The Construction Of Novel Photoelectrochemical Biosensing Systems

Photoelectrochemical（PEC）analysis technology is an emerging analytical method based on the photoelectric conversion characteristics of PEC active materials to determine the concentration of analytes.The PEC analytical method inherits the advantages of electrochemical and photochemical,it has been developed into a PEC biosensor in combination with bioanalytical technology.The excitation source（light）and the output signal（electricity）in the PEC sensor are two completely different energy forms,endowing it with a low background signal and high sensitivity.Compared to optical inspection instruments,PEC detection devices are simple,inexpensive,and easy to miniaturize.Especially compared to traditional electrochemical or optical methods,PEC biosensors can identify targets in complex samples,resulting in superior analytical performance.However,the traditional PEC analysis still faces some obstacles in actual applications.Since light illumination will inevitably damage biomolecules（immobilized bioprobes and captured target molecules,etc.）,meanwhile,the absorption or scattering of the excitation light by biomolecules can also interfere with signal.Similar to the electrochemical method,the sample incubation and signal monitoring of the PEC analysis are performed on the same working electrode that only one sample can be detected in a given period time,which results in a low-throughput disadvantage of PEC analysis.In order to solve these problems,we designed three types of split-type PEC biosensors,which achieved high sensitivity detection of several biological targets.The following is the main research contents of this paper:1.A split-type PEC immunosensor based on deposition-dissolution electron acceptorIn this paper,a PEC biosensor for modulating the anodic photocurrent intensity of netlike CdS is developed through the deposition and dissolution of electron accepting MnO₂ on the photoelectrode’ssurface.Thisdeposition-dissolutionreactionmodulatedthe photoelectrochemical of CdS effectively,enabling us to construct a split-type（i.e.,the bioreaction is separated from the photoelectrode）PEC biosensing platform for detecting Escherichia coli O157:H7（E.coli O157:H7）.We used the antimicrobial peptide（AMP）Magainin I as a recognition element for E.coli O157:H7 and glucose oxidase（GOx）as a catalytic label tracer to produce signaling molecules（i.e.,H₂O₂）in the microwell plates.The enzymatically generated H₂O₂ etched the surface deposited MnO₂ on the ITO/CdS photoelectrode,and thus greatly aroused the photocurrent for signal output.In this way,the purpose of detecting E.coli O157:H7 is achieved.Under the optimal detection conditions,the E.coli O157:H7 was detected in the range of 10 to 5.0×10⁶ CFU/mL with the limit of detection of 3.0 CFU/mL.2.A split-type PEC biosensor of pathogenic bacteria based on quantum well to increase cathode photocurrent mechanismIn this paper,water-soluble thioglycolic acid capped lead selenide quantum dots（PbSe QDs）were synthesized by a simple water bath method.PbSe QDs were assembled on the surface of indium tin oxide（ITO）electrode through the electrostatic interaction.Zn²⁺can be exchanged with Pb²⁺on the surface of the PbSe QDs to form a ZnSe/PbSe/ZnSe quantum well（QW）,which promotes electron-hole separation and improves the cathode photocurrent of the ITO/PbSe electrode.We develop a split photoelectrochemical（PEC）method for the detection of Escherichia coli O157:H7（E.coli O157:H7）with antibacterial peptide Magainin I as a recognizer.This method avoids the immobilized biomolecules on the electrodes to retard the PEC signal,with enables a highly efficient detection.The detection range of E.coli O157:H7was from 10.0 to 5.0×10⁶ CFU/mL with a quite low detection limit of 4.0?CFU/mL.3.A split-type PEC aptasensor based on quantum well to increase cathode photocurrent mechanismThis paper develops a split-type PEC sensing platform of enzyme-free displacement signal amplification based on quantum well mechanism to increase cathode photocurrent for the detections of miRNA and carcinoembryonic antigen（CEA）.The T-Hg²⁺-T[The target of H1-Hg²⁺and H5-Hg²⁺hairpin structures are the miRNA and the partially complementary DNA strands（H4）of CEA aptamers,respectively.The ring of H1（H5）-Hg²⁺hairpin hybridizes with the target.]hairpin structure was used as the probe.Firstly,the target hybridizes with H1（H5）-Hg²⁺and freed the Hg²⁺;then,the H2（H6）（that is complementary to H1（H5））binds with the DNA H1-miRNA complex（H4-H5 complex）and release the target,which is used to touch off the next reaction cycle.The released Hg²⁺exchanges with CdS QDs in the biosystem to release Cd²⁺,and Cd²⁺reacts with PbSe QDs on the electrode to form CdSe/PbSe/CdSe QW structure,which increases the cathode photocurrent of the sensor.The recycling use of the target greatly amplifies the PEC signal for ultrasensitive miRNA detection.Under the optimal experimental conditions,the detection range of miRNA-21 was from 0.5 to 5.0×10⁵ fmol/L with a quite low detection limit of 6.8×10^-2 fmol/L,and the detection range of CEA was from 0.05 to 5.0×10⁴pg/mL with the detection limit of 7.0 fg/mL.