Construction And Performance Study Of Biosensing System Based On Redox Enzyme-Mimicking Activity Of Fe/Ni-MOF

Metal-organic frameworks(MOFs)have been widely employed as signal sources/catalysts in the field of biosensing due to their large specific surface area,abundant catalytic active sites,variable components,and adjustable pore structure.The host-guest interaction between the frame and the guest molecules affects the sensing signal production or catalytic amplification,and the interaction strength and mode directly affect sensitivity of the MOF sensor.Hence,in order to achieve high sensitivity detection of the target,it is of great importance to rational design of the MOF structure to obtain the optimal host-guest interaction.In this paper,a series of Fe/Ni-MOFs with redox mimic enzyme activity was selected as host matrix,and enzyme inhibitor/signal molecules was employed as the guest.To achieve ultra-sensitive detection of target analytes,the host-guest interaction is regulated from three aspects of pore environment,action bonding mode,as well as catalytic site,further optimized the structure of MOF and screened high-performance MOF biosensors.The main research contents and results are as follows:1.Tailoring the chirality and pore size of the Ni-MOFs to promote the best match between the host and the guest in improvement of the sensitivity of the electrochemical sensor.Ni²⁺as metal centers,(+)-camphoric acid and amino equipped N-donor ligands 2-aminopyrazine(PYR),[4,4'-bipyridin]-3-amine(BPY)and 2,5-di(pyridine-4-yl)aniline(BPB)as organic linkers,a series of isomorphic chiral Ni-MOFs(D-Ni-PYR,D-Ni-BPY and D-Ni-BPB)with different pore sizes were solvothermally synthesized to immobilize ACh E for the high-efficiency detection of the drug inhibitor galantamine(GH).The sensing signals were generated and amplified by the synergetic catalyze hydrolysis of acetylthiocholine chloride(ATCl)by ACh E,and Ni(II)centers with oxidase-like activity,GH can effectively inhibit the hydrolysis process.Among them,the detection limit of the middle L-Ni-BPY system exhibits a lowest GH detection limit of 0.31 p M(detection range:1×10¹²?1×10⁶ M),which is far superior to most reported ACh E inhibitor biosensors.The sensitivity is 1.65 times of its enantiomer D-Ni-BPY system,5.55 times of D-Ni-BPB with smaller pore size and 26 times of D-Ni-PYR with a larger pore.Microcalorimetric experiments have shown that the excellent performance of the L-Ni-BPY sensing system is due to the strong host-guest interactions which produced by the well-matched pore size and chirality toward substrate,and the corresponding?H(17.700 k J mol^-1),the binding constant(1.449×10^-2 mol^-1)towards GH are far superior to other isomorphic systems.The quantitative characterization of the energy of the host-guest interactions provides forceful thermodynamic support for illustrating the structure-activity relationship of the MOF-based electrochemical biosensors and shedding further light on complete understanding the sensing behaviors.2.Designing the host-guest covalent bond chemistry to improve the sensitivity of MOF-based fluorescence biosensor.Compared with the traditional host-guest supramolecular interaction,the design of host-guest covalent bond interaction directly is an effective strategy to accelerate the energy transfer between the host and the guest and could improve the sensitivity of the sensor.Using NH₂-MIL-101(Fe)with good fluorescence signal as parent,2,4-dinitrobenzenesulfonyl chloride with strong electron withdrawing ability is covalently coupled onto the surface of MOF by amidation reaction to afford weak fluorescent NH₂-MIL-101(Fe)-DNS,which was employed as a fluorescent biosensor for the detection of ACh E inhibitor galantamine(GH).Upon treatment with nucleophilic thiocholine(TCh),which generated by the enzymatic reaction,the DNS moiety of NH₂-MIL-101(Fe)-DNS is eliminated with the release of NH₂-MIL-101(Fe),resulting in the recovery of the fluorescence signal.Whereupon,the presence of ACh E inhibitor could reduce the generation of thiocholine,hindering the recovery of fluorescence.On the basis of the fluorescence“off-on-off”strategy,an ACh E modulated fluorescence biosensor for the highly sensitive detection of inhibitor has been designed,which is significantly superior in sensitivity than similar ACh E inhibitor sensors based on host-guest supramolecular interaction.Furthermore,the visual detection of ACh E inhibitor was realized based on the excellent peroxide-like activity of NH₂-MIL-101(Fe)in a concentration-dependent manner(10^-11M?5×10^-5 M),with a lowest detection limit of 9.12 p M.Moreover,the dual-channel fluorescence biosensor exhibits excellent applicability in human serum samples and potential application in clinical diagnosis.3.Regulating the catalytic sites of MOF to enhance the host-guest catalysis interaction in improvement of the sensitivity of MOF-based electrochemical sensor.Using(+)-camphoric acid and N-donor ligands 4,4'-bipyridine(BPY),1,2-bis(4-pyridyl)ethylene(BPE),1,4-bis(pyrid-4-yl)benzene(BPB)as organic linkers,a series of isomorphic Ni-MOFs(Ni-BPY,Ni-BPE and Ni-BPB)with different pore sizes were solvothermally synthesized for encapsulating the electroactive molecule(MB)to construct a sandwich-type electrochemical sensor for the detection of thrombin(TB).Oxidase-like activity of Ni centers could catalyze dissolved oxygen to produce·O₂^-,which further complete oxidation of MB,and then signal amplification.In combination with the experiments and DFT calculation,it is concluded that the double bond in Ni-BPE system possesses stronger host-guest interaction with oxygen molecules as guest in MOF pores,and the adsorption energy of the metal site for O₂ is also the highest(E_abs=-22.205 k J·mol^-1),resulting in the rapid generation of·O₂^-and efficient catalysis of signal molecule.Therefore,the sensing platform based on Ni-BPE exhibits high analytical performance with an ultralow detection limit of 3.3 f M,which are 1.34 and 1.53times as high as that of Ni-BPY and Ni-BPB,respectively.Based on the microthermal experiment of the host-guest interaction between MOFs and MB,the Ni-BPE system presents the highest enthalpy value(?H=-47.39 k J·mol^-1),illustrating that the more suitable pore size of Ni-BPE is also the intrinsic cause of its excellent performance.