利用二維材料做為無標記之DNA感測器之研究: 石墨烯和二硫化鉬

Abstract

In this dissertation, we investigated some applications based on the label – free detection properties between deoxyribonucleic acids (DNA) and 2D materials such as graphene and MoS2. In the first part, we developed the high transconductance and low noise of graphene based field effects transistors based on large area monolayer graphene prepared by chemical vapor deposition (CVD) process. The results were obtained to achieve the DNA detection sensitivity as low as 1pM (10-12M) based on different conditions: the gate materials, buffer concentration and surface condition of graphene. These developments indicated that the surface of graphene films using conventional PMMA – assisted transfer technique exhibits PMMA residues which degrade the sensing performance of graphene. In addition, the sensing performance of the graphene samples prepared by gold – transfer is largely enhanced by 125%. These advantages render graphene as a very promising candidate for sensor detection applications. Furthermore, we also constructed the devices for testing the Hall – effect measurement based on a Vander Pauw methods to perform the single – based sequence selective detection of DNA on the graphene sheets made by CVD system. In this contribution, we concluded that the increase of only the hole carrier density corresponds to the fact of single based specific detection. With the concentration of added complementary DNA or one – based mismatched DNAs, the hole carrier density of graphene devices increase. It indicates that the hole carrier density measurement is more sensible than the conductivity or mobility techniques. In addition, the increasing in hole carrier concentration also suggests that the DNA hybridization imposes p – doping through the electrostatic gating from negative charged phosphate group. Furthermore, in order to accurately detect the hybridization of target DNAs pre – immobilized on graphene with concentration of 0.01 nM, we fabricated the graphene devices by gold transfer. The second part of this thesis concerns on the ultrasensitive detection of DNA hybridization based on graphene/MoS2 stacking films. In this hetero-structure, the sensitive detection can reach at the aM (10-18M) level of DNA concentration. A new mechanism of detection of DNA hybridization in these heterostructures was identified. This detection, besides using the field effect transistors, Hall effect measurement and Raman spectroscopy can be applied in this study. The photoluminescence is also critical to observe the DNA hybridization in these heterostructures.

本論文主要是針對於無標記感測器的應用，以石墨烯和二硫化鉬等二維材料，探討其作為DNA感測器的特性研究。首先，利用化學氣相沉積方式，在大面積的單層石墨烯上，製造出以石墨烯為基底，具有高跨導且低雜訊的場效電晶體。此元件結構可以作為一個DNA感測器，若搭配最佳化的閘極材料、緩衝液濃度與石墨烯表面狀況，偵測敏感度可達到1pM (10-12M)。研究顯示以往為了增加石墨烯傳導特性，利用聚酸甲酯(PMMA)的表面處理技術中，表面殘留的PMMA將會減弱石墨烯的感測性能。此外，若利用金製備石墨烯的感測樣品，其傳導特性將會提升125%。此特點使得石墨烯在作為感測器的應用上，成為一個相當有優勢的材料選擇。同時提出一種可測量霍爾效應(Hall effect)的裝置結構，其參考Vander Pauw方法，可量測在石墨烯上的特定DNA序列。此裝置分析數據可用以支持所提出”僅有電洞載\載子密度增加”之論點 -- 隨著添加的補充DNA或是不匹配DNA的濃度提高，石墨烯元件的電洞載子密度也將增加。這表示測量電洞載子的濃度，比導電率或遷移率都更敏感。且電洞載子濃度增加也表示DNA的雜交作用，P型參雜作用受到閘極的電荷作用而增加。為了準確的偵測到濃度僅有0.01nM的DNA之間的雜交作用，石墨烯元件必須藉由金轉換器來製造。本論文的第二部分，則是探討在石墨烯/二硫化鉬交互堆疊的薄膜上，偵測DNA雜交作用之超靈敏感測。在這種異質結構下，DNA濃度的感測靈敏度可以高達 (10-18M)。並發現一種在此類異質結構下，DNA雜交作用的感測機構。感測作用除了使用場效電晶體，本研究亦應用霍爾效應測量與拉曼光譜分析的技術。同時螢光光譜分析也是用來觀察DNA雜交作用的重要工具。