Sensing of DNA by graphene-on-silicon FET structures at DC and 101GHz

A graphene–silicon field-effect transistor (GFET) structure is demonstrated as a detector of single-stranded 13-mer DNA simultaneously at DC and 101GHz at three different molarities: 0.01, 1.0 and 100nM. The mechanism for detection at DC is the DNA-induced change in lateral sheet conductance, whereas at 101GHz it is the change in RF sheet conductance and the resulting effect on the perpendicular beam transmittance through the GFET acting as an optical etalon. For example, after application and drying of the DNA on a GFET film biased to a DC sheet conductance of 2.22mS, the 1.0nM solution is found to reduce this by 1.24mS with a post-detection signal-to-noise ratio of 43dB, and to increase the transmitted 101-GHz signal from 0.828 to 0.907mV (arbitrary units) with a post-detection signal-to-noise ratio of 36dB. The increase in transmittance is consistent with a drop of the 101-GHz sheet conductance, but not as much drop as the DC value. Excellent sensitivity is also achieved with the 0.01-nm solution, yielding a DC SNR of 41dB and a 101-GHz SNR of 23dB.