The Modulation Of Field-effect Transistor Based On Molybdenum Disulfide And Its Application In Biosensors

Over the past few years,the application of transition-metal dichalcogenides(TMD)in field-effect transistor(FET),chemical and bio-sensors and logic circuit have been extensively investigated for their intriguing electrical and optical properties.Currently,creating the devices with high performance and low power are the urgent issues in the development of TMD FET for electronics applications.Molybdenum disulfide(MoS₂)is one of the most widely studied layered semiconductor material in transition-metal dichalcogenides family,and has attracted significant interest due to its high carrier mobility and widely adjustable bandgaps.However,the conductance of MoS₂ exhibits typical n-type behavior,which significant attributed to high resistance from the Fermi level pinning at metal-MoS₂ contacts.The unipolar conductivity hinders its further application in complementary metal-oxide-semiconductor(CMOS)devices.It is thus desirable to tune conductance of MoS₂ from n-to p-type.Doping engineering has been demonstrated as an effective method to manipulate the carrier type and density.Compared to the different doping techniques such as intercalation and substitutional doping,charge transfer doping exhibits the advantage of not destroying the crystal lattice of materials.Considering that the channel material is a sensitive layer for electrical transmission,the application of TMD FET can be broadened to biosensors,which exhibit the advantages of high sensitivity,chip-capability,fast response time,and inherent signal amplification ability.The FET biosensors are suitable for many analytes such as ions,organic small molecules,DNA,protein,virus and cell.Among them,protein as the biomarker is closely related to the disease state,and can be detected based on the antibody-antigen binding mode for early diagnosis and prognosis of the disease.However,the preparation,purification and storage of antibodies always cause many problems such as time-consuming and protein denaturation,which further lead to high cost and limits the consistency of detection result of the biosensor.Therefore,developing a new type sensing platform for highly sensitive detection protein biomarker is necessary.Notably,although various new high-sensitivity FET biosensors have been designed,most of them focuse on the early diagnosis of diseases,the application of them in disease treatment have not yet attracted widely attention.To highlight the outstanding detection and analysis performance of FET biosensor,extended its applications on disease treatment exhibit great development potential.This dissertation focuses on above issues and conducts studies as following:(1)The electrical properties of few-layer MoS₂were modulated with titanium(IV)bis(ammonium lactato)dihydroxide molecules(denoted as TALH)via physisorption.The functional groups such as electronegative hydroxyl(-OH)and carboxylate group(-COO)included in TALH molecules are expected to induce p-doping effect through surface charge transfer when being attached to MoS₂.The p-doping is proved by the positive shift of threshold voltage and decreased electron density in MoS₂ field-effect transistors modified by TALH.And it was further confirmed by X-ray photoelectron spectroscopy with the downshift of Mo 3d and S 2p peaks.Control experiments and density functional theory calculations validated that the p-type doping mainly originated from the-OH group in TALH,which drew electrons from MoS₂.The results suggested that functional group-mediated p-doping effect show a path to modulate the carrier transition in MoS_2,and enriched the molecule series for device modification.(2)A new type sensor of MoS₂ FET based on de-doping method was developed for detecting ascorbic acid(AA).The negatively charged manganese dioxide(Mn O₂)films are expected to induce n-doping effect through surface charge transfer when being attached to MoS₂.The redox reaction between AA and Mn O₂ lead to the decomposition of Mn O₂,and eventually caused the weakening of the doping effect and the decrease of the electrical signal.We performed electrical test of AA with a range from 10 p M to 1?M,and the limit of detection was extracted down to 0.019 p M.This device can also work well for the AA detection in drink.Compared with commercial products,the results show smaller detection errors,indicating that the MoS₂ FET sensor based on the de-doping method exhibit high sensitivity and reliable detection results,which exhibits its promising application in real life.(3)FOLR1 level is closely related the development of cancer,and thus the detection of FOLR1 play a vital role in cancer diagnosis and prognostic analysis.Here,a miniaturized biosensor was developed based on molybdenum disulfide(MoS₂)field-effect transistor(FET)functionalized with bovine serum albumin-folic acid(BSA-FA)for monitoring FOLR1.We performed electrical test of FOLR1 with a range from 100fg/m L to 10 ng/m L,and the limit of detection was extracted down to 0.057 pg/m L.The ultrahigh sensitivity of the bioassay realized by ligand-protein interaction between FA and FOLR1,with a ligand-protein binding ratio of 3:1.The formation of FA-FOLR1was confirmed with ELISA and binding affinity dissociation constant(K_D 12 pg/m L).This device can also work well for the FOLR1 detection in human serum,which presents its promising application in point-of-care diagnosis.(4)The MoS₂ FET biosensors were designed to simulate severe acute respiratory syndrome coronavirus 2(SARS-Co V-2 S)cell entry mechanisms.Pathways of the viral entry into cells are important subjects for targeted therapy of SARS-Co V-2.Many studies have revealed that coronavirus gain entry into the host cell by acting on angiotensin converting enzyme 2(AEC2)receptors.The MoS₂ FET biosensors based on ACE2 and anti-SARS-Co V-2 S for detecting SARS-Co V-2 S protein were developed,and the binding affinity dissociation constant were also estimated to be 1.06 pg/m L and0.73 pg/m L,respectively.This result demonstrate that the binding ability of neutralizing antibody and SARS-Co V-2 S protein is stronger,which is consistent with the physiological process,and thus the device can be used to simulate the virus invasion process.That is,a changed electrical signal can be obtained after ACE2 binding to SARS-Co V-2 S protein,while the existence of anti-SARS-Co V-2 S 2 S can terminate the binding process and lead to unchanged electrical signal.This simulation process is similar to a virus neutralization experiment or a pseudovirus neutralization experiment.Therefore,the sensor can be used to screen neutralizing antibodies,and the application of FET biosensors can be extended to the diagnosis and treatment of diseases.