Highly Sensitive Detection Of Biomolecule Based On Vertical Graphene Field Effect Transistor

Graphene with its single-atom layer structure and unique energy level,its carrier transport characteristics are affected by the surface chemical state,and its conductance or field-effect conductance has a strong sensitivity to surface adsorption molecules,chemical or biological made based on this principle The sensor has the characteristics of high sensitivity,low noise,low detection limit,and low cost,and has a strong application prospect.The Vertical Graphene Field Effect Transistor(VGFET)based on the graphene/semiconductor heterojunction has a high switching ratio,and its planar structure is much more sensitive to local field effects than lateral field effects transistors.This paper studies the sensing properties of graphene/C₆₀heterojunction vertical field effect transistors for biomolecules,and explores the feasibility of detecting biomolecules based on high-performance electronic sensors with high sensitivity,low detection limits,and large amounts of data extraction.The following researchs are carried out in this paper:1.The C₆₀ layer was prepared on the surface of graphene as a transfer layer and supporting structure by an evaporation process,as a heterostructure with grapheme to prepare VGFET.Ion-gel gate-mediated VGFET and suspended VGFET were prepared separately:The ion-gel gated VGFET,its gate dielectric layer with high dielectric properties is prepared by using organic polymer polyvinylidene fluoride(PVDF)and ionic liquid 1-ethyl-3-methylimidazole bistrifluoromethanesulfonimide salt([EMIM]TF2N),and then the graphene/C₆₀ layer is transferred to the surface of ion-gel film;The suspended VGFET,graphene is transferred to the surface of silicon wafer supported by C₆₀ layer,so that the graphene surface is suspended and exposed to the microporous area,ensuring the integrity and cleanliness of the graphene surface structure,effectively simplifying the preparation of vertical field effect transistors and avoiding secondary graphene pollution.The VGFET prepared by this kind of method has a high current switching ratio of 10³ in the low gate voltage range(-5V?5V),which increases the effective area of the field effect,which is beneficial to improve the sensitivity of the current signal response,and is used for the VGFET structure with high sensitivity biomolecular detection provides the structural basis.2.In ion-gel gate-mediated VGFET,when Bovine serum albumin(BSA)molecules are adsorbed on the surface of the membrane,the micro-electric field generated by the charged groups of the molecules acts on the ion gel membrane to form an electric double layer,the charge re-arrangement inside the gel affects the change of energy barrier of the heterojunction in local graphene through the high dielectric properties,thereby changing the conductivity;when the suspended VGFET is used as a liquid gate biosensor,the obstacle of the dielectric layer is eliminated,and the BSA molecules can be directly adsorbed on the graphene On the surface,the local field effect is more obvious.The BSA molecule is negatively charged in the p H=7.4Phosphate Buffer Solution(PBS),resulting in the hole carriers in graphene increase and the graphene conductivity decreases.The results show that when the PBS ion strength is 10^-3M,the BSA molecular concentration detection limit(Limit of Detection,LOD)is as low as 10 ng/ml,and the adsorption stability time is as short as5 minutes,which is suitable for low-cost,convenient and rapid protein molecular quantification.The analysis provides a theoretical research foundation for the application of VGFET in the detection of highly sensitive biomolecules.3.As the suspended VGFET is used as a gas-gate VGFET to detect gas molecules,the gas molecules have different adsorption energy and charge transfer when they are adsorbed on the graphene surface.From the current trend,the charge transfer of NH₃ as a donor to graphene is positive.The charge transfer of C₅H₈ as an acceptor is negative,However,the effects of gas molecular electron supply/absorption characteristics on P-type graphene show different trends in current output of LGFET and VGFET.The minimum detection limit concentration reached 85 ppb(NH₃)and840 ppb(C₅H₈),which showed good detection sensitivity and versatility,and can be applied to gaseous molecular detection.It is convenient for research and development,low cost and fast response.The high-sensitivity sensor device provides the structural basis.4.In this paper,the molecular 1-pyrenebutanoic acid succinimidyl ester(PASE)conjugated specific antibody molecules on graphene surface for functional modification,which can specifically capture the target biomarkers in the solution to be tested.The minimum LOD concentration is 1pg/ml,and has a wide linear detection range(1 pg/ml to 1?g/ml),so as to achieve high sensitivity detection of specific molecules.At the same time,compared with the clinical method of electrochemiluminescence(ECLIA)to detect tumor markers in the same serum samples,the error rate was less than 5%,indicating that it has good reproducibility and potential clinical value.5.Mesoporous silica nanospheres(MSN)was modified with aldehydes and specific antibodies to make it negative in PBS solution,According to the sandwich principle of enzyme linked immunosorbent assay(ELISA),the functionalized MSN will be specifically coupled to the surface of the biomarkers,which will enhance the local field effect and make the current output of graphene change more obviously,thus improving the sensitivity of molecular concentration response.The results showed that LOD concentration decreased to 100 fg/ml,which provided the basis for high specificity and high sensitivity immunoassay for tumor markers.