Study On Interfacial Multifunctional Reconciliation Mechanism Of Ultra-high Sensitivity Semiconductor Photoelectric Biosensor

As a new type of sensor,semiconductor photoelectrochemical（PEC）biosensor is characterized by the coupling of photoexcitation process and electrochemical detection,which generates output current signal depending on photons as excitation signals.The different energy forms between the two processes can greatly reduce the background noise,enabling PEC sensors with higher theoretical upper limit of sensitivity.Meanwhile,PEC sensors have the advantages of low cost,fast detection speed and simple operation,which have a wide scope of application in many fields such as environmental monitoring,food safety,biomedical sciences,etc.However,there will still be some bottlenecks in the application of this type of biosensor,the core issues of which include:1)How to improve the transport of photoelectrons at the semiconductor/biomass interface,2)How to improve the universality of PEC biosensors when dealing with so many kinds of substances to be detected,3)How to improve the conversion efficiency of photons to biochemical electrons and the stability of photoanode materials,and 4)How to make the small,portable sensors.Based on the above issues,the paper has mediated the carrier transport process between harmonic semiconductor interface and biological interface by using Two-dimensional carbon nitride（2D-C₃N₄）.The surface morphology and oxygen vacancy concentration of photoanodes are regulated by laser recrystallization technology to expand the types of detection materials.Through the modification of the doped quantum layer and passivating the surface,the efficient separation of carriers and the stability of photoanode materials were achieved.At last,the first portable U-disk PEC biosensor was developed through the design of the structure of counter electrode combined with wireless communication technology.The main results are as follows.1.The aptamer/2D-C₃N₄/BVO PEC sensor was prepared by using ultra-thin 2D-C₃N₄layer as the link between the BVO photoanode and aptamer probe,which could detect microcystin-LR（MC-LR）,an environmental pollutant,with ultra-high sensitivity.The linear detection range of the sensor for MC-LR molecules was from 5×10^-7μg/L to 10μg/L,and the limit of detection was 4.486×10^-8μg/L,which was two orders of magnitude higher than that of reported similar sensors up to date.The results of PEIS,CIMVS/CIMPS and further theoretical calculation suggested that 2D-C₃N₄played a dual-function role in the photoelectrochemical sensor.On the one hand,it could be used as the transfer mediator of photogenerated holes in BVO photoanode to accelerate its transfer process;on the other hand,the two-dimensional surface of 2D-C₃N₄could form large-areaπ-πadsorption with the benzene ring of DNA aptamer,which improved the immobilization ability of DNA aptamer on photoanode surface.Therefore,assisted by the dual-function of 2D-C₃N₄,aptamer/2D-C₃N₄/BVO PEC sensor could detect MC-LR with ultra-high sensitivity and specificity.This finding has provided a new idea to optimize the performance of aptamer-based PEC sensors,and at the same time provided certain basic data for developing ultra-sensitive biosensors for environmental monitoring and biomedical detection.2.A new semiconductor photoelectric biosensor was prepared by laser reconstruction technology.First of all,under the instantaneous high temperature of pulsed laser,the surface of BVO was melted and recrystallized,and the original porous BVO surface became dense and the crystallinity was obviously increased.Meanwhile,the high-energy laser has introduced a large amount of oxygen vacancy defects in the surface of BVO,which could increase the concentration of majority carriers in BVO and generate photoelectric charge traps that could promote the separation of electrons and holes.Subsequently,the corresponding probe was modified on the surface of laser-treated BVO photoanode（laser-BVO）for the detection of PSA,marker of prostate tumor.The results of the detection indicated that the sensor could accurately detect PSA at an oligomolecular level.The limit of detection was as low as 0.82 ag/mL,the resolution was about 18molecules/mL.The detection showed high specificity,stability and accuracy in clinical verification of PSA serum in Shaanxi Cancer Hospital.Further mechanism studies have shown that the crystallinity,carrier separation efficiency and 2D-C₃N₄adsorption capacity of laser-treated BVO thin films were improved.The combination of these factors improved the sensitivity of sensors.On the other hand,the oxygen vacancies introduced by laser treatment formed doping energy levels at BVO Fermi,which led to the decrease of the energy of photogenerated holes.The change of surface structure and the decrease of the oxidation ability of holes led to the enhancement of steric effect,and finally the photoelectric signal suppression biosensor was generated.Nevertheless,this suppression sensor did not depend on the redox reaction between the hole and the substance to be detected,but contrarily extended the detection range of the sensor.In general,sensors prepared by laser reconstruction technology not only have higher sensitivity,but can also be applied to the detection of various target substances.Therefore,the laser crystal reconstructed PEC biosensor designed and developed in this chapter presents promising application prospects in the field of multi-tumor markers or virus biological detection.3.The hole transport layer with ohmic contact was prepared in BVO photoanode by modifying doped double-quantum-layer Ni doped ZnO（Ni:ZnO,～5 nm）and Rh doped SrTiO₃（Rh:STO,～10 nm）.Through photoelectric measurement,scanning kelvin probe（SKP）and first principle calculation,the transfer mechanism of the carriers was analyzed.The results have shown that the modified doped double quantum layer could greatly reduce the tunneling barrier and improve the carrier separation efficiency.Meanwhile,the band hybridization between Ni and Rh 3d orbitals modified by doped quantum layer improved the photon absorption ability of BVO.In terms of sensors,the outer Rh:SrTiO₃quantum layer fixed the aptamer with high efficiency,and the adsorption capacity of aptamer per unit area increased by 2.4 times compared with the BVO thin film;while the quantum layer of Ni:ZnO improved the sensitivity of the sensor,and its lower limit of detection for COVID-19 spike protein was reduced to 47.0%compared with the unmodified Ni:ZnO quantum layer sensor.To summarize,by modifying the doped double-quantum-layer Ni:ZnO/Rh:STO,not only the PEC performance of BVO photoanode,but also the sensitivity of the sensor was comprehensively improved.4.Ti₂CO₂MXene with few layers was prepared by the vacuum ozone pulse method.XRD,XPS,UV-Vis and photoelectric tests further confirmed that a new Ti₂CO₂MXene material was synthesized in the laboratory for the first time.The results show that Ti₂CO₂is a semiconductor with a band gap of 0.5 eV,and shows good hydrophilicity,biological affinity and ultra-high carrier mobility.Through first-principles calculation,the paper has selected two-dimensional materials theoretically suitable for biosensors,and Co-doped Ti₂CO₂MXene（Co:Ti₂CO₂MXene）,which had the strongest adsorptive capacity for the aptamer,was determined as the adsorptive layer on the aptamer surface.Subsequently,Ti₂CO₂MXene was prepared by hydrothermal ion doping.The results have shown that Co:Ti₂CO₂MXene showed a better performance than 2D-C₃N₄,graphene,graphene oxideand Rh:STO in the adsorption of the same type of aptamer.Finally,the reference electrode,working electrode,counter electrode and light source were integrated,and then the first portable semiconductor photoelectrochemical biosensor was successfully developed through wireless transmission technology,which was successfully used to the detection of neurotransmitter serotonin.The linear detection range of the sensor was 10 ag/ml～10 pg/ml,and the limit of detection was 0.37 ag/mL.