Study On The Electrochemical Aptasensors Based On Metal-Organic Frameworks And Covalent Organic Frameworks For Cancer Marker Detection

Electrochemical aptasensors are widely used for the detection of cancer biomarkers,owing to their high sensitivity,high selectivity,simple instrument and low cost.As the emerging multifunctional porous materials,metal-organic frameworks（MOFs）and covalent organic frameworks（COFs）have benefited from their diverse structure,adjustable pore size,large specific surface area and large number of active sites,and have been extensively applied in the field of electrochemical sensing.Exploring MOFs/COFs-based chemosensors with high selectivity and low detection limits for cancer biomarkers currently is one of the important topics in this field.For this,four different electrochemical aptasensors based on framework materials have been designed for the rapid and sensitive detection of vascular endothelial growth factor（VEGF）,prostate specific antigen（PSA）,platelet-derived growth factor-BB（PDGF-BB）,and human mucin 1（MUC1）in the serum samples,respectively.The main research contents of this thesis are as follows:（1）A sandwich-type electrochemical aptasensor based on Tp BD-COF as signal amplifier for the VEGF detectionUsually,the electroactive substance immobilized on the nanomaterial can effectively reduce the background signal.Increasing the amount of the electroactive substance is vitally important for the sensitivity of the sensor.A simple reflux method was used to effectively synthesize Tp BD-COF,which was applied in the construction of an electrochemical aptasensor for the sensitive detection of VEGF.Firstly,we synthesized gold nanoparticles modified zinc oxide nanosheets（Zn O-Au）to immobilize VEGF aptamer1（Apt1）.The semiconductor nanomaterial Zn O nanosheets have the advantages of good chemical stability and no biological toxicity.When Zn O-Au nanosheets with electrical conductivity are used,the conductivity can be improved.Then the covalent organic framework materials with large specific surface area were used to extensively immobilize the gold nanocarriers so as to abundantly carry aptamer2（Apt2-Au NPs-COFs）.The thionine as electronic medium was chemisorbed onto the gold nanoparticles via Au-NH₂ bond（Apt2-Thi@Au NPs-COFs）.In the presence of target VEGF,both Zn O-Au-Apt1 and Apt2-Thi@Au NPs-COFs bind to VEGF,and VEGF can be sensitively detected through sandwich reaction.The detection range of the aptasensor is 0.01 to 100 ng/m L,and the lowest detection limit is 3.35 pg/m L.（2）Construction of an electrochemical aptasensor based on layer-by-layer assembly of sheet-like Cu-MOF for PSA detectionExtra electroactive substance is urgently required,despite its loading amount can been increased with the COF material.To avoid introducing traditional redox media,we constructed an electrochemical aptasensor to detect PSA using a layer-by-layer self-assembly method.Firstly,the carboxylated graphene oxide nanosheets（GO-COOH）were synthesized,which was then reduced to r GO-COOH by electrodeposition and fixed onto the surface of glassy carbon electrode（GCE）.The electroactive 2D Cu-MOFs nanomaterials with abundant amino groups were synthesized by a bottom-up method,which were fixed onto r GO-COOH/GCE through amide bonds.At the same,the PSA aptamer with-COOH was continued to bind to 2D Cu-MOFs/r GO-COOH/GCE.Compared with the traditional aptasensor designed with precious metal materials,the proposed method has the advantages of low cost,simple and efficient assembly procedure.When PSA targets are present,the detection limit as low as 2.86 pg/m L can be achieved in the detection range from 0.01 to 130 ng/m L.Compared with the traditional aptasensor designed with precious metal materials,the proposed method has the advantages of low cost,simple and efficient assembly procedure.（3）A sensitive electrochemical MUC1 sensing platform based on electroactive Cu-MOFs decorated by Au Pt nanoparticlesTo further amplify the signal,a sensitive electrochemical MUC1 sensing platform has been fabricated based on copper-based metal-organic frameworks（Cu-MOFs）decorated with gold-platinum alloy nanoparticles（Au Pt NPs）.Besides serving as a redox probe to avoid introducing extra redox media,the electroactive Cu-MOFs function as catalysts in the hydrogen peroxide reduction,resulting in electrochemical signal amplification.Meanwhile,AuPtNPs loaded on the Cu-MOFs mimic horseradish peroxidase to promote the reduction of hydrogen peroxide,giving rise to the secondary-amplified electrochemical signal.Moreover,the target MUC1triggered catalytic hairpin assembly（CHA）further improves the sensitivity of the developed biosensor via the target recycling amplification.The constructed sensing platform displayed a desirable dynamic range between 10 f M and 10 n M in the MUC1 detection,with a sufficiently low limit-of-detection（3.33 f M）.（4）Label-free electrochemical aptasensor based on the core-shell Cu-MOF@Tp BD hybrid nanoarchitecture for the sensitive detection of PDGF-BBAlthough the flower-like Cu-MOF in the above-mentioned work has a large specific surface area,it is relatively unstable and easily broken in aqueous solution,just like the majority of MOF materials,which limits its practical application.To improve the stability of MOF in aqueous solution,a novel core-shell nanoarchitecture consisting of Cu-based metal-organic frameworks（Cu-MOFs）and covalent organic frameworks（denoted as Tp BD-COFs）was designed,which was used to fabricate an aptasensor for the detection of PDGF-BB.The central Cu-MOFs function as signal labels with no need for extra redox media,whereas the porous Tp BD serves as the shell to immobilize the PDGF-BB-targeted aptamer strands in abundance via the strong interactions involvingπ–πstacking,electrostatics,and hydrogen bonding.The proposed aptasensor based on Cu-MOF@Tp BD can achieve a detection limit as low as 0.034pg/m L within the dynamic detection range from 0.0001 to 60 ng/m L.In summary,four electrochemical aptasensors were successfully fabricated using the MOFs and COFs framework materials combined with targeted aptamer strands by different synthetic strategies,realizing the detection of representative cancer biomarkers.The proposed aptasensors have extended the application of framework materials in the field of sensing,and provide a promising opportunity for the detection of biomarkers in the clinical diagnosis with high selectivity and sensitivity.