilized on the Eu-MOF@Au-NPs-based sensing interface,the PEC immunosensor exhibited a specific photocurrent response to AFP.The PEC sensing principle is based on photocurrent decreases due to the blocking effect of AFP on electron and mass transfer.Experimental conditions,including ascorbic acid concentration,incubation time,and incubation temperature were optimized for the AFP assay.Under optimized conditions,the photocurrent variations were linearly correlated to the logarithm of AFP concentration from0.002 ng m L^-1 to 15.0 ng m L^-1,with a detection limit(S/N=3)of 0.16 pg m L^-1.Moreover,this sensor exhibited excellent selectivity,good reproducibility,and desirable stability.It was successfully applied to the detection of AFP in clinical serum samples.(2)A novel near-infrared(NIR)-excited photoelectrochemical(PEC)immunosensor based on ionic liquid functionalized Yb-MOF and gold nanoparticles(Au-NPs)was designed for the high-performance determination of carcinoembryonic antigen(CEA).The Yb-MOF was synthesized from the coordination of the Yb³⁺metal ion with the 1,1'-(1,5-dihydropyrene-2,7-diyl)bis(3-(4-carboxybenzyl)-1H-imidazol-3-ium)bromide[DDPDBCBIm(Br)₂]ionic liquid by a hydrothermal method.To improve the photoelectric conversion efficiency of the Yb-MOF in the NIR region,the surface of the Yb-MOF was integrated with gold nanoparticles(Au NPs)to fabricate the Yb-MOF@Au NPs nanocomposite through an in-situ reduction of chloroauric with sodium borohydride.The NIR photoelectrochemical response of the Yb-MOF@Au NPs at808 nm was enhanced 4-fold over the Yb-MOF without Au-NPs.Subsequently,a photoelectrochemical platform based on the Yb-MOF@Au NPs was constructed for loading the CEA antibody(anti-CEA).Upon cross-linking with glutaraldehyde followed by blocking with bovine serum albumin,a photoelectrochemical sensor for assaying CEA was fabricated.After optimizing the experimental conditions,the photocurrent variations before and after incubation with CEA were linearly correlated to the CEA concentration over the range of 0.005?15ng·m L^–1.The detection limit of CEA that was calculated was 0.25 pg·m L^–1(S/N=3).The immunosensor was employed for the measurement of free CEA in clinical serum samples,and the results were very consistent with the values obtained by clinical tests.The NIR PEC immunosensor also demonstrated excellent accuracy and recovery,which corroborates its potential as a practical technique in clinical diagnosis.