Carbon Nanotube Nanocomposite Based Ion-Sensitive Field-Effect Transistors for Chemical and Biological Sensing

摘要

Low-cost, transparent, and flexible ionsensitive field-effect transistors (ISFET) are presented as pH and glucose sensors. Carboxylated singlewalled carbon nanotubes (SWCNT) and poly(diallyldimethyammonium chloride, PDDA) are deposited by layer-by-layer (LbL) self-assembly between two metallic electrodes patterned on a polyethylene terephthalate substrate. The pH ISFETs are characterized based on the fact that the electronic conductance of SWCNTs nanocomposite is determined by molecular protonation/deprotonation of carboxylic groups on SWCNTs and by the external Ag/AgCl reference gate voltage. Glucose is also detected by the local pH change in the vicinity of SWCNTs with the aid of glucose oxidase (GOx) enzyme. At pH5 buffer and 10 mM glucose, the fabricated SWCNT ISFETs exhibit discernible field effects, on/off current ratios of 3.7 and 2.7, and threshold voltages of 0.8 and 1.1 V, respectively. The glucose sensor shows a sensitivity of 28.4 μA/mM on a linear range of 2-10 mM. The apparent Michaelis-Menten constant and the maximum reduced drain current are 13.8 mM and 587 μA, respectively, indicating a high affinity of LbL assembled GOx to glucose. The LbL self-assembly of nanomaterials and enzymes on the flexible substrate suggests various chemical and biological sensors suitable for in-vivo application.