Study On Molybdenum Disulfide Field-effect Transistor Biosensor

In recent years,field-effect transistor（FET）has been proposed as one of the most promising electrical technologies for rapid biomolecule detection due to their label-free,in-situ detection capabilitie,and high sensitivity.One-dimensional（1D）semiconductors,such as silicon nanowires（SiNWs）and carbon nanotubes（CNTs）are used for FET biosensors,which can improve the sensitivity due to the high switching characteristic（high current switching ratio）and excellent surface chemistry efficiency.However,there are some limitations such as lack of practical application due to device-to-device deviation and relatively high cost in large-scale manufacturing.Compared to 1D nanostructure,two-dimensional（2D）materials have larger specific surface area,leading to greater sensitivity for target molecules,and better scalabilit y which facilitates large-scale fabrication;thus these advantages and superior performances are applied for the constructions of highly effective and efficient FET biosensor.Nevertheless,due to the absence of band gap structure,using graphene and its derivatives as conductive mat erials in FET biosensors,leads to a low switch of FET,which limits the detection sensitivity of the sensor.Molybdenum disulfide（MoS₂）,on the other hand,a typical semiconducting layered transition-metal dichalcogenide（TMDC）,has attracted increasing attention because of its tunable band gap structure,comparing with graphene.It has a layer-dependent electronic band structure with excellent electrical,physical,optical,and catalytic properties,which are desirable in developing new generations of electronics and optoelectronic devices.Meanwhile,MoS₂ shows high stability in air due to a lack of dangling bonds,which significantly improves the performance of FET for biosensing.Recently reports have demonstrated that MoS₂ FET was used for electrical detection of various biomolecules.In this paper,a thin layer of MoS₂ was constructed by a simple mechanically exfoliated method,and the thickness of MoS₂ was determined by optical microscopy,Atomic force microscope（AFM）,Raman technology et al.Bovine serum albumin（BSA）was detected by lithography using a ultra-thin MoS₂ to construct a field-effect transistor with excellent performance.The sensitivity of detection and its mechanism were also studied.Multi-layer MoS₂ were used to fabricate the field-effect transistor and detection the fibroblast growth factor 21（FGF21）.The detection of sensitivity,selectivity and healthy human serum for measurement were investigated.The main conclusions are gained as follows.（1）The methods of lithography and copper TEM grid construction of devices are described in detail.We explored the different conditions of the fabricated dev ices,compared the performance of the devices before and after annealing,and built different FETs that contact metal electrodes.At the same time,the transfer characteristics of the device are also explored under different drain voltage(V_DS),and obtained the transistor sensor with high performance,better repeatability and higher sensitivity.（2）A label-free electrical biosensor based on ultrathin MoS₂ FETs,in which the hydrophobic MoS₂ surface directly serves as the adsorption layer.This transistor can successfully detect biomolecules,such as BSA,with high sensitivity within a large concentration range.Further,concentration-dependent sensing behavior and FET measurements illustrate the underlying mechanism related to the modulation of MoS ₂conductivity.The combination of doping effect（charge transfer）and mobility change（scattering sites）dominates the change after the BSA absorption on the MoS ₂ surface.Overall,this study shows that thin-layered TMDs can be used as a potential alternative platform for developing novel electrical biosensors with high sensitivit y and selectivity.（3）A label-free,simple and ultrasensitive FET biosensor for FGF21 detection is developed,directly utilizing MoS₂ without additional absorption layers.By immobilizing anti-FGF21 on MoS₂ surface,this biosensor can achieve a detection limit of FGF21 less than 10 fg?cm^-3.Highly consistency and good reproducibility are demonstrated through multiple sets of parallel experiments for the MoS ₂ FETs.Furthermore,the biosensor has great sensitivity and excellent selectivity to detect the target FGF21 in complex serum samples,which demonstrates its great potential application in disease diagnosis of NAFLD.