Towards Quantifying the electrostatic transduction mechanism in carbon nanotube molecular sensors

TL;DR

This paper investigates the electrostatic mechanisms behind carbon nanotube FET sensors by experimentally analyzing how different charged and dipolar molecules affect their electrical response, aiming to develop quantitative models.

Contribution

It provides experimental evidence linking local charge interactions and molecular dipoles to sensor response, advancing understanding of electrostatic transduction in CNT FET sensors.

Findings

Threshold voltage shifts depend on charge state and proximity of molecules.

Protonation and deprotonation cause opposite threshold shifts.

Molecular dipoles induce measurable threshold shifts.

Abstract

Despite the great promise of carbon nanotube field effect transistors (CNT FETs) for applications in chemical and biochemical detection, a quantitative understanding of sensor responses is lacking. To explore the role of electrostatics in sensor transduction, experiments were conducted with a set of highly similar compounds designed to adsorb onto the CNT FET via a pyrene linker group and take on a set of known charge states under ambient conditions. Acidic and basic species were observed to induce threshold voltage shifts of opposite sign, consistent with gating of the CNT FET by local charges due to protonation or deprotonation of pyrene compounds by interfacial water. The magnitude of the gate voltage shift was controlled by the distance between the charged group and the CNT. Additionally, functionalization with an un-charged pyrene compound showed a threshold shift ascribed to its molecular dipole moment. This work illustrates a method to produce CNT FETs with controlled values of the turnoff gate voltage, and more generally, these results will inform the development of quantitative models for the response of CNT FET chemical and biochemical sensors.