Preparation Of NiCo₂O₄ Multilevel Material And Its Application In Photoelectrochemical Immunosensor

Cancer has become one of the major threats to human life security in the world.Therefore,timely detection of tumor markers is of great importance for early diagnosis and prognosis of diseases.Photoelectrochemical（PEC）analysis technology is widely used in the environment,food,biology and other fields because of its accuracy,high efficiency and low cost.The photoelectrochemical immunosensor constructed by combining the photoelectrochemical sensing technology and tumor markers recognition technology realizes the sensitive analysis of specific markers.The key step in the preparation of the sensor is the selection of materials.Therefore,NiCo₂O₄ with suitable band gap,high optical absorption coefficient,high abundance and low cost was selected for preparation and modification in this paper.The main work is as follows:（1）In this study,a signal-on type PEC immunosensor was constructed to detect neuron-specific enolase（NSE）via Z-scheme WO₃/NiCo₂O₄ p-n heterojunction with cactus-like structure used as photoactive materials and Mn_xCd_1-xS@Au NPs（MCS@Au NPs）as signal labels.Firstly,Z-scheme WO₃/NiCo₂O₄ heterojunction could accelerate the separation efficiency of carriers and well-matched WO₃/NiCo₂O₄ may promote charge migration,which resulted in WO₃/NiCo₂O₄ generating strong and stable current.In addition,Z-scheme WO₃/NiCo₂O₄ heterojunction directly grown on the surface of FTO via hydrothermal method facilitated the preparation of PEC immunosensor with outstanding stability.Secondly,an efficient signal amplification strategy was proposed by Mn_xCd_1-xS@Au NPs incubating with secondary antibody（Ab₂）.On the one hand,the well-matched energy levels of Mn_xCd_1-xS with WO₃/NiCo₂O₄ boosted the photo-generated electrons transferred to the electrode;on the other hand,the localized Surface Plasmon Resonance（LSPR）effect of Au may convert thermion to photocurrent to achieve signal amplification.Based on the above strategies,a PEC immunosensor with outstanding reproducibility and stability was obtained for sensitive detection of NSE.Under the optimum experimental conditions,current response range of the constructed signal amplification PEC sensor to NSE was 0.1 pg/m L～50 ng/m L and the detection limit was 0.072 pg/m L（S/N=3）.It was verified that the prepared PEC immunosensor had the characteristics of good selectivity and high sensitivity.（2）In order to achieve rapid and sensitive detection of Cytokeratin 19 fragment（CYFRA21-1）,a signal-off PEC immunosensor was devised with NiCo₂O₄/Cd In₂S₄/In₂S₃ heterojunction as the substrate and Re S₂@Au NPs as the secondary antibody labels amplifying signal based on the energy band-matching cascade structure and double suppression effect.NiCo₂O₄possessed a faster charge transfer rate due to the abundance of redox electron pairs(Co³⁺/Co²⁺and Ni³⁺/Ni²⁺).To further improve the PEC properties of NiCo₂O₄ under visible light,Cd In₂S₄with matching bandgap energy was selected to form heterojunction with NiCo₂O₄ and sensitized with In₂S₃.The proposed heterojunctions with well-matched band structure promoted the separation of photo-generated carriers and were exploited as signal transducers for immobilization of antibodies and recognition of CYFRA 21-1.Furthermore,a novel urchin-like p-type Re S₂ semiconductor nanostructure functionalized by Au NPs was firstly used as a nanolabel to quench the signal.On the one hand,the Schottky heterojunction generated by Re S₂and Au NPs could compete with the substrate for both light and electron donors.On the other hand,the large space steric hindrance of Re S₂ prevented contact between the substrate and AA.Under the best experimental conditions,the sensor was sensitive in a wide range of concentrations for CYFRA 21-1（0.0001～50 ng/m L）,and the detection limit was 0.053 pg/m L（S/N=3）.（3）A novel signal-off biosensing platform based on CdLa₂S₄/SnIn₄S₈/Sb₂S₃ heterojunction as photoactive materials and NiCo₂O₄ nanospheres as photoquencher was developed to achieve sensitive detection of carbohydrate antigen（CA19-9）.Firstly,the narrow-band gap hydrangea-like Cd La₂S₄/SnIn₄S₈/Sb₂S₃ not only provided excellent photocurrent response but also supplied a mass of active sites.Secondly,double type-II Cd La₂S₄/SnIn₄S₈/Sb₂S₃ heterojunction promoted the fast separation and migration of photo-generated e^-/h⁺and overcame the problem of short carrier lifetime caused by the re-combination of photo-generated carriers.In addition,in order to improve the sensitivity of the constructed sensor to detect CA19-9,signal tags（p-type NiCo₂O₄）with large steric hindrance were introduced to accomplish signal amplification by the effect of double signal quenching.On the one hand,NiCo₂O₄,which was strongly responsive to visible light,utilized its own advantages to compete for AA with Cd La₂S₄/SnIn₄S₈/Sb₂S₃,resulting in a decrease in the hole scavenging rate of the substrate.On the other hand,the photoquencher NiCo₂O₄ also prevented AA from contacting the substrate and further aggravated the PEC signal.The PEC immunosensor was prepared with brilliant selectivity and splendid stability to detect CA19-9（0.001～50 U/m L）and the detection limit was 0.00045 U/m L（S/N=3）.