Fabrication Of MoS₂ Field-effect Transistor Biosensors And Its Applications In Disease Diagnosis

Point-of-care testing?POCT?refers to clinical tests and bedside tests performed at the patient's medical site.The instant analysis at the sampling site eliminates the need for complex processing procedures for specimens in clinical laboratory tests,thereby quickly obtaining a new type of test method for test results.In recent years,the testing equipment in clinical laboratories has been developed rapidly and the degree of automation has become higher and higher.However,there are still many disadvantages such as tedious pretreatment steps,expensive reagents,and large sample requirements.Therefore,there is an urgent need to build a sensing platform that is simple,fast,and inexpensive and suitable for bedside inspections.Because biosensors have the characteristics including rapid detection,high sensitivity,simple operation,and low cost,Nowadays they have been increasingly applied to the diagnosis of disease and life science research.Field-effect transistor?FET?biosensors based on nanomaterials have emerged as a new biosensing methodbecause they havethe advantages like label-free detection,simple operation,sensitive andspecific detection,and fast analysis speed.With the unique properties of layered sandwich structures,high on/off current ratio and high flexibility,MoS₂ nanosheet has been used to establish FET biosensor increasingly.It is believed that the unique sensing platform is potentially used as a POCT tool for disease diagnosis if FET and MoS₂ is combined to fabricate the MoS₂-based FET biosensor.This paper aims to develop a MoS₂-based FET biosensor for sensitive and specific detection of DNA based on phosphorodiamidate morpholino oligos?PMO?-DNA hybridization,Based on this,we try to explore feasibility of the MoS₂-based FET biosensor in the detection of exosomes.In this work,the FET device is fabricated on a SiO₂/Si substrate by the conventional macro-nano processing technologies.Subsequently,MoS₂ suspension is drop-casted onto the channel to contact source and drain electrode.The fabricated MoS₂ FET biosensor not only reduces the cost,but also holds good properties for detection of biomolecules The details are as follows:Chapter 1:Construction of High-performance Molybdenum Disulfide Field Effect Transistor BiosensorIn this paper,a FET device is prepared using a standard microfabrication process,and?3-aminopropyl?triethoxysilane?APTES?is used to pre-treat the chip so that the surface of the chip is positively charged.Then,negatively-charged,MoS₂ suspersion was appliedto the chip surface by a drop coating method.Because MoS₂ is negatively charged,MoS₂ can be anchored onto the channel surface tightly through electrostatic interactions,which is extremely important for effectively contructing MoS₂ layers on the SiO₂ surface.The method of fabricating MoS₂ FET is simple,fast,and inexpensive.And through the morphological and electrical characterization,it shows that the device has a good electrical properties and stability,which can be applied to the subsequent detection work.Chapter 2:Ultrasensitive Detection of DNA Based on Molybdenum Disulfide Field Effect Transistor BiosensorIn this work,PASE?the linker molecule?is fixed on the MoS₂ surface though?-?coordination interaction between the MoS₂ surface and the pyrene group.DNA analogue,PMO,was immobilized on the MoS₂ surface,and detection of PMO-DNA hybridization was conducted by the fabricated MoS₂FET biosensor.Due to the neutral character and high affinity of PMO,a limit of detection?LOD?down to 6 fM was obtained,which is lower than that of the previously reported MoS₂ FET DNA biosensor based on DNA-DNA hybridization.In addition,the MoS₂ FET biosensor also showed high sequence specificity capable of distinguishing the complementary DNA from one-basemismatchedDNA,three-basemismatchedDNAand noncomplementary DNA.Moreover,the unique FET biosensor was able to detect DNA in complex sample like serum,making the method potential in disease diagnostics..Chapter 3:Exploration of exosomes detection based on molybdenum disulfide FET biosensorBased on the above-mentioned MoS₂ FET biosensor,we also design an indirect method for the detection of novel tumor markers,exosomes.This method uses urease as the indicator enzyme because the decomposition of urea under the catalysis of urease causes the change of the solution pH.So the indirect detection of exosomes is achieved by detecting pH change.The experimental results show that the sensor respond sensitively to pH changes in the solution.It is certain than this method has a feasibility for the detection of exosomes.