Full Three-Dimensional Simulation of Ion-Sensitive Field-Effect Transistor Flatband Voltage Shifts Due to DNA Immobilization and Hybridization

A full three-dimensional simulation of the ion-sensitive field-effect transistor flatband voltage shifts due to DNA immobilization and hybridization is presented. Poisson's equation is solved for a domain consisting of an electrolyte, DNA, Stern layer, linker molecular layer, and nitride layer. DNA is modeled as an insulating cylinder with discrete negative charges at the coordinates of phosphate groups. The site binding on the nitride surface significantly suppresses the flatband voltage shift due to DNA charge, while switching off the site binding gives results close to experimentally reported values. Increasing DNA density or decreasing salt concentration leads to increasing flatband voltage shifts for both immobilization and hybridization. The flatband voltage shift due to DNA hybridization is proportional to DNA density at a high salt concentration or a low DNA density. At a low salt concentration and a high DNA density, however, the flatband voltage dependence on DNA density deviates from this proportional relationship.