Photoelectrochemical Aptamer Biosensor Based On Semiconductor Materials

Photoelectrochemical analysis method is a new type of analytical method to realize energy conversion,energy utilization,analysis and detection,which is developed by optical,photochemical and electrochemical methods.As the photoelectrochemical analysis has much advantages,such as,the low background,simple device,high sensitivity,and the possibility of the achieving the rational and effective use of solar energy,photoelectrochemical analysis method has become a great potential analysis method.In the construction of biochemical sensors,we have to find the sensing platform which could enlarge the absorption range and improve the photoelectric conversion capacity.Due to the biocompatibility of DNA sequences,the photoelectrochemical DNA biosensors have been widely used.Therefore,two systems in this thesis are designed for photoelectrochemical DNA biosensors.1.Enhanced photoelectrochemical aptasensing platform amplified by sensitization effect of CdTe@CdS core-shell quantum dots coupled with exonuclease-assisted target recyclingA novel,enhanced photoelectrochemical aptasensing platform was developed by using sensitization effect of CdTe@CdS core-shell quantum dots?QDs?coupled with exonuclease-assisted target recycling for significant signal amplification.Carcinoembryonic antigen?CEA?was selected as the target analyte to exhibit analytical performances of this platform.Specifically,nitrogen-doped mesoporous TiO₂?mTiO₂:N?was firstly synthesized by an evaporation induced self-assembly?EISA?method.Then a mTiO₂:N/Au hybrid structure was prepared by depositing Au nanoparticles on the surface of the m TiO₂:N film,which acted as the photoelectrochemical matrix for immobilizing complementary DNA?cDNA?of CEA aptamer probe?pDNA?.CdTe@CdS core-shell QDs as sensitization agents were covalently bound at the front-end of pDNA.After pDNA hybridized with cDNA,the labels of CdTe@CdS QDs were very close to the mTiO₂:N/Au electrode surface,resulting in evidently enhanced photocurrent intensity due to generation of the sensitization effect.While the aptasensor was incubated with CEA and exonuclease I?Exo I?,pDNA would specifically bind with CEA,which made the CdTe@CdS QDs labeled pDNA separate from the electrode surface,leading to obviously weakened sensitization effect and decreased photocurrent intensity.Moreover,as Exo I could digest single strand form of pDNA,the previously bound CEA were released and continuously bound with the rest of pDNA on the electrode surface,leading to further decreased photocurrent intensity.The well-designed photoelectrochemical aptasensor had not been reported and exhibited a low detection limit of 0.12 pg/m L and a wide linear range from 0.5 pg/m L to 10 ng/mL for CEA detection,and it also showed good selectivity,reproducibility and stability.2.A Novel photoelectrochemical aptasensor platform for the detection of miRNA-21 based on the sensitization effect of Cd Se quantum dotsA novel photoelectrochemical aptasensor for the sensitive detection of miRNA-21 was designed based on the sensitization effect of CdSe quantum dots as a signal amplification strategy.The TiO₂NTs/RGO/AuNPs electrode was prepared by electrodeposition of graphene oxide nanoparticles on the TiO₂ nanotube with electrochemical reduction.The electrode was prepared as the matrix of the electrochemical aptasensor.The hairpin DNA decorated with CdSe quantum dots were immobilized on the surface of the electrode by Au-S bond,and the other sites which were not bound to the mercapto group on DNA were blocked with mercaptoethylamine.Because of the card-type structure of the hairpin DNA?HP-DNA?,the CdSe quantum dots were close to the base electrode,which would lead to the sensitization effect,and cause the increase of the photocurrent intensity.When a certain concentration of the mi RNA-21 was added,miRNA-21 would hybridize with the complementary part of HP-DNA.At the same time,the hairpin structure of HP-DNA was broken into a straight chain structure,the CdSe quantum dots on the end of the DNA would be away from the electrode surface,the sensitization effect would be weakened,and the photocurrent intensity would be decreased.The designed photoelectrochemical aptasensor exhibited a low detection limit of 5.6 fM and a wide linear range from 20 fM to 0.2 nM,and it also showed good specificity,reproducibility and stability.The signal amplification strategy was also expected to provide a significant photoelectrochemical biosensor platform for sensitive detection of biomolecules.