Application Of Solution-gated Graphene Transistors In Biosensors

Sensing technology has been widely used in human life as an important part of information perception.Among others,biosensors play the important role in disease pre-diagnosis in medicine and health,monitoring of environmental pollutants,detection of toxins in food,pharmaceutical and other fields.Graphene is used in the fabrication of graphene field-effect transistors(GFETs)due to its unique electrical properties.The solution-gated graphene field-effect transistor(SGGT),a type of GFETs,has a special structure in which the channel and gate are in direct contact with the electrolyte,resulting in the chemical potential in the solution that is very sensitive to the modulation of the gate electrode.Due to its signal amplification,SGGTs combined with a specific biological probe can detect biomolecules in solution with high sensitivity at the low operating voltage.Meanwhile,due to the easy miniaturization of the transistor,SGGT biosensors are developing at a high speed towards miniaturization,integration and intelligence.They are used in various fields such as smart medicine and disease prevention and control.This thesis focuses on the functionalization of SGGTs for the detections of two biomolecules by using two biological probes with recognized high specificity.The feasibility of their application in SGGT platforms and the sensing principles have also been investigated.The details are as follows:Thrombin is an important biomarker for various diseases and biochemical reactions.Since the thrombin is rapidly neutralized early in the coagulation process of the body,rapid real-time thrombin assays are of great relevance.In this thesis,the ss DNA aptamer with 29 bases was immobilized on the surface of the gate electrode to specifically recognize the thrombin.The SGGT sensor achieved a high sensitivity with a limit of detection(LOD)up to f M.The LOD was attributed to the amplification function of SGGTs and the suitable aptamer choice.The ss DNA configuration folding induced by thrombin molecules and the electropositivity of thrombin molecules could arouse the same electrical response of SGGTs,resulting in a high sensitivity of the device.The channel current variation of sensors had a good linear relationship with the logarithm of thrombin concentration in the range of 1 f M to 10 n M.The fabricated device also demonstrated a short response time to1 f M thrombin molecules about 150 s.Thus,aptamer-based SGGTs with high sensitivity and high selectivity have a good prospect in medical diagnosis.Severe acute respiratory syndrome coronavirus 2(SARS-Co V-2)is responsible for the coronavirus disease of 2019(COVID-19),which at present causes a global pandemic.Due to the limitations of sample collection,transportation,and kit performance,the traditional RT-q PCR method does not have a high true positive rate in sample detection and has a long detection period.This means that many patients may be not detected in time,causing an increased risk of infection.The CRISPR-Cas13 a system which is considered a promising platform for nucleic acid detection can be designed for RNA identification and knockdown.Here,we designed a solution-gated graphene transistor(SGGT)biosensor based on the CRISPR-Cas13 a system.The gate functionalization by the multilayer modification,in combination with CRISPR-Cas13 a technology,can easily,rapidly,and specifically recognize SARS-Co V-2 nucleic acid sequences and no nucleic acid amplification and additional fluorescent labeling are required.The limit of detection(LOD)in both buffer and serum reached the a M level,and the reaction time was about 10 minutes.We also evaluated the detection of the clinical samples and it showed a high degree of agreement with RT-q PCR results.The responses of positive samples showed significantly higher responses than those of the negative samples.This is quite positive feedback for the practical application of the CRISPR-Cas13 a functionalized SGGT biosensor.In addition,the interchangeable gates significantly reduce the device fabrication cost and time.