Silicon Nanowire Ion-Sensitive Field Effect Transistors for Uric acid Detection

Abstract

Enzyme field effect transistors (EnFETs) based on ion-sensitive field effect transistor (ISFETs) have been widely suggested for detecting a variety of biomolecules. However, methods for immobilizing enzymes on a sensing surface have difficulties in maximizing enzyme activity and multiple use. Uric acid is an end-product of the purine metabolic breakdown. Excessive uric acid can cause a type of joint inflammation known as gout and various connected diseases.In this thesis, Silicon nanowire ion-sensitive field effect transistors (Si-NW ISFETs) were fabricated to detect uric acid. Standard top-down silicon micro-fabrication techniques give significant advantages in the aspect of high sensitivity, cost saving, large scale integration, and reliability to the FET based biosensors. Further, the use of nanowires, in contrast to a planar sensing surface, provides much higher surface areas for faster and more accurate detection. The silicon nanowires were formed by electron-beam lithography and general semiconductor processing technology. Also, Ag/AgCl reference electrode was embedded on the Si-NW ISFETs. The transfer characteristics of Si-NW ISFET show typical n-type FET behaviors with a high on/off current ratio, low gate leakage currents, and reasonable subthreshold swing. The pH responses of the Si-NW ISFETs with different pH solutions were measured at room temperature and it showed a clear lateral shift and sensitivity of 35 mV/pH from the drain current vs. gate voltage curve. For uric acid detection, we proposed a new method using a KMnO4 as an intermediate material and we found that uric acid can be detected by monitoring the threshold voltage vs. uric acid concentration characteristics. The uric acid sensitivity is calculated as high as 40 mV/mM from the threshold voltage shift.