Vertically-Oriented Zinc Oxide Nanorods Based Electrolyte-Gated Field-Effect-Transistor for High-Performance Glucose Sensing

Diabetes “a non-communicable disease” is a global disease, which could be inherited and is caused by food metabolism disorder in humans and mammals due to abnormal insulin secretion in the pancreas [1,2]. Complications (such as diabetic retinopathy, atherosclerosis, cardiac abnormalities, ocular disorder, renal dysfunction, cardiovascular diseases, and blood vessels related diseases) arise from high (hyperglycemia) and low (hypoglycemia) blood glucose levels [3]. There is an alarming increase in the number of diabetic patients. According to WHO (World Health Organization), the number of diabetic patients will increase from ~171 million in 2000 to 366 million at the close of 2030 [4]. Early diagnosis is the way to minimize the complications and prevent the blood glucose level imbalance.Over the past decade, point-of-care diagnostic technologies (such as electronic biosensors) have made exciting progress due to the integration of nanostructured nanomaterials onto the working electrode of biosensors. Combining unique features of nanostructured nanomaterials with suitable enzymes has greatly enhanced the biosensor performance, in terms of sensitivity, the limit of detection, and detection range [5-7]. Yet, most of the nanomaterial deposition methods utilize separately synthesized nanostructures, which requires additional steps for biosensor fabrications and have several limitations including a low amount of enzyme immobilization [8]. Growing nanostructures directly onto the working electrode of biosensors ease the highly reproducible fabrication process and improve the stability and enzyme loading capacity, which further help the biosensor to detect analytes in a wide linear range [5,7,9,10]. However, a limited number of nanomaterials can be grown onto the substrate/electrode using low-temperature hydrothermal methods.Nanomaterials-based biosensors are a promising fit for portable and field-deployable diagnosis sensor devices due to their mass production, miniaturization, and integration capabilities [8]. However, the fabrication of highly stable and reproducible biosensor devices is challenging. In this work, we have grown vertically-oriented architecture of zinc oxide nanorods onto the active working area (the channel between source-drain) of field-effect-transistor (FET) using the low-temperature hydrothermal method. Glucose oxidase enzyme was immobilized on zinc oxide nanorods by a physical adsorption method to fabricate the electrolyte-gated FET-based glucose biosensor. Using electrochemical sensing, based on electrolyte-gated FET, we measured the electrical properties with different concentrations of glucose and found the linear increase in current up to 80 mM glucose concentration with high sensitivity (74.78 μA/mMcm2) and low detection limit (~0.05 mM). Overall, we illustrate the facile fabrication process of uniform zinc oxide nanorods FETs, where vertically-oriented architecture with a higher surface-to-volume ratio enhances enzyme immobilization, provides a microenvironment for longer enzyme activity, and translate to better glucose detection sensing parameters. Also, our electrolyte-gated FET biosensor showed a promising application in freshly drawn mouse blood samples. These findings suggest a great opportunity to further translate into practical high-performance biosensors for a broad range of analytes.