Preparation Of MOFs-Derived Hollow Composites And Their Application In Photoelectrochemical/Electrochemical Biosensors

With the continuous development of social economy,the issues of human life health and environmental ecological safety have become a topic of increasing concern.Achieving efficient,rapid and sensitive detection of various human-related cancer markers and environmental pollutants is one of the current research priorities in the field of biosensing.Electroanalytical chemistry/photosensing techniques have been widely used in clinical diagnosis,bioanalysis and environmental monitoring due to their high sensitivity,simplicity and miniaturizable operation.This thesis is dedicated to the development of a variety of MOFs-derived materials with novel structures and superior optical/electrical properties.The various metal-based compounds derived from MOFs can serve as excellent conductive media,while the obtained hollow and multi-level porosity enhances the diffuse reflection effect of multiple light and also creates conditions for efficient compounding of other energy level-matched photoactive materials.The MOFs-derived in situ formed The heterojunction architecture of MOFs can promote a significant increase in photoelectric conversion efficiency.Based on the functional role of various metal-based MOFs-derived composites,the high-performance electrochemical/photochemical sensors constructed and their applications can be divided into the following parts:（1）Herein,the HKUST-1 MOFs and its derivative of HKUST-Cu O were coupled with Ti O₂ nanoparticles to form the heterogeneous composites of HKUST-1/Ti O₂ and HKUST-Cu O/Ti O₂ based on their well-suitable band gap energies（Eg）.Compared with monocomponent HKUST-1 or HKUST-Cu O,prepared composites displayed signally PEC response due to the synergistic effect from their heterogeneous structure.Besides,the higher photocurrent response was obtained on HKUST-Cu O/Ti O₂ modified ITO electrode（HKUST-Cu O/Ti O₂/ITO）,which could be attributed to the hollow structure with a thin shell of HKUST-Cu O greatly enhanced visible spectra harvesting.As well as the Cu O component in HKUST-Cu O not only could accelerate electron transfer on the heterojunction interface but also effectively separated the photo-generated charge carriers（e^-/h⁺）.Based on the excellent PEC performance of prepared photoactive composite material,under visible light excitation(λ（de420 nm）and with a working potential of 0 V（vs.Ag/Ag Cl）,the S1（probe DNA）/HKUST-Cu O/Ti O₂/ITO PEC platform were successfully fabricated for colitoxin DNA detection without using ascorbic acid（AA）as an electron donor.Compared with the analysis results on S1/HKUST-1/Ti O₂/ITO electrode,S1/HKUST-Cu O/Ti O₂/ITO displayed a wider linear response range from 1.0×10^-6 to 4.0×10^-1n M with a lower detection limit of 3.73×10^-7n M（S/N=3）,the linear regression equation wasΔI(10^-6 A)=0.5549-0.1858 log(C_S2/M),which confirmed the HKUST-Cu O could upgrade analysis sensitivity because of its prominent PEC property.The relative standard deviation（RSD）of the PEC sensor for 2.0×10^-4 n M target DNA detection was calculated to be 7.4%.In addition,the HKUST-Cu O@r GO/GCE modified electrode was prepared by mixing HKUST-Cu O with GO for electrochemical reduction reaction to obtain a significantly enhanced electrochemical CV response current.Based on the synergistically enhanced electrocatalytic performance of the HKUST-Cu O@r GO composite,the probe S1 was assembled onto the surface of the CS/HKUST-Cu O@r GO/GCE electrode to obtain a highly sensitive detection for the target analyte concentration in the range from 0.001～37.5 p M and with with a low detection limit of 3.89×10^-2f M（S/N=3）.These proposed DNA biosensors also possessed good specificity and stability.Hence,this reported work was a promising strategy for molecular diagnosis in the bio-analysis field.（2）Heterogeneous composite is considered a valuable material to boost the photo-electrochemical（PEC）properties.Herein,the porous hollow and thin-shell Cu O particles were prepared by calcining its MOFs precursor of HKUST-1.N-doped carbon dots（NCDs）as both reductor and stabilizer can reduce the Au⁺to gain regularly nanoflower NCDs@Au.Then NCDs@Au was combined with as-prepared Cu O particles to create type-Herein,the porous hollow and thin-shell Cu O particles were prepared by calcining its MOFs precursor of HKUST-1.N-doped carbon dots（NCDs）as botosite displayed a 7.8-fold and 3.2-fold photocurrent response than the monocomponent Cu O and Cu O/NCDs materials holding,respectively.This outstanding photoelectric property was ascribed to the multiple reflection/scattering effects from the porous hollow structure of Cu O particles increased by the visible-light absorption intensity,resulting in more photo-induced e^-/h⁺pairs.Large surface area of hollow architecture could fully couple another photoactive material of NCDs@Au to magnify synergistically the photocurrent signal.Also,Au nanoparticles accelerate the electron transfer and suppress the recombination of charge carriers.Ab（antibodies）could be accurately immobilized on the Cu O/NCDs@Au modified ITO electrode via the facility amidation reaction.Fabricated Ab/Cu O/NCDs@Au/ITO PEC sensing platform for AFP（alpha-fetoprotein）detection manifested an enhanced sensitivity(3.32×10^-4 ng m L^-1)with a wide linear range(0.001～300 ng m L^-1),which was superior compared to electrochemical characterization gained results.This works developed an excellent heterojunction nanocomposite of Cu O/NCDs@Au,which could provide well-designed and synthesized strategies for structuring high-performance photocatalysts based on the MOFs derivant.（3）Herein,a metal-organic frameworks（MOFs）of Cu-TPA（terephthalic acid）microsphere was prepared,and after calcinating the MOFs precursor of Cu-TPA/ZIF-8 mixture to obtain the Cu O/Zn O.N atom doped carbon dots（NCDs）was employed to combine the Cu O/Zn O composite to form a tripartite heterostructured architecture of NCDs@Cu O/Zn O,which led to a fierce enlargement of the photocurrent response.It was ascribed to the thinner-shell structure of the Cu O microsphere and hollow Zn O particles could sharply promote the incidence intensity of visible light.The more porous defectiveness exposed on Cu O/Zn O surface was in favour of rapidly infiltrating electrolyte ions.The p-n type Cu O/Zn O composite with more contact interface could abridge the transfer distance of photo-induced electron（e^-）/hole（h⁺）pairs and repress their recombination availably.NCDs not only could boost electron transfer rate on the electrode interface but also successfully sensitized the Cu O/Zn O composite,which resulted in high conversion efficiency of photo-to-electron.The probe DNA（S1）was firmly assembled on the modified ITO electrode surface（S1/NCDs@Cu O/Zn O）through an amidation reaction.Under optimal conditions,the prepared DNA biosensor displayed a wide linear range of1.0×10^-6～7.5×10^-1 n M and a low limit of detection（LOD）of 1.81×10^-7 n M for colitoxin DNA（S2）measure,which exhibited a better photoelectrochemistry（PEC）analysis performance than the differential pulse voltammetry techniques obtained.The relative standard deviation（RSD）of the sensing platform for target DNA detection of 5.0×10^-2 n M was 6.3%.This proposed DNA biosensor also showed good selectivity,stability,and reproducibility,demonstrating that the well-designed and synthesized photoactive materials of NCDs@Cu O/Zn O could be the most promising application in PEC analysis.（4）In this paper,a porous hollow Cd Co S₂（2）microsphere was newly synthesized based on the ZIF-67-S MOFs derived method of sulfurization reaction and calcination process.Under visible light irradiation,the resulting Cd Co S₂（2）composite showed the markedly enhanced photoelectrochemical（PEC）response.Photocurrent value of Cd Co S₂（2）modified ITO electrode was 93-fold and 41-fold than that of Co S and Cd S materials,respectively.Promoting the photo-absorption ability by internal multilight scattering/reflection was due to the porous and hollow Cd Co S₂（2）.Furthermore,obtained Cd Co S₂（2）heterostructure in-situ with a close contact interface could facilitate the separation/migration of photo-induced carriers.Then,Cd Co S₂（2）was mixed with Ag nanoparticles（NPs）to further improve the PEC response.Acetylcholinesterase（ACh E）as a bio-recognition molecule was immobilized on the glutaraldehyde-chitosan（GLD-CS）modified Cd Co S₂（2）@Ag electrode surface by cross-linking effect.Meanwhile,ACh E could hydrolyze the acetylcholine chloride（ATCl）to produce an electron donor of thiocholine which led to elevate photocurrent output.When the bioactivity of ACh E was inhibited by the organophosphate pesticides（chlorpyrifos as substrate）,the reduced production of thiocholine resulted in a decline of the photocurrent response.Under optimal conditions,the structured ACh E/GLD-CS/Cd Co S₂（2）@Ag/ITO sensing platform was successfully achieved for chlorpyrifos detection.Wide linear response range was from 0.001 to270μg m L^-1 and with a low detection limit of 0.57 ng m L^-1.The proposed PEC biosensor also exhibited excellent selectivity and good stability,demonstrating the designed porous hollow Cd Co S₂（2）@Ag heterostructured composite promised to be a great application in the PEC sensors.（5）Heterostructured construction is regarded as a valuable approach to improve photoelectrochemical（PEC）performances.Herein,porous hollow Ni S@Ni O spheres were prepared derived from the Ni（TCY）MOFs precursor.Photoactive Ti O₂ was coupled with as-prepared Ni S@Ni O to form a close heterojunction interface of Ni S@Ni O/Ti O₂.Ni S@Ni O/Ti O₂modified ITO electrode（Ni S@Ni O/Ti O₂/ITO）displayed fiercely enhanced photocurrent response,which was 4687-fold than that of Ni S@Ni O/ITO（0.008μA）and 8.5-fold than that of Ti O₂/ITO（4.41μA）,respectively.Remarkable PEC property could be ascribed to the hollow Ni S@Ni O spheres with thin-shell structure provided there is a larger active surface area for harvesting the visible light.Most importantly,the p-n type Ni S@Ni O/Ti O₂ heterojunction could lead to generating more photo-excited charge carriers（e^-/h⁺）and efficiently hinder the recombination of carriers,resulting in significantly augmented photocurrent output.Based on this outstanding PEC property,Ni S@Ni O/Ti O₂/ITO electrode fabricated sensing platform（BSA/anti-CEA/Ni S@Ni O/Ti O₂/ITO）exhibited high sensitivity for monitoring CEA（carcinoembryonic antigen）.Wide linear detection range was from 0.001 to 45 ng m L^-1 and with a low detection limit of 1.67×10^-4 ng m L^-1（S/N=3）.Prepared biosensors also showed good reproducibility,stability and had satisfying specificity.Thus,the proposed Ni S@Ni O/Ti O₂heterostructured composite afforded well-design and synthesis strategy for constructing high-performance photoactive materials from MOFs-derivate.（6）Photoactive material with heterostructures plays an important role in promoting the photochemical（PEC）property.Herein,a favose Co₃O₄@C was prepared by calcining the metal-matrix complex of Co（NO₃）₂/Mel（melamine）,and the photoactive Ti O₂ particle was coupled with Co₃O₄@C to obtain the heterostructured Co₃O₄@C/Ti O₂ composite based on their matching band gaps.Under light illumination,the Co₃O₄@C/Ti O₂ modified ITO electrode（Co₃O₄@C/Ti O₂/ITO）displayed remarkable PEC performance,gained photocurrent value was317-fold and 197-fold than that of Co₃O₄@C/ITO and Ti O₂/ITO electrode,respectively.Enhanced PEC response was ascribed to favose and thin-shell Co₃O₄@C to promote visible-light harvesting capacity.Simultaneity,the high porosity on Co₃O₄@C could infiltrate the electrolyte and speed electronic transportation.Particularly,formed p-n type heterojunction interface between the Co₃O₄@C and Ti O₂ could accelerate photoinduced carriers（e^-/h⁺pairs）migration as well as curb their recombination effectually.After that,acetylcholine esterase（ACh E）was immobilized on the chitosan（CS）/glutaraldehyde（GLD）modified Co₃O₄@C/Ti O₂/ITO electrode surface to structure the PEC sensing platform of ACh E/CS-GLD/Co₃O₄@C/Ti O₂/ITO.The acetylcholine chloride（ATCl）could be hydrolyzed by ACh E to produce the thiocholine,which as an electron donor resulted in elevation photocurrent response.However,when the bio-recognition molecule of ACh E was inhibited by the Chlorpyrifos,the reduced production of thiocholine led to decline the photocurrent output.Under optimal conditions,the prepared PEC biosensor exhibited high sensitivity for the detection of Chlorpyrifos(the wide linear range from0.0001μg m L^-1 to 225μg m L^-1 with a low detection limit of 2.9×10^-5μg m L^-1.Proposed PEC sensor also had good specificity,reproducibility,and satisfying stability.This work developed an effective photoactive material with p-n type heterojunction for the application in sensing.