Low-cost, transparent, and flexible single-walled carbon nanotube nanocomposite based ion-sensitive field-effect transistors for pH/glucose sensing

Low-cost, transparent, and flexible ion-sensitive field-effect transistors (ISFETs) are presented as pH and glucose sensors. Single-walled carbon nanotubes (SWCNTs) 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 detected by the local pH change in the vicinity of SWCNTs with the aid of glucose oxidase (GOx) enzyme. The glucose sensor shows a sensitivity of 18-45 μA/mM on a linear range of 2-10 mM. The apparent Michaelis-Menten constant is 14.2 mM, indicating a high affinity of LbL assembled GOx to glucose. The LbL self-assembly of nanomaterials and enzymes on the transparent and flexible substrate suggests various chemical and biological sensors suitable for in vivo application.