Study On Photoelectrochemical Biosensor With Bipolar Cooperative Signal Amplification

Micro RNAs（mi RNAs）are endogenous nonprotein-coding small RNAs that regulate gene expression through mi RNA cleavage,translation inhibition and attenuation,which play an important role in cell differentiation,proliferation and apoptosis.The difference of mi RNA expression between disease cells and normal cells,making disease-specific mi RNA a potential prognostic and diagnostic biomarker.Hence,the sensitive and specific analysis of mi RNA has a huge clinical application value.Photoelectrochemical（PEC）biosensor is a molecular detection technology combining electrochemical analysis and photochemical analysis,which has the advantages of simple equipment,high sensitivity and low background signal.Traditional photoelectrochemical biosensors rely on a single photoanode or photocathode for detection,and the whole system is often limited to the same electrolyte solution,which is easy to cause spatial interference to affect the detection accuracy.The signal amplification strategy directly affects the detection sensitivity,so it is necessary to design the efficient signal amplification strategy.As the basis of signal generation,photoelectric materials with excellent properties also should be explored and prepared.In order to overcome these problems,this paper attempts to design a general anode-cathode separation PEC platform based on bipolar cooperative signal amplification strategy.In the platform,the anode and cathode were modified by photoelectric materials with strong activity and good stability simultaneously and produce photoelectric effects,which promote each other to enhance the photoelectric signal.The space separation of the anode and cathode,the electrode reaction does not interfere with each other,which can greatly improve the anti-interference ability of the system.On this basis,combined with the signal amplification strategies such as DNA Walker and CRISPR/Cas,the PEC biosensors were constructed for the sensitive detection of mi RNAs.The research contents are as follows:（1）Cathode-anode spatial division photoelectrochemical platform based on a one-step DNA walker for monitoring of mi RNA-21The red-driven AgInS₂ nanoparticles are used as photoanode to construct biometric steps and amplify signals,while p-type Pb S quantum dots（QDs）are selected as photocathode to enhance signals.The two photoelectrodes are integrated in the same system to obtain greater photocurrent response.In addition,the spatial separation of the two photoelectrodes is realized by salt bridge to improve the anti-interference ability.In the presence of mi RNA-21 and T7Exo,one-step DNA walker amplification was triggered to release ALP-Au NPs-DNA on the electrode surface,resulting in the attenuation of the PEC signal due to the lack of electron donor,which finally achieved sensitive detection of mi RNA-21.（2）Photoelectrochemical platform with tailorable anode-cathode activities based on semiconductors coupling DNA walker for detection of mi RNA-155N-type ZnCdS nanorods and p-type Bi OI hollow microspheres are simultaneously sensitized by Cd S QDs to amplify the initial signals of photoanode and photocathode.The anode-cathode are integrated and miniaturized by paper chip,bipolar cooperation realizes the secondary promotion of photocurrent signal,and greatly reduces the difficulty of operation.With the participation of target mi RNA-155 and T7 Exo,the directional walking of DNA walker is activated,which makes Cd S QDs far away from the electrode surface to destroy the matched energy level structure,resulting in obvious signal attenuation.Both photoelectrodes are equipped with sensing and recognition steps,so the quenching effect of photocurrent signal is dual,which further improves the detection sensitivity,while electrode zoning and cathode detection improve the detection selectivity,and finally realize the ultrasensitive detection of mi RNA-155.（3）Dual-engine powered paper photoelectrochemical platform for detection of multiple mi RNAs activated by CRISPR/Cas12a.Integrating the advantages of flexible paper analysis device and anode-cathode platform,through the reasonable design and spatial segmentation of of paper chip,sample injection holes are functional to achieve the detection of multiple targets,which is rare in the PEC field.N-type Zn O nanostars and p-type Bi OI microspheres were combined with C₃N₄ QDs severally to realize the cascade amplification of photocurrent signal.Relying on the three-dimensional DNA nanomachine to realize the conversion and accumulation of targets,and the hairpin DNA on Bi OI/C₃N₄ photocathode and Zn O/C₃N₄ photocathode are digested respectively in combination with the nonspecific trans cutting ability of programmable CRISPR/cas12a.The C₃N₄ QDs that lose attachment are separated from the electrode surface,resulting in the decline of photocurrent.A variety of signal amplification mechanisms work together to greatly improve the sensitivity and selectivity of detection,so as to realize the detection of mi RNA-141 and mi RNA-21simultaneously.