The Research And Application Of Photoelectrochemical-microfluidic Chip Sensor Based On Signal Amplification Strategy

Photoelectrochemical（PEC）refers to the separation and transfer of charge caused by the ground state electrons of molecules,ions or semiconductor materials being excited by light,which is a phenomenon of photocurrent changes caused by electron transfer between substances and excited photoelectric materials.The analysis technique of this phenomenon can effectively separate the excitation light source from the detection signal,which significantly reduce the background signal,improve the detection sensitivity,and make it widely used in the biosensor field.However,its general practicality is greatly limited by portability,miniaturization and automation.Microfluidic chip analysis is to achieve miniaturization in micron channels and structures,which can not only overcome the above shortcomings,but also has the advantages of less consumption of samples and reagents and easy integration.In addition,to meet the requirements of trace and ultra-trace biomolecule detection in analytical methods,it is of great significance to construct photoelectric chemical biosensors with good selectivity,high sensitivity and fast response.In order to improve the sensitivity,the signal amplification strategy is introduced into the biosensor.This paper aims to explore and study a series of signal amplification strategies for improving the PEC response signal,which could prepare portable miniaturized PEC-microfluidic chip sensor and realize the sensitive detection of target analytes.The research work of this paper mainly includes the following five parts:（1）A competitive PEC microfluidic chip sensor based on signal amplification of p DNA@Ag₂S photoanode system was constructed for detection of ochroatoxin A.In this work,a Bi₂S₃/Bi OI/Zn O heterojunction nanoarray composite with excellent photocatalytic activity was proposed as the sensing platform.The band gap of the Bi₂S₃/Bi OI/Zn O composite formed a cascade structure,which effectively promoted the separation of electron-hole pair and improved the photocurrent intensity.Moreover,the array structure was conducive to improving the stability and reproducibility of the sensor signal.In order to realize signal amplification,first,the captured DNA（C DNA）was cross-linked on the Bi₂S₃/Bi OI/Zn O sensing platform with chitosan and glutaraldehyde.Then,the-SH modified aptamer probe DNA（p DNA）reacted directly with Ag NO₃ through Ag-S bond to form p DNA@Ag₂S competitive marker,which could hybridize with c DNA to form DNA double strand after modification on the electrode,resulting in a significant decrease in photocurrent intensity.This is because some of the photogenerated electrons are transferred to Ag₂S instead of Bi₂S₃/Bi OI/Zn O electrodes.Finally,when the OTA target analyte was modified,the photocurrent intensity increased significantly after the OTA induced removal of p DNA@Ag₂S,so as to achieve signal amplification.Under the optimal conditions,the prepared PEC microfluidic chip sensor can realize sensitive OTA detection with a linear range of 0.01 pg/m L to 200 pg/m L and a detection limit of 0.0035 pg/m L（S/N=3）.The sensor has high specificity and excellent stability,which provides an effective strategy for the detection of other mycotoxins.（2）A self-powered photocathode signal amplification strategy was designed for the detection of prostate specific antigen（PSA）.In order to realize signal amplification,a self-powered PEC microfluidic chip sensor without external power supply was constructed by using iodide-doped bismuth chloride oxide array(I_0.2:Bi OCI_0.8)as photocathode and cadmium sulfide sensitized Zn O nanorod array（Zn O NA/Cd S）as photoanode.Among them,p-type semiconductor I_0.2:Bi OCI_0.8has a special internal electric field between the iodide ion layer and the[Bi₂O₂]²⁺layer,which can promote the separation of electron-hole pair under visible light excitation and improve the intensity of cathode photocurrent.In the self-powered cathodic PEC analysis,the dissolved oxygen as electron acceptor can be reduced by photo-generating electrons to form superoxide radical（·O₂^-）.Then,the generated·O₂^-reacts with luminol anion radical to produce chemiluminescence as an internal excitation light source to enhance the intensity of cathode photocurrent.In addition,the array structure is beneficial to improve the stability and reproducibility of the sensor signal.The photoelectric anode and the photoelectric cathode are integrated into the microfluidic chip to realize the automatic sample injection and detection.The sensor showed a good linear relationship for prostate cancer marker PSA in the range of 50 fg/m L～50 ng/m L,the detection limit was as low as 25.8 fg/m L（S/N=3）,and it had the advantages of good anti-interference ability,strong specificity and high accuracy.Moreover,it has important practical application value in early warning and clinical detection of prostate cancer.（3）An integrated microelectrode and cathode PEC microfluidic chip sensor was designed for signal amplification detection of cell keratin 19 fragment（CYFRA 21-1）in non-small cell lung cancer.To realize signal amplification,the p-n heterojunction of Ag I/Bi₂Ga₄O₉ was used as the sensing base,and the honeycomb manganese oxide loaded superoxide dismutase（SOD@h Mn O₂）was used as signal amplification marker to realize the cooperative catalysis.When p-n heterojunction of Ag I/Bi₂Ga₄O₉ is photoexcited,the photoelectron captures dissolved O₂ to produce superoxide anion radical（·O₂^-）,while SOD can catalyze·O₂^-to generate O₂ and H₂O₂ through disproportionation reaction.Then,h Mn O₂ can catalyze the decomposition of H₂O₂ to O₂ and H₂O.Therefore,the increase of O₂ can consume more photoelectrons and promote the separation of photoelectron-hole pair,thus effectively enhancing the photocurrent signal of the cathode.In addition,the p-n heterojunction of Ag I/Bi₂Ga₄O₉ nanoarray structure is beneficial to improve the stability and reproducibility of the sensor signal.The PEC microfluidic chip sensor has a good linear relationship in the range of 0.1 pg/m L to 100 ng/m L for CYFRA 21-1,and the detection limit is 0.026 pg/m L（S/N=3）.A gold-polyaniline-loaded superoxide dismutase（SOD-Au@PANI）was proposed as a signal amplification marker to construct a sand-wich cathode PEC microfluidic chip sensor for ultra-sensitive detection of cardiac troponin I（c Tn I）.Pd nanoparticles loaded on I-doped bismuth oxybromide with oxygen vacancies（Pd/I:Bi OBr-OVs）as a sensing platform can effectively enhance the cathode photocurrent response.This is because the doping of I can improve the absorption range of visible light,which is conducive to the effective separation of photoelectron-hole pairs.Pd nanoparticles can increase the electron transfer rate and photogenerated electrons can capture dissolved O₂ and promote the generation of superoxide anion radical（·O₂^-）,and Pd/I:Bi OBr-OVs nanoarray structure is conducive to improving the stability and reproducibility of the sensing signal.In order to further enhance PEC signal,SOD on antibody marker catalyzes decomposition of·O₂^-into H₂O₂ and O₂.Then,Au@PANI with good reducing and catalytic properties can catalyze the generated H₂O₂ into H₂O and O₂.After that,the generated O₂ can be dissolved or absorbed to capture more photoelectrons,so that the cathode photocurrent signal can be significantly amplified.The linear detection range of c Tn I is from 0.1 pg/m L to 100 ng/m L,and the minimum detection limit is 0.042 pg/m L.The PEC microfluidic chip sensor has good sensitivity and selectivity,which can be extended to the detection of other disease markers.Double nano-enzyme of Au Pt@Ce VO₄ was prepared as signal amplification marker and Z-structured Cu I/Bi OI nanoarray composite was used as sensing substrate to construct sand-wich PEC microfluidic chip sensor for the detection of neuron specific enolase（NSE）.Firstly,the Z-type structure of Cu I/Bi OI nanocomposite can promote the separation of electron-hole pairs,and the separated photoelectron capture of dissolved oxygen increases the generation rate of superoxide anion radical（·O₂^-）.Moreover,Cu I/Bi OI nanoarray structure is beneficial to improve the stability and reproducibility of sensor signals.Ce VO₄ nano-enzyme with superoxide dismutase function can catalyze·O₂^-to produce O₂ and H₂O₂ through disproportionation reaction.Au Pt nano-enzyme can further catalyze H₂O₂ to produce O₂ and H₂O.The produced O₂ increases the content of dissolved oxygen in the electrolyte,which can consume more photogenerated electrons to promote the separation efficiency of electron-hole pair and realize the amplification of PEC signal in the microfluidic sensor.The PEC microfluidic chip sensor has a good linear relationship in the NSE concentration range from0.01 pg/m L to 100 ng/m L,and the detection limit is 0.0046 pg/m L（S/N=3）.It has the advantages of rapid detection,high selectivity and low cost,which could be applied to the detection of actual human serum samples.