Construction And Application Of Sensing Platform Based On Zirconium-based Metal-organic Frameworks

Biomolecules are substances closely related to various life activities of the human body,which can participate in human metabolism and maintain the normal operation of physiological functions.Biomolecules are also used as biomarkers to provide the basis for early diagnosis of human diseases.Therefore,the quantitative detection of biomolecules is of great significance in the field of biomedicine.For early diagnosis and precise treatment of diseases,there is an urgent need to develop simple,easy operation,sensitive,convenient and low-cost analytical methods.Compared with the traditional methods for detecting biomolecules,the techniques of optical analysis based on Metal-organic Frameworks(MOFs)are widely used due to the advantages of simple operation,high sensitivity and good specificity.Among them,Zirconium-based Metal-organic Frameworks(Zr-MOFs)have great potential in biosensing due to their tunable structure,large specific surface area,good stability,high biocompatibility and easy to be functionalized at surface,etc.Therefore,the main targets of this research focuse on the construction of a sensing platform based on Zr-MOFs for the sensitive detection of small biomolecules and biological enzymes,and explore its sensing mechanism in detail.Seven chapters as follows are included in this paper:In the first chapter,the Zr-MOFs was briefly introduced.Meanwhile,the preparation method of Zr-MOFs and the application of Zr-MOFs in biosensing were described in detail.On this basis,the key points and research significance of this paper were proposed.In the second chapter,a sensing platform for colorimetric and fluorescence dual-mode detection of sarcosine was constructed based on Zr-MOFs modified with enzyme immobilisation and CDs.In this study,Zr-MOFs with peroxidase-like activity was successfully prepared by a solvothermal method.Sarcosine oxidase and horseradish peroxidase were loaded onto the Zr-MOFs under mild conditions.When sarcosine was added,it could be reacted with sarcosine oxidase to produce hydrogen peroxide.Hydrogen peroxide was decomposed by Zr-MOFs and horseradish peroxidase to generate free radicals that could oxidize the p-phenylenediamine(PPD)and lead to the quenching of CDs.Therefore,the dual-mode fluorescence and colorimetric detection of sarcosine was achieved.This sensing platform was successfully used for the determination of sarcosine in the urine of prostate cancer patients,demonstrating the potential of this sensing platform for the early diagnosis of prostate cancer.In the third chapter,a colorimetric and fluorescence dual-mode sensing platform for the rapid detection of butyrylcholinesterase(BChE)had been developed based on Cerium-doped Zirconium-based Metal-organic Frameworks(Oxidized UiO-66-NH2@Ce).Oxidized UiO-66-NH2@Ce had excellent oxidase-like activity after activation,which could catalytically oxidise the substrate 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)to generate green oxABTS.And the generated oxABTS could quench the fluorescence of Oxidized UiO-66-NH2@Ce.BChE could hydrolyse S-butyrylthiocholine iodide(BTCh)to generate thiocholine which had the reducing property to hinder the oxidation of ABTS,thus achieving the dual-mode detection of BChE.The sensing platform showed sensitive response to BChE,and the limits of detection(LODs)were as low as 0.056 and 0.050 U/L,respectively.With the advantages of high sensitivity and low background interference,the sensing platform could be successfully used for the detection of BChE in human serum.In the fourth chapter,Phosphate-modified Zirconium-based Metal-organic Frameworks Composites(Oxidized Pi@UiO-66-NH2(Zr/Ce))were successfully prepared.It was negatively charged due to the surface modification of phosphate,which significantly enhanced the affinity for the chromogenic substrate 3,3’,5,5’-tetramethylbenzidine(TMB).Thus,the Oxidized Pi@UiO-66-NH2(Zr/Ce)could rapidly oxidize TMB due to its oxidase-like activity,resulting in the solution changing from colorless to blue.Glutathione(GSH),as a reducing substance,could inhibit the above process.And glutathione S-transferase(GST)could catalyse the reaction between GSH and 1-chloro-2,4-dinitrobenzene(CDNB)to form a complex and lose its reducing property,thus restoring the blue colour of the solution.As a result,a colorimetric sensing platform for the detection of GST was constructed based on Oxidized Pi@UiO-66-NH2(Zr/Ce).The linear range was 0.0002-0.01 U/L,and the detection limit was 0.18 mU/L.In addition,we constructed a point-of-care testing(POCT)platform for GST by combining the above system with polyvinyl alcohol(PVA)hydrogel and obtained satisfactory results.In the fifth chapter,we enhanced the peroxidase-like activity of Pt nanoparticles by in situ synthesizing them on Zr-MOFs.And a colorimetric sensing platform for glucose detection was constructed based on Zirconium-based Metal-organic Frameworks Composites(Zr-MOFs@Pt NPs).Glucose oxidase(GOx)produced hydrogen peroxide(H2O2)by enzymatic reaction with glucose.Zr-MOFs@Pt NPs,due to their peroxidase-like activity,enabled to decompose H2O2 to generate free radicals,which in turn oxidized TMB to produce blue oxTMB.This achieved highly sensitive colorimetric detection of glucose.Afterward,we constructed a polyvinyl alcohol hydrogel microneedle sensing platform based on Zr-MOFs@Pt NPs for the detection of glucose.There was a good linear relationship between the glucose concentration and the color intensity value of the display layer of the microneedle sensing platform in the range of 0.1-18 mM.And the microneedle sensing platform based on Zr-MOFs@Pt NPs had been successfully applied to detect glucose in serum samples.The method not only provided a multi-modal sensing platform for the detection of blood glucose,but also extended the application of Zr-MOFs in microneedle sensing platforms.In the sixth chapter,a colorimetric and fluorescence dual-mode sensing platform for the detection of captopril was constructed based on Zirconium-based Metal-organic Frameworks Composites(UiO-66-NH2@ZIF-8)and Co,N-doped nanozymes.The Co,N-doped nanozymes possessed the oxidase-like activity,which oxidized N,N-diethyl-p-p-phenylenediamine(DPD)to change the solution from colorless to pink and caused the fluorescence quenching of UiO-66-NH2@ZIF-8.In contrast,captopril could inhibit the above process,thus enabling colorimetric and fluorescence dual-mode detection of captopril.More importantly,we developed a portable paper-based hydrogel sensing platform with fluorescence and colorimetric dual-signal readout.The paper-based hydrogel sensing platform was composed of a qualitative filter paper and two layers of polyvinyl chloride(PVC).Therein,the qualitative filter paper was made by soaking in a solution containing UiO-66-NH2@ZIF-8 and Co,N-doped nanozymes and then drying.Afterwards,the paper-based hydrogel sensing platform was constructed by assembling the qualitative filter paper with a PVC layer and forming a hydrogel layer by dropping a polyvinyl alcohol solution and borax solution in the center of the filter paper.Similarly,this paper-based hydrogel sensing platform produced a pink substance visible to the naked eye by catalyzing the redox reaction of DPD and caused the fluorescence quenching of UiO-66-NH2@ZIF-8.And the above process was hindered in the presence of captopril.The images were acquired by taking pictures with smartphone,and ImageJ software was used to convert the image parameters into data information for quantitative detection of captopril.In the seventh chapter,we summarized the contents of this paper systematically and discussed the perspectives of Zr-MOFs in the field of biosensing in future.