Adsorption Performance And Applications Of Metal-organic Frameworks In Biosensors With Signal Amplication

Metal organic frameworks?MOFs?are a new type of ordered porous crystalline materials.MOFs exhibit a wide variety of potential applications in catalysis,gas storage and separation,drug delivery,and chemical sensors,owing to their specific features,such as structural diversity,flexibility and tailorability,high porosity,large surface area,and extraordinary adsorption affinities.In this thesis,the adsorption kinetic processes of I₂ vapor onto MOFs films were monitored by a quartz crystal microbalance?QCM?technique.A high performance photoelectrochemical sensors for H₂O₂ was repored based on the molecular sieve and catalytic effects of MOFs.The electrochemical immunosensors with MOFs as the signal tage or biometallization were applied to detect biomarkers.The detailed results are summarized briefly as follows:1.Combination of piezoelectric and spectrometric methods to monitor adsorption kinetics of iodine on MOFs filmsIn this work,the combination of an electrodeless quartz crystal microbalance?EL-QCM?and spectrometric techniques was designed to investigate the adsorption kinetics of iodine onto two metal-organic frameworks film,MIL-101 and ZIF-67.To eliminate the electrode damage from I₂ corrosion,the configuration of electrodeless QCM?EL-QCM?was employed.The concentrations of I₂ adsorbed on film and in vapor phase were monitored simultaneously in real time by the frequency of EL-QCM and the absorbance,respectively.It was shown that ZIF-67 film has a high adsorption capacity of 4.41 g/g to I₂,which is much higher than that of MIL-101?0.58 g/g?.The 2-methylimidazole unit in ZIF-67 plays an important role for I₂ adsorption with a capacity of 3.15 g/g.For adsorption on MIL-101,the amount of I₂ adsorbed at equilibrium obeys the Henry‘s law.The amounts of I₂ adsorbed on ZIF-67 film increases with increasing concentration of I₂ vapor in accelerating slope due to the condensation of I₂ vapor.The adsorption isotherms are in the shape of parabola.The diffusion coefficients of I₂ in MIL-101 and ZIF-67 films were estimated to be 6.1 × 10^-16 and 3.7 × 10^-16 m²/min,respectively.By using the concentration-time curves,adsorption kinetic parameters were estimated based on a simplified model including reversible and irreversible adsorption states.2.High performance photoelectrochemical sensor for hydrogen peroxide based on molecular sieve and catalytic effects of MOFsHerein,we proposed a simple strategy to improve both of the sensitivity and selectivity of a photoelectrochemical?PEC?sensor to hydrogen peroxide.By using TiO₂ nanotubes array?NTs?as the base,a composite of g-C₃N₄ and carbon nanotubes?CNTs?was deposited to prepared a photoelectrode of g-C₃N₄-CNTs/TiO₂ NTs.A Cu-MOFs layer of Cu₃?BTC?₂was grew on the surface of the photoelectrode by a liquid-phase epitaxy process.The Cu₃?BTC?₂ layer acts as a size-exclusion filter,preventing the diffusion of molecules with size larger than the apertures in MOFs layer while allowing diffusion ofthe smaller molecules,which improves the selectivity of the PEC sensor to smaller molecules?e.g.,H₂O₂?.On the other hand,the additional catalytic effect of the Cu₃?BTC?₂ to H₂O₂ enhances the sensitivity by a factor of 10.The influence of the CNTs content and Cu₃?BTC?₂ layer thickness on the PEC response were investigated.Under optimized conditions,the as-prepared Cu₃?BTC?₂/g-C₃N₄-CNTs/TiO₂ NTs sensor was applied to the detection of H₂O₂ with a detection limit of 1.1 nmol/L.The interference from large molecules?e.g.,ascorbic acid,uric acid and dopamine?was reduced significantly.3.Using MOFs as the signal tage for electrochemical determination of two cancer biomarkersStable and highly dispersed polyaniline?PANI?nanofiber aqueous colloids prepared via a facile chemical method were used to modify glassy carbon electrodes?GCEs?,combining the good conductivity and network structure of PANI nanofibers with the complexing capacity of mercaptosuccinic acid?MSA?.The as-prepared modified electrode exhibits high sensitivity to Cd²⁺ and Pb²⁺ ions with the detection limits?S/N = 3?of 0.05 ?g/L for Cd²⁺ and 0.2 ?g/L for Pb²⁺ respectively.By using aminated Cd-MOFs and Pb-MOFs particles to label anti-alphafetoprotein?AFP?and anti-carcinoembryonic antigen?CEA?separately for the electrochemical signal tags,the thiolated PANI nanofiber modified GCE was applied to the simultaneous detection of AFP and CEA with linear range of 0.0003³ ng/m L.The detection limits were 0.1 pg/mL for AFP and 0.03 pg/mL for CEA,respectively.The present study provides a new path for fabricating high performance modified electrodes suitable for the highly sensitive and simultaneous determination of cancer biomarkers.4.A piezoelectric immunosensor array with biometallization and successive signal amplification strategyA differential piezoelectric immunosensor array was reported to to eliminate the influence of non-mass effects,including the changes in conductivity,viscosity,density and temperature of the solution,as well as the baselines draft of piezoelectric sensors.The responses of the differential piezoelectric immunosensor in fundamental frequency,third and fifth overtones were investigated.In immunoanalysis,the primary antibody probes were immobilized on the aminated quartz surface in piezoelectric sensor array.After bounding with the corresponding antigen and alkaline phosphatase?ALP?conjugated second antibody,Pd?II?was reduced to Pd NPs by enzyme-generated p-aminophenol from the substrate of p-aminophenyl phosphate under the catalyst of ALP in the sandwich-type immunocomplex.A subsequent signal amplification was performed by a Pd NPs-promoted catalytic electroless deposition of Ni-P layer,improving significantly the sensitivity of piezoelectric immunosensor.The proposed method is applied to the determination of human IgG with a detection limit of 1 pg/mL.Compared with biometallization of Pd NPs,the sensitivity is enhanced by three orders of magnitude due to high activation energy in Ni-P deposition reaction and low baseline draft in differential measurement mode.