Research On Biosensor Based On Organic Photoelectrochemical Transistor

Photoelectric（PEC）bioanalysis is an analytical technique that photo-active substances generate photocurrent by carrier migration caused by photo-excitation.The separation of input（light）and output（electricity）and different energy forms make this method have lower background signal and higher sensitivity.So far,many materials and signal strategies have been developed in this field,and the developed biosensors have been widely used from macroscopic in vitro detection to nanoscale in vivo detection.Organic transistor（OECT）,which involves the electrochemical doping and dedoping process of electrochemical polymers,is another rapidly developing detection technology.Because of its advantages of miniaturization,unique signal amplification and good biocompatibility,OECT has been widely used in biological detection.A typical OECT consists of a thin layer of organic semiconductor,such as conductive polymer poly（3,4-ethylenedioxythienyl）:polyphenylsulfonate（PEDOT:PSS）,which is coated on the channel between the drain（D）and the source（S）of the transistor and soaked in the electrolyte solution（E）.Generally speaking,any slight potential change at the gate-electrode interface of a transistor will cause a relatively large step change in channel current,which makes OECT have high sensitivity when biological events change.Up to now,OECT biosensor has been used to detect many kinds of targets,such as breath,sweat,saliva,urine,blood,etc.,aiming at clinically relevant analytical substances.Considering the low background signal of PEC and the unique amplification effect of OECT,a new biosensing technology based on OPECT was constructed by replacing the gate electrode of OECT with the working electrode of PEC.By combining DNA,immune reaction and other biological events,high sensitivity and high specificity of biomolecule detection can be realized.In this paper,a series of new biosensing methods of OPECT are established based on various semiconductor nanomaterials,starting from the channel regulation effect of photosensitive gate electrode on OPECT.The main contents are as follows:（1）DNA sensing analysisIn this paper,an OPECT biosensor based on the coordinated adjustment of effective gate voltage of charge is proposed to detect ATP.The gate electrode of photosensitive cadmium sulfide quantum dots（Cd S QDs）was used as the substrate,and the DNA superstructure with ATP stimulation response release characteristics was modified on the electrode.The DNA molecules with high negative charges were self-assembled by sequential hybridization,and then split by ATP recognition.In this process,the change of interface properties would lead to the corresponding change of effective gate voltage,thus coordinating the photoinduced photovoltage,the negative charge effect of DNA and the interface dynamics of solution species.The constructed sensor is used for high sensitivity detection of ATP,and the detection limit is 0.1 pg m L-1.The DNA-based OPECT sensor proposed in this work converts the events of charged molecules into amplified electrical signals,which provides a new idea for the future development of OPECT sensors for the interaction between light and biological substances.（2）Immunosensor analysisCombined with photoelectric heterojunction materials,this work proposes an OPECT biosensor based on immune events,which is used for highly sensitive detection of C-reactive protein（CRP）.The sensing principle is mainly based on the fact that the type-II heterojunction is transformed into plasma interaction,which leads to the decrease of photoelectric conversion efficiency,thus reducing the current response of the photo-sensitive grid anode.Essentially,the function of this integrated biosensor depends on the photo-induced photovoltage(V_photo)of the grid and the corresponding undoping of poly（3,4-ethylenedioxythiophene）-polystyrene sulfonic acid（PEDOT:PSS）.Specifically,compared with the dark state,the generation of light will cause the change of channel current.In the dark state,there is no V_photo,and PEDOT:PSS remains in the oxidized state,which makes the polymer film have higher conductivity.However,under illumination,V_photo will trigger cations in electrolyte to migrate to PEDOT:PSS film,which will reduce the oxidation state of PEDOT:PSS film,thus reducing the conductivity of polymer film.Under this background,different transition states in the growth process from Au NCs/Ti O₂/CFM to Au NPs/Ti O₂/CFM will produce different effective gate voltages,thus producing different doping states.Through sandwich immune recognition of representative analyte CRP and detection of associated alkaline phosphatase,the model system shows the modulation ability dominated by the target and good analytical performance at zero gate voltage.The OPECT immunosensor with high selectivity and sensitivity,which is based on the type-II heterogeneous transfer to plasma interaction,has a detection limit of 0.001 ng m L^-1for CRP.We believe that this sensing technology has very high universality,can be extended to the research of viruses,marine microorganisms,cell detection and many other fields,and has good sustainable scientific research value.