Reduced Graphene Oxide (rGO) Based Alzheimer's Disease Diagnosing Biosensor with High Throughput
Authors: Kim Jinsik , Chae Myung-Sic , Jeong Dahye , Yoo Yong Kyoung , Kim Gangeun , Hwang Kyo Seon 
Published: February 2020

Graphene has been studied in various fields such as bio-sensing, electrical applications and so on, due to its great electrical1 and mechanical properties.2 Even though the graphene has great properties, the graphene based practical devices has not been realized in daily day. Our group tried to find the reason in the absence of batch process fabrication method of graphene based device. Many method of graphene based device fabrications have low yields and cost-consuming. The synthesis of graphene was also time and cost consuming properties.

 After achievement of graphene oxide (GO) synthesis in liquid phase by Hummer’s method, the possibility of graphene-usage in low cost was increased. The cost-effective graphene oxide was reduced to utilize the same novel properties of graphene. The mass-productive patterning methods of GO or reduced GO (rGO) is also essential to realize graphene-based devices.

 The biosensing devices-consuming has been increasing as follows the demand increasing for disposable sensors applications for rapid detection in bio-research as a point of care. For the mass-productive devices, laser writing after forming the GO layer by spin coating3 and spray coating of rGO with shadow mask4 were introduced. However, the method also need huge amount of apparatus for the patterning such as laser and position controlling system. And the controlled thickness of GO is quite thick to have micron scale of thickness which is not sufficient in biological applications.

 Here, we introduce a cost-effective rGO patterning and biosensor fabrication method based on conventional micro-electro-mechanical systems (MEMS) technique for Alzheimer’s disease diagnosis. The GO layer was formed with meniscus dragging method to accomplish the freely controllable thickness from nanoscale to microscale on silicon dioxide wafer. After formation of GO layer, the GO layer was reduced with chemical reduction method. Photolithography and dry etching in oxygen atmosphere were utilized to form the patterns of the rGO layer. Various rGO patterns with dimensions from sevral ~µm up to several hundred µm achieved through the optimization of patterning with dry etching. The patterns were used as a sensing zone which contains immobilized antibody for detection of amyloid beta (Aβ) peptide. The Aβ is the most remarkable biomarker of Alzheimer's disease. The gold electrodes were also accomplished on the rGO patterns with photolithography and lift-off process. Generally, the graphene based fabrication was done at the forming graphene layer with MEMS technique. However, we could form the additional layer after the forming rGO layer without any deformation of rGO layer. All process of fabrication was proceeded in 4-inch wafer. For the high throughput of sensing, the rGO patterns was formed as an array. The array of sensor might increase the accuracy of biomolecule detection.

 Finally, the high-uniformly formed rGO-based biosensor arrays on 4-inch wafers was prepared to detect the Aβ as a diagnosis of Alzheimer's disease. The resistance changes or rGO layer according to the reaction of Aβ peptide was measured. The rGO biosensor has reproducible response ranging in 100fg mL-1 to 100pg mL-1 with most of devices from same wafer with high sensitivity. The sensor also detected the Aβ peptide level from mouse and human plasma. The array type of sensing process lead the high throughput of rGO based Aβ detection as a diagnosis of Alzheimer's disease.