Solution processable carbon nanotube network thin-film transistors operated in electrolytic solutions at various pH

Abstract

We investigate the electronic properties of solution-gated carbon nanotube (CNT) thin-film transistors, where the active layer consists of a randomly distributed single-walled CNT network of >90% semiconducting nanotubes, deposited from an aqueous solution by spin-coating. The devices are characterized in different electrolytic solutions, where a reference electrode immersed in the liquid is used to apply the gate potential. We observe a gate-potential shift in the transfer characteristic when the pH and/or ionic strength of the electrolytic solution is changed with a pH sensitivity of ≈19 mV/pH. This sensitivity is attributed to a surface charging effect at the CNT/electrolyte interface.

Sensing Reversible Protein–Ligand Interactions with Single-Walled Carbon Nanotube Field-Effect Transistors

“…As SWNT FETs are intrinsically sensitive toward changes of the electrolyte’s pH, all transfer curves were taken at pH 4, however the 15 min protein incubations were performed at pH 4 or pH 5. 26 , 27 At pH 4 and pH 5, dissociation constants of 43 ± 7 and 308 ± 170 nM were obtained, respectively.…”

Flexible Electrolyte-Gated Ion-Selective Sensors Based on Carbon Nanotube Networks

“…A higher ion concentration leads to a thinner electrical double layer at the interface of the CNT-network and the electrolyte, which increases the amount of these surface charges getting screened by salt ions. In this way the effective gate potential at the CNT surface gets decreased and the threshold voltage shifts towards more negative gate voltages [9], [10], [32], [33]. The unmodified electrolyte-gated CNT-FET shows an ionsensitive response towards changes in the ion concentration of the electrolyte for both types of salt, KCl and CaCl 2 , in the relative small concentration range from 10 -1 M to 10 -4 M. We therefore modify the active semiconducting CNT network with different types of PVC-based ion-selective membranes.…”

“…The CNTs solution prepared is highly uniform and provides a shelf life of several months without rebundeling of the CNTs together. This has enabled a reproducible production of several devices based on lowdensity CNT networks films with excellent performance [10], [11], [25]- [29]. A 1 wt% aqueous solution of CMC is obtained by adding adequate amount of it to Millipore deionized water (DI-H 2 O).…”

“…It has already been proven that unfunctionalized CNTFETs are very sensitive towards changes in the pH value or the ionic strength of an electrolyte [10]- [12]. However, especially by the emerging fields of point-of-care diagnostics and environmental monitoring high standards are set for developing new sensors, in particular the independent sensing of physiological electrolytes (pH, K + , Na + and Ca 2+ ) or other biological species in complex samples.…”

“…Especially the possibility of down-scaling the devices and their solution processability makes fieldeffect transistors (FETs) based on carbon nanotube networks (CNT-FETs) promising candidates to meet the demand of cost-effective, scalable and flexible sensors for different kinds of biosensing applications [10]- [12].…”