Construction Of Graphene Field-effect Transistors Based Biochemical Sensor

Field-effect transistors（FETs）are among the core components of various electronic devices,such as integrated circuits,active matrix displays,electronic paper,smart cards,sensors,etc.FETs possess signal conversion and amplification functions,at the same time they can be integrated in large quantities on the same tiny chip at low cost,thus attracting widespread attention and considered as a good vehicle for preparing biochemical sensors.Graphene,a new type of carbon nanomaterial,is one of the most promising substrate materials for assembling electronic devices owing to its excellent optoelectronic properties and mechanical properties.Based on this,researchers have constructed a variety of graphene FET devices and used them extensively as biochemical sensors.However,the electrodes and the semiconductor layer of these FETs are connected to substrates by noncovalent bonds,which make them easily damaged by external force,resulting in shortened device life.Moreover,their electrical signals also become vulnerable to physical,chemical and other external factors interference,which exacerbates the instability of electrical signal output.Such shortcomings greatly hinder the practical applications of FET devices in sensing fields,especially in healthcare and environmental monitoring,where real-time monitoring in solution is required.Therefore,fabricating high-performance FETs biochemical sensor devices with both solvent resistance and electrical stability for rapid,sensitive,stable,and reliable detection of molecules is an urgent issue,which is of great importance in the fields of medical health and environmental monitoring.In this thesis,the construction of highly electrostable and solvent-stable graphene FET devices and the biochemical sensors were prepared based on such devices as follows:The（3-aminopropyl）trimethoxysilane（APTMS）was introduced and subtle all-graphene field-effect transistors（AG-FETs）were designed and constructed by means that of the covalent layer-by-layer（LBL）assembly of graphene oxide（GO）through the covalent reaction between GO and APTMS.This covalent configuration results in good solvent stability and electrical stability of the FET.Moreover,based on the inherent electrical properties of AG-FET and the fluorescence quenching of GO,the device could serve as a highly sensitive and stable dual-signal mi RNA biosensor,which could analyze mi RNA sensitively,stably and faithfully through electrical and fluorescence dual signals.This is evaded the utilization of any amplification techniques.In addition,the complementary nature of the electrical and fluorescence signals makes the biosensor good reliability and accuracy,and enables the detection of mi RNA in simulated serum.This is evaded the utilization of any amplification techniques.To further streamline the construction method and improve device performance,we introduce 5,10,15,20-tetra（4-aminophenyl）-21H,23H-porphyrin（TAPP）coupling agents on top of a working base.Leveraging discrepancy in charge conduction properties between the（3-aminopropyl）trimethoxysilaneand5,10,15,20-tetrakis（4-aminophenyl）-21H,23H-porphine caused by conjugacy structural differences,we assemble two kinds of covalently bonded films with different electrical properties by means of“planting”graphene oxide on Si/Si O₂ substrates and a simple one-step reduction method.The two covalently bonded reduced graphene oxide films are then respectively used as a semiconductor layer and as source/drain electrodes to fabricate a stable covalent-assembled,all-graphene FET（CAAG-FET）.Given the covalently functionalized configuration and the functionally diverse cross-linkages,the CAAG-FET obtained by this simple method achieves high-performance electrical characteristics,the hole,electron mobility and the shelflife could reach 3.79 cm²/（V·s）,3.78 cm²/（V·s）,and 18 months,respectively.In addition,sensible material stability and glorious device structure endow the device electrical stability and solvent resistance,rising its application prospect in solution-phase sensing/detection.Combining the thymine–Hg²⁺–thymine interaction,the CAAG-FETs can serve as an ideal sensor platform for the detection of mercury ions in sewage,even in flowing water inside municipal water pipeline monitoring.This platform’s limit of Hg²⁺detection can reach as low as 16 picomolar（p M）,with a detection error of less than 17%in simulated sewage.