| Photoelectrochemical sensor has attracted wide attention because of its weak bankground signal,high sensiitivity,simple equipment and easy miniaturization.In view of the good application potential of photoelectrochemical and immunological technology in detection of cancer markers,we carried out study on photoelectrochemical immunosensors.We prepared several tungsten-based semiconductors(e.g.,tungsten trioxide,bismuth tungstate)composites by compounding,doping,surface modification and dye sensitization,and investigated their photoelectric conversion efficiency,carrier separation efficiency,and electron transfer mechanism.The composite semiconductors were used as anode and cathode photoelectric materials to construct photoelectrochemical immunosensors.Through improving protein immobilization method,signal amplification strategy and adopting new sensing mode(e.g.,cathode-anode-combing type),we achieved the highly sensitive detection of carcinoembryonic antigen,prostate-specific antigen,human epididymal protein 4 and neuron-specific enolase.The details are as follows:(1)A novel Z-scheme Zn In2S4/WO3 photocatalyst based photoelectrochemical immunosensor for the sensitive detection of prostate specific antigenA novel three-dimensional Zn In2S4/WO3photocatalyst was prepared via a simple hydrothermal method.The photocatalyst presented excellent photoelectric activity,and its photocurrent intensity was up to 23 and 7 times of WO3 and Zn In2S4 respectively,under 430 nm light illumination.The improved PEC property was due to three reasons:(i)the sensitization of Zn In2S4promoted the light absorption;(ii)the 3D structure of Zn In2S4 increased the loading of WO3 and(iii)the formation of Z-scheme heterojunction between Zn In2S4 and WO3 promoted the spatial separation of interfacial charges and prolonged the lifetime of photogenerated electrons.A label-free photoelectrochemical immunosensor was fabricated by using the photocatalyst for PSA detection.Under optimal conditions,the linear response range was 0.01-500 ng/m L,and the detection limit was 5 pg/m L.Moreover,the PEC immunosensor afforded high stability,specificity and reproducibility and possessed great application potential in biological/clinical analysis.(2)LED visible-light driven label-free photoelectrochemical immunosensor based on WO3/Au/Cd S photocatalyst for the sensitive detection of carcinoembryonic antigenBased on the cathodic electrochromic properties of WO3,the plasmonic photocatalyst of WO3/Au was successfully synthesized by a reversible charge-discharge method.And based on this,the ternary photocatalyst WO3/Au/Cd S was prepared by successive ion adsorption and reaction.The photocatalyst exhibited higher photocatalytic activity and better photoelectrochemical property in comparison with WO3,Cd S,WO3/Au and WO3/Cd S.The reasons were as follows:(i)the localized surface plasmon resonance effect of Au nanoparticles and the sensitization of Cd S synergistically enhanced the absorption of visible light and(ii)the formation of heterojunction between WO3and Cd S benefited the spatial separation of photogenerated electron-hole pairs.Thus,the photocurrent response intensity of WO3/Au/Cd S was up to about 218-fold of WO3 and 87-fold of Cd S under 430 nm LED light irradiation.Based on this photoanode and the carcinoembryonic antibody,a novel label-free PEC immunosensor was constructed for the sensitive and selective detection of carcinoembryonic antigen.Under optimal conditions,the sensor detected carcinoembryonic antigen with a linear range of 0.01-10 ng/m L and a detection limit as low as 1 pg/m L.Additionally,the immunosensor also showed good stability,reproducibility and repeatability.It was successfully applied to the detection of carcinoembryonic antigen in serum samples.(3)In situ formation of inorganic/organic heterojunction photocatalyst of WO3/Au/polydopamine for immunoassay of human epididymal protein 4In order to simplify the protein immobilization step and replace the toxic Cd S,on the basis of the previous work,a novel inorganic/organic heterojunction photocatalyst WO3/Au/polydopamine was prepared by auto-oxidation polymerization,and used for the construction of human epididymal protein 4 immunosensor.Compared with WO3,polydopamine and WO3/Au,the photocatalytic performance of WO3/Au/polydopamine was significantly improved.This was due to the fact that the plasmon resonance effect of Au and the sensitizing effect of polydopamine together promoted light collection and interface charge transfer.In addition,the formation of inorganic/organic heterojunction between WO3 and polydopamine greatly inhibited the recombination of photogenerated carriers,prolonged the lifetime of photogenerated electrons,and increased the carrier density.Importantly,due to the protective effect of polydopamine film on WO3/Au and the good immobilization effect for biomolecules,the photoelectrochemical immunosensor exhibited excellent stability.This work is expected to promote the design and application of other novel inorganic/organic heterojunctions for the high-performance photoelectrochemical bioanalysis.(4)A novel Bi2+xWO6p-n homojunction nanostructure:preparation,characterization,and application for a self-powered cathodic photoelectrochemical immunosensorA novel photocathode material of Bi self-doped Bi2WO6(i.e.,Bi2+xWO6)was prepared via a simple ethylene glycol-assisted solvothermal reduction.Due to the Bi doping,the material exhibited the characteristics of p-n homojunction,which was proved by the positive open circuit potential,the cathodic photocurrent and the“V-shaped”Mott-Schottky curve.In addition,it was proved by density functional theory that Bi was incorporated into the lattice of Bi2WO6 instead of W,which made the valence band maximum of Bi2WO6go upward and exceeded the Fermi level,resulting in producing a new type of p-type conductivity,thereby forming a p-n homojunction in Bi2WO6.Due to the Bi doping and p-n homojunction formation,the Bi2+xWO6possessed narrower band gap and higher light harvesting ability then Bi2WO6(The photocurrent response of Bi2.1WO6 was 25 times that of pure Bi2WO6).Based on this,Bi2.1WO6 p-n homojunction was used as photocathode for sensing and plasmonic WO3/Au composite was used as photoanode for signal amplifying,a new self-powered,membrane-less photoelectrochemical immunosensor was established for the highly sensitive detection of human epididymal protein 4.The study offers a new idea for designing novel photocatalyst with satisfactory performance,and is expected to act as a promising PEC platform for developing various self-powered biosensors.(5)“Signal-on”cathodic photoelectrochemical immunosensing of neuron-specific enolase:A novel Z-scheme Bi2+xWO6/Bi2S3 homo/heterojunction coupling with Ti3C2@Au for signal amplificationThe narrow band gap semiconductor Bi2S3 was loaded on the surface of Bi2+xWO6through in-situ ion exchange reaction to form a novel direct Z-scheme Bi2+xWO6/Bi2S3photocathode heterojunction.Due to the p-n homojunction property of Bi2+xWO6 and the formation of Z-scheme,Bi2+xWO6/Bi2S3 exhibited the characteristics of a photocathode.Among a series of Bi2+xWO6/Bi2S3 composites,the Bi2+xWO6/Bi2S3-3(treated with 1 m M of Na2S)showed the highest cathodic photocurrent response,which was about 5 and 100 times of those induced by Bi2+xWO6 and Bi2S3 under visible-light irradiation,respectively.Subsequently,using Bi2+xWO6/Bi2S3-3 as the substrate material and self-assembled three-dimensional Ti3C2@Au as the labeling material,a cathodic“sandwich”photoelectrochemical immunosensor was established for the detection of neuron-specific enolase(NSE).Owing to(i)the matched potential level between Bi2+xWO6/Bi2S3-3 and Ti3C2@Au and(ii)the excellent conductivity and promising electron affinity of Ti3C2,the photo-excited electrons could easily transfer from substrate to label,thereby promoting the separation of electron-hole pairs and enhancing photo-to-current conversion efficiency.In addition,the Ti3C2 with multilayer structure provided more catalytical active sites for the reduction of the electron acceptor H2O2.Therefore,the“signal-on”signal output was realized,false positive signal was reduced and the detection reliability was improved.This immunosensor showed a wide linear range(i.e.,0.001-500 ng/m L)and low detection limit(i.e.,0.235 pg/m L).Furthermore,the developed sensor was successfully applied to determine NSE in clinical serum samples. |
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