Study On Transition Metal Chalcogenide Quantum Dots-based Photoelectrochemical Aptasensors

Photoelectrochemical（PEC）biosensing integrates the photoelectric conversion with the biomolecule recognition process,which mechanism involves excitation of the photoactive materials to produce photocurrent signal that correlates with the biological interactions between biorecognition element and its target.Owing to complete separation and different energy forms of excitation source（light）and detection signal（photocurrent）,PEC detection possesses significantly reduced background noise and higher sensitivity than typical optical or electrochemical detection methods.Additional merits of simple instrument,low cost and easy miniaturization make PEC analysis a promising methodology for high performance detection of various targets.In a conventional PEC biosensor,the photoactive material is an indispensable brick in switching photoirradiation to photocurrent,which governs the analytical performance.Rational design and engineering of high-quality photoactive material has become one of the most critical steps to developing high-performance PEC biosensors.With the development of two‐dimensional transition-metal dichalcogenides（TMDs）,TMDs quantum dots（TMDs QDs）have attracted considerable research interests due to their fascinating properties.Owing to the quantum confinement effects,TMDs QDs possesses unique electronic structure,high electron mobility and superior photo-physical properties.Due to high solubility,tunable optical properties,amenable ability of hybridization and functionalization,TMDs QDs are promising candidates of heterojunctioned photoactive components.In this dissertation,a series of TMDs QDs-based heterojunctioned photoactive materials were designed and synthesized.Their optical absorption,photoelectric conversion and the mechanism of photogenerated charge separation,transport and recombination were systematically studied.Combining with several signal amplification strategies and new detection modes,several high-performance PEC aptasensors were developed.The main contents include the following sections:（1）The MoS2 QDs-Bi OI p-n heterojunctioned material was proposed by a simple impregnation method of water-soluble monolayer Mo S2 QDs and flower-like hierarchical Bi OI microspheres.The improved photoelectric conversion capacity of the heterojunction was ascribed to intense visible-light harvesting,accelerated separation and transfer of photo-generated carriers driven by internal electric field in the heterojunction,which leading to the magnified photocurrent intensity.Taking TNF-αas model analyte and by coupling the simplest target-induced conformational change mechanism,high selectivity and ultrasensitive self-power cathodic PEC detection was exemplified.（2）A high-performance cathodic PEC aptasensing platform for detection of amyloid-beta oligomers（AβO）was developed by integrating Cu O/g-C₃N₄ p-n heterojunction with Mo S2 QDs@Cu NWs multifunction signal amplifier.The Cu O/g-C3N4 with intense visible light-harvesting and high photoelectric conversion efficiency,was synthesized by in-situ pyrolysis of Cu-MOF（Cu3（BTC）2）and dicyandiamide.The Mo S2 QDs@Cu NWs was obtained by electrostatically self-assembly,which acted not only as a sensitizer to boost PEC response,but also as a nanozyme for biocatalytic precipitation.The aptasensor was fabricated by DNA hybridization between the c DNA on photocathode and Mo S₂ QDs@Cu NWs-labeled aptamer.Based on“on-off-on”photocurrent response generated by multifunction signal amplification,ultrasensitive aptasensing of AβO was realized in a wider linear range from with a low detection limit.（3）An ultrasensitive controlled-release cathodic PEC aptasensor was constructed for supersensitive determination of AβO.The Mo S₂ QDs@Cu NWs was employed as photocathode material.Mesoporous silica nanocontainers（MSNs）was used as containers and Au NPs-labeled AβO aptamer（Au NPs-Apt）as the molecular gate.The rich porous structure of MSNs is favor of entrapment of thionine（Th）molecule.When AβO was specifically bounded with Apt,Au NPs-Apt was separated from MSN.The photosensitive dye molecule Th released from MSN could assemble with Mo S2 QDs based on electrostatic/π-stacking interaction,leading to an increased photocurrent signal.Consequently,the target AβO could be ultrasensitively and specifically detected.（4）The commonly used single-mode signal biosensor suffers from certain instinct drawbacks that restrict its assay performances.A split-type PEC and electrochemical dual-modal aptasensor for ultrasensitively tracing of tumor necrosis factor-alpha（TNF-α）was designed and constructed.By smart integrating Mo S2 QDs/ZIF-8@Zn O nanorods arrays with methylene blue（MB）-liposome-mediated signal amplification strategy,“dual signal-on”detection was accomplished based on a sandwich reaction of the target with aptamer-anchored carboxyl magnetic beads and aptamer-confined MB-liposome.Independent signal transduction mechanism supports the accuracy improvement,and separate biological process from translator enables convenient fabrication,short time consumption,wide linearity,as well as outstanding reproducibility and stability in practical application.（5）The VS2 QDs-Bi2S3 heterostructure was obtained via one-step hydrothermal method by using VS2 QDs as precursor.The intrinsic metallic feature of VS2,efficient visible light absorption of Bi2S3 nanotube,well-aliened band structure and intimate interfacial contact between them were responsible to the dramatically enhanced photoelectric conversion capacity as well as substantially enhanced photocurrent.Employing lysozyme aptamer（Lya）as biorecognition element,a self-power PEC aptasensor for lysozyme（Lys）was fabricated.Ultrasensitive and selective detection of lysozyme is established in a wide linear range with low detection limit.Trace monitoring Lys in biological systems is realized with desired accuracy and satisfactory recovery.