Research On Construction Of Photoelectrochemical Biosensors By N-type Semiconductor Combined With Nucleic Acid Signal Amplification

The biomarker is a kind of biochemical index with broad application,which can reflect the disease and its severity or a certain characteristic during treatment.In order to realize the early diagnosis and monitoring of the disease,the specific disease biomarker is usually measured.Therefore,it is of great significance to establish a simple,rapid and sensitive detection method for biomarker.Photoelectrochemical（PEC）biosensor is a new type of analysis technology that uses light as the excitation source,photocurrent as the detection signal.Compared with traditional electrochemical analysis,PEC biosensor has a lower background signal and higher sensitivity,which exhibits extensive potential clinical applications in disease diagnosis and disease monitor.Studies have shown that the photoelectric conversion efficiency of photoelectric materials is a key factor to restrict the sensitivity of PEC biosensor.Although the n-type semiconductors dominated by electronic conduction have a large number of free electrons,the recombination rate of electron-hole pair for a single n-type semiconductor is relatively high,and the photoelectric conversion efficiency is limited.Therefore,searching a simple and effective method to significantly enhance the photoelectric conversion efficiency of n-type semiconductors and obtain a high PEC signal for constructing highly sensitive and accurate PEC biosensors have become key issues to be solved urgently.Meanwhile,the design of efficient and fast nucleic acid signal amplification strategies is also essential for further improving the detection sensitivity of PEC biosensors.As a result,we constructed a series of PEC biosensors for the detection of biomarkers based on significant amplified output signal achieved by various efficient nucleic acid signal amplification strategies coupled with enhanced photoelectric conversion efficiency of n-type semiconductors by dye sensitization,compounding with other materials and ions co-doping.The research work is as follows:1.Dependent signal quenching and enhancing triggered by bipedal DNA walker for ultrasensitive photoelectrochemical biosensorThe organic dye perylene-3,4,9,10-tetracarboxylic acid（PTCA）is an n-type photoelectric active material with richedπelectrons,which has a narrow band gap and excellent optoelectronic performance.At the same time,the small molecules of methylene blue（MB）and ferrocene（Fc）could be used as sensitizer and quencher of PTCA at the same wavelength,respectively,and their electron transfer efficiency depends on distance.Thus,by utilizing bipedal DNA walker formed by target thrombin（TB）and its two aptamers（P₁ and P₂）as booster to adjust the distance of quencher Fc and sensitizer MB to photoactive material PTCA via the mechanical movement on electrode surface,a novel“onoff-super on”PEC biosensor was proposed for ultrasensitive detection of TB.The sensitizer MB close to PTCA and Fc far away from PTCA could effectively reduce the electron-hole recombination efficiency of PTCA for significantly enhancing PEC signal.Such an“on-off super on”strategy avioded disadvantages of background signal from“signal on”or“signal off”detection mode and the shortcoming of 100%photocurrent signal recovery from“on-off-on”detection mode,significantly inmproving the detection sensitivity and brodening detection range.Furthermore,the mechanical movement of bipedal DNA Walker on electrode surface realized the circulation of target,which further improved the detection sensitivity.2.Dual sensitized heterojunction PDA/ZnO@MoS₂ QDs combined with Nt.Bst NBI mediated multilocus domino-like DNA cascade reaction for ultrasensitive photoelectrochemical biosensorThe combination of multiple photoelectric materials can effectively reduce the recombination efficiency of electron-hole in a single material and improve the photoelectric conversion efficiency.Therefore,a ultrasensitive PEC biosensor based on dual sensitized heterojunction PDA/ZnO@MoS₂ QDs formed by p-type semiconductor molybdenum disulfide quantum dots（MoS₂ QDs）,n-type semiconductor ZnO and PDA coupled with multilocus domino-like DNA cascade reaction triggered by Nt.Bst NBI was constructed for the detection of mi RNA-182-5p.The porous ZnO nanospheres can effectively improve the utilization rate of light via the multiple reflections of light.Meanwhile,the double heterojunction formed by three materials effectively promoted the transfer of photogenerated electrons,reduced the recombination efficiency of electron-hole and significantly improved the photocurrent signal.In addition,the multilocus domino-like DNA cascade reaction triggered by target mi RNA-182-5p and Nt.Bst NBI on DNA nanonet with orderly position of substrate strands can not only utomatically advance along the specific DNA hairpin path,accelerate the cut rate of Nt.Bst NBI enzyme,significantly shorten the reaction time and improve the reaction stability,but also avoid the negative results of the non-uniform spatial effect caused by the disorderly fixation of substrate strands,improving the detection sensitivity.3.Functional carbon nitride coupled with dual catalytic hairpin assembly amplification strategy for sensitive and accurate photoelectrochemical-electrochemical biosensorThe single detection mode is susceptible to experimental errors and background signals.Therefore,we constructed a photoelectrochemical-electrochemical（PEC-EC）dual-mode biosensor with different output signals based on n-type semiconductor material g-C₃N₄ co-doped by K⁺,Na⁺ions and compounded with organic dye MB to form a multifunctional carbon nitride material Na KCN-MB,improving the detection sensitivity and accuracy.The ion-doping not only reduced the recombination of electron-hole pairs,but also rendered high glucose oxidase（GOx）-mimicking catalytic activity to in situ generate high levels of H₂O₂ as its own electron donor of Na KCN-MB under visible light irradiation.Meanwhile,the dye in-plant could implement superior synergetic sensitization,thereby forming a novel ternary self-enhanced photoactive material.Further,the enzyme cascade electrocatalytic signal amplification system composed of hemin polymer and Na KCN-MB could accelerate the redox reaction of electroactive substance MB,significantly enhancing the electrochemical response signal.Moreover,the dual-catalytic hairpin assemble（dual CHA）could convert the small amount of target into a large amount of output substance,further improving the sensitivity of the PEC biosensor.