Effect of Ionic Atmosphere around DNA/Electrolyte Interface on Potentiometric Signal

Abstract

Biomolecular recognitions with an ion sensitive field effect transistor (ISFET) are mostly reported to strongly depend on the structure and dynamics of the electric double layer (EDL) at the gate electrode/electrolyte interface, while the effect of an ionic behavior around a biomolecule/electrolyte interface on the potentiometric detection has not been clarified. In this study, we investigated the behavior of water and ions around a DNA/electrolyte interface using molecular dynamics (MD) simulations, where the charge distribution may induce a field effect contributing to electrical signals of a DNA-modified ISFET sensor. As a result, MD simulations showed that the interfacial charge distribution with a gentle slope (ionic atmosphere) was more clearly found around the DNA duplex at a lower concentration of NaCl electrolyte, while the counter ion condensation was observed nearby the DNA duplex with increasing the concentration of NaCl electrolyte. This means the EDL structure was found at the DNA/electrolyte interface. Such an ionic atmosphere around the DNA duplex would cause the shift in the threshold voltage for DNA molecular recognition events such as hybridization on the gate of ISFET. Our knowledge based on the MD simulation for the biomolecule/electrolyte interface contributes to design and develop an optimum device on potentiometric biosensors.