Impedimetric Sensing of DNA with Silicon Nanowire Transistors as Alternative Transducer Principle

Abstract

Silicon nanowires (SiNW) are highly sensitive to biomolecules. In some publications, changes of SiNW conductance in relation to their concentration levels are displayed. Upon binding, biomolecule charges change the surface potential and, thereby, the SiNW conductance. We discussed earlier that SiNWs can be regarded as long-channel, ion-sensitive field-effect transistors (ISFETs). The choice of a stable working point is important and defines the SiNW conductance. The common detection principle is based on the shift in threshold voltage. Regardless of conductance change or threshold voltage shift, relative values are related to biomolecule concentrations. However, potentiometric detection suffers from Debye screening of biomolecule charges by counter ions of the test solution. This makes biosensing in physiological buffer solutions difficult if not impossible. In this report, a method for impedance sensing with SiNWs, which was earlier used for ISFET devices is introduced. This method gains comparable results to potentiometric sensing. The change of interface impedance is indirectly linked with the biomolecule charges. In addition, the dielectric property of the interface layer plays an important role. At elevated frequencies, our method can be regarded as an alternative mechanism similar to dielectric spectroscopy at low frequencies. Thereby, Debye screening does no longer dominate the recordings.