Development Of Nanocomposite-based Photo/ Electrochemical Biosensor And Its Application In The Detection Of Hg(Ⅱ) And Aβ

Biosensor is a detection system for measuring biological or chemical reactions and generating a signal proportional to the concentration of the targeted analyte.Photoelectrochemistry（PEC）biosensors have attracted much attention because of their easy miniaturization,high sensitivity,low cost,straightforward designs,and simple instrumentation.PEC biosensors have been used to detect various analytes such as tumor markers,metal ions,gas molecules,and biomolecules such as DNA and mi RNA.In this thesis,three novel photoelectrochemical biochemical sensors were constructed to achieve the detection of mercury ions(Hg²⁺)andβ-amyloid（Aβ）with the following main sensing strategies:1)Photoelectrochemical sensor for detection Hg²⁺based on in situ generated MOFs-like structuresIn this work,a novel photoelectrochemical（PEC）biosensor was developed for the ultrasensitive detection of Hg²⁺based on the MOFs-like composite/Cd S quantum dots（QDs）as photoactive substrate materials.The MOFs-like composite in situ formed by hydrophobically modified alginate（HMA）with europium ion(Eu³⁺)not only offered a friendly platform for bioconjugation but also resulted in enhancing sensor photocurrent response.Furthermore,the immobilized thymidine-rich probe DNA on the MOFs-like composite surface was bent to produce a T-Hg²⁺-T structure in the presence of Hg²⁺,resulting in enlarged steric hindrance on the electrode surface and decreased the proposed biosensor PEC response.The PEC sensing platform constructed in this work achieved a sensitive and selective detection of Hg²⁺with a linear range of 0.1 p M to 1.0μM and a detection limit of 0.067 p M,and the sensor has good reproducibility.2)A dual-mode sensing platform for the sensitive detection of Aβ:combining dual Z-scheme heterojunction enhanced photoelectrochemistry analysis and dual-wavelength ratiometric electrochemiluminescence strategyIn this work,we designed a novel photoelectrochemical（PEC）and electrochemiluminescence resonance energy transfer（ECL-RET）dual-mode sensor to achieve ultra-sensitive detection of Aβo.Specifically,the electrode surface modified Carbon Dots（C Dots）and the electrodeposited polyaniline（PANI）film formed a Z-scheme heterojunction,and then the multifunctional recognition peptide of Aβo（COOH-CPPPPDKDKDKDKKLVFF）was attached to the surface via amide bonding.The Aβo and the Cd Te-labeled Aβaptamer（Cd Te-Apt）were added to electrode to construct a“sandwich”sensor.The formation of double Z-scheme heterojunction promotes the charge separation efficiency and thus exhibits a“signal-on”cathodic photocurrent response.In addition,the proposed sensor also caused a ratiometric change in the electrochemiluminescence intensity at 555 nm and 640 nm.Therefore,the developed sensor achieved dual-mode detection of Aβo,where the PEC detection range of Aβo was from 10 f M to 0.1μM（with a detection limit of 4.27 f M）and the ECL method provided a linear detection range of 10 f M to 10 n M（with a detection limit of 6.41 f M）.The experimental results show that the biosensor has the advantages of high analytical sensitivity,good selectivity,and high accuracy,enabling it to be extended to the detection and analysis of other biomolecules.3)Ultrasensitive PEC/ECL detection of Aβvia a dual-mode sensor based on Au NRs modulated HOFs@g-C₃N₄ composite functional materialIn this work,we reported the synthesis of a heterojunction composite of HOFs@g-C₃N₄ using the solution-reformulation of hydrogen-bonded organic frameworks,which was employed as a photoactive material to construct a dual-mode biosensor for Aβo detection.To enhance the framework stability of HOFs materials,a self-assembly strategy was employed to combine g-C₃N₄ with HOFs materials viaπ-πstacking.And the generated heterojunction structure suppressed the compounding of photogenerated electron-hole pairs,and improved the photogenerated carrier separation efficiency thus enhancing the PEC response of HOFs@g-C₃N₄.First,HOFs@g-C₃N₄ was drop-coated on the electrode surface,and then the Aβaptamer was modified on the electrode surface by amide bonding.The Aβo and the Au NRs-labeled Aβrecognition peptide（Au NRs-KLVFF）were added to the electrode to construct a“sandwich”dual-mode sensor.In the presence of Aβo,the surface plasmon resonance effect of Au NRs enhances the visible light absorption of HOF@g-C₃N₄,and the sensor exhibits a“signal-on”photocurrent signal.However,in the ECL mode,the ECL emission spectrum of HOF@g-C₃N₄ overlaps with the UV-vis absorption of Au NRs,and the sensor shows a“signal-off”phenomenon.Under optimal conditions experiments,the constructed dual-mode sensor showed a wider detection range and lower detection limit for Aβo.Among them,PEC detected Aβo in the concentration range of 10 f M to 10 n M with a detection limit of 5.97 f M,and ECL detected Aβo in the concentration range of 0.1 p M to 1μM with a detection limit of 0.051 p M.The sensor showed satisfactory results in the analysis of real samples.