(Invited) Electrical Sensing with a Tube-in-a-Tube Semiconductor

The fundamental idea of field-effect transistors has fueled the development of innovative electrical sensing technologies for the detection of biological and chemical species. However, it is generally challenging to attain simultaneous ultrahigh sensitivity and selectivity as required for chemical sensing. In this talk, we will discuss progress from our lab toward the demonstration of a tube-in-a-tube (Tube^2) semiconductor for the electrical detection of small molecules and biological molecules. A Tube^2 is equivalent to a single-walled carbon nanotube nested within a chemically tailored, impermeable, and atomically-thick functional shell. This structure is created from double-walled carbon nanotubes through outer wall-selective covalent chemistry. Compared with single-walled carbon nanotubes and graphene, electrical sensors created using Tube^2 can be readily tailored with robust covalent chemistries to high functional densities for enabling chemical selectivity while maintaining exceptional sensitivity. We show that 4-carboxylbenzene groups can be covalently attached to the outer wall to the exclusion of the inner tube using diazonium chemistry. Preliminary thin-film transistor sensors based on this novel semiconductor show an ammonia sensitivity of 60 nM (or ~1 ppb) with ~6,000 fold higher chemical selectivity towards amine-containing analytes over other small molecules. Implication of these findings towards biosensing with Tube^2 will be discussed.