Analysis of Sensing Mechanisms in a Gold-Decorated SWNT Network DNA Biosensor

Abstract

Abstract-We show that carbon nanotube sensors with gold particles on the single-walled carbon nanotube (SWNT) network operate as Schottky barrier transistors, in which transistor action occurs primarily by varying the resistance of Au-SWNT junction rather than the channel conductance modulation. Transistor characteristics are calculated for the statistically simplified geometries, and the sensing mechanisms are analyzed by comparing the simulation results of the MOSFET model and Schottky junction model with the experimental data. We demonstrated that the semiconductor MOSFET effect cannot explain the experimental phenomena such as the very low limit of detection (LOD) and the logarithmic dependence of sensitivity to the DNA concentration. By building an asymmetric concentricelectrode model which consists of serially-connected segments of CNTFETs and Schottky diodes, we found that for a proper explanation of the experimental data, the work function shifts should be ~ 0.1 eV for 100 pM DNA concentration and ~ 0.4 eV for 100 µM.

Particle simulation of electrolytic ion motions for noise in electrolyte–insulator–semiconductor field-effect transistors

“…[1][2][3][4][5] For nanobiosensors to have a very good sensitivity of femtomolar level, noise processes in nanobiosensors must be understood, because noise sets a limit on the signal level that can be detected. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] We study a nanobiosensor whose central part is the electrolyte-insulator-semiconductor (EIS) system. 26,27) In the EIS system, there are various different noise sources, including thermal noise sources in the electrolyte, [11][12][13][14][15][16] adsorption= desorption noise sources from probe-target binding=unbinding, [17][18][19] thermal noise sources in the channel of field-effect transistors, 16) trapping=detrapping noise sources in the oxide, 9,10) and ubiquitous 1=f noise sources.…”

“…There have been many models and experiments for noise in biosensors. [6][7][8][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] In previous studies, many noise sources, such as binding=unbinding noise sources and 1=f noise sources, have been taken into account to compare experimental results. 6,[17][18][19] These approaches are based on the continuum model and include the diffusion and Poisson-Boltzmann equations to model ion movements in the electrolyte.…”